Field of the Invention The present invention relates to an electrical generator power system which includes an engine/generator set integrated with a direct current (DC) power supply.

Background of the Invention In many applications of electrical generator systems, load demand relative to generator power capacity is often low. However, in most generator systems, the engine/generator must be run even when only a small load is present. Another problem with many electrical generator systems is that the speed of the internal combustion engine has to be operated at a constant high speed to provide power even though only a small electrical load is present. Thus, a substantially constant level of noise is created regardless of the load present.

- In many applications, such as recreational vehicle (RV) applications or commercial mobile vehicles, storage batteries in conjunction with DC (direct current) to AC (alternating current) inverter circuitry are often used to provide "silent" power during periods of time when little or no noise is desired. However, the storage batteries can only be used for a limited period of time without any charging. After use of the storage batteries for a limited period of time, the engine/generator has to be run to provide the AC power which often creates an undesired level of noise.

While storage batteries can provide power for a limited period of time during low load demands, storage batteries typically do not supply sufficient power for high load demands, such as air conditioners (A/C) or a clothes washing machine, etc. Thus it is necessary to run the engine/generator to meet the relatively high load demands of these appliances. In addition, even for a small load, the storage batteries

can only be used for a limited period of time as discussed above.

Engineers have designed so-called load management systems which control power distribution to various loads by varying the speed of the engine/generator set. When a new load is added into a power supply bus line, the load management system senses the additional load and requires more power from the engine/generator. In addition to other problems, one problem with these systems is that the engine at the reduced speed might not have the power to satisfy new load demands and unacceptable low voltage excursions might be experienced.

Moreover, despite the fact that the speed of the generator set is varied, the engine/generator set is operated even when extremely low loads are present. Moreover, the engine/generator set typically has a top end speed which limits the electrical load it can support . ^' The present invention solves these and other problems associated with existing systems.

Summary of the Invention The present invention relates to a generator power system which integrates an engine/generator set with a DC power supply.

In one embodiment, DC batteries are used as a power resource when a small load, such as a light, a radio, etc., is present. The DC voltage output of the batteries is a low voltage, such as about 12 volts. The

DC voltage output from the batteries is boosted or stepped up during a "boost stage" to a higher DC voltage, about 170 volts, by a boost transformer circuit. The high DC voltage is further inverted to an AC voltage by an inverter circuit, at about 120 volts RMS (root mean square) , which is needed for many consumer appliances.

In one embodiment of the invention, an inverter circuit is present which includes switching transistors for the conversion of DC current from the battery source to AC current. In one embodiment of the present invention, a high frequency inverter system is used to boost or increase the DC voltage provided by the batteries. DC voltage is drawn from the battery or batteries to a transformer with the primary transistors switching at a higher frequency to create an AC output. The AC output of the transformer secondary winding is rectified resulting in a high DC voltage, about 170 volts. To complete the inversion into AC power, the DC power is alternatively switched in an H-bridge inverter configuration of field effect transistors in an inverter circuit. This produces a quasi-sine wave output to a load bus .

In yet another embodiment, the DC power is inverted by an inverter circuit into a synthesized sine wave.

In one embodiment, the engine/generator is operated when the load is relatively high and the storage batteries cannot provide sufficient power. When the load demand is high, the DC voltage which is provided by the storage batteries starts to drop. Upon detecting this drop in voltage, the engine/generator starts to run and provides a DC voltage to keep the combined DC voltage output of the engine/generator and storage batteries constant. The greater the load, the faster the engine/generator runs. When the DC power generated by the engine/generator set is higher than the DC power provided from the storage batteries, the engine/generator set is also used to charge the storage batteries while providing DC power to the load bus. While the storage batteries are being charged, the storage batteries cannot be boosted so as to provide high voltage DC power, ultimately inverted to provide AC

power to the electrical loads, and vice versa.

