A POWER SPLIT DEVICE FOR A COMBINED HEAT AND POWER

(CHP) SYSTEM BACKGROUND

[0001] The present disclosure relates to a combined heat and power system. More particularly, the present disclosure relates to use of a power split device in a combined heat and power system to variably distribute mechanical shaft energy to a motor-generator and to a chiller system.

[0002] A combined heat and power (CHP) system, also known as on-site power generation, may produce electricity using a motor-generator and also provide cooling through use of a chiller system. The motor-generator may use mechanical shaft energy from a prime mover or other mechanical power source to generate electrical energy. The electrical energy may then be exported to an electrical grid or supplied to a local electrical load. The chiller may also use electrical energy from the motor-generator in order to chill a liquid or generate ice for cooling. Optimal operation of the CHP system may be limited by fluctuations in output from the mechanical power source, as well as fluctuations in demand from an electrical load and from the chiller.

[0003] There is a need for a more efficient CHP system having a motor- generator and a chiller system, such that the CHP system is able to handle fluctuations from an electrical load and a thermal load.

BRIEF SUMMARY

[0004] A combined heat and power (CHP) system includes a mechanical power source having a mechanical shaft output configured to produce mechanical shaft energy. A power split device is coupled to the mechanical shaft output and is configured to variably distribute the mechanical shaft energy to a motor/generator and a chiller. The motor/generator is coupled to the power split device and configured to generate electrical energy from the mechanical shaft energy. The chiller is coupled to the power split device and is configured to generate chilled liquid from the mechanical shaft energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a schematic diagram of a combined heat and power

(CHP) system, which includes a power split device used with a prime mover and a chiller system.

[0006] FIG. 2 is another embodiment of the CHP system of FIG. 1 with the power split device used with an organic rankine cycle (ORC) system for producing mechanical shaft energy.

[0007] FIG. 3 is a plot illustrating operation of the CHP system of FIG. 2 for supporting an electrical load and a thermal load from the chiller system.

[0008] FIG. 4 is a plot similar to FIG. 3 illustrating operation of the CHP system when there is an increased demand from the chiller system. [0009] FIG. 5 is a diagram illustrating an exemplary embodiment of a control scheme for controlling operation of the CHP system of FIG. 2. DETAILED DESCRIPTION

[0010] As described herein, a power split device may be used in a combined heat and power (CHP) system to improve operation of the CHP system. A mechanical power source that generates mechanical shaft energy may commonly be mechanically coupled to a motor-generator, which uses the shaft energy to produce electrical energy. The electrical energy may then be distributed to an electrical load or to an electrical energy storage system. Typically in a CHP system that includes a chiller, the motor-generator also supplies electrical energy to the chiller, which uses the energy input for cooling. In those designs, it may be common that only the motor-generator is mechanically coupled to the mechanical power source. However, as detailed below, a CHP system operates more efficiently by selectively supplying the mechanical shaft energy directly to the chiller from the mechanical power source. The chiller may receive mechanical energy directly from the mechanical power source, in addition to being able to receive electrical energy from the motor- generator. A power split device, which is mechanically coupled to the mechanical power source, is used to variably distribute mechanical shaft energy between the motor-generator and the chiller.

[001 1] FIG. 1 is a schematic diagram of combined heat and power (CHP) system 10, which includes prime mover 12, power split device 14, motor/generator 16, chiller system 18 and power controller 20. System 10 may be used, for example, to supply electricity and cooling to a building (commercial or residential). Prime mover 12 may be any type of mechanical power source capable of generating shaft power, including, but not limited to, a reciprocating

engine, a turbine, a windmill and an organic rankine cycle (ORC) system. Prime mover 12 is mechanically coupled to power split device 14 such that shaft energy produced by prime mover 12 may be transferred to power split device 14. Prime mover 12 also receives shaft energy from power split device 14. (A two-way transfer of shaft energy between prime mover 12 and power split device 14 is represented by the two-way arrow in FIG. 1 between prime mover 12 and power split device 14.)

