Abstract:
A system and method for improved system efficiency of an integrated power and control unit (IPCU) of an aircraft is disclosed. The system uses an open-loop cooling system and turbo machine power matching to provide wide operation range without over-sizing. In order to reduce the temperature of the air flow through the cooling heat exchanger, the cooling turbine need to expand further in the same time generating power but the power could be higher than the compressor could absorb so a generator that would convert the power and used in supplying the aircraft would result in more efficient system.

Description:
BACKGROUND 
       [0001]    The invention relates generally to electrical power and cooling systems for aircraft and more particularly to enabling high energy system operation using an integrated power and cooling unit for high performance aircraft. 
         [0002]    Modern aircraft integrate a number of systems to perform the functions required for flight and operation. A propulsion engine provides power to the aircraft when in flight and also drives the main generator to provide electrical power, either during flight or when on the ground. In order to provide the emergency backup power in the event of main engine or main generator failures, aircraft have evolved to include a supplemental non-propulsion engine such as the auxiliary power unit (APU). Since the cooling system is a major function of an aircraft, it has been integrated with the APU to provide not only cooling but also power in the event that it is required if the main generator system failed. 
         [0003]    This integrated system (APU and cooling system) is often referred to as an integrated power and cooling unit (IPCU) that not only provides pneumatic or electrical power for starting the propulsion engine; it also generates electrical power and provides conditioned cooling air to the aircraft, both during flight and while on the ground. With the increasing use of systems having high energy requirements on aircraft, the IPCU can also be used to help meet short term high peak power when needed so as to minimize over-sizing the main generator system. 
         [0004]      FIG. 1  is a schematic block diagram of portions of an aircraft electrical power and cooling system. As shown in  FIG. 1 , a prior art IPCU  100  includes cooling turbine  102 , compressor  104 , starter/generator  106  and power turbine  108 , all connected to a common drive shaft  110 . In order for the IPCU to come up to operating speed, initial startup of IPCU  100  is driven by starter/generator unit  106  in starter mode using battery or ground power. After compressor  104  is capable of providing air for combustion then power turbine  108  generates enough power to sustain the power requirements with the system configured to burn fuel using combustor  112  and thus, continues to drive the power turbine to generate power. After IPCU  100  is started in combustion mode, it can provide electrical power for various aircraft systems through integrated control unit (ICU)  114  which sends the power to integrated power unit (IPU) Bus  115 . When in normal flight mode, IPCU  100  is then configured to provide cooling air by running off of propulsion engine bleed air instead of power input from burning fuel. This is accomplished by means of cooling turbine  102 , which also provides low pressure cool air to an avionics cooling system. This system includes heat exchangers  116  and  118  as well as pump  120 . The avionics cooling system is used to provide temperature controlled air flow to the avionics equipment and cabin of the manned aircraft, as well as for other needs as understood by one of ordinary skill in the art. 
         [0005]    Also in  FIG. 1 , main engine  122  is shown, together with an engine high pressure spool coupled starter/generator  124  and an engine low pressure spool driven generator  126 . High pressure spool starter generator  124  is connected to engine  122  as well as to an electrical power distribution bus  128  through an inverter control unit  130 . Low pressure spool generator (LP GEN)  126  is also connected to engine  122  as well as to an electrical power bus  132  through generator control unit (GCU)  134 . 
         [0006]    There are several connections between IPCU  100  and engine  122 . High pressure, warm air from compressor  104  can be directed into fan duct heat exchanger  136  of engine  122  when operating in the cooling air mode. This air can also be directed into combustor  112  to generate more power by burning fuel and driving the power turbine  108  using valve  148 . Compressor  104  also receives ambient air through input  142  when operating in ground operating mode or in-flight emergency mode. 
         [0007]      FIG. 1  shows a closed loop system, which includes heat exchanger  138  that provides pre-cooled engine bleed air to compressor  104 . The air is compressed by the compressor  104  and then cooled by the engine fan air through the fan duct heat exchanger  136 . An additional heat exchanger  140  cools the air provided to the cooling turbine using the relatively cool air returned from the avionics heat exchanger  116 . The air is expanded by cooling turbine  102  to generate very cold air to cool the avionics liquid cooling loop through avionics cooler  116 . The cooling capacity of the system is determined by the exit air temperature and the mass flow rate of the cooling turbine. A closed loop system has the advantage of allowing lower bleed air usage which conserves fuel, however, IPCU system pressure is limited by the compressor  104  pressure ratio capability. In other words, in order for the air flow exiting from cooling turbine  102  to feedback to the compressor  104  through heat exchanger  140 , the return pressure has to be higher that the replenish flow from the engine. This pressure is set by the operating parameters of compressor  104  when operating at a high altitude. Often, selector/regulator valves  144  and  146  are used to select the engine bleed air according to the operating altitude. Due to the high pressure ratio of the modern engine compressor, this limits the cooling turbine  102  discharging pressure and the temperature of the cooling flow. 
