Abstract:
A power transfer method in a variable frequency electric power generation system includes determining that initial power quality conditions the variable frequency electric power generation system are satisfied, sending a power-ready signal, receiving an acknowledgement to the power-ready signal, indicating that an associated alternating current bus is ready to receive power generated in the variable frequency electric power generation system, receiving a bus-ready signal and in response to receiving the bus-ready signal, activating a generator line contactor driver.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to power transfer, and more specifically, to fault tolerant bus power transfer for multichannel, variable frequency electric power generation systems. 
         [0002]    In aircraft, a Variable Frequency (VF) Electric Power Generation System (EPGS) has three independent alternating current (AC) power channels, including a left engine driven main generator (LGEN), a right engine main generator (RGEN), and an auxiliary power unit (APU) generator (AGEN), where each of the LGEN, RGEN, and AGEN can have access to one or more AC power buses. In the VF EPGS, power transfer is coordinated through a Bus Power Control Unit (BPCU). It is a design feature that each power generation channel has no evidence is an AC power present on associated bus or not. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    Exemplary embodiments include a power transfer method in a variable frequency electric power generation system, including determining that initial power quality conditions for the variable frequency electric power generation system are satisfied, sending a power-ready signal, receiving an acknowledgement to the power-ready signal, indicating that an associated bus is ready to receive power generated in the variable frequency electric power generation system, receiving a bus-ready signal and in response to receiving the bus-ready signal, activating a generator line contactor driver. 
         [0004]    Additional exemplary embodiments include a computer program product including a non-transitory computer readable medium storing instructions for causing a computer to implement a power transfer method in a variable frequency electric power generation system. The method includes determining that initial power quality conditions for the variable frequency electric power generation system are satisfied, sending a power-ready signal, receiving an acknowledgement to the power-ready signal, indicating that an associated alternating current bus is ready to receive power generated in the variable frequency electric power generation system, receiving a bus-ready signal and in response to receiving the bus-ready signal, activating a generator line contactor driver. 
         [0005]    Further exemplary embodiments include a variable frequency electric power generation system including a first generator coupled to a first generator control unit and to a first alternating current bus through a first generator line contactor, a second generator coupled to a second generator control unit and to a second alternating current bus through a second generator line contactor and an auxiliary generator coupled to a third generator control unit and to a plurality of bus tie contactors, through a third generator line contactor, and coupled to at least one of the first and second alternating current buses through the plurality of bus tie contactors, wherein the first, second and third generator control units are configured to determine that initial power quality conditions for the variable frequency electric power generation system are satisfied, send a power-ready signal, receive an acknowledgement to the power-ready signal, indicating that an associated alternating current bus is ready to receive power generated in the variable frequency electric power generation system, receive a bus-ready signal, set a first timer, in response to receiving the bus-ready signal, activate a generator line contactor driver for at least one of the first, second and third generator line contactors and in response to the first timer exceeding the first predetermined time period, opening a subgroup of the plurality of the bus tie contactors coupled to the associated alternating current bus, wherein the first timer is compared to a first predetermined time period to wait for the acknowledgement to the power-ready signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  schematically illustrates an electric power generation system in which exemplary power transfer methods can be implemented. 
           [0008]      FIG. 2  illustrates an electrical interface between each generator control unit and associated generator line contactor; 
           [0009]      FIG. 3  schematically illustrates a bus tie contactor electrical interface of the system of  FIG. 1 ; 
           [0010]      FIG. 4  illustrates a flow chart for a bus power transfer method in accordance with exemplary embodiments; 
           [0011]      FIG. 5  illustrates electric interface between each generator control unit and the and a bus power control unit; 
           [0012]      FIG. 6  schematically illustrates an interface between an auxiliary power unit generator control unit and the rest of system of  FIG. 1 ; 
           [0013]      FIG. 7  illustrates a table of bus tie contactor open/close status in respect to the power transfer from the auxiliary power unit generator when the left generator is active; 
           [0014]      FIG. 8  illustrates a table of bus tie contactor open/close status in respect to the power transfer from the auxiliary power unit generator when the right generator is active; and 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  schematically illustrates an electric power generation system  100  in which exemplary power transfer methods can be implemented. The system  100  includes a VF EPGS  105  having three AC power channels and an electric power distribution system (EPDS)  150 . In more detail, the illustrated VF EPGS  100  includes three independent AC power channels including an LGEN  110 , an RGEN  115 , and an AGEN  120 . For control, protection and indication functions, each of the LGEN  110 , the RGEN  115 , the AGEN  120  has a designated stand-alone generator control unit (GCU) LGCU  111 , RGCU  116 , AGCU  121 , respectively. The EPDS  150  includes two different AC power buses LAC  155 , and RLC  160 . The EPDS further includes two bus tie contactors (BTC) LBTC  171 , and RBTC  181 . In one embodiment, with two different BTCs, the two individual AC power busses LAC  155 , and RAC  160  can be combined in different configurations to allow power sharing. The EPDS  150  further includes a bus power control unit (BPCU)  190  as a part of power transfer control process described herein. The LGCU  111 , the RGCU  116 , the AGCU  121 , and the BPCU  190  are all connected to a digital bus  106 . It can be appreciated that two AC power sources with different frequencies cannot be connected to the same bus. 