In one embodiment, the engine/generator also starts to run when the storage batteries are low on charge or potential energy and charges the storage batteries.

In one embodiment, when the load keeps increasing and reaches the maximum engine/generator's power supply capacity, the storage batteries stop being charged and enter the boost stage to assist the engine/generator in maintaining the high voltage DC bus and ultimately the AC power output of the integrated system.

In one embodiment, when the load reaches the maximum capacity of the engine/generator's power supply capacity, the speed of the engine/generator is fixed.

In one embodiment, the battery boost stage fulfills the need to improve performance of the system during load-on transient operation created when an electrical load is initially added to the load bus by boosting the storage batteries voltage to overcome any voltage deficiency or voltage undershoot of the system.

In one embodiment, the battery charge stage fulfills the need to improve performance of the system during load-off transient operation created when an electrical load is deleted from the load bus by charging battery to overcome any excess voltage or voltage overshoot of the system.

In one embodiment, a DC voltage sensor is used to sense the DC voltage at the input of the DC load bus to H-bridge inverter circuitry which converts the DC current into AC current for use by the AC loads such as appliances. The sensor sends an electrical signal to a microprocessor representative of the DC voltage so sensed, and the microprocessor controls the operating speed of the engine/generator set and the boost/charge status of the batteries to maintain the proper, constant DC voltage level on the high voltage, 170 volts, DC load

bus .

In one embodiment, an AC voltage sensor is used to sense the AC voltage at the output of the H- bridge inverter circuitry. The AC voltage sensor sends an electrical signal representative of the AC voltage so sensed to the microprocessor. In response to this signal the microprocessor controls operation of the inverter circuitry so as to regulate the electrical output from the inverter circuitry to provide constant root mean square (RMS) AC voltage.

In one embodiment, a current sensor is used to sense the electrical current present at the output of the inverter. The current sensor sends an electrical signal representative of the electrical current so sensed to the microprocessor. In response to this signal, the microprocessor controls operation of the system in accordance with the varying electrical load demand which is present including transient conditions. In one embodiment, a battery voltage sensor is used to sense an output voltage of the storage batteries . The battery voltage sensor sends an electrical signal to the microprocessor representative of the sensed battery output voltage, which controls charging of the batteries by use of suitable battery charger circuitry.

In one embodiment, a charging current sensor senses the charging current being input to the batteries . The charging current sensor sends an electrical signal representative of the sensed charging current to the microprocessor, and the microprocessor appropriately varies the charging current input to the batteries.

These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention and its advantages and

objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

Brief Description of the Drawings In the drawings in which like reference numerals and letters generally indicate corresponding parts throughout the several views:

FIG. 1 is a functional block diagram of an integrated power system providing power to various AC loads in accordance with the principles of the present invention; FIG. 2 is a functional block diagram of an integrated power system similar to that of Figure 1 further showing inclusion of an engine/generator set and DC batteries in the integrated power system;

FIG. 3 is a functional block diagram of an integrated power system similar to that of Figure 2 showing additional details;

FIG. 4 is an electrical schematic diagram of battery boost circuitry, battery charging circuitry, and inverter circuitry of the integrated power system; FIG. 5A and FIG. 5B are control signal diagrams of the integrated power system;

FIG. 6 is a power management graph of the different modes of operation of the integrated power system; FIG. 7 is a diagram of output load vs. the engine speed of the engine generator power system;

FIG. 8 is a functional view of an integrated power system in accordance with the principles of the present invention illustrating use of an engine/generator set and DC batteries to provide 170 volts DC to an inverter which provides household like power at 120 volts RMS AC/60 Hz for use by various

electrical loads;

FIG. 9 is a graph of different voltage waves including a sinewave, a quasi-sine wave, and a squarewave superimposed over one another so as to illustrate the basic differences in each of the three types of voltage waves;

FIGS. 10A and 10B are graphs of a quasi-sine wave and a high frequency synthesized sine wave; and

FIG. 11 is a block diagram of the input and output of an inverter circuit producing a high frequency synthesized sine wave.

