Patent Publication Number: US-2016221684-A1

Title: Apparatus for aircraft with high peak power equipment

Description:
CROSS-REFERENCE TO A RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 13/667,079, filed Nov. 2, 2012, and titled “Apparatus for Aircraft with High Peak Power Requirement”, that claims the benefit of U.S. Provisional Patent Application Ser. No. 61/555,010, filed Nov. 3, 2011, and titled “Apparatus and System Design for Aircraft with High Peak Power Requirement”, both of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to electrical power systems, and more particularly to power systems that are capable of satisfying short term peak power demands. 
     BACKGROUND OF THE INVENTION 
     High performance aircraft require a light weight cooling and power system that has a low impact on the propulsion engine. Such aircraft also need an auxiliary and emergency power source that can provide electrical power both on the ground and in the event of an engine flame out or main generator failure. 
     Aircraft may also include equipment that requires a high peak power. Such equipment requires power extraction beyond the capability of state-of-the-art (SOA) engine high pressure spool driven generators. Discharging high peak power may affect the normal system operation. If the high peak power equipment has a low usage duty cycle, sizing the generator to provide the peak power imposes a weight penalty that is undesirable when there is only an occasional need for a high peak power output. 
     A high power density energy storage device, effective high altitude auxiliary power, and thermal management are needed to support the high peak power equipment. In addition, a robust electrical power system architecture is required to manage electrical power distribution. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method for providing electrical power and cooling for an aircraft includes: connecting a starter generator to an energy accumulator bus; selectively connecting the energy accumulator bus to a first power distribution unit in a first power channel or a second power distribution unit in a second power channel; wherein the starter generator is coupled to a shaft in an integrated power and cooling unit that includes a cooling turbine coupled to the shaft; a compressor coupled to the shaft and including an input for receiving engine bleed air or ambient air and an output for discharging compressed air; a flywheel coupled to the shaft; and a power turbine coupled to the shaft; and using energy stored in the flywheel to rotate the shaft enabling the starter generator to supply electrical power to the energy accumulator bus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of an aircraft power generation system. 
         FIG. 2  is a schematic block diagram of an aircraft power distribution system in combination with the power generation system of  FIG. 1 . 
         FIGS. 3 through 8  are schematic block diagrams of portions of an aircraft electrical power distribution system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In one embodiment, a method is provided for operating an integrated flywheel power and cooling system (IFWPCS) for an aircraft. In another aspect, the a power system distribution architecture is operated in combination with the integrated flywheel power and cooling system. 
     Aircraft power and cooling systems can be driven by an aircraft engine, for example, using bleed air from the engine. During idle descent flight of an aircraft, engine power extraction and bleed air capability is low and would result in a high penalty if used to drive the power and cooling system. An IFWPCS can use stored energy (e.g., rotation of a flywheel) to assist with power generation and cooling during idle descent flight. In addition, the IFWPCS can provide improved system performance as compared to the state of the art technologies that would be required to enable similar capability. 
       FIG. 1  is a schematic block diagram of portions of an aircraft electrical power system  10 . The system includes an integrated flywheel power and cooling system  12  coupled to an aircraft engine  14 . The integrated flywheel power and cooling system includes a flywheel  16 , an expansion turbine  18 , a compressor  20 , a starter-generator  22 , and a power turbine  24 , all coupled to a common shaft  26 . The IFWPCS can provide electrical power for various aircraft systems and temperature controlled air that can be used to cool equipment on the aircraft. In this example, the aircraft includes a directed energy system (DES). Cooling components  28  for the directed energy system include an avionics/DES heat exchanger  30  and a phase change material heat exchanger  32 , connected to each other through a pump  34 . 
     The starter generator in the integrated flywheel power and cooling system is connected to an energy accumulator unit (EAU) bus  36  through an inverter control unit (ICU)  38 . Low pressure cool air comes out of the expansion turbine  18  and passes into the avionics/DES cooler heat exchanger through line  40 . 
     A high pressure spool driven starter generator  42  (also called a first generator) is connected to the engine and also connected to a high power bus  44  (also referred to as a first bus) through an inverter control unit  46 . A low pressure spool driven generator  48  (also called a second generator) is connected to the aircraft engine and is also connected to a low-power bus  50  (also referred to as a second bus) through a generator control unit  52 . High pressure, warm air that comes out of the compressor  20  can be directed into a fan duct heat exchanger  54 . Alternatively or additionally, this high-pressure warm air can be used as a supercharger in a combustor  56  to create more power. An additional heat exchanger  58  is connected between the engine and the input to the compressor  20 . Compressor  20  receives engine bleed air or ambient air through input  60 . Power turbine  24  is connected to an exhaust port  62 . 
