Fault current mitigation for power conversion systems

Abstract

A power conversion system includes: an alternating current (AC) source including a plurality of AC terminals for conducting AC power; a voltage source electrically coupled to the AC terminal; and a controller operably coupled to the voltage source, the controller configured to operate the voltage source to apply a fault reduction voltage at the AC terminal that reduces a fault current (If) between the AC lines.

Description

Technical Field

[0001] The present subject matter relates generally to electrical power systems, such as electrical power systems for aircraft. Background Art

[0002] Conventional commercial aircraft typically include a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system typically includes at least two aircraft engines, such as turbofan jet engines. Each turbofan jet engine is typically mounted to a corresponding one of the wings of the aircraft, such as in a suspension position below the wing that is separate from the wing and the fuselage.

[0003] Electric and hybrid electric propulsion systems are being developed to improve the efficiency of conventional commercial aircraft. Such propulsion systems may include motors or generators that produce three-phase alternating current (AC) power. The AC power may be fed through an AC / DC converter to convert the power to direct current (DC) and regulate the voltage supplied to an external load.

[0004] It is worth noting that electric and hybrid electric propulsion systems occasionally experience electrical faults. For example, an AC line-to-line fault may occur within a motor or generator, between a generator and an AC / DC converter, or elsewhere within the propulsion system, and such a fault may result in very high fault currents flowing between the fault terminals. This may heat the conductors in the fault path and result in a complete system failure or even a fire. Mitigating these electrical faults presents several challenges. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A full and enabling disclosure of the present disclosure, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0006] Figure 1 A schematic top view of an aircraft having a hybrid electric propulsion system is provided according to various exemplary embodiments of the present disclosure.

[0007] Figure 2 Provides Figure 1 A schematic cross-sectional view of a gas turbine engine for use with an exemplary aircraft.

[0008] Figure 3 Provided are exemplary embodiments of the present subject matter. Figure 1 A schematic representation of a power generation distribution system for use with an exemplary hybrid-electric propulsion system.

[0009] Figure 4 A phasor diagram according to an exemplary embodiment of the present subject matter is shown.

[0010] Figure 5A fault current vector representation according to an exemplary embodiment of the present subject matter is shown.

[0011] Figure 6 A fault line-to-fault reference frame according to an exemplary embodiment of the present subject matter is shown.

[0012] Figure 7 A fault frame phasor diagram of mixed positive-sequence injection and negative-sequence injection of a fault current cancellation voltage (FCCV) according to an exemplary embodiment of the present subject matter is shown.

[0013] Figure 8 An exemplary embodiment of the present subject matter is shown which can be used to adjust Figure 3 An exemplary method of controlling operation of a power generation distribution system.

[0014] Fig. 9 A contour plot showing average converter input power for varying control values ​​is shown according to an exemplary embodiment of the present subject matter.

[0015] Fig.10 A contour plot showing average converter power ripple percentage for varying control values ​​is shown according to an exemplary embodiment of the present subject matter.

[0016] Fig.11 The present invention shows an exemplary embodiment of the present invention. Figure 8 An exemplary control method is as follows: Figure 3 Plot of various operating parameters of an exemplary power generation distribution system.

[0017] Fig.12 The present invention shows an exemplary embodiment of the present invention. Figure 8 An exemplary control method is as follows: Figure 3 Plot of various operating parameters of an exemplary power generation distribution system.

[0018] Fig.13 A block diagram for extracting converter side current with residual negative sequence correction according to an exemplary embodiment of the present subject matter is shown.

[0019] Fig.14 A block diagram for extracting machine-side current with residual negative sequence correction according to an exemplary embodiment of the present subject matter is shown.

[0020] Fig.15 A block diagram for deriving fault current from machine-side and converter-side currents according to an exemplary embodiment of the present subject matter is shown.

[0021] Fig.16 Sensor locations for measuring fault current according to an exemplary embodiment of the present subject matter are shown.

[0022] Fig.17 A block diagram of a control algorithm for injecting only positive sequence voltage according to an exemplary embodiment of the present subject matter is shown.

