Abstract:
A method and apparatuses are used for power conversion. The apparatus according to one embodiment comprises a plurality of power conversion modules ( 130   —   1, . . . , 130   —   n ), the plurality of power conversion modules ( 130   —   1, . . . , 130   —   n ) being optionally controllable to function independently of each other to supply a plurality of systems ( 200   —   1, . . . , 200   —   n ), function in an inter-relational mode in which at least one power conversion module from the plurality of power conversion modules ( 130   —   1, . . . , 130   —   n ) drives a system and, upon a failure of the at least one power conversion module, at least another power conversion module from the plurality of power conversion modules ( 130   —   1, . . . , 130   —   n ) will drive the system, and function in a scalable mode in which at least two power conversion modules of the plurality of power conversion modules ( 130   —   1, . . . , 130   —   n ) are connected to provide an additive output.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This non-provisional application is related to co-pending non-provisional application titled “An Architecture and a Multiple Function Power Converter for Aircraft” filed concurrently herewith, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to power conversion systems, and more particularly to a method and apparatus for a modular and scalable power conversion system for an aircraft. 
   2. Description of the Related Art 
   Electric systems used in complex environments such as aerospace systems, more electric aircraft systems, industrial environments, vehicles, etc., include a large number of electric systems and modules. During operation of such complex environments, various electric systems and modules may need to be connected to electric power sources, disconnected from electric power sources, maintained in a powered-up state, etc., at various times. Moreover, various electric systems and modules in a complex environment may require different amounts and type of electrical power. For example, some electric systems and modules may require DC power while others may require AC power. Some electric systems and modules may require 28 Vdc, others 230 Vac, yet others 115 Vac at 400 Hz. The power levels required by various parts of a complex environment may also depend on the operational stage of the environment. For example, different levels of power may be needed during a start-up and during a continuous operation of a complex environment, such as an aircraft. 
   Aircraft are currently being designed to use less non-electric power (such as hydraulic and pneumatic power) and more electrical power. Aircraft system architectures that rely solely, or to a great extent, on electrical power, are also referred to as More Electric Aircraft (MEA) system architectures. Typically, MEA system architectures use starter-generators to start the aircraft main engines, as well as supply electrical power to various system loads that may utilize electrical power at various frequencies and voltages. Hence, many MEA system architectures, and/or starter-generators currently used to power MEA system architectures, typically include relatively complex power electronics circuits with large weight. In these heavy power electronics circuits, motor controllers are used for main engine start and after the start, to supply the motors in the Environmental Control System (ECS) or other motor loads in the aircraft systems, such as hydraulic system loads. 
   One such power system architecture for aircraft is described in patent application US 2004/0129835 A1, by W. Atkey et al. In this patent application, an electric power distribution system includes AC generators. High voltage AC power can be converted to high voltage DC power by one or more AC-to-DC conversion devices, such as auto transformer rectifier units (ATRUs), that receive AC power from AC busses. Using the ATRUs, the power distribution system provides high voltage AC and DC power to support conventional 115V and 28 Vdc bus architectures. An output from an ATRU is alternatively connected to an AC generator during start, and to a load such as an air compressor system, during normal operation. 
   However, typical/conventional power conversion systems place design constraints on the generating and conversion equipment such as the motor controllers, since the design of the generating and conversion equipment is heavily dependent on the larger power typically required to achieve the main engine start. The output current required for main engine start is 2 to 5 times larger than the current required to drive motors in the ECS or in other systems. This discrepancy in power requirements leads to designs with large output ratings, and imposes weight, volume and cost penalties on existing aircraft systems, resulting in sub-optimal approaches to the design of architectures used for MEA. Moreover, in typical/conventional power generation and conversion systems, the availability of the start system is negatively affected, because a failure of one of the motor controllers used for start removes at once the start capability for the starter generator associated with the failed controller. 
