BACKGROUND OF THE INVENTION [0002] In a gas turbine engine, inlet air is continuously compressed, mixed with fuel in an inflammable proportion, and then contacted with an ignition source to ignite the mixture that will then continue to burn. The heat energy thus released then flows in the combustion gases to a turbine where it is converted to rotary energy for driving equipment such as an electrical generator. The combustion gases are then exhausted to the atmosphere after exchanging some of their remaining heat to the incoming air provided from the compressor.

[0003] Quantities of air in excess of stoichiometric amounts are typically compressed and utilized to keep the combustor liner cool and dilute the combustor exhaust gases so as to avoid damage to the turbine nozzle and blades. Generally, primary sections of the combustor are operated near stoichiometric conditions that produce combustor gas temperatures up to approximately four thousand (4,000) degrees Fahrenheit. Further along the combustor, secondary air is admitted that raises the air-fuel ratio and lowers the gas temperatures so that the gases exiting the combustor are in the range of two thousand (2,000) degrees Fahrenheit.

[0004] It is well established that NOx formation is thermodynamically favored at high temperatures. Since the NOx formation reaction is so highly temperature dependent, decreasing the peak combustion temperature can provide an effective means of reducing NOx emissions from gas turbine engines, and so can limiting the residence time of the combustion products in the combustion zone. Operating the combustion process in a very lean condition (i. e. , high excess air) is a known method of achieving lower temperatures and hence lower NOx emissions.

[0005] In a liquid fuel turbine system, the liquid fuel injector orifices or outlets are within the combustor and thus exposed to substantial heat. During normal operations, this does not present a problem since the flow of liquid fuel through the liquid fuel injector provides a

cooling effect. Further, the propagation of combustion along with the flow of air serves to prevent undesirable overheating of the liquid fuel injectors. Once operation ceases, however, neither liquid fuel nor air flows through the liquid fuel injector. Consequently, residual heat in the combustor area can cause elevation of the temperature of the liquid fuel injectors.

[0006] In terms of the materials of which the liquid fuel injectors are constructed, this temperature elevation experienced upon cessation of operation does not present a problem.

However, the presence of residual liquid fuel in the liquid fuel injector at such time can cause a coking problem. The liquid fuel is carbonaceous in nature and upon being heated will begin to undergo a destructive distillation reaction, producing a coke-like and/or tarry residue.

[0007] This tendency to deposit carbon on fuel flow passages when liquid fuel is exposed to hot surfaces inside a gas turbine (coking) can quickly build up and may become severe enough so as to restrict, or even completely block liquid fuel flow through the fuel injector passages. Because in small gas turbines the liquid fuel atomization is generally controlled by small orifices that are located in regions of high temperature, the coking problem is of particular importance. With generally small fuel passages and atomizers, the effects of coking are more pronounced in a small gas turbine and can lead to poor fuel flow distribution and poor atomization, resulting in increased emissions, reduced combustor performance, and reduced system life.

[0008] In general, liquid fuel systems are designed so that the liquid fuel will not be hot enough to coke prior to injection into the combustor or into the premixing section of a lean pre-vaporize premix (LPP) combustor. During a shut down procedure, any stagnant liquid fuel left in the fuel injectors or passages that experiences high enough temperatures will very rapidly coke and lead to the aforementioned problems. The general approach to remedy this problem has been to purge the liquid fuel system by utilizing the engine pressure to push the liquid fuel out of the liquid fuel system through the injectors and other fuel passages. This approach may be employed when the engine pressure is high enough to overcome the various flow restrictions of the liquid fuel system, but it also results in a known amount of liquid fuel being discarded to the atmosphere. Further, if the engine pressure is not high enough, the fuel injectors and passages may not be cleared of liquid fuel, thus leading to coking.

[0009] What is needed is a method of purging liquid fuel from the fuel injectors of a gas turbine combustor at shutdown before any portion of the fuel is transformed into a solid deposit by the residual heat in the combustor, and without discharging the purged liquid to the atmosphere.

SUMMARY OF THE INVENTION [0010] In one aspect, the present invention provides a method of shutting down a turbine engine having a fuel line for conducting liquid fuel from a fuel supply to a combustor fuel injector, the method comprising shutting off the fuel supply and passing compressed gas through the fuel line to purge fuel from the fuel line and the fuel injector into the combustor.

[0011] In another aspect, the present invention provides a turbogenerator comprising a turbine; a combustor for combusting fuel and compressed air to generate hot gas to drive the turbine, the combustor including a fuel injector; a fuel line connected to the fuel injector to supply fuel to the combustor from a liquid fuel source; an electric generator rotationally coupled to the turbine to generate electric power; and a source of compressed gas selectively coupled to the fuel line for passing compressed gas through the fuel line after shutdown of the turbogenerator to purge fuel from the fuel line and the fuel injector into the combustor.

[0012] In a further aspect of the present invention, the purged fuel is combusted in the combustor, and an igniter in the combustor may be used to ignite the purged fuel in the combustor. In a yet further aspect of the invention, the compressed gas is regulated to control combustion of the purged fuel in the combustor, and the compressed gas pressure may be regulated in accordance with a predicted combustor pressure.

BRIEF DESCRIPTION OF THE DRAWINGS [0013] Figure 1 is a perspective view, partially cut away, of a turbogenerator with a combustion system according to the present invention; [0014] FIG. 2 is a plan view of the combustor housing of the turbogenerator of FIG. 1; [0015] FIG. 3 is a sectional view of the combustor housing of FIG. 2 taken along line 3-3 of FIG. 2; [0016] FIG. 4 is a sectional view of the combustor housing of FIG. 3 taken along line 4-4 of FIG. 3; [0017] FIG. 5 is a block diagram of a power controller used with the turbogenerator of FIG.

1; [0018] FIG. 6 is a block diagram of the power controller of FIG. 5 including a dynamic brake resistor; [0019] FIG. 7 is a block diagram of a shut down burn system for the turbogenerator of FIG.

1; and [0020] FIG. 8 is a block diagram of an alternate shut down burn system for the turbogenerator of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION [0021] Referring to Fig. 1, integrated turbogenerator system 12 generally includes generator 20, power head 21, combustor 22, and recuperator (or heat exchanger) 23. Power head 21 of turbogenerator 12 includes compressor 30, turbine 31, and bearing rotor 32. Tie rod 33 to magnetic rotor 26 (which may be a permanent magnet) of generator 20 passes through bearing rotor 32. Compressor 30 includes compressor impeller or wheel 34 that draws air flowing from an annular air flow passage in outer cylindrical sleeve 29 around stator 27 of the generator 20. Turbine 31 includes turbine wheel 35 that receives hot exhaust gas flowing

from combustor 22. Combustor 22 receives preheated air from recuperator 23 and fuel through a plurality of fuel injector guides 49. Compressor wheel 34 and turbine wheel 35 are supported on bearing shaft or rotor 32 having radially extending air-flow bearing rotor thrust disk 36. Bearing rotor 32 is rotatably supported by a single air-flow journal bearing within center bearing housing 37 while bearing rotor thrust disk 36 at the compressor end of bearing rotor 32 is rotatably supported by a bilateral air-flow thrust bearing.

[0022] Generator 20 includes magnetic rotor or sleeve 26 rotatably supported within generator stator 27 by a pair of spaced journal bearings. Both rotor 26 and stator 27 may include permanent magnets. Air is drawn by the rotation of rotor 26 and travels between rotor 26 and stator 27 and further through an annular space formed radially outward of the stator to cool generator 20. Inner sleeve 25 serves to separate the air expelled by rotor 26 from the air being drawn in by compressor 30, thereby preventing preheated air from being drawn in by the compressor and adversely affecting the performance of the compressor (due to the lower density of preheated air as opposed to ambient-temperature air).

[0023] In operation, air is drawn through sleeve 29 by compressor 30, compressed, and directed to flow into recuperator 23. Recuperator 23 includes annular housing 40 with heat transfer section or core 41, exhaust gas dome 42, and combustor dome 43. Heat from exhaust gas 110 exiting turbine 31 is used to preheat compressed air 100 flowing through recuperator 23 before it enters combustor 22, where the preheated air is mixed with fuel and ignited such as by electrical spark, hot surface ignition, or catalyst. The fuel may also be premixed with all or a portion of the preheated air prior to injection into the combustor. The resulting combustion gas expands in turbine 31 to drive turbine impeller 35 and, through common shaft 32, drive compressor 30 and rotor 26 of generator 20. The expanded turbine exhaust gas then exits turbine 31 and flows through recuperator 23 before being discharged from turbogenerator 12.

[0024] Referring to Figs. 2-4, combustor housing 39 of combustor 22 generally comprises cylindrical outer liner 44 and tapered inner liner 46 that, together with combustor dome 43, form generally expanding annular combustion housing or chamber 39 from combustor dome 43 to turbine 31. Plurality of fuel injector guides 49 may position the fuel injectors 14 to tangentially introduce a fuel/air mixture at the combustor dome 43 end of the annular

combustion housing 39 along the fuel injector axis or centerline 47. Centerline 47 includes an igniter cap to position an igniter (not shown) within the combustor housing 39. Combustion dome 43 is rounded out to permit the swirl pattern from fuel injectors 14 to fully develop and to reduce structural stress loads in the combustor.

[0025] Flow control baffle 48 extends from tapered inner liner 46 into annular combustion housing 39. Baffle 48 is typically skirt-shaped and may extend between one-third and one- half of the distance between tapered inner liner 46 and cylindrical outer liner 44. Three rows of spaced offset air dilution holes 52,53, and 54 are formed in tapered inner liner 46 underneath flow control baffle 48 to introduce dilution air into annular combustion housing 39. The first two (2) rows of air dilution holes 52 and 53 (closest to fuel injector centerline 47) may be the same size as one another but both are typically smaller than the third row of air dilution holes 54.

[0026] In addition, two (2) rows of a plurality of spaced air dilution holes 50 and 51 are formed in cylindrical outer liner 44 to introduce more dilution air downstream from flow control baffle 48. The plurality of holes 50 closest to flow control baffle 48 may be larger and less numerous than the second row of holes 51.