[0023] Fig.18 The present invention shows an exemplary embodiment of the present invention. Fig.17 An exemplary control method is as follows: Figure 3 Plot of various operating parameters of an exemplary power generation distribution system.

[0024] Fig.19 A block diagram of a control algorithm implementing minimum fault current tracking (MFCT) for fault current control is shown according to an exemplary embodiment of the present subject matter.

[0025] Fig. 20 The present invention shows an exemplary embodiment of the present invention. Fig.19 An exemplary control method is as follows: Figure 3 Plot of various operating parameters of an exemplary power generation distribution system.

[0026] Fig.21 The present invention shows an exemplary embodiment of the present invention. Fig.19 An exemplary control method is as follows: Figure 3 Plot of various operating parameters of an exemplary power generation distribution system.

[0027] Fig. 22 Shows Figure 3 System diagram of the computing system of the power generation distribution system.

[0028] Fig.23 An exemplary embodiment of the present subject matter is shown which can be used to adjust Figure 3 An exemplary method of controlling operation of a power generation distribution system. DETAILED DESCRIPTION

[0029] Reference will now be made in detail to the present embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter references to refer to features in the drawings. Like or similar reference numbers in the drawings and description have been used to refer to like or similar parts of the present disclosure.

[0030] As used herein, the terms "first", "second" and "third" can be used interchangeably to distinguish one component from another, and are not intended to indicate the position or importance of each component. The term "include" is intended to be inclusive in a manner similar to the term "comprising". Similarly, the term "or" is generally intended to be inclusive (i.e., "A or B" is intended to mean "A or B or both"). The term "at least one" in the context of, for example, "at least one of A, B, and C" refers to only A, only B, only C, or any combination of A, B, and C. In addition, herein and throughout the specification and claims, range limitations can be combined and / or interchanged. Unless otherwise indicated by the context or language, such ranges are identified and include all sub-ranges contained therein. For example, all ranges disclosed herein include endpoints, and the endpoints can be combined independently of each other. Unless otherwise clearly defined by the context, the singular forms "one", "a kind of" and "the" include plural references.

[0031] As used herein throughout the specification and claims, approximate language is applied to modify any quantitative representation that can be permitted to vary without resulting in a change in the basic function to which it is associated. Therefore, a value modified by one or more terms such as "approximately," "about," "approximately," and "substantially" is not limited to the precise value specified. In at least some cases, approximate language may correspond to the precision of an instrument used to measure a value, or the precision of a method or machine used to construct or manufacture a component and / or system. For example, approximate language may refer to within a 10% margin, that is, including values ​​within 10% greater or less than the stated value. In this regard, for example, when used in the context of an angle or direction, such terms include within 10 degrees greater or less than the stated angle or direction.

[0032] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Additionally, references to "an embodiment" or "one embodiment" do not necessarily refer to the same embodiment, although they may. Any implementation described herein as "exemplary" or "an embodiment" is not necessarily to be construed as being superior or better than other implementations. Furthermore, each example is provided by way of explanation of the disclosure, not limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the disclosure without departing from the scope of the disclosure. For example, features shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, the disclosure is intended to cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0033] The terms "front" and "rear" refer to relative positions within a gas turbine engine or vehicle, and refer to the normal operating attitude of the gas turbine engine or vehicle. For example, for a gas turbine engine, the front refers to a position closer to the engine inlet, while the rear refers to a position closer to the engine nozzle or exhaust. The terms "upstream" and "downstream" refer to relative directions relative to the flow in a path. For example, for fluid flow, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows. However, the terms "upstream" and "downstream" as used herein may also refer to current.