Detailed Description of the Preferred Embodiment

Referring now to the drawings, FIG. 1 shows an integrated power system 40 which provides AC power to various loads in accordance with the principles of the present invention. In this drawing the entire electrical load is generally represented by the reference numeral 67 which includes several different electrical loads which might typically be present in a system. It will be appreciated that the electrical loads might be of various types depending on the application. For example in the case of a recreational vehicle (RV) , the electrical load will include the various appliances typically present in the RV such as air conditioners, furnaces, washer/dryers, lights, televisions, etc. The electrical power provided to these electrical devices is like typical household power; i.e. 120 volts RMS AC at 60 Hz. As shown more particularly in FIG. 2 thru FIG.

4, the integrated power system 40 includes two primary sources of power: storage battery or batteries 42 and an engine/generator set 44 including an engine 43 and a three phase permanent magnet alternator (PMA) 45 mounted on a drive shaft 41 of the engine 43. In the preferred embodiment, the engine is a reciprocating combustion engine such a gasoline or diesel engine and the

alternator is of the permanent magnet variety. However, it will be appreciated that other engines might be used such as gas turbine engines and still be in keeping with the principles of the invention. Due to the somewhat limited speed range of a gas turbine engine, additional DC voltage regulatory control circuitry might have to be added to the system in order to provide additional regulation of the DC voltage. Moreover, the alternator might be a wound field alternator. With a wound field alternator, the DC voltage might be maintained at least in part by varying the excitation of the would field.

In the embodiment shown, the storage batteries 42 provide 12 volts DC power. The engine/generator set 44 and the batteries 42 are integrated under the control of a microprocessor based control system 70 so as to form two compensationally integrated power resources. The control system 70 senses the electrical load status of the system and controls the power resource distribution between the storage batteries 42 and the engine/generator 48. Illustrated in FIG 5A and FIG 5B are control signal diagrams of one embodiment of such a control system. It will be appreciated that this is but one embodiment and that various other control signal arrangements might be utilized. As shown in FIG. 2 and FIG. 3, rectifier bridge circuitry 46 rectifies the sinewave of the three phase AC power output of the three-phase permanent magnet alternator (PMA) 45 into a square wave to provide about 170 volts DC to a high voltage DC bus 48. In one embodiment, this is a three-phase rectifier although other phase rectifiers might be used. The operating speed of the engine/generator set 44 is variable in response to the power requirements of the system. The larger the electrical load placed on the system such as when more appliances are added, the faster the engine/generator set 44 runs so that greater engine power is available and so that the 170 volt DC output is

maintained when a permanent magnet alternator is used. FIG. 7 is an illustrative graph showing increasing engine/generator set 44 speed with increasing load. In the embodiment shown, the engine/generator set 44 has a fixed speed at its lower end and a fixed speed at its upper end. In between, the engine/generator set 44 might be increased in stair step fashion or be linearly increased as the load is increased.

The storage batteries 42 provide a similar high voltage DC power to the DC bus 48 only when the storage batteries 42 are used as a power resource in the power system 40. This will typically occur when there is a small electrical load on the system, which electrical demand the storage batteries 42 can satisfy without the assistance of the engine/generator set 44, or a large load for a very short duration, or when there is a large electrical load on the system requiring both the engine/generator set 44 and the storage batteries 42 to provide power together. The storage batteries 42 are boosted from 12 volts low DC power to 170 volts DC power by first inverting and boosting the DC current by use suitable boost circuitry 50 and then rectifying the resultant current into DC current by the use of suitable rectifier bridge circuitry 52. In one embodiment, single phase rectifier circuitry is used although other phase rectifiers might be used.