[0027] Fuel may be provided individually to each fuel injector or alternatively a fuel manifold may be provided to supply fuel to all three fuel injectors. The fuel manifold may include a fuel inlet to receive fuel from a fuel source and flow control valves 17 on each fuel line from the manifold to the individual fuel injectors. To sustain low power operation, maintain fuel economy and low emissions, the flow control valves may be individually controlled to an on/off position (to separately use any combination of fuel injectors individually) or may be modulated together. The flow control valves can be opened by fuel pressure or their operation can be controlled or augmented with a solenoid.

[0028] A more detailed description of a preferred combustor and fuel injector system can be found in United States Patent No. 5,850, 732, issued December 22,1998 to Jeffrey W. Willis et al, entitled"Low Emissions Combustion System", assigned to the same assignee as this application, and hereby incorporated in its entirety by reference thereto.

[0029] The turbogenerator has a steady-state turbine exhaust temperature limit and is typically operated at this limit at most speeds to maximize efficiency. This turbine exhaust temperature limit is decreased at low ambient temperatures to prevent engine surge.

[0030] Referring to FIG. 5, power controller 140 may be a digital controller, and enables a distributed generation power networking system by providing bi-directional (i. e. reconfigurable) power converters connected to common DC bus 154 to connect a plurality of energy generation and/or storage components. Each power converter 144 and 146 operates essentially as a customized bi-directional switching converter configured, under the control of power controller 140, to provide an interface for a specific energy component to DC bus 154.

In this manner power controller 140 controls how each energy component sinks or sources power to or from DC bus 154, and thus regulates DC bus 154. In this way, various energy components can be used to supply, store and/or use power in an efficient manner.

[0031] The energy components may include energy source 142 which may be turbogenerator 12, energy load 148 which may be an utility grid, and energy storage device 150 which may be a battery. Energy source 142 is connected to DC bus 154 via power converter 144 under the control of signal processor 145, which may be a digital signal processor (DSP). Energy load 148 is connected to DC bus 154 via power converter 146 under the control of signal processor 147. Energy storage device 150 is likewise connected to DC bus 154 via power converter 152. Main CPU 149 provides supervisory operation of power controller 140 by controlling signal processors 145 and 147 and power converters 144,146, and 152.

[0032] Main CPU 149 provides both local control and sufficient intelligence to form a distributed processing system. In the case of turbogenerator 12 operating as energy source 142, power controller 140 regulates turbine speed to control the power output independently of turbine speed to regulate the bus voltage.

[0033] With continued reference to FIG. 5, turbogenerator 12 typically provides power to DC bus via power converter 144 during normal power generation mode. Similarly, during power generation, power converter 146 converts the power on DC bus 154 to the form required by utility/load 148. During utility start up, power converters 144 and 146 are

controlled by the main processor to operate in different modes. For example, the energy needed to start turbogenerator 12 may be provided by load/utility 148 (utility start) or by energy source 150 (battery start). During a utility start up, power converter 146 is required to apply power from load/utility 148 to the DC bus for subsequent conversion by power converter 144 to AC power required by turbogenerator 12 to start up. During utility start, turbogenerator 12 is controlled in a local feedback loop to maintain the turbine revolutions per minute (RPM).

[0034] Similarly, in a battery start, the power applied to DC bus 154 to start turbogenerator 12 is provided by energy storage device 150. Energy storage device 150 applies power to DC bus 154 through power converter 152, which allows enough power to flow to DC bus 154 to start turbogenerator 12 while limiting current surge. A more detailed description of a power controller suitable for use with the invention can be found in United States Patent Application No. 09/207,817, filed December 8,1998 by Mark G. Gilbreth et al. entitled"Power Controller", assigned to the same assignee as this application, and hereby incorporated in its entirety by reference thereto. A copy of S/N 09/207,817 is attached hereto as Appendix A.

[0035] Referring to FIG. 6, power controller 140 incorporates dynamic brake resistor 170 and associated controls. Turbogenerator 12 produces three phase AC power that is applied to AC-to-DC power converter 144 (labeled in FIG. 6 as the engine control module). Power converter 144 applies DC voltage to DC bus 154, which is also connected to DC-to-AC power converter 146 (labeled in FIG. 6 as the load control module). Power converter 146 is connected to load 148, which may be a utility grid.

[0036] Brake resistor 170 is connected across DC bus 154. Power in the DC bus can be dissipated in brake resistor 170 by modulation of switch 172. Voltage sensor 174 is also connected across DC bus 154 to produce DC bus voltage signal 176 that is compared in comparator 178 with brake resistor turn on voltage signal 180 to produce DC bus error signal 182. Brake resistor turn on voltage signal 180 is adjustable by CPU 149.

[0037] DC bus error signal 182 from comparator 178 is used to control the modulation of switch 172 after being conditioned through proportional integral compensator 184, brake resistor temperature feedback limit 186, pulse width modulator 188, and gate drive 190.

Switch 172 may be an IGBT switch, although other switches can be utilized. Switch 172 is controlled in accordance with the magnitude of DC bus voltage signal 176. CPU 149 (as shown in FIG. 5) typically maintains the DC bus voltage to a selected value by appropriate control of the power flowing through load control module 146 and engine control module 144. If a rise in the DC bus voltage is detected, switch 172 is modulated on and off to allow power to discharge through brake resistor 170 until the DC bus voltage is restored to the desired, selected value.

[0038] As outlined above, a typical turbogenerator combustion system is a low emissions system including a gas turbine coupled with a recuperator. A relatively small amount of fuel is required at idle speeds because the recuperator is capable of supplying most of the energy required to sustain gas turbine operation. To achieve low emissions at operating speed, the fuel provided to the turbine combustor is diluted into a large volume of air, thereby resulting in a high air-to-fuel ratio (AFR) mixture that reduces the stability of the combustion. If the AFR increases beyond a certain level, combustion may cease and cause a flame-out, resulting in a time consuming shutdown and restart cycle.

[0039] In a multi-injector combustion system, one approach to preventing flame-out is to operate on fewer injectors. When low levels of fuel flow are detected, the delivery of fuel to some injectors is turned off. By turning off injectors, fuel flow can be concentrated into fewer injectors to reduce AFR and increase combustion stability. At very low power levels, even operating on a single injector may not provide low enough AFR levels to prevent flame-out conditions. An example of a multi-injector combustion system suitable for use with the invention is described in United States Patent Application No. 453,825 filed December 1, <BR> <BR> 1999 by Guillermo Pont et al. , entitled"System and Method for Modular Control of a Multi- Fuel Low Emissions Turbogenerator", assigned to the same assignee as this application and incorporated herein in its entirety by reference thereto.

[0040] Referring to FIGS. 7 and 8, turbine combustor 22 has a plurality of liquid fuel injectors, each controlled by a respective solenoid SOL1, SOL2, SOL3. Fuel shut/off solenoid 200 controls the flow of liquid fuel to manifold 201, that can also receive compressed air through air shut/off solenoid 202. The liquid fuel is supplied to manifold 201 by fuel pump 206 through filter 204 and check valve 208. The compressed air is supplied to

manifold 201 from a compressed air source (not shown) through compressed air shut/off valve 210, compressed air regulator 212, and check valve 214. Check valves 208 and 214 can be replaced by any other means for generating pressure and controlling flow.

[0041] In operation, when the turbogenerator is commanded to shut down, fuel pump 206 (or fuel control valve) and fuel shut/off solenoid 200 are closed, thus stopping the flow of liquid fuel from the main fuel supply. At the same time, compressed air shut/off valve 210 and compressed air shut/off solenoid 202 are opened, allowing compressed air into fuel manifold 201. This air must be at pressures higher than the combustion chamber pressure to be able to force the fuel remaining in manifold 201 and injectors into the combustion chamber. The fuel in manifold 201 thus continues to flow through the injectors and into the combustor, thereby maintaining combustion for a short period of time following the shut down command. If combustion is interrupted, an igniter can be turned on to re-establish and complete combustion of the purged fuel.

[0042] The method of the invention ensures that the fuel passages and fuel injectors are free of liquid fuel following shutdown of the system, and that fuel that would otherwise be discarded is completely combusted. While this does result in continued power generation by the system for a short time after shut down is commanded, brake resistor 170 connected across DC bus 154 can absorb such excess power. The additional power generated can also be stored in energy storage device 150 or applied to load 148.

[0043] The flow and pressure of the liquid fuel to manifold 201 may be controlled by a liquid fuel pressurization and control system such as described in United States Patent No.

5,873, 235 issued February 23,1999 to Robert W. Bosley et al. , entitled"Liquid Fuel<BR> Pressurization and Control Method, "assigned to the same assignee as this application and incorporated herein in its entirety by reference thereto.

[0044] Referring to FIG. 8, compressed air for the shut down burn is available from air assist compressor 220 and associated filter 222, which supplies compressed assist air to air assist manifold 226 through air assist shut/off valve 224. Air compressor 220 may be regulated by measuring the air compressor discharge pressure and comparing this feedback to the predicted combustion pressure. The combustion pressure may be calculated based upon

turbine speed, and a look-up table listing values for combustion pressure as a function of turbine speed may be built into the controller for use in regulating the air compressor during shut down purge. By regulating the air pressure, the fuel flow (which is a function of the pressure drop across the fuel injectors) during the shutdown burn is optimized to insure complete combustion of the fuel.

[0045] Air assist compressor 220 may be a helical flow compressor such as described in <BR> <BR> United States Patent No. 5,899, 673 issued May 4,1999 to Robert W. Bosley et al. , entitled<BR> "Helical Flow Compressor/Turbine Permanent Magnet Motor Generator, "assigned to the same assignee as this application and incorporated herein in its entirety by reference thereto.

Such a compressor may be utilized as an air compressor as described in United States Patent No 5,819, 524 issued October 13,1998 to Robert W. Bosley et al. entitled"Gaseous Fuel Compression and Control System, "assigned to the same assignee as this application and incorporated herein in its entirety by reference thereto.

[0046] The present invention may be employed with turbogenerators using various types of fuel injectors, including airblast, or air assist atomizers, and pressure atomizers. Pressure atomizers would typically require higher air pressures to purge liquid fuel at shutdown.

[0047] Having now described the invention in accordance with the requirements of the patent statutes, those skilled in the art will understand how to make changes and modifications to the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as defined and limited solely by the following claims.

Appendix A

POWER CONTROLLER REFERENCE TO RELATED APPLICATION This application claims the benefit of U. S. Provisional Application No. 60/080,457, filed on April 2,1998.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to power generation and processing systems and in particular to distributed generation power systems.