   Disclosed embodiments of this application address these and other issues by utilizing a modular and scalable power conversion system consisting of power conversion modules, which are designed and optimized for continuous operation when they supply motors used in aircraft systems, or aircraft busses with fixed frequency. During main engine start, a number of power conversion modules are operated in parallel and used to supply start power to a starter generator. The power conversion modules may be controlled for connection to any starter generator or motor in the electric system, hence allowing for power conversion modules to be designed for much lower ratings, to realize weight, volume and cost savings. In the power conversion system described in the current application, the availability of the start system is increased over previous systems, because a failure of one of the power conversion modules used in parallel during start will remove only partially the start capability, as the other connected power conversion modules are able to supply start power. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a method and apparatuses for power conversion. According to a first aspect of the present invention, a power conversion apparatus comprises: a plurality of power conversion modules, the plurality of power conversion modules being optionally controllable to function independently of each other to supply a plurality of systems, function in an inter-relational mode in which at least one power conversion module from the plurality of power conversion modules drives a system and, upon a failure of the at least one power conversion module, at least another power conversion module from the plurality of power conversion modules will drive the system, and function in a scalable mode in which at least two power conversion modules of the plurality of power conversion modules are connected to provide an additive output. 
   According to a second aspect of the present invention, a power conversion module comprises: an input assembly; a 3 phase bridge; an output assembly including at least one isolation device; and a control unit, wherein the control unit controls the 3 phase bridge via a driver, and controls a state of at least one isolation device within the output assembly. 
   According to a third aspect of the present invention, a method for converting power comprises: controlling a plurality of power conversion modules to function independently of each other to supply a plurality of systems; controlling the plurality of power conversion modules to function in an inter-relational mode in which at least one power conversion module from the plurality of power conversion modules drives a system and, upon a failure of the at least one power conversion module, at least another power conversion module from the plurality of power conversion modules will drive the system; and controlling the plurality of power conversion modules to function in a scalable mode in which at least two power conversion modules of the plurality of power conversion modules are connected to provide an additive output. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects and advantages of the present invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a general block diagram of an electrical system to which principles of the present invention can be applied according to an embodiment of the present invention; 
       FIG. 2  is a block diagram of a typical/conventional power system for an aircraft; 
       FIG. 3  is a block diagram of a modular and scalable power conversion system for aircraft according to an embodiment of the present invention; 
       FIG. 4A  is a block diagram of a system including two power conversion modules connected in parallel to supply power to a starter generator according to an embodiment of the present invention illustrated in  FIG. 3 ; 
       FIG. 4B  is a block diagram of an exemplary modular and scalable power conversion system for aircraft according to an embodiment of the present invention illustrated in  FIG. 3 ; 
       FIG. 4C  is a block diagram of another exemplary modular and scalable power conversion system for aircraft according to an embodiment of the present invention illustrated in  FIG. 3 ; and 
       FIG. 5  is a block diagram illustrating an implementation for a power conversion module for a modular and scalable power conversion system for aircraft according to an embodiment of the present invention illustrated in  FIG. 3 . 
   

   DETAILED DESCRIPTION 
   Aspects of the invention are more specifically set forth in the accompanying description with reference to the appended figures.  FIG. 1  is a general block diagram of an electrical system to which principles of the present invention can be applied according to an embodiment of the present invention. The electrical system  100  illustrated in  FIG. 1  includes the following components: input power systems  206 ; a modular and scalable power conversion system  250 ; individual loads/motors  200 ; and starter generators  210 . Operation of the electrical system  100  in  FIG. 1  will become apparent from the following discussion. 
   Electrical system  100  may be associated with environments with electrical components such as a cabin air compressor system, a hydraulic system, a heating system, a traction system, etc., in an aircraft, a ship, a train, a laboratory facility, etc. Input power systems  206  provide electrical power to individual loads/motors  200  and starter generators  210 , through the modular and scalable power conversion system  250 . Input power systems  206  handle wattage power that can be on the order of W, kW, hundreds of kW, MW, etc., and voltages that can be on the order of Volts, hundreds to thousands of Volts, etc. The outputs of input power systems  206  may be DC voltages, AC voltages, etc. Input power systems  206  may include motors, turbines, generators, transformers, filters, circuit breakers, etc. 