[0034] The present disclosure generally relates to power systems, such as those found in aircraft hybrid electric and electric propulsion systems. More specifically, these power generation and distribution systems may include a motor or generator that produces three-phase alternating current (AC) power (e.g., to obtain power from a battery or output power to a load). The AC power may be fed through an AC / DC converter to convert the power to direct current (DC) and regulate the voltage supplied to an external load. Embodiments of the present subject matter may not be limited to power generation systems, but may include any system with a machine and a power converter. For example, the motor may operate as a motor or a generator, the system may operate with three-phase or single-phase power, etc. It is worth noting that electric and hybrid electric propulsion systems may occasionally experience electrical faults. For example, an alternating current (AC) line fault within a generator or between a generator and an AC / DC converter may cause very high fault currents to flow between fault terminals. This may heat the conductors in the fault path for a period of time, resulting in a complete system failure or even a fire.

[0035] Mitigating these electrical faults presents certain challenges. In this regard, one way to overcome these electrical faults may include cutting the shaft of the motor from the prime mover (e.g., the drive shaft of a gas turbine engine) as it can prevent the motor from feeding the fault. In a multi-winding generator system, shaft cutting may reduce the reliability of the system as the fault tolerance provided by other winding sets may also be affected. In addition, due to inertia, the motor may still operate and feed the electrical fault while the machine is rotating. Therefore, systems and operating methods designed to mitigate electrical faults in electric and hybrid-electric propulsion systems (or any other system that includes machines and converters) would be a welcome addition to the art.

[0036] Thus, aspects of the present subject matter provide a control solution that can reduce fault current to an acceptable value without cutting the machine shaft. For example, aspects of the present subject matter are directed to an active scheme that reduces fault current, such as by driving the negative sequence converter current to zero, thereby ensuring that the motor current is bypassed to the converter rather than the fault path. In this way, fault current and machine torque oscillations can be significantly reduced or completely eliminated. According to an exemplary embodiment, the proposed method can utilize a power converter to maintain the converter voltage at the AC link and the DC link for fault current elimination.

[0037] The power systems and methods for controlling these systems provided herein can provide certain advantages and benefits. For example, as described above and herein, the proposed control method can eliminate many problems or dangers associated with line-to-line (LL) faults, such as heating, arcing, fire and explosion. In addition, the proposed solution does not require cutting the generator shaft, slowing down or stopping the motor rotation, or disconnecting the motor terminals using a switch or circuit breaker. In addition, the fault tolerance provided by the multi-winding generator system can be unaffected. Using the control method, the machine torque oscillation can be reduced in steady state as the machine current imbalance is reduced. In addition, the proposed method does not require any additional sensors. The power system provided herein can provide other advantages and benefits not explicitly stated herein.

[0038] Referring now to the drawings, wherein like numerals represent like elements throughout, Figure 1 A schematic top view of an exemplary aircraft 10 is provided that may incorporate one or more inventive aspects of the present disclosure. Figure 1 As shown, for reference, the aircraft 10 defines a longitudinal direction L1 and a transverse direction L2. The transverse direction L2 is perpendicular to the longitudinal direction L1. The aircraft 10 also defines a longitudinal centerline 12 extending therethrough along the longitudinal direction L1. The aircraft 10 extends, for example, along the longitudinal direction L1 between a front end 14 and a rear end 16.

[0039] As shown, the aircraft 10 includes a fuselage 20 that extends longitudinally from a front end 14 of the aircraft 10 to a rear end 16 of the aircraft 10. The aircraft 10 also includes a tail 22 at the rear end 16 of the aircraft 10. In addition, the aircraft 10 includes a wing assembly that includes a first port wing 30 and a second starboard wing 32. The first and second wings 30, 32 each extend laterally outward relative to the longitudinal centerline 12. The first wing 30 and a portion of the fuselage 20 together define a first side 34 of the aircraft 10, and the second wing 32 and another portion of the fuselage 20 together define a second side 36 of the aircraft 10. For the depicted embodiment, the first side 34 of the aircraft 10 is configured as the port side of the aircraft 10, and the second side 36 of the aircraft 10 is configured as the starboard side of the aircraft 10.