2. Description of the Prior Art Conventional power generation and distribution systems are configured to maximize the specific hardware used. In the case of a turbine power motor, for example, the output or bus voltage in a conventional power distribution system varies with the speed of the turbine.

In such systems, the turbine speed must be regulated to control the output or bus voltage.

Consequently, the engine cannot be run too low in speed else the bus voltage would not be high enough to generate some of the voltages that are needed. As a result, the turbine would have to be run at higher speeds and lower temperatures, making it less efficient.

What is needed therefore is a power generation and distribution system where the bus voltage is regulated by a bi-directional controller independent of turbine speed.

SUMMARY OF THE INVENTION The present invention provides in a first aspect, a power controller which provides a distributed generation power networking system in which bi-directional power converters are used with a common DC bus for permitting compatibility between various energy components. Each power converter operates essentially as a customized bi-directional switching converter configured, under the control of the power controller, to provide an interface for a specific energy component to the DC bus. The power controller controls the

way in which each energy component, at any moment, will sink or source power, and the manner in which the DC bus is regulated. In this way, various energy components can be used to supply, store and/or use power in an efficient manner. The various energy components include energy sources, loads, storage devices and combinations thereof.

In another aspect, the present invention provides a turbine system including a turbine engine, a load, a power controller, an energy reservoir for providing transient power to the DC bus and an energy reservoir controller, in communication with the power controller for providing control to the energy reservoir. The power controller includes an engine power conversion in communication with the turbine engine, an utility power conversion in communication with the load and a DC bus.

These and other features and advantages of this invention will become further apparent from the detailed description and accompanying figures that follow. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawing figures and the written description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a power controller according to the present invention.

FIG. 2 is a detailed block diagram of a power converter in the power controller illustrated in FIG. 1.

FIG. 3 is a simplified block diagram of a turbine system including the power architecture of the power controller illustrated in FIG. 1.

FIG. 4 is a block diagram of the power architecture of a typical implementation of the power controller illustrated in FIG. 1.

FIG. 5 is a schematic diagram of the internal power architecture of the power controller illustrated in FIG. 1.

FIG. 6 is a functional block diagram of an interface between load/utility grid and turbine generator using the power controller according to the present invention.

FIG. 7 is a functional block diagram of an interface between load/utility grid and turbine generator using the power controller for a stand-alone application according to the present invention.

FIG. 8 is a schematic diagram of an interface between a load/utility grid and turbine generator using the power controller according to the present invention.

FIG. 9 is a block diagram of the software architecture for the power controller including external interfaces.

FIG. 10 is a block diagram of an EGT control mode loop for regulating the temperature of the turbine.

FIG. 11 is a block diagram of a speed control mode loop for regulating the rotating speed of the turbine.

FIG. 12 is a block diagram of a power control mode loop for regulating the power producing potential of the turbine.

FIG. 13 is a state diagram showing various operating states of the power controller.

FIG. 14 is a block diagram of the power controller interfacing with a turbine and fuel device.

FIG. 15 is a block diagram of the power controller in multi-pack configuration.

FIG. 16 is a block diagram of a utility grid analysis system for the power controller according to the present invention.

FIG. 17 is a graph of voltage against time for the utility grid analysis system illustrated in FIG. 16.

FIG. 18 is a diagram of the power controller shown in FIG. 16, including brake resistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, power controller 10 provides a distributed generation power networking system in which bi-directional (i. e. reconfigurable) power converters are used with a common DC bus for permitting compatibility between one or more energy components. Each power converter operates essentially as a customized bi-directional switching converter configured, under the control of power controller 10, to provide an interface for a specific energy component to DC bus 24. Power controller 10 controls the way in which each energy component, at any moment, will sink or source power, and the manner

in which DC bus 24 is regulated. In this way, various energy components can be used to supply, store and/or use power in an efficient manner.

One skilled in the art will recognize that the particular configurations shown herein are for illustrative purposes only. In particular, the present invention is not limited to the use of three bi-directional converters as shown in FIG. 1. Rather, the number of power converters is dependent on various factors, including but not limited to, the number of energy components and the particular power distribution configuration desired. For example, as illustrated in FIGS. 5 and 6, power controller 10 can provide a distributed generation power system with as few as two power converters.

The energy components, as shown in FIG. 1, include energy source 12, utility/load 18 and storage device 20. The present invention is not limited to the distribution of power between energy source 12, energy storage device 20 and utility/load 18, but rather may be adapted to provide power distribution in an efficient manner for any combination of energy components.

Energy source 12 may be a gas turbine, photovoltaics, wind turbine or any other conventional or newly developed source. Energy storage device 20 may be a flywheel, battery, ultracap or any other conventional or newly energy storage device. Load 18 may be an utility grid, dc load, drive motor or any other conventional or newly developed utility/load 18.

Referring now to FIG. 2, a detailed block diagram of power converter 14 in power controller 10, shown in FIG. 1, is illustrated. Energy source 12 is connected to DC bus 24 via power converter 14. Energy source 12 may be, for example, a gas turbine driving an AC generator to produce AC which is applied to power converter 14. DC bus 24 connects power converter 14 to utility/load 18 and additional energy components 36. Power converter 14 includes input filter 26, power switching system 28, output filter 34, signal processor 30 and main CPU 32. In operation, energy source 12 applies AC to input filter 26 in power converter 14. The filtered AC is then applied to power switching system 28 which may conveniently be a series of insulated gate bipolar transistor (IGBT) switches operating under the control of signal processor (SP) 30 which is controlled by main CPU 32. One skilled in the art will recognize that other conventional or newly developed switches may be utilized as well. The

output of the power switching system 28 is applied to output filter 34 which then applies the filtered DC to DC bus 24.

In accordance with the present invention, each power converter 14,16 and 22 operates essentially as a customized, bi-directional switching converter under the control of main CPU 32, which uses SP 30 to perform its operations. Main CPU 32 provides both local control and sufficient intelligence to form a distributed processing system. Each power converter 14,16 and 22 is tailored to provide an interface for a specific energy component to DC bus 24. Main CPU 32 controls the way in which each energy component 12,18 and 20 sinks or sources power, and DC bus 24 is regulated at any time. In particular, main CPU 32 reconfigures the power converters 14,16 and 22 into different configurations for different modes of operation.

In this way, various energy components 12,18 and 20 can be used to supply, store and/or use power in an efficient manner. In the case of a turbine power generator, for example, a conventional system regulates turbine speed to control the output or bus voltage. In the power controller, the bi-directional controller independently of turbine speed regulates the bus voltage.

Operating Modes FIG. 1 shows the system topography in which DC bus 24, regulated at 800 v DC for example, is at the center of a star pattern network. In general, energy source 12 provides power to DC bus 24 via power converter 14 during normal power generation mode.

Similarly, during the power generation mode, power converter 16 converts the power on DC bus 24 to the form required by utility/load 18, which may be any type of load including a utility web. During other modes of operation, such as utility start up, power converters 14 and 16 are controlled by the main processor to operate in different manners.

For example, energy is needed to start the turbine. This energy may come from loadlutility grid 18 (utility start) or from energy storage 20 (battery start), such as a battery, flywheel or ultra-cap. During a utility start up, power converter 16 is required to apply power from load 18 to DC bus 24 for conversion by power converter 14 into the power required by energy source 12 to startup. During utility start, energy source or turbine 12 is controlled in a local feedback loop to maintain the turbine revolutions per minute (RPM). Energy storage or battery 20 is disconnected from DC bus 24 while load/utility grid 10 regulates VpC on DC bus 24.

Similarly, in the battery start mode, the power applied to DC bus 24 from which energy source 12 is started may be provided by energy storage 20 which may be a flywheel, battery or similar device. Energy storage 20 has its own power conversion circuit in power converter 22, which limits the surge current into DC bus 24 capacitors, and allows enough power to flow to DC Bus 24 to start energy source 12. In particular, power converter 16 isolates DC bus 24 so that power converter 14 can provide the required starting power from DC bus 24 to energy source 12.

Electronics Architecture Referring to FIG. 3, a simplified block diagram of a turbine system 50 using the power controller electronics architecture of the present invention is illustrated. The turbine system 50 includes a fuel metering system 42, turbine engine 58, power controller 52, energy reservoir conversion 62, energy/reservoir 64 and load/utility grid 60. The fuel metering system 42 is matched to the available fuel and pressure. The power controller 52 converts the electricity from turbine engine 58 into regulated DC then converts it to utility grade AC electricity. By separating the engine control from the converter that creates the utility grade power, greater control of both processes is realized. All of the interconnections are comprised of a communications bus and a power connection.

The power controller 52 includes an engine power conversion 54 and utility power conversion 56 which provides for the two power conversions that take place between the turbine 58 and the load/utility grid 60. One skilled in the art will recognize that the power controller 52 can provide a distributed generation power system with as few as two power converters 54 and 56. The bi-directional (i. e. reconfigurable) power converters 54 and 56 are used with a common regulated DC bus 66 for permitting compatibility between the turbine 58 and load/utility grid 60. Each power converter 54 and 56 operates essentially as a customized bi-directional switching converter configured, under the control of the power controller 10, to provide an interface for a specific energy component 58 or 60 to the DC bus 66. The power controller 10 controls the way in which each energy component, at any moment, will sink or source power, and the manner in which the DC bus 66 is regulated. Both of these power conversions 54 and 56 are capable of operating in a forward or reverse direction. This allows starting the turbine 58 from either the energy reservoir 64 or the load/utility grid 60. The regulated DC bus 66 allows a standardized interface to energy reservoirs such as batteries,

flywheels, and ultra-caps. The architecture of the present invention permits the use of virtually any technology that can convert its energy to/from electricity. Since the energy may flow in either direction to or from the energy reservoir 64, transients may be handled by supplying energy or absorbing energy. Not all systems will need the energy reservoir 64.

The energy reservoir 64 and its energy reservoir conversion 62 are not contained inside the power controller 52.

Referring to FIG. 4, the power architecture 68 of a typical implementation of the power controller 70 is shown. The power controller 70 includes a generator converter 72 and output converter 74 which provides for the two power conversions that take place between the turbine 76 and the loadlutility grid 78. In particular, the generator converter 72 provides for AC to DC power conversion and the output converter 74 provides for DC to AC power conversion. Both of these power converters 72 and 74 are capable of operating in a forward or reverse direction. This allows starting the turbine 76 from either the energy storage device 86 or the load/utility grid 78. Since the energy may flow in either direction to or from the energy storage device 86, transients may be handled by supplying energy or absorbing energy. The energy storage device 86 and its DC converter 84 are not contained inside the power controller 70. The DC converter 84 provides for DC to DC power conversion.