   Modular and scalable power conversion system  250  receives power from input power systems  206 , and provides electrical power to individual loads/motors  200  and starter generators  210 . Modular and scalable power conversion system  250  includes power conversion modules. Modular and scalable power conversion system  250  may also include other electrical circuits and components such as transformers, rectifiers, filters, battery banks, etc., magnetic components such as coils and permanent magnets, etc. 
   Individual loads/motors  200  and starter generators  210  are systems that enable functioning of services onboard a vehicle, in an aircraft, in a lab, etc. Individual loads/motors  200  and starter generators  210  may include an air conditioning system, a navigation system, an aircraft control system, a cabin air compressor, a starter generator, a braking system, etc. 
   Input power systems  206  and modular and scalable power conversion system  250  may provide, and individual loads/motors  200  and starter generators  210  may use various AC or DC voltages. For example, some electrical systems may utilize AC voltages of 115V or 230V or higher, with fixed frequencies (such as, for example, 50/60 Hz or 400 Hz), or variable frequencies (such as, for example 360-800 Hz for aerospace applications, 1000-2000 Hz for high frequency), or DC voltages such as, for example, 28V, 270V, or ±270V. 
   Although the systems in electrical system  100  are shown as discrete units, it should be recognized that this illustration is for ease of explanation and that the associated functions of certain functional modules or systems can be performed by one or more physical elements. 
     FIG. 2  is a block diagram of a typical/conventional power system  204  for an aircraft. During the aircraft engine start, a motor controller  207  is used to supply power to the starter generator  210 M for main engine start. After the start, motor controller  207  is used to supply a motor  213 . The motor  213  may be included in the ECS, in the hydraulic aircraft system, etc. The typical/conventional aircraft power system  204  imposes design constraints on the generating and conversion equipment that includes motor controller  207 . Design constraints are imposed on the motor controller  207  because its design is heavily dependent the power required to achieve the main engine start at starter generator  210 M. The output current required for main engine start is typically 2 to 5 times larger than the current required to drive the motor  213 . This results in a motor controller  207  designed with a large output rating, needed for the main engine start, but not for the subsequent control of an aircraft motor load. This large output rating imposes weight, volume and cost penalties on existing power systems, resulting in sub-optimal approaches to power conversion and distribution. Another negative aspect of the typical/conventional aircraft power system  204  is that the availability of the starter generator  210 M is negatively affected, because a failure of the motor controller  207  removes at once the start capability for its associated starter generator. 
     FIG. 3  is a block diagram of a modular and scalable power conversion system  250 A for aircraft according to an embodiment of the present invention. As illustrated in  FIG. 3 , modular and scalable power conversion system  250 A includes n power conversion modules (PCMs)  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n . The PCMs are designed and optimized for continuous operation when they supply the loads/motors  200 _ 1 ,  200 _ 2 , . . . ,  200   —   n  used in aircraft systems, such as the ECS, the hydraulic system, etc. During main engine start, a certain number of PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  are operated in parallel and used to supply the start power to a starter generator (SG)  210 _ 1 . The aircraft electrical architecture allows to connect each of the PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  to any of the SGs in the electric system, such as SG  210 _ 1 , . . .  210   —   m , as required for main engine start, auxiliary power unit (APU) start, etc. This approach allows for the PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  to be designed for a much lower rating, hence realizing weight, volume and cost savings. 