         [0016]    The EPDS  150  also includes a left generator line contactor (LGLC)  185  located between the LGEN  110  and the LAC bus  155 , a right generator line contactor (RGLC)  186  located between the RGEN  115  and the RAC bus  160 , an AGEN line contactor (AGLC)  187  connected between the AGEN  120  and BTCs. The LGLC  185  is a 3 phase contactor that connects/disconnects the LGEN  110  from the LAC bus  155 . The RGLC  186  is a 3 phase contactor that connects/disconnects the RGEN  115  from the RAC bus  160 . The AGLC  187  is a 3 phase contactor that connects/disconnects the AGEN  120  from designated AC buses. It shall be noted that the AGEN  120  has no designated bus, but in one case, the AGLC  187  connects/disconnects the AGEN  120  from the rest of aircraft electric network. 
         [0017]    As described herein, the LGEN  110  and the RGEN  115  have designated AC buses, the LAC bus  155 , and the RAC bus  160 , respectively, while the AGEN  120  is connected to one or both buses (LAC bus  155 , and/or the RAC bus  160 ) through the BTCs, LBTC  171 , and RBTC  181  which are used for the aircraft electric power transfer. In one embodiment, where each channel in the system  100  has an independent power transfer process, if two or more VF power sources are connected to the same AC Bus (e.g., the LAC bus  155 , and the RAC bus  160 ), a significant damage to the generators (e.g., the LGEN  110 , the RGEN  115  and the AGEN  120 ) can occur. As such, a fault tolerant bus power transfer protocol is included in respective GCUs (e.g., the LGCU  111 , the RGCU  116 , the AGCU  121 ). The fault tolerant bus power transfer protocol is based on communication between each of the LGCU  111 , the RGCU  116 , the AGCU  121 , and the BPCU  190 . If the BPCU  190  has a failure, then the fault tolerant bus power transfer protocol can rely on the status (e.g., open/close) of the BTCs, LBTC  171 , and RBTC  181 . For example, an open/close BTC status is indicated through pair of auxiliary BTC contacts (one normally open, and one normally closed) which are connected to the respective GCU. In one embodiment, the LGCU  111 , and the RGCU  116  have a direct interface with the LBTC  171 , and RBTC  181  respectively. The AGCU  121  has no direct interface with the BTCs, LBTC  171 , and RBTC  181 . As such, the fault tolerant bus power transfer protocol for the AGEN  120  implements communication with main generator power channels. As such as described further herein, the fault tolerant bus power transfer protocol is implemented separately for the LGEN  110  and the RGEN  115 , and separately for the AGEN  120 . 
         [0018]    In one embodiment, where there exists failures of the EPGS  105 , in order to protect the overall system  100  and to allow reconfiguration with other power sources, each of the LGCU  111 , the RGCU  116  and the AGCU  121  in each power channel, has exclusive control over the respective LGLC  185 , RGLC  186  and AGLC  187 . In on embodiment, each of the LGCU  111 , the RGCU  116 , and the AGCU  121  provides a 28V/Open discrete signal to control the respective LGLC  185 , RGLC  186  and AGLC  187 .  FIG. 2  illustrates a circuit portion  200  of the system  100  of  FIG. 1 . The portion  200  includes a generator control switch (GCS)  205  connected to a respective GCU  210  (e.g., any of the LGCU  111 , the RGCU  116  and the AGCU  121 ) through logic control  215 . The logic control is “anded” with a power quality conditions module  220  through an “AND” gate  225 . The 28V/Open discrete signal controls a switch  230  to a GLC  235  (e.g., any of the LGLC  185 , the RGLC  186 , and the AGLC  187 ). The GLC  235  includes a switching three phase contacts  236  and solenoid  237 . In one embodiment, the high side of the solenoid  237  is connected to the GCU  210 , and the low side of the solenoid  237  is connected directly to ground. 