     The integrated flywheel power and cooling system is capable of providing both ground auxiliary power and in-flight emergency power, normal cooling, peak power for high power equipment, and energy storage to reduce transient load impact on the engine. 
     The integrated flywheel power and cooling system (IFWPCS) includes a flywheel that can be used to enable avionics cooling and to provide peak power for directed energy weapon operation. The flywheel provides energy storage, and the stored energy can be released when needed. The described system uses electrical power to provide cooling power and the flywheel can reduce the power demand on the engine during idle descent transition. The IFWPCS can also provide electrical power to high peak power equipment such as electronic attack and directed energy weapon systems. 
     The IFWPCS can be used in an electrical power system architecture that distributes the generated engine power to other systems.  FIG. 2  is a schematic diagram of portions of an aircraft electrical power system that include the elements of  FIG. 1  and further include power storage and distribution components. The high pressure spool driven starter-generator  42  is shown to include a permanent magnet generator  68  that is coupled to a converter/regulator unit  70 . The inverter control unit  46  can be connected to a 270 volt power distribution unit  72  for the first bus  44 . The power distribution unit  72  can be connected to a first 270 volt bus  74  and a second 270 volt bus  76 . Bus  74  can be connected to DC-to-DC converter  78  that supplies voltage to a 28 volt bus  80 . Bus  76  can be connected to DC-to-DC converter  82  that supplies voltage to a 28 volt bus  84 . 
     The low pressure spool driven generator  48  is shown to include a permanent magnet generator  86  that is coupled to a converter/regulator unit  88 . The low pressure spool driven generator  48  is also connected to a generator control unit  52 . The generator control unit can be connected to a 270 volt power distribution unit  90  on the second bus  50 . The 270 volt power distribution unit  90  can be connected to a first 270 volt bus  92  and a second 270 volt bus  94 . Bus  92  can supply voltage to the aircraft avionics  96 , and bus  94  can supply power to the aircraft radar  98 . The power distribution unit  90  can be connected to DC-to-DC converter  100  that supplies voltage to a 28 volt bus  102 . Bus  102  can be connected to a 28 volt bus  104 . 
     The power distribution unit  72  can also be connected to an ultra capacitor  104  and a solid state power controller  106 . In addition, the power distribution unit  90  can be connected to an energy accumulator unit bus  36  that can supply power to high power load devices  108 . Inverter control unit  38  can be connected to the energy accumulator unit bus  36  through an energy accumulator unit bus/BAT/ultra capacitor  112 . 
     Batteries  114 ,  116  and  118  can be connected to battery charger and control units  120 ,  126  and  124 , respectively. Battery charger and control units  120 ,  122  and  124  can be connected to busses  80 ,  84  and  104 , respectively. A plurality of switches  126 ,  128 ,  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 ,  148 ,  150 ,  152 ,  154 ,  156 ,  158 ,  160 ,  162  and  164 , are provided to connect the various components of  FIG. 2  under various operating scenarios. A power control command signal  166  can be supplied to the inverter control unit  46  and the solid state power controller  106 . Bus  74  can supply power to actuators  168 . Bus  76  can supply power to actuators  170 . Bus  80  supplies voltage to a first vehicle management computer  172  and a first full authority digital engine controller  174 . Bus  84  supplies voltage to a second vehicle management computer  176  and a second full authority digital engine controller  178 . Bus  104  supplies voltage to a third vehicle management computer  180  and avionics  182 . An external power source  184  such as a ground power service cart could be connected to power distribution unit  90  during aircraft maintenance or ground operation. 