   The availability of the start system is increased over typical/conventional systems. In the system illustrated in  FIG. 3 , a failure of one of the PCM modules  130 _ 1 ,  1302 , . . . ,  130   —   n  used in parallel during start, will remove only partially the start capability of the system, as the other PCM modules which have not failed are still able to supply start power. After the start, some of the PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  can be disconnected from the parallel configuration, and used individually for other functions, such as for supplying power to individual loads/motors  200 _ 1 ,  200 _ 2 , . . . ,  200   —   n , etc. More weight and volume savings are hence realized, because of the multiple functionality of PCMs  130 _ 1 ,  1302 , . . . ,  130   —   n.    
   Each one of the power conversion modules (PCMs)  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  can be designed to have independent power output and controls. The independent controls capability of the PCMs is used during the continuous operation, when the PCM modules supply power to individual loads and motors, such as ECS motors, hydraulic system motors, other aircraft systems, etc. 
   The PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  also include the capability and the interfaces required to communicate with each other, to use common controls during the main engine start, when the outputs of the PCMs are paralleled. During main engine start, when a certain number of PCMs are operated in parallel and used to supply the start power to a starter generator among  210 _ 1 ,  210 _ 2 , . . . ,  210   —   m , two or more PCMs use the same controls supplied via a controls and communication interface  255 . One of the PCM is the master and the other PCM(s) is/are the slave(s). In case the master PCM has a failure, it will be turned off and one of the remaining PCM controllers will become master and continue the start. The controls and communication interface  255  manages the PCM hierarchy based on PCM functionality. The PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n  may control connections/switch arrangement for contactors  302 _ 1   a ,  302 _ 1   b ,  302 _ 2   a ,  302 _ 2   b , . . . ,  302   —   na ,  302   —   nb  to enable combinations of different PCMs to be connected to a starter generator and at the same time to be disconnected from any individual loads. Contactors  302 _ 1   a ,  302 _ 1   b ,  302 _ 2   a ,  302 _ 2   b , . . . ,  302   —   na ,  302   —   nb  may, alternatively or additionally, be controlled by the controls and communication interface  255 . 
   For example, connections/switch arrangement for contactors  302 _ 1   a ,  302 _ 1   b ,  302 _ 2   a ,  302 _ 2   b , . . . ,  302   —   na ,  302   —   nb  may be controlled to establish an independent PCM configuration, or an interdependent PCM configuration such as, for example, a paralleled PCM configuration. The contactors  302 _ 1   a ,  302 _ 1   b ,  302 _ 2   a ,  302 _ 2   b , . . . ,  302   —   na ,  302   —   nb  may be separate units from PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n , or may be included in the PCMs  130 _ 1 ,  130 _ 2 , . . . ,  130   —   n.    
     FIG. 4A  is a block diagram of a system including two power conversion modules connected in parallel to supply power to a starter generator according to an embodiment of the present invention illustrated in  FIG. 3 . 
   In typical/conventional aircraft systems, a start converter may have dual use as a motor controller, by powering a starter generator and a cabin air compressor (CAC) load sequentially. However, such a start converter used to power both a starter generator and a CAC load uses a large amount of power and is inefficiently used, because the start function for a starter generator typically requires power on the order of 100 kW, while a CAC load start function requires less power than the starter generator. Hence, the excess power capacity corresponding to the starter generator is not used when the start converter powers a CAC load, and the start converter is typically oversized for the use of powering a CAC. 
   As illustrated in  FIG. 4A , two PCMs  130 A and  130 B are operated in parallel to provide power to a starter generator  210 A for start. After providing power to starter generator  210 A, the PCMs  130 A and  130 B are operated independently of each other, to provide power to CAC  1  ( 213 B) and CAC  2  ( 213 A). Hence, the output of the two PCMs  130 A and  130 B are combined during start of the system to obtain a larger start power (for starter generator  210 A), and are decoupled after start, to obtain smaller powers (for loads  213 A and  213 B). 
   In an exemplary embodiment, instead of using a fixed 100 kW power controller to power a 100 kW starter generator and a 50 kW CAC, PCMs  130 A and  130 B, which provide 50 kW each, output 100 kW power for starter generator  210 A when the PCMs  130 A and  130 B are operated together in parallel, and output 50 kW each for 2 separate loads, when the PCMs  130 A and  130 B are operated independently. Weight and volume system savings are hence achieved. 