[0040] The aircraft 10 includes various control surfaces. For this embodiment, each wing 30, 32 includes one or more leading edge flaps 38 and one or more trailing edge flaps 40. The aircraft 10 further includes, or more specifically, the tail 22 of the aircraft 10 includes: a vertical stabilizer 42, which has a rudder flap (not shown) for yaw control; and a pair of horizontal stabilizers 44, each horizontal stabilizer having an elevator flap 46 for pitch control. The fuselage 20 additionally includes an outer surface or skin 48. It should be understood that in other exemplary embodiments of the present disclosure, the aircraft 10 may additionally or alternatively include any other suitable configuration. For example, in other embodiments, the aircraft 10 may include any other control surface configuration.

[0041] Figure 1 The exemplary aircraft 10 also includes a hybrid electric propulsion system 50. For this embodiment, the hybrid electric propulsion system 50 has a first propeller 52A and a second propeller 52B, both of which are operable to generate thrust. The first propeller 52A is mounted to the first wing 30, and the second propeller 52B is mounted to the second wing 32. In addition, for the depicted embodiment, the first propeller 52A and the second propeller 52B are each configured as an underwing mounting configuration. However, in other exemplary embodiments, one or both of the first and second propellers 52A, 52B can be mounted in any other suitable location in other exemplary embodiments.

[0042] The first propulsion device 52A includes a first gas turbine engine 54A and one or more motors, such as a first motor 56A mechanically coupled to the gas turbine engine 54A. For example, the first motor 56A can be directly mechanically coupled to the shaft of the first gas turbine engine 54A, or indirectly mechanically coupled to the shaft of the first gas turbine engine 54A via a gearbox. The first motor 56A can be a generator, an electric motor, or a combined generator / motor. For this example embodiment, the first motor 56A is a combined generator / motor. In this way, when operating as a generator, the first motor 56A can generate electricity when driven by the gas turbine engine 54A. When operating as a motor, the first motor 56A can drive or start the first gas turbine engine 54A. The first gas turbine engine 54A can be any suitable type of gas turbine engine, including a turbofan engine, a turbojet engine, a turboprop engine, a turboshaft engine, etc.

[0043] Likewise, the second propulsion device 52B includes a second gas turbine engine 54B and one or more motors, such as a second motor 56B mechanically coupled to the second gas turbine engine 54B. For example, the second motor 56B may be directly mechanically coupled to the shaft of the second gas turbine engine 54B, or indirectly mechanically coupled to the shaft of the second gas turbine engine 54B via a gearbox. The second motor 56B may be a generator, an electric motor, or a combined generator / motor. For this example embodiment, the second motor 56B is a combined generator / motor. In this way, when operating as a generator, the second motor 56B may generate electricity when driven by the gas turbine engine 54B. When operating as a motor, the second motor 56B may drive or start the spool of the gas turbine engine 54B. The second motor 56B may be constructed and operated in a manner similar to the first motor 56A described herein. The second gas turbine engine 54B may be any suitable type of gas turbine engine, including a turbofan engine, a turbojet engine, a turboprop engine, a turboshaft engine, and the like.

[0044] The hybrid electric propulsion system 50 also includes an electrical energy storage system 60. The electrical energy storage system 60 may include one or more electrical energy storage devices, such as batteries, ultracapacitor arrays, one or more ultracapacitor arrays, some combination of the above, and the like. For example, for this embodiment, the electrical energy storage system 60 includes a battery 62. The battery 62 is electrically connected to a DC / DC converter 70 or a voltage regulating power supply. In some embodiments, the DC / DC converter 70 may be a bidirectional DC / DC converter. In this regard, the DC / DC converter 70 can control the power drawn from the battery 62 and the power provided to the battery 62, depending on whether it is desired to discharge or charge the battery 62. The DC / DC converter 70 is electrically connected to a power bus 72.

[0045] The power distribution unit 74 is located along the power bus 72. The power distribution unit 74 can be controlled to distribute power to various loads of the aircraft 10. For example, power drawn from the battery 62 can be directed to the power distribution unit 74 through the power bus 72, and the power distribution unit 74 can distribute the power to various aircraft loads, such as the first motor 56A and / or the second motor 56B. A first AC / DC converter 76A (or a first DC / AC converter) associated with the first motor 56A can be located along the power bus 72 for converting direct current to alternating current or vice versa. Similarly, a second AC / DC converter 76B (or a second DC / AC converter) associated with the second motor 56B can be located along the power bus 72 for converting direct current to alternating current or vice versa. Both the first AC / DC converter 76A and the second AC / DC converter 76B can be bidirectional converters.