Referring to FIG. 5, a schematic 90 of a typical internal power architecture, such as that shown in FIG. 4, is shown. The turbine has an integral PMG that can be used as either a generator (for starting) or a generator (normal mode of operation). Because all of the controls can be performed in the digital domain and all switching (except for one output contactor) is done with solid state switches, it is easy to shift the direction of the power flow as needed.

This permits very tight control of the turbine during starting and stopping. In a typical configuration, the power output is a 480 VAC, 3-phase output. One skilled in the art will recognize that the present invention may be adapted to provide for other power output requirements such as a 3-phase, 400 VAC, and single-phase, 480 VAC.

Power controller 92 includes generator converter 94 and output converter 96.

Generator converter 94 includes IGBT switches 94, such as a seven-pack IGBT module 94, driven by control logic 98, providing a variable voltage, variable frequency 3-phase drive to the PMG 100. Inductors 102 are utilized to minimize any current surges associated with the

high frequency switching components which may affect the PMG 100 to increase operating efficiency.

IGBT module 94 is part of the electronics that controls the engine of the turbine.

IGBT module 94 incorporates gate driver and fault sensing circuitry as well as a seventh IGBT used to dump power into a resistor. The gate drive inputs and fault outputs require external isolation. Four external, isolated power supplies are required to power the internal gate drivers. IGBT module 94 is typically used in a turbine system that generates 480 VAC at its output terminals delivering up to 30 kWatts to a freestanding or utility-connected load.

During startup and cool down (and occasionally during normal operation), the direction of power flow through the seven-pack reverses. When the turbine is being started, power is supplied to the DC bus 112 from either a battery (not shown) or from the utility grid 108. The DC is converted to a variable frequency AC voltage to generator the turbine.

For utility grid connect operation, control logic 110 sequentially drives the solid state IGBT switches, typically configured in a six-pack IGBT module 96, associated with load converter 96 to boost the utility voltage to provide start power to the generator converter 94.

The IGBT switches in load converter 96 are preferably operated at a high (15 kHz) frequency, and modulated in a pulse width modulation manner to provide four quadrant converter operation. Inductors 104 and AC filter capacitors 106 are utilized to minimize any current surges associated with the high frequency switching components which may affect load 108.

Six-pack IGBT module 96 is part of the electronics that controls the converter of the turbine. IGBT module 96 incorporates gate driver and fault sensing circuitry. The gate drive inputs and fault outputs require external isolation. Four external, isolated power supplies are required to power the internal gate drivers. IGBT module 96 is typically used in a turbine system that generates 480 VAC at its output terminals delivering up to approximately 30 kWatts to a free-standing or utility-connected load. After the turbine is running, six-pack IGBT module 96 is used to convert the regulated DC bus voltage to the approximately 50 or 60 hertz utility grade power. When there is no battery (or other energy reservoir), the energy to run the engine during startup and cool down must come from utility grid 108. Under this condition, the direction of power flow through the six-pack IGBT module 96 reverses. DC bus 112 receives its energy from utility grid 108, using six-pack IGBT module 96 as a boost converter (the power diodes act as a rectifier). The DC is converted to a variable frequency

AC voltage to generator the turbine. To accelerate the engine as rapidly as possible at first, current flows at the maximum rate through seven-pack IGBT module 94 and also six-pack IGBT module 96.

Dual IGBT module 114, driven by control logic 116, is used to provide an optional neutral to supply 3 phase, 4 wire loads.

Startup Energy is needed to start the turbine. Referring to FIGS. 3 and 4, this energy may come from utility grid 60 or from energy reservoir 64, such as a battery, flywheel or ultra-cap.

When utility grid 60 supplies the energy, utility grid 60 is connected to power controller 52 through two circuits. First is an output contactor that handles the full power (30 kWatts).

Second is a"soft-start"or"pre-charge"circuit that supplies limited power (it is current limited to prevent very large surge currents) from utility grid 66 to DC bus 62 through a simple rectifier. The amount of power supplied through the soft-start circuit is enough to start the housekeeping power supply, power the control board, and run the power supplies for the IGBTs, and close the output contactor. When the contactor closes, the IGBTs are configured to create DC from the AC waveform. Enough power is created to run the fuel metering circuit 42, start the engine, and close the various solenoids (including the dump valve on the engine).

When energy reservoir 64 supplies the energy, energy reservoir 64 has its own power conversion circuit 62 that limits the surge circuit into DC bus capacitors. Energy reservoir 64 allows enough power to flow to DC bus 62 to run fuel-metering circuit 42, start the engine, and close the various solenoids (including the dump valve on the engine). After the engine becomes self-sustaining, the energy reservoir starts to replace the energy used to start the engine, by drawing power from DC bus 62. In addition to the sequences described above, power controller senses the presence of other controllers during the initial power up phase. If another controller is detected, the controller must be part of a multi-pack, and proceeds to automatically configure itself for operation as part of a multi-pack.

System Level Operation Referring to FIG. 6, a functional block diagram 130 of an interface between utility grid 132 and turbine generator 148 using power controller 136 of the present invention is shown. In this example, power controller 136 includes two bi-directional converters 138 and

140. Permanent magnet generator converter 140 starts turbine 148 (using the generator as a generator) from utility or battery power. Load converter 138 then produces AC power using an output from generator converter 140 to draw power from high-speed turbine generator 148.

Power controller 136 also regulates fuel to turbine 148 and provides communications between units (in paralleled systems) and to external entities.

During a utility startup sequence, utility 132 supplies starting power to turbine 148 by "actively"rectifying the line via load converter 138, and then converting the DC to variable voltage, variable frequency 3-phase power in generator converter 136. As is illustrated in FIG. 7, for stand-alone applications 150, the start sequence is the same as the utility start sequence shown in FIG. 6 with the exception that the start power comes from battery 170 under the control of an external battery controller. Load 152 is then fed from the output terminals of load converter 158.

Referring to FIG. 8, a schematic illustration 180 of an interface between utility grid 132 and turbine generator 148 using the power controller is illustrated. Control logic 184 also provides power to fuel cutoff solenoids 198, fuel control valve 200 and igniter 202. An external battery controller (not shown), if used, connects directly to DC bus 190. In accordance with an alternative embodiment of the invention, a fuel system (not shown) involving a compressor (not shown) operated from a separate variable speed drive can also derive its power directly from DC bus 190.

In operation, control and start power comes from either the external battery controller (for battery start applications) or from the utility, which is connected to a rectifier using inrush limiting techniques to slowly charge internal bus capacitor 190. For utility grid connect operation, control logic 184 sequentially drives solid state IGBT switches 214 associated with load converter 192 to boost the utility voltage to provide start power to generator converter 186. Switches 214 are preferably operated at a high (15 kHz) frequency, and modulated in a pulse width modulation manner to provide four quadrant converter operation. In accordance with the present invention, load converter 192 either sources power from DC bus 190 to utility grid 222 or from utility grid 222 to DC bus 190. A current regulator (not shown) may achieve this control. Optionally, two of the switches 214 serve to create an artificial neutral for stand-alone applications (for stand-alone applications, start power from an external DC

supply (not shown) associated with external DC converter 220 is applied directly to DC bus 190).

Solid state (IGBT) switches 214 associated with generator converter 186 are also driven from control logic 184, providing a variable voltage, variable frequency 3-phase drive to generator 218 to start turbine 208. Control logic 184 receives feedback via current sensors Isens as turbine 206 is ramped up in speed to complete the start sequence. When turbine 206 achieves a self sustaining speed of, for example, approx. 40,000 RPM, generator converter 186 changes its mode of operation to boost the generator output voltage and provide a regulated DC bus voltage.

PMG filter 188 associated with generator converter 186 includes three inductors to remove the high frequency switching component from permanent magnet generator 208 to increase operating efficiency. Output AC filter 194 associated with load converter 192 includes three or optionally four inductors (not shown) and AC filter capacitors (not shown) to remove the high frequency switching component. Output contactor 210 disengages load converter 192 in the event of a unit fault.

During a start sequence, control logic 184 opens fuel cutoff solenoid 198 and maintains it open until the system is commanded off. Fuel control 200 may be a variable flow valve providing a dynamic regulating range, allowing minimum fuel during start and maximum fuel at full load. A variety of fuel controllers, including but not limited to, liquid and gas fuel controllers, may be utilized. One skilled in the art will recognize that the fuel control can be by various configurations, including but not limited to a single or dual stage gas compressor accepting fuel pressures as low as approximately 1/4 psig. Igniter 202, a spark type device similar to a spark plug for an internal combustion engine, is operated only during the start sequence.

For stand-alone operation, turbine 206 is started using external DC converter 220 which boosts voltage from a battery (not shown), and connects directly to the DC bus 190.

Load converter 192 is then configured as a constant voltage, constant frequency (for example, approximately 50 or 60 Hz) source. One skilled in the art will recognize that the output is not limited to a constant voltage, constant frequency source, but rather may be a variable voltage, variable frequency source. For rapid increases in output demand, external DC converter 220

supplies energy temporarily to DC bus 190 and to the output. The energy is restored after a new operating point is achieved.

For utility grid connect operation, the utility grid power is used for starting as described above. When turbine 206 has reached a desired operating speed, converter 192 is operated at utility grid frequency, synchronized with utility grid 222, and essentially operates as a current source converter, requiring utility grid voltage for excitation. If utility grid 222 collapses, the loss of utility grid 222 is sensed, the unit output goes to zero (0) and disconnects. The unit can receive external control signals to control the desired output power, such as to offset the power drawn by a facility, but ensure that the load is not backfed from the system.

Power Controller Software Referring to FIG. 9, power controller 230 includes main CPU 232, generator SP 234 and converter SP 236. Main CPU software program sequences events which occur inside power controller 230 and arbitrates communications to externally connected devices. Main CPU 232 is preferably a MC68332 microprocessor, available from Motorola Semiconductor, Inc. of Phoenix, Arizona. Other suitable commercially available microprocessors may be used as well. The software performs the algorithms that control engine operation, determine power output and detect system faults.