     FIG. 4B  is a block diagram of an exemplary modular and scalable power conversion system for aircraft according to an embodiment of the present invention illustrated in  FIG. 3 . In  FIG. 4B , PCMs  130 A and  130 B are operated with their outputs in parallel during a main engine start with starter generator  210 _L 1 , with PCMs  130 A and  130 B being controlled by a common control algorithm. The two contactors closer to the PCM at the output of each PCM module (contactors  302 A and  302 B), are closed. This contactor arrangement allows for start operation using one PCM module in the case of failure of the other module. After the start, these contactors (contactors  302 A and  302 B) are open and the contactor connection to Cabin Air Compressor (CAC)  1  (contactor  302 D) and CAC  2  (contactor  302 C) are closed. PCMs  130 A and  130 B are now operated independently, each supplying one CAC of the ECS, CAC  1  and  2  ( 213 A and  213 B). PCMs  130 A and  130 B are designed for continuous operation to drive the CAC  1  and CAC  2  ( 213 A and  213 B) and therefore weight and volume savings are realized. 
   Similarly, PCMs  130 C and  130 D are operated with their outputs in parallel during a main engine start using starter generator  210 _L 2 , or starter generator  210 _R 1 , or auxiliary starter generator  210 A, and are controlled by a common control algorithm. After the start, PCMs  130 C and  130 D are operated independently, each supplying a motor driving the hydraulic system ( 215 A and  215 B). 
   PCMs  130 E and  130 F are also operated with their outputs in parallel during a main engine start using starter generator  210 _R 2  and are controlled by a common control algorithm. After the start, PCMs  130 E and  130 F are operated independently, each supplying a CAC load ( 213 C and  213 D). 
   General motor controllers  207 A,  207 B,  207 C, and  207 D are also present. Each general motor controller supplies only one load, such as: a condenser fan  213 E, a vapor cycle system (VCS)  213 G, a VCS  213 H, and a condenser fan  213 F. 
   The availability of the start system illustrated in  FIG. 4B  is increased, since the left engine start capability is 200% when both starter generators ( 210 _L 1  and  210 _L 2 ) and all four PCMs  130 A,  130 B,  130 C, and  130 D are available. The left engine start capability will degrade from 200% to 150% when any one of the PCMs  130 A,  130 B,  130 C, and  130 D fails. The left engine start capability will degrade to 100% when two PCMs among  130 A,  130 B,  130 C, and  130 D fail. In traditional/conventional aircraft start systems, the 150% engine start capability and availability step is non-existent. Also, since multiple PCMs are available per starter generator and engine as illustrated in  FIG. 4B , the aircraft system can withstand more failures than a typical system with 2 generators and 2 start converters (one per generator). Using systems implemented in the current application, engine start can still be performed with a failed generator or any combination of 2 failed PCMs. 
   The PCMs in  FIGS. 3 ,  4 A and  4 B may include Multiple Function Power Converters (MFPCs), described in the non-provisional application titled “An Architecture and a Multiple Function Power Converter for Aircraft”, the entire contents of which are hereby incorporated by reference. When the PCMs include MFPCs, the PCMs can perform multiple functions, including functions of motor controllers, functions of static inverters, and functions of start converters, as illustrated in  FIG. 4C . In  FIG. 4C , MFPCs  130 _ 1   a  and  130 _ 1   b  are used in parallel to starter generator  210 _L 1 , and are used afterwards to provide power to CAC  213 A and  213 B. MFPCs  130 _ 2   a  and  130 _ 2   b  are used in parallel to starter generator  210 _R 2 , and are used afterwards to provide power to CAC  213 C and  213 D. MFPCs  130 _ 3   a  and  130 _ 3   b  are used in parallel to provide power to starter generators  210 _L 2  and  210 _R 1 , and are used afterwards to provide power to hydraulic loads  215 A and  215 B, and to 400 Hz loads  218 A and  218 B through left and right autotransformers (OAT)  291 A and  291 B. 400 Hz is one of the standard frequencies used in aircraft electrical systems. While 400 Hz loads are shown in  FIG. 4C , loads using other frequencies can also receive conditioned power from the MFPCs. MFPCs may provide power to loads using other constant or variable frequencies, such as loads associated with MEA aircraft. 