[0046] The power distribution unit 74 and other controllable electrical components of the hybrid electric propulsion system 50 may be managed by a power management system. Among other components, the power management system may include a supervisory controller 80 operable to control or provide data to the power distribution unit 74 and the DC / DC converter 70. For example, the DC / DC converter 70 may include a controller operable to receive input from the supervisory controller 80, and based on such input, the controller may cause the switching elements of the DC / DC converter 70 to perform a duty cycle.

[0047] like Figure 1 As further shown, supervisory controller 80 may form part of computing system 90 of aircraft 10. Computing system 90 of aircraft 10 may include one or more processors and one or more memory devices embodied in one or more computing devices. Figure 1 As shown, computing system 90 includes supervisory controller 80 and other computing devices, such as computing device 92. Computing system 90 may also include other computing devices, such as an engine controller (not shown). The computing devices of computing system 90 may be communicatively coupled to each other via a communication network. For example, computing device 92 is located in the cockpit of aircraft 10 and is communicatively coupled to supervisory controller 80 of hybrid electric propulsion system 50 via a communication link 94 of the communication network. Communication link 94 may include one or more wired or wireless communication links.

[0048] For this embodiment, the computing device 92 is configured to receive and process input and / or other information, such as from a pilot or other crew member. In this manner, as an example, one or more processors of the computing device 92 may receive input indicating a command to change the thrust output of the first and / or second thrusters 52A, 52B. In response to the input, the supervisory controller 80 may manage the power drawn from the battery 62 by controlling or providing data to the controller of the DC / DC converter 70, and managing the power distribution unit 74 and the AC / DC converters 76A, 76B to distribute and supply the power required to meet the power requirements of the motors 56A, 56B. In this way, the motors 56A, 56B may drive their respective gas turbine engines 54A, 54B to ultimately change the thrust output of one or both of the thrusters 52A, 52B.

[0049] Although Figure 1 The aircraft 10 depicted in FIG. 1 includes a hybrid electric propulsion system 50, but it should be understood that the inventive aspects of the present disclosure may be equally applicable to all-electric propulsion systems. Furthermore, the inventive aspects of the present disclosure may be applied to other power systems outside of the aviation industry, including a voltage source (such as a battery) and a power converter supply electrically coupled thereto. In fact, aspects of the present subject matter may be applied to any system including an electric machine and a power converter.

[0050] As mentioned above, Figure 1 The exemplary aircraft 10 of FIG. 1 includes a propulsion system 50 having a first thruster assembly 52A and a second thruster assembly 52B. Referring now also to FIG. Figure 2 , a schematic cross-sectional view of a first propeller assembly 52A is provided according to an exemplary embodiment. It should be understood that the second propeller assembly 52B can be the same or similar to the first propeller assembly 52A, and each propeller assembly can be configured as an underwing mounted propeller assembly. In general, the first propeller assembly 52A can generally be configured as a turbofan engine 100. As shown in FIG. Figure 2 As shown, the turbofan engine 100 defines an axial direction A1 (extending parallel to a longitudinal centerline 101 for reference), a radial direction R1, and a circumferential direction C (extending about the axial direction A1; Figure 2 not depicted).

[0051] In general, the turbofan engine 100 includes a fan section 102 and a core turbine engine 104 disposed downstream of the fan section 102. The depicted exemplary core turbine engine 104 generally includes a substantially tubular casing 106 defining an annular inlet 108. The casing 106 encloses, in serial flow relationship: a compressor section including a supercharger or low pressure (LP) compressor 110 and a high pressure (HP) compressor 112; a combustion section 114; a turbine section including a high pressure (HP) turbine 116 and a low pressure (LP) turbine 118; and an ejection exhaust nozzle section 120. The compressor section, the combustion section 114, and the turbine section together define a core air flow path 121 extending from the annular inlet 108 through the LP compressor 110, the HP compressor 112, the combustion section 112, the HP turbine section 116, the LP turbine section 118, and the ejection exhaust nozzle section 120. A high pressure (HP) shaft or spool 122 drivingly connects the HP turbine 116 to the HP compressor 112. A low pressure (LP) shaft or spool 124 drivingly connects the LP turbine 118 to the LP compressor 110.