         [0008]    In contrast,  FIG. 2  depicts a prior art open loop system where heat exchanger  140  does not provide an input to compressor  104  but is controlled by a venting valve  150  then vented to the ambient condition. This open loop system allows a lower cooling temperature exit from the cooling turbine, which means a higher expansion ratio is available at high altitude. However, bleed air usage is higher and is limited by the flow and temperature required to cool the avionics. Traditionally, in order to regulate the flow and the cooling capability, the system exit flow pressure and thus the system operating speed is controlled by placing back pressure to the cooling turbine using an exhaust control valve  150 . However, in order to deep discharge the cooling turbine  102 , power must be absorbed by compressor or the starter/generator  106  on the same shaft of IPCU  100 . Since this prior art system is not designed to use the starter/generator in generating mode to absorb the power, it is thus incapable of operating economically at a wide range of power and cooling capacities. Specifically, if there is peak power equipment that only requires peak power occasionally during the flight mission, then the system must be over sized to be capable of providing the maximum cooling capability. Therefore, the system is operating at a much lower setting and lower efficiency most of the time thus resulting in a less efficient system. In prior art systems, starter/generator  106  is only used during system startup, and not during cooling modes of the system. 
         [0009]    Thus, a need exists for an improved integrated power and cooling system that is capable of providing efficient peak power and cooling not limited by the operating pressure of the closed loop system or the by the power balance required to maintain IPCU  100  main shaft speed using only the air control valves of the open-loop system. 
       SUMMARY 
       [0010]    The invention provides improved system efficiency of open-loop cooling system and maintained turbo machine power matching resulted in wide operation range without over-sizing. In order to reduce the temperature of the air flow through the cooling heat exchanger, the cooling turbine need to expand further in the same time generating power but the power could be higher than the compressor could absorb so a generator that would convert the power and used in supplying the aircraft would result in more efficient system. 
         [0011]    The invention in one implementation encompasses a system for providing electrical power and cooling for an aircraft having an engine, the system including an integrated power and control unit (IPCU) starter/generator coupled to a shaft, a cooling turbine coupled to the shaft, a compressor coupled to the shaft between the IPCU starter/generator and the cooling turbine, said compressor having an input for receiving engine bleed air and an output for discharging compressed air while rotating the shaft and a power summing controller for coupling power from the IPCU starter/generator to a load of the aircraft in parallel with power from the engine. 
         [0012]    In an embodiment, the system includes first and second buses for receiving power from the engine and coupling the power to one or more loads, a third bus for receiving power from the IPCU starter/generator and coupling the power to one or more loads and first and second contactors, coupled to the power summing controller, for coupling the third bus to the first and second buses. 
         [0013]    In an embodiment, the first and second contactors further comprise one or more bi-directional solid state, high power contactors. 
         [0014]    In a further embodiment, the system includes a first integrated control unit (ICU) coupled to the IPCU starter/generator, a first current sensing unit (CSU) receiving an input from the ICU and a IPCU contactor coupling the first CSU to the third bus such that the power summing controller further comprises a first electrical system distribution control unit (DCU) for controlling at least the IPCU contactor and the first and second contactors. 
         [0015]    In any of the above embodiments, the system includes a low pressure (LP) generator coupled to the engine, a generator control unit (GCU) receiving an input from the LP generator, a second current sensing unit (CSU) receiving input from the GCU and an LP contactor coupling the second CSU to the first bus such that the power summing controller further comprises a second electrical system distribution control unit (DCU) for controlling at least the LP contactor and the first contactor to couple the first bus to the third bus. 
         [0016]    In an embodiment, the system includes a high pressure (HP) starter/generator coupled to the engine and a second integrated control unit (ICU) receiving an input from the HP generator and coupling it to a high pressure bus, a third current sensing unit (CSU) receiving input from the second ICU and an HP contactor coupling the second CSU to the second bus such that the power summing controller further comprises a third electrical system distribution control unit (DCU) for controlling at least the HP contactor and the second contactor to couple the second bus to the third bus. 
         [0017]    In any of the above embodiments, the system includes or more energy storage devices operatively coupled to the third bus. 
         [0018]    In any of the above embodiments, the aircraft is operated as an open loop system. 