[0012] Power split device 14 is also mechanically coupled to motor/generator 16 and to chiller system 18, such that power split device 14 is able to distribute shaft energy from prime mover 12 to both motor/generator 16 and chiller system 18. Chiller system 18 is used for cooling; more specifically it may be used to chill a liquid or generate ice. Chiller system 18 may include, but is not limited to, a vapor compression chiller. Chiller system 18 uses shaft energy from power split device 14, as well as electrical energy. As described below, the electrical energy to chiller 18 may come from various electrical sources. In system 10, chiller system 18 directly receives mechanical shaft energy from prime mover 12, through power split device 14. This allows for more efficient operation of chiller system 18, compared to systems in which all energy input to chiller system 18 is electrical energy coming primarily from motor/generator 16.

[0013] Motor/generator 16 is used in CHP system 10 to convert mechanical energy into electrical energy. The electrical energy from motor/generator 16 may then be distributed to an electrical grid, an electrical load (i.e. grid or load 22 of FIG. 1) and/or electrical energy storage 24. Power controller 20 is used in system 10 to control a distribution of electrical energy from motor/generator 16 to grid or load 22 and to electrical energy storage 24. [0014] Electrical energy from electrical energy storage 24 and grid or load 22 may be distributed back to motor/generator 16, through power controller 20 (as indicated by two-way arrows in FIG. 1). Motor/generator 16 is commonly used to export or push electrical energy out to an electrical grid represented by grid or load 22. However, in some cases, grid 22 may conversely supply electrical energy to components within system 10. Motor/generator 16 may use the electrical energy to generate mechanical shaft energy that may be used by

prime mover 12, for example, during a start-up of prime mover 12. In that case, mechanical shaft energy is transferred from motor/generator 16 to prime mover 12, through power split device 14.

[0015] Electrical energy from grid or load 22 and storage 24 also may be used by chiller system 18 as alternative energy or supplemental energy in addition to shaft energy from power split device 14. Again, the distribution of electrical energy from grid or load 22 and storage 24 may be monitored and controlled by power controller 20. In some embodiments, as shown in FIG. 1, electrical energy from grid or load 22 or storage 24 is distributed to chiller system 18 through power split device 14. In that case, power split device 14 is configured to split electrical energy, in addition to its ability to split mechanical energy. However, in other embodiments, two power split devices are used in which a first device is configured for mechanical energy and a second device is configured for electrical energy. [0016] Power controller 20 also may be used to control power split device

14 as it variably distributes mechanical shaft energy from prime mover 12 to motor/generator 16 and to chiller system 18. Controller 20 may be configured to operate power split device 14 in various control modes depending, in part, on electrical demands from grid or load 22 and a cooling load of chiller system 18. For example, in a first operating mode, controller 20 may designate priority to motor/generator 16 such that any electrical energy demands to motor/generator 16 (from grid or load 22) may first be met. Controller 20 works to ensure that motor/generator 16 satisfies its electrical load by channeling mechanical shaft energy through power split device 14 to motor/generator 16. In this case, chiller system 18 receives limited shaft energy or zero shaft energy, depending on the electrical load and output from prime mover 12. If motor/generator 16 receives the necessary shaft energy, controller 20 distributes any excess shaft energy from prime mover 12, through power split device 14, to chiller system 18. [0017] In a situation in which chiller system 18 does not require any shaft energy (i.e. zero cooling load), any excess electrical energy generated by motor/generator 16 that is not needed by grid or load 22 may be distributed to electrical energy storage 24. Alternatively, chiller system 18 may use the electrical energy, as well as mechanical shaft energy, to generate a thermal output

that may be distributed to a thermal storage system, which may be connected to chiller system 18. Uses of the thermal storage system may include, but are not limited to, a chilled water system, an ice box, a glycol storage system, and any high-thermal capacity liquid or phase change material. [0018] In a second operating mode, controller 20 may instead designate priority to chiller system 18, such that motor/generator 16 receives limited shaft energy or zero shaft energy, ϊn this operating mode, a cooling load of chiller system 18 is first satisfied by distributing the required shaft energy from prime mover 12, through power split device 14, to chiller system 18. Any excess shaft energy from prime mover 12 not needed by chiller system 18 is then channeled to motor/generator 16 through power split device 14. In this second operating mode, if prime mover 12 is not able to satisfy the load requirements of motor/generator 16, because more shaft energy is distributed to chiller 18, electrical energy storage system 24 may supply electrical energy to grid or load 22.