The storage batteries 42 have a limited capacity and after a period of use, the storage batteries 42 have to be charged. The integrated power system 40 uses the engine/generator set 44 to charge the storage batteries 42 through battery charging circuitry 54. Alternatively, AC utility power 56 can be used to charge the storage batteries 42 through rectifier circuitry 51 and the charging circuitry 54. Battery voltage sense circuitry 58 senses the voltage at the output of the storage batteries 42, and charging current sense circuitry 60 senses a charging current at the

input of the storage batteries 42. Signals representing the sensed battery voltages and the battery charging currents are sent to the microprocessor based control system 70 which controls operation of the battery charging/converter circuitry 54.

The high voltage DC power on the high voltage DC bus 48 is inverted into AC power, usually 120 volts, by suitable inverter circuitry 62, and then distributed to the electrical load 67. AC voltage sense circuitry 59 senses the output of the inverter circuitry 62. A signal representative of the sensed AC voltage is sent to the microprocessor control system 70. The microprocessor control system 70 in response thereto generates a pair of PWM (pulse width modulated) signals (one for each half cycle) to control the AC output voltage of the inverter circuitry 62. During steady state operation (constant DC voltage) , the inverter is driven by constant width pulses. During transients, the DC voltage is reduced when electrical load is increased or the DC voltage is increased when electrical load is reduced due to the delay in engine response time. When the DC voltage changes during such transients, the RMS voltage output from the inverter circuitry 62 is maintained constant by changing the inverter circuitry 62 control pulse width in response to variations in the DC voltage on the high voltage DC bus 48 until such time as the engine 43 is able to respond and either speed up or slow down as required to maintain the DC voltage on the high voltage bus 48 at 170 volts. The inverter circuitry 62 includes a plurality of switching transistors 64 which invert high voltage DC, 170 volts, into a quasi-sine wave 65 as generally illustrated in FIG 9. When a load at the output of the inverter circuitry 62 is changed, the width of the quasi-sine wave 65 is changed accordingly because the engine speed cannot immediately be adjusted to maintain the high voltage DC power at the input of

the inverter circuitry 62. This adjustment of the quasi-sine wave 65 output from the inverter circuitry 62 , maintains AC RMS output voltage constant without changing the high voltage DC power. In yet another embodiment, the inverter circuitry 62 is utilized as generally shown in FIG. 11 to produce a synthesized sine wave output. Pulse width modulated (PWM) circuitry 63 provides a pulse width modulated signal at 20,000 Hz to the inverter circuitry 62. The output of the inverter circuitry 62 includes an inductor 71 and capacitive bridge 69. As the load varies, the width of the pulse width modulated signal is varied to provide a synthesized sine wave output . The difference between a quasi-sine wave output and a synthesized sine wave output is generally illustrated in FIGS 10A and 10B.

Further in FIG. 3, the storage batteries 42 are boosted from 12 volts to 170 volts AC power through a boost transformer 66. In the embodiment shown, the single-phase rectifier bridge 52 changes the 170 volts AC power output from the boost transformer 66 to 170 volts DC power which is sent on the high voltage DC bus 48 to the input of the inverter circuitry 62. The microprocessor based control system 70 controls boost control circuitry 70 which adjusts input to the boost transformer 66.

The microprocessor based control system 70 generates an engine speed control signal (PWM) to maintain the constant DC rail voltage, preferably at 170 DC volts. The PWM signal is generated by DC voltage sense circuitry 61 which monitors the DC voltage of the high voltage DC bus 48. This arrangement provides the variable engine speed system of the integrated power system 40 by speeding up or slowing down the engine 43 as the system power requirements change while maintaining the voltage on the high voltage DC bus substantially constant at 170 DC volts.

As illustrated in FIG. 6, there are two modes of the operation in the integrated power system wherein the batteries are relied on as a power source. One is called "quiet power mode" in which the storage batteries 42 are the only power resource. Since the engine/generator 48 does not run during this mode, a quiet power is created. In one embodiment of the invention the "quiet power mode" provides up to 2.0 kw of steady state, continuous power and up to 2.4 kw of intermittent power.