Commanded operating modes are used to determine how power is switched through the major converts in the controller. The software is responsible for turbine engine control and issuing commands to other SP processors enabling them to perform the generator converter output converter power switching. The controls also interface with externally connected energy storage devices (not shown) that provide black start and transient capabilities.

Generator SP 234 and converter SP 236 are connected to power controller 230 via serial peripheral interface (SPI) bus 238 to perform generator and converter control functions.

Generator SP 234 is responsible for any switching which occurs between DC bus 258 and the output to generator. Converter SP 236 is responsible for any switching which occurs between DC bus 258 and output to load. As illustrated in FIG. 5, generator SP 234 and converter SP 236 operate IGBT modules.

Local devices, such as a smart display 242, smart battery 244 and smart fuel control 246, are connected to main CPU 232 in power controller 230 via intracontroller bus 240, which may be a RS485 communications link. Smart display 242, smart battery 244 and smart fuel control 246 performs dedicated controller functions, including but not limited to display, energy storage management, and fuel control functions.

Main CPU 232 in power controller 230 is coupled to user port 248 for connection to a computer, workstation, modem or other data terminal equipment which allows for data acquisition and/or remote control. User port 248 may be implemented using a RS232 interface or other compatible interface.

Main CPU 232 in power controller 230 is also coupled to maintenance port 250 for connection to a computer, workstation, modem or other data terminal equipment which allows for remote development, troubleshooting and field upgrades. Maintenance port 250 may be implemented using a RS232 interface or other compatible interface.

The main CPU processor software communicates data through a TCP/IP stack over intercontroller bus 252, typically an Ethernet 10 Base 2 interface, to gather data and send commands between power controllers (as shown and discussed in detail with respect to FIG.

15). In accordance with the present invention, the main CPU processor software provides seamless operation of multiple paralleled units as a single larger generator system. One unit, the master, arbitrates the bus and sends commands to all units.

Intercontroller bus 254, which may be a RS485 communications link, provides high- speed synchronization of power output signals directly between converter SPs, such as converter SP 236. Although the main CPU software is not responsible for communicating on the intercontroller bus 254, it informs converter SPs, including converter SP 236, when main CPU 232 is selected as the master.

External option port bus 256, which may be a RS485 communications link, allows external devices, including but not limited to power meter equipment and auto disconnect switches, to be connected to generator SP 234.

In operation, main CPU 232 begins execution with a power on self-test when power is applied to the control board. External devices are detected providing information to determine operating modes the system is configured to handle. Power controller 230 waits for a start command by making queries to external devices. Once received, power controller 230

sequences up to begin producing power. As a minimum, main CPU 232 sends commands to external smart devices 242,244 and 246 to assist with bringing power controller 230 online.

If selected as the master, the software may also send commands to initiate the sequencing of other power controllers (FIG. 15) connected in parallel. A stop command will shutdown the system bringing it offline.

System I/O The main CPU 232 software interfaces with several electronic circuits (not shown) on the control board to operate devices that are universal to all power controllers 230. Interface to system I/O begins with initialization of registers within power controller 230 to configure internal modes and select external pin control. Once initialized, the software has access to various circuits including discrete inputs/outputs, analog inputs/outputs, and communication ports. These external devices may also have registers within them that require initialization before the device is operational.

Each of the following sub-sections provides a brief overview that defines the peripheral device the software must interface with. The contents of these sub-sections do not define the precise hardware register initialization required.

Communications Referring to FIG. 9, main CPU 232 is responsible for all communication systems in power controller 230. Data transmission between a plurality of power controllers 230 is accomplished through intercontroller bus 252. Main CPU 232 initializes the communications hardware attached to power controller 230 for intercontroller bus 252.

Main CPU 232 provides control for external devices, including smart devices 242,244 and 246, which share information to operate. Data transmission to external devices, including smart display 242, smart battery 244 and smart fuel control 246 devices, is accomplished through intracontroller communications bus 240. Main CPU 232 initializes any communications hardware attached to power controller 230 for intracontroller communications bus 240 and implements features defined for the bus master on intracontroller communications bus 240.

Communications between devices such as switch gear and power meters used for master control functions exchange data across external equipment bus 246. Main CPU 232 initializes any communications hardware attached to power controller 230 for external

equipment port 246 and implements features defined for the bus master on external equipment bus 246.

Communications with a user computer is accomplished through user interface port 248. Main CPU 232 initializes any communications hardware attached to power controller 230 for user interface port 248. In a typical configuration, at power up, the initial baud rate will be selected to 19200 baud, 8 data bits, 1 stop, and no parity. The user has the ability to adjust and save the communications rate setting via user interface port 248 or optional smart external display 242. The saved communications rate is used the next time power controller 230 is powered on. Main CPU 232 communicates with a modem (not shown), such as a Hayes compatible modem, through user interface port 248. Once communications are established, main CPU 232 operates as if were connected to a local computer and operates as a slave on user interface port 248 (it only responds to commands issued).

Communications to service engineers, maintenance centers, and so forth are accomplished through maintenance interface port 250. Main CPU 232 initializes the communications to any hardware attached to power controller 230 for maintenance interface port 250. In a typical implementation, at power up, the initial baud rate will be selected to 19200 baud, 8 data bits, 1 stop, and no parity. The user has the ability to adjust and save the communications rate setting via user port 248 or optional smart external display 242. The saved communications rate is used the next time power controller 230 is powered on. Main CPU 232 communicates with a modem, such as a Hayes compatible modem, through maintenance interface port 250. Once communications are established, main CPU 232 operates as if it were connected to a local computer and operates as a slave on maintenance interface port 250 (it only responds to commands issued).

Controls Referring to FIG. 9, main CPU 232 orchestrates operation for motor, converter, and engine controls for power controller 230. The main CPU 232 does not directly perform motor and converter controls. Rather, generator and converter SP processors 234 and 236 perform the specific control algorithms based on data communicated from main CPU 232. Engine controls are performed directly by main CPU 232 (see FIG. 14).

Main CPU 232 issues commands via SPI communications bus 238 to generator SP 234 to execute the required motor control functions. Generator SP 234 will operate the motor

(not shown) in either a DC bus mode or a RPM mode as selected by main CPU 232. In the DC bus voltage mode, generator SP 234 uses power from the motor to maintain the DC bus at the setpoint. In the RPM mode, generator SP 234 uses power from the motor to maintain the engine speed at the setpoint. Main CPU 232 provides Setpoint values.

Main CPU 232 issues commands via SPI communications bus 238 to converter SP 236 to execute required converter control functions. Converter SP 236 will operate the converter (not shown) in a DC bus mode, output current mode, or output voltage mode as selected by main CPU 232. In the DC bus voltage mode, converter SP 236 regulates the utility power provided by power controller 230 to maintain the internal bus voltage at the setpoint. In the output current mode, converter SP 236 uses power from the DC bus to provide commanded current out of the converter. In the output voltage mode, converter SP 236 uses power from the DC bus to provide commanded voltage out of the converter. Main CPU 232 provides Setpoint values.

Referring to FIGS. 10-12, control loops 260,282 and 300 are used to regulate engine controls. These loops include exhaust gas temperature (EGT) control (FIG. 10), speed control (FIG. 11) and power control (FIG. 12). All three of the control loops 260,282 and 300 are used individually and collectively by main CPU 232 to provide the dynamic control and performance required of power controller 230. These loops are joined together for different modes of operation.

The open-loop light off control algorithm is a programmed command of the fuel device used to inject fuel until combustion begins. In a typical configuration, main CPU 232 takes a snap shot of the engine EGT and begins commanding the fuel device from about 0% to 25% of full command over about 5 seconds. Engine light is declared when the engine EGT rises about 28° C (50° F) from the initial snap shot.

Referring to FIG. 10, EGT control mode loop 260 provides various fuel output commands to regulate the temperature of the turbine. Engine speed signal 262 is used to determine the maximum EGT setpoint temperature 266 in accordance with predetermined setpoint temperature values. EGT setpoint temperature 266 is compared by comparator 268 against feedback EGT signal 270 to determine error signal 272, which is then applied to a proportional-integral (PI) algorithm 274 for determining the fuel command required to regulate EGT at the setpoint. Maximum/minimum fuel limits 278 are used to limit EGT

control algorithm fuel command output 276 to protect from integrator windup. Resultant output signal 280 is regulated EGT signal fuel flow command. In operation, EGT control mode loop 260 operates at about a 100 ms rate.

Referring to FIG. 11, speed control mode loop 282 provides various fuel output commands to regulate the rotating speed of the turbine. Feedback speed signal 288 is read and compared by comparator 286 against setpoint speed signal 284 to determine error signal 290, which is then applied to PI algorithm 292 to determine the fuel command required to regulate engine speed at the setpoint. EGT control (FIG. 10) and maximum/minimum fuel limits are used in conjunction with the speed control algorithm 282 to protect output signal 294 from surge and flame out conditions. Resultant output signal 298 is regulated turbine speed fuel flow command. In a typical implementation, speed control mode loop 282 operates at about a 20ms rate.

Referring to FIG. 12, power control mode loop 300 regulates the power producing potential of the turbine. Feedback power signal 306 is read and compared by comparator 304 against setpoint power signal 302 to determine error signal 308, which is then applied to PI algorithm 310 to determine the speed command required to regulate output power at the setpoint. Maximum/minimum speed limits are used to limit the power control algorithm speed command output to protect output signal 312 from running into over speed and under speed conditions. Resultant output signal 316 is regulated power signal turbine speed command. In a typical implementation, the maximum operating speed of the turbine is generally 96,000 RPM and the minimum operating speed of the turbine is generally 45,000 RPM. The loop operates generally at about a 500 ms rate.

Start Only Battery Referring to FIG. 14, energy storage device 470 may be a start only battery. In the DC bus voltage control mode, start only battery 470 provides energy to regulate voltage to the setpoint command. Main CPU 472 commands the bus voltage to control at different values depending on the configuration of power controller 478. In the state of charge (SOC) control mode, the start only battery system provides a recharging power demand when requested.

Available recharging power is generally equivalent to maximum engine power less power being supplied to the output load and system parasitic loads. Main CPU 472 transmits a

recharging power level that is the minimum of the original power demand and available recharging power.

Transient Batter The transient battery provides the DC bus voltage control as described below as well as the state of charge (SOC) control mode described for the start only battery. The transient battery contains a larger energy storage device than the start only battery.