[0019] In the second operating mode, if motor/generator 16 does not require any shaft energy, because there are no electrical demands from grid or load 22, then controller 20 may channel all shaft energy from prime mover 12 to chiller system 18 through power split device 14. Moreover, if the shaft energy is still not sufficient to meet the demands of chiller system 18, then electrical energy may be supplied from electrical energy storage system 24 to motor/generator 16, to operate motor/generator 16 as a motor. In that case, motor/generator 16 provides additional mechanical shaft energy to power split device 14, which may then be provided to chiller system 18. [0020] Through the use of power split device 14 and power controller 20, system 10 is able to operate more efficiently and effectively, especially given that there are common fluctuations in the electrical load requirements for motor/generator 16 and the cooling loads for chiller system I S. By mechanically coupling chiller system 18 to prime mover 12 and to motor/generator 16, power split device 14 allows chiller system 18 to directly use shaft energy from prime mover 12 and, in some cases, shaft energy from motor/generator 16. Based on electrical demands and cooling demands, power controller 20 controls how power

split device 14 distributes shaft energy between motor/generator 16 and chiller system IS.

[0021] As stated above, prime mover 12 may include any type of mechanical power source capable of generating mechanical shaft energy. FIG. 2 illustrates another embodiment of the CHP system of FIG. 1 in which the prime mover is an organic rankine cycle (ORC) system. As shown in FIG. 2, CHP system 110 includes ORC system 112 and thermal energy source 113. Other components within CHP system 1 10 are similar to those illustrated in FIG. 1 and described above for CHP system 10. [0022] ORC system 1 12 uses waste heat from thermal energy source 1 13 to convert thermal energy into mechanical shaft energy. An ORC system operates similarly to a traditional steam engine, except that an ORC system uses an organic chemical instead of steam. Because organic fluids may boil at lower temperatures, an ORC system may be able to use lower temperature heat sources than those which may be used by a steam engine.

[0023] Thermal energy source 113 may include any device that generates an exhaust stream, or streams, from which heat may be recovered. Thermal energy source 113 may include, but is not limited to, fuel cells, microturbines, reciprocating engines, solar, geothermal or waste gas (including waste gas from burning landfill gas), liquid streams from a process or the like, and geothermal liquid water streams.

[0024] Mechanical shaft energy generated by ORC system 112 is essentially the same as mechanical shaft energy produced by prime mover 12 in FIG. 1. Power split device 1 14 distributes the mechanical shaft energy from ORC system 1 12 between motor/generator 1 16 and chiller system 118. Motor generator 116, as described above in reference to motor/generator 16 of FIG. 1, then generates electrical energy which may be distributed to grid or load 122 and/or electrical energy storage 124. [0025] In system 1 10, mechanical shaft energy produced by ORC system 112 may be limited by an amount of waste heat available from thermal energy source 1 13. Prime mover 12 of FIG. 1 utilizes a fuel to generate shaft energy. By providing a constant or near constant supply of fuel, an output from prime mover 12 may be relatively constant. However, an output from ORC system 112

may exhibit greater fluctuations since operation of system 1 12 is dependent on waste heat from thermal energy source 113. In those cases in which ORC system 112 receives an abnormally low amount of waste heat (i.e. input energy) from thermal energy source 113, controller 120 may reduce an output of mechanical shaft power from ORC system 112. In that case, a cooling load from chiller 118 may be met by supplying electrical energy from electrical energy storage system 124. By configuring system 110 such that mechanical shaft energy or electrical energy may be distributed to chiller 118 through power split device 1 14, system 110 is better able to handle fluctuations of this kind within system 110. [0026] To start-up ORC system 1 12, motor/generator 116 may be used to initiate spinning of a turbine within ORC system 1 12. In that case, motor/generator 116 receives electrical energy from grid 122 and/or electrical energy storage 124 and uses that electrical energy to generate shaft energy. The shaft energy is then channeled from motor/generator 1 16 to ORC system 112 through power split device 114.