     The power system architecture can manage engine power extraction and load matching and can be optimized for maximum efficiency.  FIGS. 3-8  are schematic diagrams of portions of an aircraft power distribution system showing various operating modes. Abbreviations used in  FIGS. 1-8  include:
     BCCU: battery charger and control unit   SSPC: solid state power controller   EAU: energy accumulator unit   DC-DC: 270-28 VDC converter   CRU: converter/regulator unit   UCAP: ultra capacitor   PDU: power distribution unit   GCU: generator control unit   ICU: inverter convert unit   LP GEN: low pressure spool driven generator   HP ST/GEN: high pressure spool starter/generator   FD HX: fan duct heat exchanger   IFWPCU: integrated flywheel power and cooling unit   Tc: cooling turbine   C 1 : compressor   C 2 : combustor   S/G: starter/generator   Tp: power turbine   DES: direct energy system   P: pump   PCM Hx: phase change material   PMG: permanent magnet generator   CRU: converter regulator unit   ESS: essential bus   VMC: vehicle management computer   FADEC: full authority digital engine controller   

       FIG. 3  shows a power distribution system that can be connected to an integrated flywheel power and cooling unit and includes an ultra capacitor  104  on the high pressure spool driven generator  42 . The channel and EAU bus  36  supplied by either or a combination of the IFWPCU, a battery, an EAU, and an ultra-capacitor. The various energy storage components are connected through switches to reduce generator transient rating requirements. The ultra capacitor  104  reduces high pressure spool driven generator  42  transient rating requirements. The power from EAU bus  36  reduces low pressure spool driven generator  48  transient power rating requirements.  FIG. 3  shows the normal power control operation mode of the electrical power distribution system. The SSPC is commanded to be off when power sharing is off so the power distribution unit  72  is disconnected from EAU bus  36  but in a standby mode that could be turned on in a few mini-seconds. The high pressure spool driven generator  42  would supply power to the power distribution unit  72  and is supplemented by ultra capacitor  104  to meet the continuous and transient power demands respectively. The low pressure spool driven generator  48  would provide power to power distribution unit  90  for the continuous loads and can be supplemented by the ultra capacitor (UCAP) and energy accumulator unit (EAU)  112  for the transient loads. In the event that the transient or the peak power of equipment such as the radar  95  exceeds the capability of the battery, UCAP and EAU  112 , the IFWPCU energy stored in the flywheel would be converted into electrical power and supply power through EAU bus  38 . In this scenario, the IFWPCU  12  handles high peak power for loads such as radar. Thus the low pressure spool driven generator  48  does not need to be oversized for the peak power requirements. This saves system weight and reduces cooling requirements that typically limit the generator output power rating. 
     The distribution system shown in  FIG. 3  also enables energy optimization in vehicle operation. The SSPC  106  is used for optimizing the utilization of engine power extraction. Depending on the flight conditions of aircraft speed, altitude, and engine thrust requirements, the vehicle management computer (VMC) would determine the best operating configuration and turn on and off the power from high pressure spool driven generator  42  by commanding the ICU  46  and switching on/off the SSPC  106 . The SSPC is used, rather than a conventional electrical power contactor since higher endurance life is required from such solid state device. This system enables using the lowest cost/penalty of engine power and thus provides high system efficiency. Analysis has shown the cost of extracting power from high pressure spool driven generator would have a higher fuel consumption penalty to the engine. 
       FIG. 4  shows the power distribution system of  FIG. 3  wherein the 270 volt power distribution units are electrically disconnected from each other.  FIG. 4  shows how the high pressure spool driven generator  42  channel is disconnected from the low pressure spool driven generator  48  channel. This configuration can be used in the event that a non-power control mode is more desired, such as if there is a fault in either channel.  FIG. 4  differs from  FIG. 3  in that contactor  164  is opened to allow the system to operate in the non-power controlled mode. The UCAP  104  still supports the high pressure spool driven generator  42  and the IFWPCU/EAU/BAT/UCAP  112  would supplement the low pressure spool driven generator  48 . In the event that higher system integrity is more desirable than achieving higher system efficiency, the non-power controlled mode may be selected in lieu of the more energy efficient power control mode. 
       FIG. 5  shows the power distribution system of  FIG. 3 , wherein the IFWPCU provides power to a failed generator bus.  FIG. 5  differs from  FIG. 3  in that switches  146  and  164  are open, and switch  162  is closed. This switch configuration allows the IFWPCU to provide power to a failed generator bus. This configuration utilizes the PMG  86  to provide backup power to the VMC  180  through the CRU  88 . This configuration is used to continue providing power to the VMC channel for system reliability even if the low pressure spool driven generator  48  failed and needs to be disconnected from the bus  50 . 
       FIG. 6  shows the power distribution system of  FIG. 3 , wherein the IFWPCU provides power to a failed generator bus.  FIG. 6  differs from  FIG. 3  in that switches  126  and  128  are open, and switches  136  and  140  are closed. This configuration utilizes the PMG  68  to provide backup power to the VMC  172  and VMC  176  through the CRU  70 . This configuration is used to continue providing power to the VMC channels for system reliability even if the high pressure spool driven generator  42  failed and needs to be disconnected from the bus. 
       FIG. 7  shows the power distribution system of  FIG. 3  configured to support the high power device operation. The various components are connected through switches to reduce generator transient rating requirements.  FIG. 7  differs from  FIG. 3  in that switches  148  and  164  are open. The high power device operation could have created power ripple effects and it is desired to isolate the high power devices from the other equipment to avoid additional filtering requirements or system operation impacts. 