         [0019]    In one embodiment, to maintain independence among the power sources, and to protect the generators LGEN  110 , RGEN  115  and AGEN  120  from electric energy coming from an opposite AC Bus, or wiring faults, the LGCU  111 , the RGCU  116  and the AGCU  121  in each power channel has partial control of associated BTCs.  FIG. 3  schematically illustrates a BTC electrical interface  300  of the system  100  of  FIG. 1 .  FIG. 1  schematically illustrates that a GCU  305  such as the LGCU  111 , and RGCU  116  of  FIG. 1  is configured to receive a lockout request logic signal  306  that can be logically combined with protection logic  310  as described further herein. As illustrated, a logic “OR”  307  generates a lockout command logic output  308  that can control switch  315  to BTC  320 , such as the LBTC  171 , or RBTC  181 , of  FIG. 1 . The BTCs  320  are connected to a BPCU  325  such as the BPCU  190  of  FIG. 1 . The BTC  320  is connected to the BPCU  325  via switches  326 .  FIG. 3  illustrates that BTC  320  can be switched ON and OFF from the BPCU  325  but only switched OFF from the associated GCU  305 . An Open/Close status of the each BTC is indicated to associated GCUs through a pair of auxiliary contacts  327 . 
         [0020]    In one embodiment, the lockout command  308  is set TRUE if any of the EPGS conditions from the protection logic  310  are TRUE. When lockout command  308  is FALSE, the GCU  305  is providing a ground state to the BTC  320 . Setting lockout command  308  causes the GCU  305  to inhibit (lockout) the closure of the BTC  320  in order to isolate associated AC Bus. 
         [0021]    In one embodiment, LGCU  111  and RGCU  116  are continuously monitoring two auxiliary contacts of its associated BTC. The AGCU  121  has no direct interface with any of the BTCs and no interface with any BTC auxiliary contacts. An open/close BTC status is communicated from the LGCU  111  and the RGCU  116  to the AGCU  121  through the digital communication bus  106 . If the BTC lockout is required by the AGCU  121 , the request for the lockout is communicated through combination of analog discrete and digital bus signals: one pair for the LGCU  111  and one pair for the RGCU  116 . Once either the LGCU  111  or the RGCU  116  receives a BTC lockout request signals from the AGCU  121 , a lockout command is issued and the associated BTC is opened. 
         [0022]    As described herein, in the system  100  of  FIG. 1 , a power generation process is independent from power distribution. As such, the LGCU  111 , the RGCU  116 , and the AGCU  121  have no direct indication if power is present on the other side of the associated GLC. If the associated AC Bus is already powered, the LGCU  111 , the RGCU  116 , and the AGCU  121  have no visibility of the powered state, and power transfer through the LGLC  185 , RGLC  186  or AGLC  187  GLC shall cause GCU protection to trip due to a Sustained Parallel Sourcing condition. In one embodiment, the system  100  includes a bus power transfer method in the respective GCUs to coordinate between the power generation side (i.e., EPGS  105 ) and the power distribution side (i.e., the EPDS  150 ) of the system, where the BPCU has visibility of AC buses power status. 
         [0023]      FIG. 4  illustrates a flow chart for a bus power transfer method  400  for the main generators LGEN  110 , RGEN  115  in accordance with exemplary embodiments. In one embodiment, power transfer is implemented without adding additional AC power sensing devices to EPGS channels through communication (e.g., a “handshake”) between the LGCU  111 , the RGCU  116 , AGCU  121  and the BPCU  190 , where intentions to transfer bus power from the EPGS  105  is acknowledged and confirmed. 