         [0019]    The invention in one implementation encompasses a method for providing electrical power and cooling for an aircraft having an engine, having the steps of generating power for the aircraft using the engine, generating power for the aircraft using an integrated power and control unit (IPCU) and summing the power from engine and the IPCU and applying it to a load of the aircraft. 
         [0020]    In a further embodiment, the step of generating power for the aircraft using an engine further has steps of generating power using a low pressure (LP) generator and coupling it to an LP bus and generating power using a high pressure (HP) starter/generator and coupling it to a HP bus. 
         [0021]    In an embodiment, the step of generating power for the aircraft using an IPCU further includes the step of coupling the power to an IPCU bus. 
         [0022]    In an embodiment, the step of summing the power includes the steps of coupling the low pressure bus to the IPCU bus using one or more contactors and coupling the high pressure bus to the IPCU bus using one or more contactors. 
         [0023]    In an embodiment, the summing step includes the steps of receiving inputs from the IPCU, LP generator and the HP generator at one or more distribution control units (DCUs) and controlling the one or more contactors using the one or more DCUs. 
         [0024]    In any of the above embodiments, the one or more contactors further comprise bi-directional solid state, high power contactors. 
         [0025]    In any of the above embodiments, the aircraft is operated as an open loop system. 
         [0026]    In any of the above embodiments, the method includes the step of storing power generated by at least one of the engine and the IPCU in one or more energy storage devices. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]    Features of example implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which: 
           [0028]      FIG. 1  is a schematic block diagram of a prior art aircraft engine and integrated power and cooling unit (IPCU) in a closed loop configuration. 
           [0029]      FIG. 2  is a schematic block diagram of a prior art aircraft engine and integrated power and cooling unit (IPCU) in an open loop configuration. 
           [0030]      FIG. 3  is a schematic block diagram of an aircraft engine and integrated power and cooling unit (IPCU) according to the present invention. 
           [0031]      FIG. 4  is a schematic block diagram of a power summing apparatus according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    In one aspect, the invention provides an integrated power and cooling unit (IPCU) with improved peak power generation and cooling capability. A power summing technology is used to enable the cooling power generation and the control of the IPCU power balance. 
         [0033]    Turning to  FIG. 3 , an apparatus  300  according to the present invention is shown. Elements in common with  FIGS. 1 and 2  have the same reference numerals. IPCU  100  of  FIG. 3  is in an open loop configuration with engine  122 , where the output of heat exchanger  140  is vented to ambient air by means of exhaust control valve  150 . Cooling turbine  102 , compressor  104 , starter/generator  106  and power turbine  108  are all located on the same shaft  110 , thus requiring power balancing between the elements. In other words, the power required by compressor  104 , starter/generator  106 , and the drag of the shaft bearing system must be equal to the power generated from the air expansion of cooling turbine  102  so that the proper operating speed is maintained. 
         [0034]    An additional input from engine  122  to IPCU  100  is provided through valve  149 . This valve provides for a bleed air driven mode in the event that additional power is required to use engine bleed air boost. Valve  149  allows the use of engine bleed air from selector/regulator valves  144  and  146  to drive power turbine  108  so additional power is added to IPCU shaft  110  for cooling or power generation. 
         [0035]    In an embodiment according to the present invention, starter/generator  106  is used throughout the operation of the aircraft to support cooling generation and power regulation, especially during periods of peak cooling needs. Instead of limiting the discharging pressure of the cooling turbine  102  and the power generated from air expansion by limiting the air flow through heat exchanger  140  using regulator valve  150 , excess power added to the system in the form of spinning shaft  110  by cooling turbine  102  is diverted by starter/generator  106  in generating mode through ICU  114  onto IPU bus  115 . The power sum control  302  adds the extra power to LP bus  132  while power sum control  304  adds the extra power to HP bus  128  according to the bus loading conditions and operating modes and configuration of the entire electrical power system. 
         [0036]      FIG. 4  shows a block diagram of a power summing apparatus according to the present invention. Elements in common with  FIG. 3  have the same reference numerals. LP GEN  126  is connected to generator control unit (GCU)  134 , which moderates the output power of the LP generator  126 . GCU  134  is connected to current sensing unit (CSU)  402  which senses the current output from LP generator  126  and provides the sensed current to the point of regulation (POR)  406 . POR  406  is placed in the LP generator  126  distribution system to measure the voltage of the system and provide it to GCU  134  for voltage control. From POR  406 , energy originating from LP GEN  126  is transferred to BUS  132 , then through power distribution system contactors  408  to loads  410 , which can be any power or electrical needs in the aircraft. GCU  134  and power distribution system contactors  408  receive control signals from the electrical system distribution control unit (DCU)  404 . 