       FIG. 8  shows the power distribution system of  FIG. 3  configured for an engine out scenario.  FIG. 8  differs from  FIG. 3  in that switches  126  and  146  are open. The IFWPCU  12  is turned on to provide the emergency power required at high altitude using either the energy stored in the flywheel or the EAU/Batter power until the aircraft could descend to the lower altitude. When a lower altitude is reached, the IFWPCU  12  would be able to take in sufficient ambient air to support a combustion mode and thus generate power to support the aircraft operation and engine  14  re-start. In the event that engine  14  is re-started, the aircraft could climb back to altitude or divert to a landing site. 
     In various embodiments, the IFWPCS combines a flywheel with the integrated power and cooling unit to provide the ground power and cooling; normal cooling; peak power at altitude by supercharging using engine bleed air; emergency power; and energy storage. The system management is executed by the VMC. The multi-channel VMC would monitor the system operation and commands the ICU  46 , ICU  38 , and GCU  52 , all the contactors, and SSPC accordingly. The VMC also communicates with the engine full authority digital engine control (FADEC) to command the IFWPCU mode switching. 
     The IFWPCU supplies power like an auxiliary power unit using a power turbine. It also stores power in a flywheel, and for peak power it harvests kinetic energy from the flywheel using the generator. The kinetic energy stored in the flywheel can also be used for other purposes. For example, it can cool the directed energy system by expanding air using a cooling turbine, running it through a heat exchanger and compressing it to go back through the Fan Duct Heat Exchanger. In the example of  FIG. 1 , the flywheel, compressors, generator and power turbine are all on the same shaft (i.e., with no gears) and can operate at 30-40 kRPM. 
     The flywheel could be constructed by leveraging many state-of-the-art developments. The flywheel can be constructed with a composite hub and high strength material in the rim to achieve a desired material density and moment of inertia. The flywheel would be operated at high speed and is a good match to the IFWPCU  12  since the turbo-machine would operate in a similar speed range. The flywheel could be spun up using battery power or ground power before the IFWPCU  12  enters the combustion mode to burn fuel to generate power. This could facilitate the IFWPCU startup since flywheel speed could be built up gradually, thus reducing the power required for starting. 
     The flywheel allows for a reduction in IFWPCU starter/generator size for engine starting. The flywheel also enables a reduction of engine bleed air or power extraction during idle descent and maintains stall margin during throttle transients. Peak engine bleed air and power extraction could force the operating points closer to the turbo-machine operation stall limits. A stalled turbo-machine could have detrimental effects on the engine operation and a strict operating margin is mandated to assure safe operation. The peak power loads would demand a system capable of higher margin just to support the occasional demands. The flywheel and EAU/Battery system would handle the peak loads thus mitigating the need for the engine to operate closer to the stall margin if over-design is not implemented. 
     A flywheel enabled EAU provides the transient and peak power required to support high power devices. A supercharged IFWPCU enables high power generation at high altitude. 
     The drawings show a detailed architecture for storing and distributing power for peak energy in an aircraft implementation that uses a single shaft to run the generator to create steady electric power from the power turbine on the shaft. A flywheel is used to store energy, allowing for harvesting peak electric power from the flywheel using the generator when demanded by a peak power load. Expander and compressor turbines are run to create cooling by cycling between a fan duct (heat sink) and a directed energy system or avionics (heat source). 
     The integrated power and cooling system is capable of multi-function operation, including providing ground auxiliary power and in-flight emergency power, normal cooling, peak power for high power equipment, and energy storage to reduce transient load impact to the engine. 
     The cooling and power system is integrated with a flywheel to enable vehicle avionics cooling and to provide peak power for direct energy weapon operation. The flywheel enables energy storage and releasing when needed. The system can use electrical power to provide cooling power and the flywheel can reduce the power demand to the engine during idle descent transition. The electrical power system architecture distributes the engine power generation and the IFWPCS power to support high peak power equipment such as electronic attack and direct energy weapon systems. 
     The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. 
     The described power system can provide electrical power and cooling for an aircraft when operating in accordance with a method that includes: connecting a starter generator to an energy accumulator bus; selectively connecting the energy accumulator bus to a first power distribution unit in a first power channel or a second power distribution unit in a second power channel; wherein the starter generator is coupled to a shaft in an integrated power and cooling unit that includes a cooling turbine coupled to the shaft; a compressor coupled to the shaft and including an input for receiving engine bleed air or ambient air and an output for discharging compressed air; a flywheel coupled to the shaft; and a power turbine coupled to the shaft; and using energy stored in the flywheel to rotate the shaft enabling the starter generator to supply electrical power to the energy accumulator bus. 
     While the invention has been described in terms of several embodiments, it will be apparent to those skilled in the art that various changes can be made to the described embodiments without departing from the scope of the invention as set forth in the following claims.