The second mode is called "full power mode" in which both the storage batteries 42 and the engine/generator set 44 work together to provide power as required by the system. This mode happens when there is an increase in the electrical load applied to the output of the inverter circuitry 62. This might be a transient situation wherein the engine/generator set 44 isn't operating at full speed and has to increase its speed to maintain DC voltage on the high voltage DC bus 48 in which case the batteries 42 assist the engine/generator set 44 during this transient phase. This might also be a steady state situation wherein the system electrical load exceeds the engine/generator set 44 capacity in which case the batteries assist the engine/generator set 44 to increase the overall capacity of the integrated power system 40. In one embodiment, the full power mode provides 5.0 kw to 7.0 kw steady state, continuous power and up to 7.4 kw of intermittent power. The voltage of the batteries 42 will preferably be boosted to provide 170 volts DC to the high voltage DC bus 48 under only two conditions: 1) the engine speed of the engine/generator set 44 is in the fixed or constant speed mode such as in mode 3 or when a change in the current at the output of the inverter 62 is detected by a current sensor 57 as greater than a predetermined amount, i.e. 42 amps. The later is a

transient condition created by changing electrical loads on the system which create fluxuations in the current. The batteries 42 are never boosted to provide power to the high voltage DC bus 48 while being charged. Likewise, the batteries 42 are never charged at the same time they are boosted to provide power to the high voltage DC bus 48.

In the first mode, power is drawn from the storage batteries 42 to the transformer 66 through the boost control circuitry 50 having primary unidirectional transistors 50a switching at a high frequency. The output of the transformer secondary winding is rectified by the rectifier bridge circuitry 52 having diodes 52a resulting in 170 volts of DC power. A filter inductor circuit 74 is used to reduce current spikes during transistor switching in both the boost and charge modes. The inverter circuitry 62 uses an H-bridge configuration of field effect transistors (FET) 64 to alternatively switch the DC power to produce a quasi-sinewave output to the system electrical load 67. Thus, the energy source of the first mode are the storage batteries 42 with DC-AC-DC conversion to get the constant high voltage DC power before the inversion to AC power by the inverter circuitry 62. The microprocessor based control system 70 controls the boost control circuitry 50 to maintain the proper step-up in power.

In the second mode, the storage batteries 42 are used as an additional power supply to engine/generator set 44. In the steady state situation, when the load exceeds the engine/generator 44 power capacity, the control algorithm of the microprocessor based control system 70 converts the engine speed from a variable speed mode to a fixed speed mode. Accordingly, the constant high voltage DC power at the input of the inverter 58 is not constant any more, and instead begins to decrease. At this time, the storage batteries 42 are utilized to keep the high DC voltage constant.

In the embodiment shown, the battery charging (converter) circuitry 54 has two power sources. One source is the engine/generator set 44, and the other source is the AC utility power 56. The engine/generator set 44 and the AC utility power 56 provide rectified DC power. The DC power is switched to AC power by transistors 54a of the battery charging circuitry 54 which creates an AC current to flow in the transformer winding #2 (secondary winding) . By way of the turns ratio, winding #1 reduces the voltage, diodes 53a of rectifier circuitry 53 rectifies the AC current, and produces the current to charge the storage batteries 42. The transformer 66 used during the charging is the same transformer 66 used during boost operation. Therefore, the battery boost and battery converter circuitry utilize a common transformer as bi¬ directional .

At initial start-up, the battery charging circuitry 54 output is regulated to 50 amps total. A constant current is held until the voltage reaches a temperature compensated 14.2 volts DC. The charging mode is then changed from current to voltage, and the voltage output is reduced to 13.6 volts DC (temperature compensated) , whereby the charging operation continues at a lower rate. When current charging naturally reduces to less than 10 amps per battery, the voltage output is again reduced to 13.2 volts DC (temperature compensated) and held at this voltage as long as the battery charging circuitry is on. The final charge rate maintains the battery charge level if no other loads are consuming.