         [0037]    DCU  404  monitors the electrical system operating modes, generator conditions, and POR  406  measurements to control the amount of energy generated from the LP generator  126 . In a preferred embodiment, measurements from POR  406  are sent to GCU  134  and communicated with DCU  404 . Typically, all controllers are on a control network and sharing data and information. LP generator  126  system DCU  404  also cross communicates with IPCU ST/Gen  106  system&#39;s DCU  414  and HP ST/Gen  124  system&#39;s DCU  426  to control the overall system operation. DCU  404  and DCU  414  also jointly control contactor  436  to determine whether of not electrical bus  132  and bus  115  should be connected to each other as explained in more detail below. 
         [0038]    Similarly, IPCU starter/generator  106  is connected to ICU  114 , which moderates the output power of the IPCU starter/generator  106 . ICU  114  is connected to CSU  412  which senses the current output from IPCU starter/generator  106  and provides the sensed current to the POR  416 , which is placed in the IPCU starter/generator  106  distribution system to measure the voltage of the system. From POR  416 , energy originating from IPCU starter/generator  106  is transferred to BUS  115 , then through power distribution system contactors  418  to loads  420  and  422 , which can be any power or electrical needs in the aircraft. ICU  114  and power distribution system contactors  418  receive control signals from DCU  414 , which monitors the electrical system operating modes, generator conditions, and POR  416  measurements to control the amount of energy generated from the IPCU starter/generator  106 . 
         [0039]    Likewise, HP starter/generator  124 , ICU  130 , CSU  424 , POR  428 , BUS  128 , contactors  430 , loads  432  and DCU  426  are interconnected similarly. 
         [0040]    A key feature of the present invention is found in cross-tie contactors  434  and  436 . Unlike prior art relay type contactors, which provide operation on the order of  100  milliseconds, the inventive contactors  434  and  436  are, for example, electronic semiconductor switches, controlled by DCUs  404 ,  414  and  426 . These switches operate on the order of microseconds, much faster than prior art relays. This allows near real time combination of power/energy from LP and IPCU by contactor  436 , and IPCU  106  and HP  124  by contactor  434 . 
         [0041]    Contactor  434  is a bi-directional solid state, high power controller which can be turned on and off in high speed, contrary to conventional mechanical relays. When contactor  434  is turned on, bus  128  and bus  115  are connected to each other and loads  432  and loads  420 / 422  are able to receive power from either HP generator  124  or IPCU ST/Gen  106 . Even if conditions are such that contactor  434  is controlled to be in an on state, it may be opened to maintain system independence for system safety. This also limits the IPCU ST/Gen system transient due to peak loads operation from being propagated into the HP ST/Gen  124  system and thus, to avoid impacting the electrical power quality. 
         [0042]    Contactor  436  is a bi-directional solid state, high power controller which can be turned on and off at a high speed, contrary to conventional mechanical relays. When contactor  436  is turned on, bus  132  and bus  115  are connected to each other and loads  410  and loads  422  are able to receive power from either LP generator  126  or IPCU ST/Gen  106 . Even if conditions are such that contactor  436  is controlled to be in an on state, it may be opened to maintain system independence for system safety. This also limits the IPCU ST/Gen system transient due to peak loads operation from being propagated into the LP ST/Gen  126  system and thus, to avoid impacting the electrical power quality. 
         [0043]    In an alternative embodiment, one or more energy storage devices (not shown) such as batteries or ultra-capacitors may be connected to bus  115  to store the energy generated from IPCU ST/gen  106  when additional cooling from cooling turbine  102  is generated. IPCU  100  can also be configured to receive engine  122  high pressure bleed air to drive the power turbine  108  to generate additional energy to charge the energy storage devices. In a further alternative embodiment, energy storage devices connected to bus  115  could also be charged by the LP generator  126  since contactor  436  allows the energy to flow from bus  132 . During the time during which peak power loads are present, energy storage devices could be sized to provide the transient power needs and contactor  436  may be opened to limit the power transient propagated into the LP Gen  126  system. These two operating modes complement each other for efficient energy utilization. 
         [0044]    Numerous alternative implementations of the present invention exist. With advent of high power, light weight batteries, the IPCU generation requirements could be reduced but the cooling function would not be totally replaced. This configuration and principles could also be applied to power system requires more than two main generators and a backup generators for example multiple-engines aircraft. 
         [0045]    The steps or operations described herein are just for example. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. 
         [0046]    Although example implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.