DC Bus Voltage Control DC bus 462 supplies power for logic power, external components and system power output. TABLE 1 defines the setpoint the bus voltage is to be controlled at based on the output power configuration of power controller 478: TABLE 1 B3 POWER OUTPUT SETPOINT 480/400 VAC Output 800 Vdc 240/208 VAC Output 400 Vdc In the various operating modes, power controller 478 will have different control algorithms responsible for managing the DC bus voltage level. Any of the battery options 470 as well as SPs 456 and 458 have modes that control power flow to regulate the voltage level of DC bus 462. Under any operating circumstances, only one device is commanded to a mode that regulates DC bus 462. Multiple algorithms would require sharing logic that would inevitably make system response slower and software more difficult to comprehend.

System States Referring to FIG. 13, state diagram 320 showing various operating states of power controller 478 is illustrated. Sequencing the system through the entire operating procedure requires power controller to transition through the operating states defined in TABLE 2.

TABLE 2 STATE SYSTEM DESCRIPTION # STATE

0 Power Up Performs activities of initializing and testing the system.

1 Stand By Closer power to bus and continues system monitoring while waiting for a start command.

2 Prepare to Initializes any external devices preparing for the start Start procedure.

3 Bearing Configures the system and commands the engine to be Lift Off rotated to a predetermined RPM, such as 25,000 RPM.

4 Open Loop Turns on ignition system and commands fuel open loop Light Off to light the engine.

5 Closed Loop Continues motoring and closed fuel control until the Acceleration system reaches the no load state.

6 Run Engine operates in a no load self-sustaining state producing power only to operate the controller.

7 Load Converter output contactor is closed and system is producing power.

8 Re-Charge System operates off of fuel only and produces power for recharging energy storage device if installed.

9 Cooldown System is motoring engine to reduce EGT before shutting down.

10 Re-Start Reduces engine speed to begin open loop light when a start command is received in the cooldown state.

11 Re-Light Performs a turbine re-light in transition from the cooldown to warmdown state. Allows continued engine cooling when motoring is no longer possible.

12 Warmdown Sustains turbine operation with fuel at a predetermined RPM, such as 50,000 RPM, to cool when engine motoring is not possible.

13 Shutdown Reconfigures the system after a cooldown to enter the stand by state.

14 Fault Turns off all outputs when presence of fault which

disables power conversion exists. Logic power is still available for interrogating system faults.

15 Disable Fault has occurred where processing may no longer be possible. All system operation is disabled.

Main CPU 472 begins execution in the"power up"state 322 after power is applied.

Transition to the"stand by"state 324 is performed upon successfully completing the tasks of the"power up"state 322. Initiating a start cycle transitions the system to the"prepare to start"state 326 where all system components are initialized for an engine start. The engine then sequences through start states and onto the"run/load"state 328. To shutdown the system, a stop command which sends the system into either"warm down"or"cool down" state 332 is initiated. Systems that have a battery may enter the"re-charge"state 334 prior to entering the"warm down"or"cool down"state 332. When the system has finally completed the"warm down"or"cool down"process 332, a transition through the"shut down"state 330 will be made before the system re-enters the"standby"state 324 awaiting the next start cycle.

During any state, detection of a fault with a system severity level indicating the system should not be operated will transition the system state to"fault"state 334. Detection of faults that indicate a processor failure has occurred will transition the system to the"disable"state 336.

One skilled in the art will recognize that in order to accommodate each mode of operation, the state diagram is multidimensional to provide a unique state for each operating mode. For example, in the"prepare to start"state 326, control requirements will vary depending on the selected operating mode. Therefore, the presence of a stand-alone"prepare to start"state 326, stand-alone transient"prepare to start"state 326, utility grid connect "prepare to start"state 326 and utility grid connect transient"prepare to start"state 326 will be required. Each combination is known as a system configuration (SYSCON) sequence.

Main CPU 472 identifies each of the different system configuration sequences in a 16-bit word known as a SYSCON word, which is a bit-wise construction of an operating mode and system state number. In a typical configuration, the system state number is packed in bits 0 through 11. The operating mode number is packed in bits 12 through 15. This packing method provides the system with the capability of sequence through 4096 different system states in 16 different operating modes.

Separate"power up"322, "re-light"338,"warm down"332, "fault"334 and"disable" 336 states are not required for each mode of operation. The contents of these states are mode independent.

"Power Up"State Operation of the system begins in the"power up"state 322 once application of power activates main CPU 472. Once power is applied to power controller 478, all the hardware components will be automatically reset by hardware circuitry. Main CPU 472 is responsible for ensuring the hardware is functioning correctly and configure the components for operation. Main CPU 472 also initializes its own internal data structures and begins execution by starting the Real-Time Operating System (RTOS). Successful completion of these tasks directs transition of the software to the"stand by"state 324. Main CPU 472 performs these procedures in the following order: 1. Initialize main CPU 472 2. Perform RAM Test 3. Perform FLASH Checksum 4. Start RTOS 5. Run Remaining POST 6. Initialize SPI Communications 7. Verify Generator SP Checksum 8. Verify Converter SP Checksum 9. Initialize IntraController Communications 10. Resolve External Device Addresses 11. Look at Input Line Voltage 12. Determine Mode 13. Initialize Maintenance Port 14. Initialize User Port 15. Initialize External Option Port 16. Initialize InterController 17. Chose Master/Co-Master 18. Resolve Addressing 19. Transition to Stand By State (depends on operating mode)

"Stand By"State Main CPU 472 continues to perform normal system monitoring in the"stand by"state 324 while it waits for a start command signal. Main CPU 472 commands either energy storage device 470 or utility 468 to provide continuous power supply. In operation, main CPU 472 will often be left powered on waiting to be start or for troubleshooting purposes.

While main CPU 472 is powered up, the software continues to monitor the system and perform diagnostics in case any failures should occur. All communications will continue to operate providing interface to external sources. A start command will transition the system to the"prepare to start"state 326.

"Prepare to Start"State Main CPU 472 prepares the control system components for the engine start process.

Many external devices may require additional time for hardware initialization before the actual start procedure can commence. The"prepare to start"state 326 provides those devices the necessary time to perform initialization and send acknowledgment to the main CPU 472 that the start process can begin. Once also systems are ready to go, the software shall transition to the"bearing lift off"state 328.

"Bearing Lift Off'State Main CPU 472 commands generator SP 456 to motor the engine 454 from typically about 0 to 25,000 RPM to accomplish the bearing lift off procedure. A check is performed to ensure the shaft is rotating before transition to the next state occurs.

"Open Loop Light Off'State Once the motor 452 reaches its liftoff speed, the software commences and ensures combustion is occurring in the turbine. In a typical configuration, main CPU 472 commands generator SP 456 to motor the engine 454 to a dwell speed of about 25,000 RPM. Execution of the open loop light off state 340 starts combustion. Main CPU 472 then verifies that the engine 454 has not met the"fail to light"criteria before transition to the"closed loop accel" state 342.

"Closed Loop Accel"State Main CPU 472 sequences engine 454 through a combustion heating process to bring the engine 454 to a self-sustaining operating point. In a typical configuration, commands are provided to generator SP 456 commanding an increase in engine speed to about 45,000 RPM

at a rate of about 4000 RPM/sec. Fuel controls are executed to provide combustion and engine heating. When engine 454 reaches"no load" (requires no electrical power to motor), the software transitions to"run"state 344.

"Run"State Main CPU 472 continues operation of control algorithms to operate the engine at no load. Power may be produced from engine 454 for operating control electronics and recharging any energy storage device 470 for starting. No power is output from load converter 458. A power enable signal transitions the software into"load"state 346. A stop command transitions the system to begin shutdown procedures (may vary depending on operating mode).

"Load"State Main CPU 472 continues operation of control algorithms to operate the engine 454 at the desired load. Load commands are issued through the communications ports, display or system loads. A stop command transitions main CPU 472 to begin shutdown procedures (may vary depending on operating mode). A power disable signal can transition main CPU 472 back to"run"state 344.

"Re-charge"State Systems that have an energy storage option may be required to charge energy storage device 470 to maximum capacity before entering the"warmdown"348 or"cooldown"332 states. During the"re-charge"state 334 of operation, main CPU 472 continues operation of the turbine producing power for battery charging and controller supply. No out power is provided. When the energy storage device 470 has charged, the system transitions to either the"cooldown"332 or"warmdown"348 state depending on system fault conditions.

"Cool Down"State "Cool down"state 332 provides the ability to cool the turbine after operation and a means of purging fuel from the combustor. After normal operation, software sequences the system into"cool down"state 332. In a typical configuration, engine 454 is motored to a cool down speed of about 45,000 RPM. Airflow continues to move through engine 454 preventing hot air from migrating to mechanical components in the cold section. This motoring process continues until the engine EGT falls below a cool down temperature of about 193°C (380°F).

Cool down may be entered at much lower than the final cool down temperature when engine

454 fails to light. The engine's combustor requires purging of excess fuel which may remain.

The software always operates the cool down cycle for a minimum purge time of 60 seconds.

This purge time ensures remaining fuel is evacuated from the combustor. Completion of this process transitions the system into the"shutdown"state 330. For user convenience, the system does not require a completion of the enter"cooldown"state 332 before being able to attempt a restart. Issuing a start command transitions the system into the"restart"state 350.

"Restart"State Engine 454 is configured from the"cool down"state 332 before engine 454 can be restart. In a typical configuration, the software lowers the engine speed to about 25,000 RPM at a rate of 4,000 RPM/sec. Once the engine speed has reached this level, the software transitions the system into the"open loop light off state to perform the actual engine start.

"Shutdown"State During the"shutdown"state 330, the engine rotor is brought to rest and system outputs are configured for idle operation. In a typical configuration, the software commands the rotor to rest by lowering the engine speed at a rate of 2,000 RPM/sec or no load condition, whichever is faster. Once the speed reaches about 14,000 RPM, the generator SP is commanded to reduce the shaft speed to about 0 RPM in less than 1 second.

"Re-light"State When a system fault occurs where no power is provided from the utility or energy storage device 470, the software re-ignites combustion to perform a warm down. The generator SP is configured to regulate voltage (power) for the internal DC bus. Fuel is added as defined in the open loop light off fuel control algorithm to ensure combustion occurs.

Detection of engine light will transition the system to"warm down"state 348.