Steady State Operational Modes Referring to FIG. 6 and FIG. 8, various steady state operational modes will now be discussed for one embodiment of the invention. Mode l :

1 . Loads < 2 . 0 kw (kilowatts ) ; or

2. 2.0 kw < Loads < 2.4 kw for less than 50% of time in proceeding 1 hour (through a temporary sensor) ; and 3. Battery condition > 10 Volts DC.

In Mode I, the loads of the system are low, and only the batteries 42 are used to provide the high voltage DC power. The engine/generator set 44 does not run. No battery charging is allowed with the batteries 44 being used as a source of power. Likewise, when the batteries are being charged they are not used as a source of power.

Mode II : 1. Loads >= 2.4 kw; or

2. 2.0 kw < Loads < 2.4 kw for more than 50% of time in preceding hour; or

3. Battery condition is <= 10 VDC (low battery) ; or ^' 4. 2.4 kw < Loads < 3.0 for greater than 30 seconds; or 5. Load demands > 4.0 kw.

In Mode II, the loads are higher than Mode I, and the power generated from the batteries 42 is not enough to satisfy the loads. The engine/generator set 44 starts to run. The batteries 42 provide enough electricity to start the engine/generator set 44. The battery boost is turned off, and the battery charging is turned on. This transition is seamless to any loads on the system such that there is uninterrupted AC power. The engine/generator set 44 is made to run at a speed which maintains 170 volts DC on the high voltage DC. The speed of the engine/generator set 44 is dependent on the electrical load on the system.

Mode III:

1. Loads > 5 kw.

In Mode III, the power which is generated only from the engine/generator set 44 is not enough to satisfy the electrical load. The operating speed of the engine is fixed at its maximum. The batteries 42 are boosted to supply additional power to the electrical load, and the battery charging is turned off. Accordingly, the power is generated from both the batteries 42 and the engine/generator set 44.

Transient State Operational Modes When new loads are applied to the output of the inverter circuitry 62 or when loads are removed from the output of the inverter circuitry 62, a smooth system transient state is accomplished in the present invention. A smooth system transient state is required to reduce the voltage undershoot when the electrical load is increased and to reduce the voltage overshoot when the electrical load is decreased.

The following table shows ten transient state

(five load on and five load off) operating conditions:

Pre During After transient transient transient

Current Load + Mode 1 Gen=N Mode 1 New Load << Gen Gen=N Charge=N Gen=N Max Load (LoadOn) Charge=N Boost=Y Charge=N Boost=Y Boost=Y

Current Load + Mode 1 Gen=V Mode 2 New Load < Gen Gen=N Charge=N Gen=V Max Load (LoadOn) Charge=N Boost=Y Charge=Y Boost=Y Boost=N

Current Load + Mode 2 Gen=V Mode 2 New Load < Gen Gen=V Charge=N Gen=V Max Load (LoadOn) Charge=Y Boost=Y Charge=Y Boost=N Boost=N

Current Load + Mode 2 Gen=V Mode 3 New Load > Gen Gen=V Charge=N Gen=F Max Load (LoadOn) Charge=Y Boost=Y Charge=N Boost=N Boost=Y

Current Load + Mode 3 Gen=F Mode 3 New Load > Gen Gen=F Charge=N Gen=F Max Load (LoadOn) Charge=N Boost=Y Charge=N Boost=Y Boost=Y