         [0024]    At block  405 , initial power quality conditions are satisfied, and a GCS (e.g., the GCS  205  of  FIG. 2 ) is ON. At block  410 , the GCU (e.g., either of the LGCU  111  or RGCU  116  of  FIG. 1 ) generates analog and digital signals “Power Ready” to the BPCU (e.g., BPCU  190  of  FIG. 1 ). At block  415 , a GCU signal “Power Ready” signal initiates an internal TIMER T 1  to count. At block  420 , the GCU waits for a handshake “Bus Ready Acknowledge” from the BPCU. In one embodiment, once the BPCU receives the analog and digital signals “Power Ready,” as a request from GCU to apply power to the associated AC bus, and if there is no other power source present on associated AC bus, the BPCU acknowledges the request and responds with analog and digital signals “Bus Ready Acknowledged”. As the GCU recognizes that the AC bus is ready through analog and digital signals “Bus Ready Acknowledged” from BPCU at block  425 , then at block  430 , the GCU generates a GLC Command ON signal at block  430 , and activates the GLC driver command at block  435 . As such, a bus power transfer with a “handshake protocol” has been completed with confirmation time Tc&lt;T 1 . In one embodiment, a loss of “Bus Ready Acknowledged” signal from BPCU after the “handshake protocol” has been completed will have no impact on specific power channel operation. However, several events can occur in the bus power transfer protocol as a result of a failure where a “handshake protocol” cannot be completed within T 1  time window. With the signal “Power Ready” still valid after T 1  time, and associated BTC is open, the GCU activates the GLC at block  430 , activates the GLC driver command at block  435 , and the bus power transfer is completed in time T=T 1 . 
         [0025]    If associated BTC is not open, and the signal “Power Ready” is still active after T 1  time, and there is no acknowledgment from BPCU, the GCU will activate signal “Lockout Command” to open associated BTC, thereby indicating that the bus is not ready at block  425 . With Ti elapsed at block  440 , the GCU starts a second TIMER T 2  at block  445  to count. At block  455 , with the conditions for the lockout met, the BTC is locked out at block  460 . Once associated BTC is open, and the signal “Power Ready” is valid at block  425 , before T 2  has elapsed at block  465 , the GCU activates GLC at block  430 , activates the GLC driver command at block  435  and the bus power transfer is completed in time T 1 &lt;T&lt;(T 1 +T 2 ). 
         [0026]    In one embodiment, the “Bus Ready Acknowledged” signal from BPCU takes priority and the GCU activates “GLC Command ON” when confirmation time Tc is T 1 &lt;Tc&lt;T 2  regardless of BTCs status. As result of “Bus Ready Acknowledged” signal, the GCU resets the signal “Lockout Command” so that BPCU can operate the BTCs if necessary. 
         [0027]    In one embodiment, the method  400  can also be applied in the event of two independent failures, in which a first failure is associated with the BPCU causing an absence of the “Bus Ready Acknowledged” signal, and the second failure is associated with the absence of an indication that associated BTC is open, where associated BTC is stuck in a permanent closed position. In this dual failure scenario, each power generation channel is still able to deliver power to designated bus. In this scenario, a bus power transfer is completed only after (T 1 +T 2 ) time elapsed. 
         [0028]      FIG. 5  illustrates a circuit portion  500  of the system  100  of  FIG. 1 , illustrating an electric interface between a GCU  505  (e.g., either of LGCU  111 , the RGCU  116 , and AGCU  121  in  FIG. 1 ) and a BPCU  510  (e.g., the BPCU  190  in  FIG. 1 ). In one embodiment, to maintain redundancy in the system  100 , several discrete signals are transmitted over a digital bus  506  between the GCU  505  and the BPCU  510 . The discrete signals include, but are not limited to: “Power Ready”; “Not Power Ready”; “Bus Ready Acknowledged”; and “Not Bus Ready Acknowledged”. 
         [0029]    In one embodiment, the methods described herein, such as the method  400  of  FIG. 4  combines the “Power Ready” signal generated by logic in the GCU  505 , BTC status and signal an “AC Load Bus Ready” signal. Based on a response from the BPCU  510  with discrete signals “Bus Ready Acknowledged”, “NOT Bus Ready Acknowledged” and the same set of parameters on the digital bus  506 , a signal “AC Load Bus Ready” is generated. 