[0027] FIG. 3 is a plot illustrating operation of system 110 of FIG. 2.

More specifically, FIG. 3 illustrates how system 110 may be used to satisfy an electrical load from grid or load 122 and a thermal load from chiller system 1 IS. FIG. 3 includes ORC Output (mechanical shaft power produced by ORC system 112), Electrical Energy Storage (a rate at which electrical energy is distributed to storage 124 from motor/generator 1 16), VCC Power Input (power supplied to [vapor compression] chiller system 1 18 to generate chilling) and Load Power (an electrical load from grid or load 122). All units shown in FIG. 3 are arbitrary. It is recognized that there may be energy losses in system 1 10 which are omitted from FIG. 3 for simplicity.

[0028] As shown in FIG. 3, ORC Output remains constant between 0 and

10 seconds. Between 0 and 6 seconds, Load Power is equal to 1.0 unit, VCC Power Input is equal to zero, and Electrical Energy Storage is equal to zero. In this exemplary embodiment, system 1 12 is operating in a mode in which an electrical load from grid or load 122 receives priority over a cooling load from chiller system 118. (Alternatively, a cooling load may be equal to zero.) Essentially all of the mechanical shaft energy from ORC system 1 12 is

distributed through power split device 114 to motor/generator 116, in order to meet the electrical demand of grid or load 122.

[0029] At time equal to 6 seconds, Load Power is reduced from 1.0 to 0.8 units. This reduction in Load Power is a result of a decreased demand from grid or load 122. Because ORC Output remains constant, the excess mechanical shaft energy from ORC system 112 that is no longer required by grid 122 may be supplied to chiller 118. However, chiller 118 is most likely not able to immediately receive all of the excess shaft energy; instead, the input to chiller 118 from prime mover 112 is gradually increased. As shown in FIG. 3, VCC Power Input steadily increases between 6 and 7 seconds until it reaches 0.2 units. During the time period between 6 and 7 seconds, electrical energy storage 124 may receive excess electrical energy generated by motor/generator 116, while chiller 118 is ramping up. This is shown in FIG. 3 by the increase to Electrical Energy Storage at time equal to 6 seconds. However, the rate at which electrical energy storage 124 is receiving electrical energy from motor/generator 1 16 decreases as power to chiller 118 increases. At time equal to 7 seconds, VCC Power Input has reached a set point of 0.2 units and chiller system 118 is receiving all of the mechanical shaft energy from prime mover 112 that is not required by motor/generator 116. At this same point in time, electrical energy storage system 124 is consequently at zero.

[0030] FIG. 3 illustrates that system 1 10 may redistribute mechanical shaft energy from ORC system 1 12 when there is a reduction in an electrical load, which reduces an amount of mechanical shaft energy required by motor/generator 116. . Through use of power controller 120 and power split device 114, the excess mechanical shaft energy may easily be redistributed to chiller 1 18. In the case where chiller 1 18 does not have a cooling load, excess mechanical shaft energy may still be used by motor/generator 116. The resulting excess electrical energy from motor/generator 116 may then be distributed to electrical energy storage 124. As described above in reference to FIG. 1 , chiller 118 may alternatively use the electrical energy to generate a thermal output that may be distributed to a thermal storage system, such as an ice box or a chilled water system, which is connected to chiller 1 18.

[0031] FIG. 4 is a plot similar to FIG. 3 illustrating operation of CHP system 110 when there is an increased demand from chiller system 118. In contrast to FIG. 3, FIG. 4 includes Power from Electrical Energy Storage, which is an amount of electrical energy distributed from storage 124 to chiller 1 18. As in FIG. 3, all units in FIG. 4 are arbitrary. As shown in FIG. 4, ORC Output is constant over time and Load Power also remains constant (i.e. an electrical demand from grid or load 122 is constant). Between time equal to zero and 6 seconds, VCC Power Input is equal to 0.1 units, meaning that chiller system 1 18 is receiving some mechanical shaft energy from ORC system 112. Power from Electrical Energy Storage is equal to zero between time equal to zero and 6 seconds, meaning that ORC system 1 12 is able to provide enough shaft energy to chiller system 1 18 to meet a cooling load of chiller 118.