Current Load - Mode 2 Gen=V Mode 2

Load Change < Gen=V Charge=Y Gen=V

Gen Max Load (LoadOff) Charge=Y Boost=N Charge=Y Boost=N Boost=N

Current Load - Mode 3 Gen=V Mode 2

Load Change < Gen=F Charge=Y Gen=V

Gen Max Load (LoadOff) Charge=N Boost=N Charge=Y Boost=Y Boost=N

Current Load - Mode 3 Gen=F Mode 3

Load Change > Gen=F Charge=N Gen=F

Gen Max Load (LoadOff) Charge=N Boost=Y Charge=N Boost=Y Boost=Y

Current Load - Mode 2 Gen=V Mode 1 Load Change << Gen=V Charge=Y Gen=N Gen Max Load (LoadOff] Charge=Y Boost=N Charge=N Boost=N Boost=Y

Current Load - Mode 1 Gen=N Mode 1 Load Change << Gen=N Charge=N Gen=N Gen Max Load (LoadOff) Charge=N Boost=Y Charge=N Boost=Y Boost=Y

WHERE: V = Variable Speed

F = Fixed Speed

Y = Yes (On)

N = No (Off)

The five load on conditions will now be discussed: When the current load is within the capacity of the boost and the battery condition is good (Gen Max Load) , the engine/generator set 44 (Gen) is turned off. The power output of the batteries 42 is boosted to provide the system power requirements, and battery charging is turned off. At this time, if a new load is added and the total load is still within the capacity of the boost and the battery condition is good, then the engine/generator set 44, the battery charge, and the battery boost status during the transient and after transient remain the same as those before the transient.

If the current load and the new load are within the capacity of the boost but with little excess capacity to spare, and if before the transient, the engine/generator set 44 and the charge are off and the boost are on, then during the transient, the engine/generator set 44 starts and runs at variable speeds, the charge is off, and the boost is on. After the transient, the engine generator set 44 runs at variable speeds, the engine/generator set 44 charges the batteries, and the boost is turned off.

If the load condition is the same as above, but before the transient, the engine/generator set 44 runs at variable speed, the charge is on, and the boost is off, then during the transient, the boost is turned on to overcome the undershoots resulting from the load transient, and the charge is turned off accordingly. After the transient, the boost is turned off, and the charge is turned on. During and after the transient, the engine/generator set 44 keeps running at variable speed.

If, after adding the new load, the load is greater than the capacity of the engine/generator set 44, then the engine/generator set's running speed is changed from variable speed to a fixed speed, which is the engine/generator set's highest speed. At this time, the high DC voltage at the input of the inverter 58 cannot be kept constant anymore until the batteries 42 are boosted to keep the high DC voltage constant . Before the transient, the batteries are charged, and the boost is off. During and after the transient, the boost phase is on and the batteries are not charged.

If the load condition is the same as the fourth condition, and if the engine/generator set 44 runs a fixed speed and the batteries have already been boosted, then during and after the transient, the load condition keeps the same as the condition before the transient .

The five load off conditions will now be discussed:

When the total current load is smaller than the capacity of the engine/generator set 44 after some loads are removed, and if the running speed of the engine/generator set 44 before the transient is variable, and the batteries 42 are being charged, then during and after the transient the engine/generator set 44 still runs the variable speeds, the boost is off, and the charge is on.

If the load condition is the same as the above condition, and before the transient, the running speed of the engine/generator set 44 is fixed and the batteries 42 are boosted, then during the transient, the charge is turned on to overcome the overshoots, and the running speed of the engine/generator set 44 is variable. After the transient, the batteries 42 are charged by the charging circuitry. If the total load is still larger than the capacity of the boost after the transient (some loads are removed) , and if before the transient, the running

speed of the engine/generator set 44 is fixed, and the batteries are boosted, then during and after the transient the batteries are boosted, and the engine/generator set 44 still keeps its fixed speed. If the total load after the transient is within the capacity of the boost and battery condition is good, and if before the transient, the running speed of the engine/generator set 44 is variable, and the batteries are being charged, then during the transient, the engine/generator set is turned off, but the batteries are still charged to overcome the overshoots. After the transient, the batteries are not charged but boosted to keep the high DC voltage constant.