   Hence, the MFPCs in  FIG. 4C  perform functions for electric engine start, for driving the ECS or cabin air compressors, and functions of static inverters. In one exemplary embodiment, the MFPCs provide 115 VAC or 230 VAC, 3-phase, 400 Hz (or other standard frequencies used in aircraft electrical systems) electrical power for aircraft systems and equipment that require such power. Aircraft wiring saving may be achieved by using the generator main feeders during engine start, thus eliminating the need for dedicated feeders for start. Since MFPCs can perform the functions of motor controllers, start converters, and inverters, a reduced number of MFPCs is sufficient to power a variety of loads. 
     FIG. 5  is a block diagram illustrating an implementation for a power conversion module (PCM)  130 A for a modular and scalable power conversion system for aircraft according to an embodiment of the present invention illustrated in  FIG. 3 . As illustrated in  FIG. 5 , a PCM  130 A includes: an input assembly  301 ; a 3 phase bridge  303 ; an output assembly  305 ; drivers  307 ; and power conversion module (PCM) controls  309 . Input power passes through the input assembly  301 , the 3 phase bridge  303 , and the output assembly  305 , from which output power is obtained. Input signals and control power are received at PCM controls  309 , and an output for the controls and communication interface  255  (as illustrated in  FIG. 3 ) is obtained. PCM controls  309  control the input assembly  301 , the output assembly  305 , and the 3 phase bridge  303 . 
   The input assembly  301  contains filter elements and isolation devices. The isolation devices may be, for example, contactors or relays. The output assembly  305  contains filter elements and isolation devices. PCM controls  309  control states of the isolation devices included in the input assembly  301  and output assembly  305 . PCM controls  309  also control the 3 phase bridge  303  via the drivers  307 . In one embodiment, PCM controls  309  control switching of devices inside  3  phase bridge  303  via gate devices included in drivers  307 . 
   The PCM  130 A may be sized for main engine start (MES), or by other criteria. The size of the 3 phase bridge  303 , and the size of the electromagnetic interference (EMI) filters and heat sink associated with the PCM  130 A may be reduced, to obtain a compact PCM  130 A. 
   By controlling isolation devices in the input assembly  301  and the output assembly  306 , the 3-phase bridges  303  of neighboring PCMs can be coordinately driven for main engine start, for example in parallel for 3-phase Variable Frequency Starter Generators (VFSG), or at 30° shift for 6-phase VFSGs, etc. 
   In one embodiment, the 3-phase bridge  303  is compatible with high-power industrial equipment. 
   The power output from the output assembly  305  is used for main engine start or to drive motors and loads. In an exemplary embodiment, the output power from independent PCM channels is used to drive permanent magnet (PM) cabin air compressor (CAC) motors, and the 3 phase bridges  303  of the PCMs are rated for CAC at about 65 A/phase. In another exemplary embodiment, the output power from one PCM channel is used for main engine start (MES), and the 3 phase bridge  303  is rated for MES at about 220 A/phase for a limited start duration. 
   Embodiments of the current invention are not limited to the particular numbers of starter generators, or the particular number and types of loads illustrated, and can be used with any quantities and types of starter generators and loads. Although some aspects of the present invention have been described in the context of aerospace applications, the principles of the present invention are applicable to any environments that use electrical power, such as industrial environments, vehicles, ships, etc., to provide various amounts of power, at various frequencies.