[0032] At time equal to 6 seconds, VCC Power Input begins to increase from 0.1 to 0.2 units. Thus, at time equal to 6 seconds, chiller system 118 has an increased energy demand. However, ORC system 112 has not increased its output of mechanical shaft energy and there has not been a decrease in demand from electrical load 122. Thus, power split device 114 does not have any excess mechanical shaft energy that may be distributed to chiller 118 without reducing shaft energy to motor/generator 116. In that case, an energy demand by chiller 118 may be met by electrical energy storage system 124. System 124 distributes electrical energy to chiller 118 through power split device 1 14. As shown in FIG. 4, Power from Electrical Energy Storage is increasing between 6 and 7 seconds until VCC Power Input has reached its set point. At time equal to 7 seconds, electrical energy storage system 124 then delivers a constant amount of electrical energy to chiller 118 to maintain the set point for chiller 118.

[0033] FIG. 5 is a schematic diagram of control architecture 150 for controlling operation of CHP system 110 of FIG. 2. Control architecture 150 includes all components of CHP system 110, as well as load management system 152 and supervisory controller 154. Load management system 152 may be used for controlling an overall operation of the building that system 1 10 is connected to. Supervisory controller 154 is configured to control operation of CHP system 110 and may be configured to interface with load management system 152. As illustrated in FIG. 5, supervisory controller 154 receives information from ORC

system 1 12, thermal energy source 1 13, chiller system 1 18 and power controller 120. As described above in reference to FIG. 1, power controller 120 may control operation of power split device 1 14, motor/generator 116 and a distribution of electrical energy to and from electrical energy storage 124 and grid or load 122.

[0034] In the exemplary embodiment shown in FIG. 5, control architecture 150 includes a cascaded control scheme, and power split device 114 is controlled by supervisory controller 154 through power controller 120. It is recognized that in additional embodiments of control architecture 150, power split device 1 14 may include its own controller that is directly connected to supervisory controller 154.

[0035] Supervisory controller 154 controls operation of CHP system 110 by monitoring and controlling the various components within system 1 10. For example, controller 154 monitors data from thermal energy source 113, including operating conditions and an amount of waste heat generated by energy source 1 13, which impacts mechanical shaft output from ORC system 112. Supervisory controller 154 feeds this data to power controller 120, which controls the distribution of mechanical shaft energy from prime mover 1 12 to motor/generator 116 and chiller 1 18, based on an amount of shaft output. Power controller 120 also controls a distribution of electrical energy to and from motor/generator 116. [0036] Power controller 120 may control a distribution of shaft energy from power split device 114 as a function of shaft output from prime mover 1 12 and demands from an electrical load and a cooling load. The distribution of shaft energy from power split device 1 14 may also be based upon desired operating conditions for each mechanical shaft of device 114, motor/generator 116 and chiller 1 18, including shaft rpm and torque. The shaft distribution from power split device 114 may frequently change as a function of fluctuations in the electrical loads and the cooling loads. Moreover, the distribution may change depending on an operating mode of controller 120 (i.e. whether controller 120 is operating in a mode in which priority is given to motor/generator 116 over chiller 118, or vice versa). In the embodiment shown in FIG. 5, the demands on chiller system 118 are monitored by supervisory controller 154, whereas the electrical load is monitored through power controller 120. This data, in combination, may

be used to control the mechanical energy split by power split device 1 14 and the electrical energy split by power controller 120.

[0037] It is recognized that control of CHP system 110 may be accomplished in a number of different ways. The cascaded control architecture of system 150 is one example of a type of control scheme that may be used for CHP system 1 10.

[0038] The terminology used herein is for the purpose of description, not limitation. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.