If the load condition is the same as the above condition, and if before the transient, the engine/generator set 44 is turned off, then the batteries 42 are boosted both during the transient and after the transient. The batteries are not charged. The above ten transient-state operations illustrate the integration of the battery power source and the engine/generator set power source to provide seamless AC power to electrical loads of varying size. The microprocessor based control system 70 programmed with suitable control logic to enable these operations. The control logic for the integrated power system 40 controls and coordinates the interaction between the various components of the system. The control logic performs various functions during operation of the

integrated power system 40 including the following functions :

- System Initialization

- System Start - Engine/Generator Control

- Boost Control

- Converter/Charge Control

- System Test

- Inverter Control - Faults and Shutdowns

- Operating set points

- System variables

- Time delays

The output voltage of the engine/generator set 44 is regulated by controlling the running speed of the engine/generator set 44. The minimum running speed of a reciprocating combustion engine is preferably 1800 RPM, and the maximum running speed of a reciprocating combustion engine is preferably 3600 RPM. It is appreciated that the minimum and maximum running speed can be varied.

The control logic monitors various parameters and shuts down the engine/generator set 44 if certain parameters are exceeded; for example: 1) the speed of the engine/generator set 44 exceeds a predetermined limit (overspeed controlling) ,

2) the output of the inverter circuitry 62 exceeds a predetermined limit (called chopper overvoltage) , 3) the voltage output of the engine/generator set 44 exceeds a predetermined limit (called engine/generator overvoltage) , or

4) the boost voltage at the input of the inverter circuitry 62 exceeds a predetermined limit (called booster overvoltage) .

The control logic provides four control loops : the inverter control loop, the boost control loop, the

battery charging loop, and the engine/generator control loop.

The boost will provide high DC voltage to the system when enabled. The magnitude of the high DC voltage is controlled with a variable reference input provided by a microprocessor PWM output . In the system test control, the boost is allowed to be disabled and enabled manually. In normal operating mode, the boost is enabled when the engine speed control is in constant speed mode and the power demand exceeds engine/generator set 44 capacity.

The software further controls that the battery charge and battery boost are never enabled at the same time. The inverter 58 outputs a pseudo-sinewave at 60

Hz using two output bits. One is for the positive half cycle, and the other one is for the negative half cycle.

The voltage is regulated to 120 RMS VAC. The control logic insures that the inverter 58 is enabled any time adequate voltage is available at the high voltage DC bus

48. The software limits the duty cycle to 48 percent.

Minimum duty cycle should be around 35 percent. The software controls the battery charging/converting function in three operating modes : 1. Constant current charging mode:

The software measures the battery voltage.

If the battery voltage is over 10.5 VDC, the software instructs to begin a constant current charging mode.

The software controls the maximum current not to exceed 50 amps DC. When the voltage is charged to 14.2 VDC, then the software controls the batteries 42 to go to the constant voltage mode.

2. Constant voltage charging mode:

The batteries 42 are maintained charging at the voltage of 13.6 VDC until the charging current decays to less than 10 ADC for greater than 3 seconds.

Then, the batteries 42 go to the maintenance voltage

charging mode. If the charge current exceeds the maximum charge current for more than 3 seconds, the batteries 42 are switched back from the maintenance voltage charging mode to the constant current charging mode.

3. Maintenance voltage charging mode:

The charging voltage is held constant at 13.2 V.

In one embodiment, the microprocessor's memory requirements include 500 bytes of RAM and 24K of ROM. Memory of the microprocessor 72 is large enough to support the entire system and variables in down loadable memory or permanent memory. In one embodiment a Motorolla 86HC11 processor is utilized. The microprocessor's speed is capable of performing calculations for up to 4 closed loops in less than 6 milliseconds. The microprocessor's input/output (I/O) includes A/D channels, discrete inputs, discrete outputs, PWM outputs, output compares, and input compares. Alternatively, the microprocessor 72 allows all the system functions in a single chip.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.