"Warm Down"State Fuel is provided when no electric power is available to operate engine 454 at a no load condition to lower the operating temperature in"warm down"state 348. In a typical configuration, engine speed is operated at about 50,000 RPM by supplying fuel through the speed control algorithm. Engine temperatures less than about 343°C (650°F) causes the system to transition to"shutdown"state 330.

"Fault"State

The present invention disables all outputs placing the system in a safe configuration when faults that prohibit safe operation of the turbine system are present. Operation of system monitoring and communications will continue if the energy is available.

"Disable"State The system disables all outputs placing the system in a safe configuration when faults that prohibit safe operation of the turbine system are present. System monitoring and communications will most likely not continue.

Modes of Operation The turbine works in two major modes-utility grid-connect and stand-alone. In the <BR> <BR> utility grid-connect mode, the electric power distribution system i. e. , the utility grid, supplies a reference voltage and phase, and the turbine supplies power in synchronism with the utility grid. In the stand-alone mode, the turbine supplies its own reference voltage and phase, and supplies power directly to the load. The power controller switches automatically between the modes.

Within the two major modes of operation are sub-modes. These modes include stand- alone black start, stand-alone transient, utility grid connect and utility grid connect transient.

The criteria for selecting an operating mode is based on numerous factors, including but not limited to, the presence of voltage on the output terminals, the black start battery option, and the transient battery option.

Referring to FIG. 14, generator converter 456 and load converter 458 provide an interface for energy source 460 and utility 468, respectively, to DC bus 462. For illustrative purposes, energy source 460 is a turbine including engine 454 and generator 452. Fuel device 474 provides fuel via fuel line 476 to engine 454. Generator converter 456 and load converter 458 operate as customized bi-directional switching converters under the control of controller 472. In particular, controller 472 reconfigures the generator converter 456 and load converter 458 into different configurations to provide for the various modes of operation. These modes include stand-alone black start, stand-alone transient, utility grid connect and utility grid connect transient as discussed in detail below. Controller 472 controls the way in which generator 452 and utility 468 sinks or sources power, and DC bus 462 is regulated at any time.

In this way, energy source 460, utility/load 468 and energy storage device 470 can be used to supply, store and/or use power in an efficient manner. Controller 472 provides command

signals via line 479 to engine 454 to determine the speed of turbine 460. The speed of turbine 460 is maintained through generator 452. Controller 472 also provides command signals via control line 480 to fuel device 474 to maintain the EGT of the engine 454 at its maximum efficiency point. Generator SP 456 is responsible for maintaining the speed of the turbine 460, but putting current into generator 452 or pulling current out of generator 452.

Stand-alone Black Start Referring to FIG. 14, in the stand-alone black start mode, energy storage device 470, such as battery, is provided for starting purposes while energy source 460, such as turbine including engine 454 and generator 452, supplies all transient and steady state energy.

Referring to TABLE 3, controls for a typical stand-alone black start mode are shown.

TABLE 3 SYSTEM ENGINE MOTOR CONVERTER ENERGY STORAGE STATE CONTROLS CONTROLS CONTROLS CONTROLS Power Up---- Stand By---DC Bus Prepare to Start---DC Bus Bearing Lift Off-RPM-DC Bus Open Loop Light Off Open Loop RPM-DC Bus Light Closed Loop Accel EGT RPM-DC Bus Run Speed DC Bus-SOC Load Speed DC Bus Voltage SOC Recharge Speed DC Bus-SOC Cool Down-RPM-DC Bus Restart-RPM-DC Bus Shutdown-RPM-DC Bus Re-light Speed DC Bus Warm Down Speed DC Bus Fault Disable Stand-alone Transient

In the stand-alone transient mode, storage device 479 is provided for the purpose of starting and assisting the energy source 460, in this example the turbine, to supply maximum rated output power during transient conditions. Storage device 479, typically a battery, is always attached to DC bus 462 during operation, supplying energy in the form of current to maintain the voltage on DC bus 462. Converter/SP 458 provides a constant voltage source when producing output power. As a result, load 468 is always supplied the proper AC voltage value that it requires. Referring to TABLE 4, controls for a typical stand-alone transient mode are shown.

TABLE 4 SYSTEM ENGINE MOTOR CONVERTER ENERGY STORAGE STATE CONTROLS CONTROLS CONTROLS CONTROLS Power Up---- Stand By---DC Bus Prepare to Start---DC Bus Bearing Lift Off-RPM-DC Bus Open Loop Light Off Open Loop RPM-DC Bus Light Closed Loop Accel EGT RPM-DC Bus Run Power & EGT RPM-DC Bus Load Power & EGT RPM Voltage DC Bus Recharge Power & EGT RPM-DC Bus Cool Down-RPM-DC Bus Restart-RPM-DC Bus Shutdown-RPM-DC Bus Re-light Speed DC Bus- Warm Down Speed DC Bus Fault Disable Utility Grid Connect Referring to FIG. 14, in the utility grid connect mode, the energy source 460, in this example the turbine is connected to the utility grid 468 providing load leveling and

management where transients are handled by the utility grid 468. The system operates as a current source, pumping current into utility 468. Referring to TABLE 5, controls for a typical utility grid connect mode are shown.

TABLE 5 SYSTEM ENGINE MOTOR CONVERTER ENERGY STORAGE STATE CONTROLS CONTROLS CONTROLS CONTROLS Power Up---N/A Stand By---N/A Prepare to Start--DC Bus N/A Bearing Lift Off-RPM DC Bus N/A Open Loop Light Off Open Loop RPM DC Bus N/A Light Closed Loop Accel EGT RPM DC Bus N/A Run Power & EGT RPM DC Bus N/A Load Power & EGT RPM DC Bus N/A Recharge N/A N/A N/A N/A Cool Down-RPM DC Bus N/A Restart-RPM DC Bus N/A Shutdown-RPM DC Bus N/A Re-light Speed DC Bus-N/A Warm Down Speed DC Bus-N/A <BR> <BR> Fault---N/A<BR> Disable---N/A Utility Grid Connect Transient In the utility grid connect transient mode, the energy source 460, in this example the turbine, is connected to the utility grid 468 providing load leveling and management. The turbine that is assisted by energy storage device 470, typically a battery, handles transients.

The system operates as a current source, pumping current into utility 468 with the assistance of energy storage device 470. Referring to TABLE 6, controls for a typical utility grid connect transient mode are shown.

TABLE 6 SYSTEM ENGINE MOTOR CONVERTER ENERGY STORAGE STATE CONTROLS CONTROLS CONTROLS CONTROLS Power Up Stand By---DC Bus<BR> Prepare to Start---DC Bus Bearing Lift Off-RPM-DC Bus Open Loop Light Off Open Loop RPM-DC Bus Light Closed Loop Accel EGT RPM-DC Bus Run Power & EGT RPM-DC Bus Load Power & EGT RPM Current DC Bus Recharge Power & EGT RPM-DC Bus Cool Down-RPM-DC Bus<BR> Restart-RPM-DC Bus Shutdown-RPM-DC Bus Re-light Speed DCBus Warm Down Speed DC Bus Fault Disable Multi-pack Operation In accordance with the present invention, the power controller can operate in a single or multi-pack configuration. In particular, power controller, in addition to being a controller for a single turbogenerator, is capable of sequencing multiple systems as well. Referring to FIG. 15, for illustrative purposes, multi-pack system 510 including three power controllers 518,520 and 522 is shown. The ability to control multiple controllers 518,520 and 522 is made possible through digital communications interface and control logic contained in each controllers main CPU (not shown).

Two communications busses 530 and 534 are used to create the intercontroller digital communications interface for multi-pack operation. One bus 534 is used for slower data

exchange while the other bus 530 generates synchronization packets at a faster rate. In a typical implementation, for example, an IEEE-502.3 bus links each of the controllers 518,520 and 522 together for slower communications including data acquisition, start, stop, power demand and mode selection functionality. An RS485 bus links each of the systems together providing synchronization of the output power waveforms.

One skilled in the art will recognize that the number of power controllers that can be connected together is not limited to three, but rather any number of controllers can be connected together in a multi-pack configuration. Each power controller 518,520 and 522 includes its own energy storage device 524,526 and 528, respectively, such as a battery. In accordance with another embodiment of the invention, power controllers 518,520 and 522 can all be connected to the same single energy storage device (not shown), typically a very large energy storage device which would be rated too big for an individual turbine.

Distribution panel, typically comprised of circuit breakers, provides for distribution of energy.

Multi-pack control logic determines at power up that one controller is the master and the other controllers become slave devices. The master is in charge of handling all user-input commands, initiating all inter-system communications transactions, and dispatching units.

While all controllers 518,520 and 522 contain the functionality to be a master, to alleviate control and bus contention, one controller is designated as the master.

At power up, the individual controllers 518,520 and 522 determine what external input devices they have connected. When a controller contains a minimum number of input devices it sends a transmission on intercontroller bus 530 claiming to be master. All controllers 518,520 and 522 claiming to be a master begin resolving who should be master.

Once a master is chosen, an address resolution protocol is executed to assign addresses to each slave system. After choosing the master and assigning slave addresses, multi-pack system 510 can begin operating.

A co-master is also selected during the master and address resolution cycle. The job of the co-master is to act like a slave during normal operations. The co-master should receive a constant transmission packet from the master indicating that the master is still operating correctly. When this packet is not received within a safe time period, 20 ms for example, the co-master may immediately become the master and take over master control responsibilities.

Logic in the master configures all slave turbogenerator systems. Slaves are selected to be either utility grid-connect (current source) or standalone (voltage source). A master controller, when selected, will communicate with its output converter logic (converter SP) that this system is a master. The converter SP is then responsible for transmitting packets over the intercontroller bus 530, synchronizing the output waveforms with all slave systems.

Transmitted packets will include at least the angle of the output waveform and error-checking information with transmission expected every quarter cycle to one cycle.

Master control logic will dispatch units based on one of three modes of operation: (1) peak shaving, (2) load following, or (3) base load. Peak shaving measures the total power consumption in a building or application using a power meter, and the multi-pack system 510 reduces the utility consumption of a fixed load, thereby reducing the utility rate schedule and increasing the overall economic return of the turbogenerator. Load following is a subset of peak shaving where a power meter measures the total power consumption in a building or application and the multi-pack system 10 reduces the utility consumption to zero load. In base load, the multi-pack system 10 provides a fixed load and the utility supplements the load in a building or application. Each of these control modes require different control strategies to optimize the total operating efficiency.