         [0030]    The bus transfer protocol for the AGEN (see AGEN  120  in  FIG. 1  for example) is now described.  FIG. 6  schematically illustrates an interface  600  of the system  100  of  FIG. 1 . The interface  600  is between the AGCU  121 , the LGCU  111 , RGCU  116  and BPCU  190 . In one embodiment, for redundancy purposes, the control parameters “Lockout Request Left” and “Lockout Request Right” are transmitted over the digital bus  606  from the AGCU  621  to LGCU  611  and RGCU  616  respectively while “Left Gen”, and “Right Gen” are digital bus parameters, transmitted from other power sources to AGCU  621 . Those power source parameters indicate that power source is active and present on aircraft electric network. At the same time, as the AGCU  621  has no interface with the BTCs, the BTCs open/close status is transmitted over the digital bus  606  from the LGCU  611  and the RGCU  616  to the AGCU  621 . 
         [0031]    As described herein, since the AC bus architecture is different for the AGCU  621 , and because the AGCU  621  has not direct interface with the BTCs, a different implementation of a bus power transfer method is implemented with the AGCU  621 . In one embodiment, a difference occurs when a single failure eliminates a “handshake protocol” from the BPCU. In that case, if a BTC lockout is requested for the left and right side BTCs, as a preventive measure, it will not bring any benefit to the aircraft network because AGEN has no designated AC bus and activation of the main contactor (i.e., an AGLC) does not provide power to any of aircraft loads. As such, in a single failure case, to allow power transfer to the LAC bus or to the RAC bus (see LAC  155  and RAC  160  in  FIG. 1  for example), an AGCU should know is there any other source of energy present on the left or on the right side, so that power transfer can be safe without causing a conflict with other source of energy. 
         [0032]    In one embodiment, AGEN power transfer can proceed with a complete “Handshake Protocol” with Tc confirmation time Tc&lt;T 1 , as described with respect to  FIG. 4 . As such, this case is common to the main generators and the auxiliary power generator. 
         [0033]    In one embodiment, AGEN power transfer can proceed with an absence of “handshake protocol” due to BPCU single failure with no other power sources present. In this case a Bus Power Transfer Protocol will not issue request for a BTC lockout due to the absence of the other power sources. In this case, regardless of BTCs open/closed status, an AGEN will complete power transfer after Ti time. 
         [0034]    In one embodiment, AGEN power transfer can proceed with an absence of a “handshake protocol” due to BPCU single failure with one or more AC power sources present. In this case, the different BTC arrangements and AC Bus power sources can create multiple configurations which can create a conflict. In one group of configurations, AC power from the main Generators is present on either the LAC bus or the RAC bus (see LAC  155  and RAC  160  in  FIG. 1  for example). The status of all two BTCs is arbitrary. One out of four BTCs combinations can cause conflict and in this combination is shown in  FIG. 7  that illustrates a table  700  of BTC Closed status with the LGEN power present, which can cause an AGCU lockout request on the left side, and  FIG. 8  that illustrates a table  800  of BTC Closed status with the RGEN power present, which can cause an AGCU lockout request on the right side. In both the tables  700 ,  800  of  FIGS. 7 and 8 , a Left or Right BTC lockout request is issued respectively. Once the BTC configuration has changed so that Lockout is no longer required, a power transfer is completed within T 1 &lt;T&lt;(T 1 +T 2 ). 
         [0035]    In a case that any of the BTCs has a mechanical failure and are stuck closed the AGEN power transfer can proceed after (T 1 +T 2 ) time expired. In one embodiment, if a power transfer has been completed after T 1 +T 2  time with one BTC stack closed, creating two independent sources of AC power in a parallel condition, a separate function called Sustained Parallel Source (SPS) protection reacts. As result of SPS protection, a main AGLC is disconnected, and the SPS protection logic will shut down Generator excitation field of the AGEN. 
         [0036]    The GCUs and BPCU can be any suitable microcontroller or microprocessor for executing the instructions (e.g., on/off commands) described herein. As such, the suitable microcontroller or microprocessor can be any custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors, a programmable logic devices (in the form of a microchip or chip set), a macroprocessor, or generally any device for executing software instructions. 
         [0037]    As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
         [0038]    Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
         [0039]    The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
         [0040]    In exemplary embodiments, where the methods are implemented in hardware, the methods described herein can implemented with any or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
         [0041]    Technical effects include the implementation of a fault tolerant bus power transfer without additional hardware. 
         [0042]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.