A minimum number of input devices are typically desired for a system 510 to claim it is a master during the master resolution process. Input devices that are looked for include a display panel, an active RS232 connection and a power meter connected to the option port.

Multi-pack system 510 typically requires a display panel or RS232 connection for receiving user-input commands and power meter for load following or peak shaving.

In accordance with the present invention, the master control logic dispatches controllers based on operating time. This would involve turning off controllers that have been operating for long periods of time and turning on controllers with less operating time, thereby reducing wear on specific systems.

Utility Grid Analysis and Transient Ride Through Referring to FIGS. 16-18, transient handling system 580 for power controller 620 is illustrated. Transient handling system 580 allows power controller 620 to ride through transients which are associated with switching of correction capacitors on utility grid 616 which causes voltage spikes followed by ringing. Transient handling system 580 also allows

ride through of other faults, including but not limited to, short circuit faults on utility grid 616, which cleared successfully, cause voltage sags. Transient handling system 580 is particularly effective towards handling transients associated with digital controllers, which generally have a slower current response rate due to A/D conversion sampling. During a transient, a large change in the current can occur in between A/D conversions. The high voltage impulse caused by transients typically causes an over current in digital power controllers.

As is illustrated in FIG. 17, a graph 590 showing transients typically present on utility grid 616 is shown. The duration of a voltage transient, measured in seconds, is shown on the x-axis and its magnitude, measured in volts, is shown on the y-axis. A capacitor switching transient, such as shown at 592, which is relatively high in magnitude (up to about 200%) and short in duration (somewhere between 1 and 20 milliseconds) could be problematic to operation of a power controller.

Referring to FIGS. 16-18, changes on utility grid 616 are reflected as changes in the magnitude of the voltage. In particular, the type and seriousness of any fault or event on utility grid 616 can be determined by magnitude estimator 584, which monitors the magnitude and duration of any change on utility grid 616.

In accordance with the present invention, the effect of voltage transients can be minimized by monitoring the current such that when it exceeds a predetermined level, switching is stopped so that the current can decay, thereby preventing the current from exceeding its predetermined level. The present invention thus takes advantage of analog over current detection circuits that have a faster response than transient detection based on digital sampling of current and voltage. Longer duration transients indicate abnormal utility grid conditions. These must be detected so power controller 620 can shut down in a safe manner.

In accordance with the present invention, algorithms used to operate power controller 620 provide protection against islanding of power controller 620 in the absence of utility-supplied grid voltage. Near short or near open islands are detected within milliseconds through loss of current control. Islands whose load is more closely matched to the power controller output will be detected through abnormal voltage magnitudes and frequencies as detected by magnitude estimator 584.

In particular, referring to FIG. 18, power controller 620 includes brake resistor 612 connected across DC bus 622. Brake resistor 612 acts as a resistive load, absorbing energy

when converter SP 608 is turned off. In operation, when converter SP 608 is turned off, power is no longer exchanged with utility grid 616, but power is still being received from the turbine, which is absorbed by brake resistor 612. The present invention detects the DC voltage between generator and converter SPs 606 and 608. When the voltage starts to rise, brake resistor 612 is turned on to allow it to absorb energy.

In a typical configuration, AC motor 618 produces three phases of AC at variable frequencies. AC/DC converter 602 under the control of motor SP 606 converts the AC to DC which is then applied to DC bus 622 (regulated for example at 800 vDC) which is supported by capacitor 610 (for example, at 800 microfarads with two milliseconds of energy storage).

AC/DC converter 604, under the control of converter SP 608, converts the DC into three- phase AC, and applies it to utility grid 616. In accordance with the present invention, current from DC bus 622 can by dissipated in brake resistor 612 via modulation of switch 614 operating under the control of motor SP 606. Switch 614 may be an IGBT switch, although one skilled in the art will recognize that other conventional or newly developed switches may be utilized as well.

Motor SP 606 controls switch 614 in accordance to the magnitude of the voltage on DC bus 622. The bus voltage of DC bus 622 is typically maintained by converter SP 608, which shuttles power in and out of utility grid 616 to keep DC bus 622 regulated at, for example, 800 vDC. When converter SP 608 is turned off, it no longer is able to maintain the voltage of DC bus 622, so power coming in from the motor causes bus voltage of DC bus 622 to rise quickly. The rise in voltage is detected by motor SP 606, which turns on brake resistor 612 and modulates it on and off until the bus voltage is restored to its desired voltage, for example, 800 vDC. Converter SP 608 detects when the utility grid transient has dissipated, i. e. , AC current has decayed to zero and restarts the converter side of power controller 620. Brake resistor 612 is sized so that it can ride through the transient and the time taken to restart converter.

Referring to FIGS. 18 and 20, in accordance with the present invention, both the voltage and zero crossings (to determine where the AC waveform of utility grid 616 crosses zero) are monitored to provide an accurate model of utility grid 616. Utility grid analysis system includes angle estimator 582, magnitude estimator 584 and phase locked loop 586.

The present invention continuously monitors utility grid voltage and based on these

measurements, estimates the utility grid angle, thus facilitating recognition of under/over voltages and sudden transients. Current limits are set to disable DC/AC converter 604 when current exceeds a maximum and wait until current decays to an acceptable level. The result of measuring the current and cutting it off is to allow DC/AC converter 604 to ride through transients better. Thus when DC/AC converter 608 is no longer exchanging power with utility grid 616, power is dissipated in brake resistor 612.

In accordance with the present invention, converter SP 608 is capable of monitoring the voltage and current at utility grid 616 simultaneously. In particular, power controller 620 includes a utility grid analysis algorithm. One skilled in the art will recognize that estimates of the utility grid angle and magnitude may be derived via conventional algorithms or means.

The true utility grid angle OAC, which is the angle of the generating source, cycles through from 0 to 2n and back to 0 at a rate of 60 hertz. The voltage magnitude estimates of the three phases are designated Vl magS V2 mag and V3 mag and the voltage measurement of the three phases are designated Vl, V2 and V3.

A waveform, constructed based upon the estimates of the magnitude and angle for each phase, indicates what a correct measurement would look like. For example, using the first of the three phase voltages, the cosine of the true utility grid angle OAC is multiplied by the voltage magnitude estimate Vl mag, with the product being a cosine-like waveform.

Ideally, the product would be voltage measurement Vl.

Feedback loop 588 uses the difference between the absolute magnitude of the measurement of Vl and of the constructed waveform to adjusts the magnitude of the magnitude estimate VI mag. One skilled in the art will recognize that the other two phases of three-phase signal can be adjusted similarly, with different angle templates corresponding to different phases of the signal. Thus, magnitude estimate Vu gag and angle estimate OEST are used to update magnitude estimate Vl mag. Voltage magnitude estimates Vs mag, V2 mag and V3 mag are steady state values used in a feedback configuration to track the magnitude of voltage measurements Vi, V2 and V3. By dividing the measured voltages Vl by the estimates of the magnitude Vl mag, the cosine of the angle for the first phase can be determined (similarly, the cosine of the angles of the other signals will be similarly determined).

In accordance with the present invention, the most advantageous estimate for the cosine of the angle, generally the one that is changing the most rapidly, is chosen to determine

the instantaneous measured angle. In most cases, the phase that has an estimate for the cosine of an angle closest to zero is selected since it yields the greatest accuracy. Utility grid analysis system 580 thus includes logic to select which one of the cosines to use. The angle chosen is applied to angle estimator 582, from which an estimate of the instantaneous angle OEST of utility grid 616 is calculated and applied to phase locked loop 586 to produce a filtered frequency. The angle is thus differentiated to form a frequency that is then passed through a low pass filter (not shown). Phase locked loop 586 integrates the frequency and also locks the phase of the estimated instantaneous angle OEST, which may have changed in phase due to differentiation and integration, to the phase of true utility grid angle OAC.

In a typical operation, when the phase changes suddenly on measured voltage Vl, the algorithm of the present invention compares the product of the magnitude estimate Vl mag and the cosine of true utility grid angle OAc against the real magnitude multiplied by the cosine of a different angle. A sudden jump in magnitude would be realized.

Thus, three reasonably constant DC voltage magnitude estimates are generated. A change in one of those voltages indicates whether the transient present on utility grid 616 is substantial or not. One skilled in the art will recognize that there are a number of ways to determine whether a transient is substantial or not, i. e. whether abnormal conditions exist on the utility grid system, which require power controller 620 to shut down. A transient can be deemed substantial based upon the size of the voltage magnitude and duration. Examples of the criteria for shutting down power controller 620 are shown in FIG. 17. Detection of abnormal utility grid behavior can also be determined by examining the frequency estimate.

On detecting abnormal utility grid behavior, a utility grid fault shutdown is initiated.

When system controller 620 initiates a utility grid fault shutdown, output contactor is opened within a predetermined period of time, for example, 100 msec, and the main fuel trip solenoid (not shown) is closed, removing fuel from the turbogenerator. A warm shutdown ensues during which control power is supplied from generator 618 as it slows down. In a typical configuration, the warm-down lasts about 1-2 minutes before the rotor (not shown) is stopped.

The control software does not allow a restart until utility grid voltage and frequency are within permitted limits.

Having now described the invention in accordance with the requirements of the patent statutes, those skilled in this art will understand how to make changes and modifications in

the present invention to meet their specific requirements or conditions. For example, the power controller, while described generally, may be implemented in an analog or digital configuration. In the preferred digital configuration, one skilled in the art will recognize that various terms utilized in the invention are generic to both analog and digital configurations of power controller. For example, converters referenced in the present application is a general term which includes inverters, signal processors referenced in the present application is a general term which includes digital signal processors, and so forth. Correspondingly, in a digital implementation of the present invention, inverters and digital signal processors would be utilized. Such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.

ABSTRACT OF THE DISCLOSURE POWER CONTROLLER A power controller provides a distributed generation power networking system in which bi-directional power converters are used with a common DC bus for permitting compatibility between various energy components. Each power converter operates essentially as a customized bi-directional switching converter configured, under the control of the power controller, to provide an interface for a specific energy component to the DC bus. The power controller controls the way in which each energy component, at any moment, will sink or source power, and the manner in which the DC bus is regulated. In this way, various energy components can be used to supply, store and/or use power in an efficient manner. The various energy components include energy sources, loads, storage devices and combinations thereof.