[0052] For the described embodiments, the fan section 102 may include a fixed or variable pitch fan 126 having a plurality of fan blades 128 coupled to a disk 130 in a spaced apart manner. As depicted, the fan blades 128 extend outwardly from the disk 130 generally along a radial direction R1. For the variable pitch fan embodiments, each fan blade 128 is rotatable relative to the disk 130 about a pitch axis P1 by virtue of the fan blades 128 being operably coupled to a suitable actuation member 132, the actuation member 132 being configured to collectively change the pitch of the fan blades 128 in unison. The fan blades 128, the disk 130, and the actuation member 132 together are rotatable about the longitudinal axis 12 via the LP shaft 124.

[0053] Still reference Figure 2 In an exemplary embodiment of the present invention, the disk 130 is covered by a rotatable forward hub 136 that is aerodynamically shaped to facilitate airflow through a plurality of fan blades 128. Additionally, the exemplary fan section 102 includes an annular fan case or outer nacelle 138 that circumferentially surrounds the fan 126 and / or at least a portion of the core turbine engine 104. The nacelle 138 is supported relative to the core turbine engine 104 by a plurality of circumferentially spaced outlet guide vanes 140. A downstream section 142 of the nacelle 138 extends over an outer portion of the core turbine engine 104 so as to define a bypass airflow passage 144 therebetween.

[0054] In addition, the depicted exemplary turbofan engine 100 includes a first electric machine and a second electric machine. For the illustrated embodiment, the first electric machine can rotate with the LP shaft 124 and the fan 126, and the second electric machine can rotate with the HP shaft 122. In this manner, it will be understood that for the illustrated embodiment, the first electric machine is the HP electric machine 146, and the second electric machine is the LP electric machine 148.

[0055] Specifically, for the depicted embodiment, the HP motor 146 is configured as a generator coaxially mounted to the HP shaft 122 and rotatable with the HP shaft 122. As used herein, "coaxial" refers to axis alignment. The HP motor 146 is also positioned inside the core air flow path 121, but is positioned within the compressor section of the turbofan engine 100, and therefore may also be referred to as an embedded motor. Similarly, for the depicted embodiment, the LP motor 148 is configured as a generator coaxially mounted to the LP shaft 124 and rotatable with the LP shaft 124. In addition, for the illustrated embodiment, the LP motor 148 is positioned inside the core air flow path 121 in or behind the turbine section of the turbofan engine 100, and therefore may be referred to as an embedded motor. The LP motor 148 and the HP motor 146 each include a rotor 150 and a stator 152. The LP motor 148 and the HP motor 146 may be constructed according to one or more of the exemplary motors described herein.

[0056] However, it should be understood that in other embodiments, the axes of the LP motor 148 and / or the HP motor 146 may be radially offset from the axes of the LP shaft 124 and the HP shaft 122, respectively, and further, the LP motor 148 and / or the HP motor 146 may be tilted from the axes of the LP shaft 124 and the HP shaft 122, respectively. In addition, in one or more exemplary embodiments, the LP motor 148 and / or the HP motor 146 may be located outside the core air flow path 121, for example, within the casing 106 of the turbofan engine 100 or the nacelle 138. In addition, although the LP motor 148 and the HP motor 146 are described above as generators, in certain exemplary embodiments, one or both of the LP motor 148 and the HP motor 146 may be configured as motors, or may be switched between a generator mode and a motor mode.

[0057] Furthermore, it should be understood that Figure 2The exemplary turbofan engine 100 depicted in FIG. 1 is provided as an example only, and in other exemplary embodiments, the turbofan engine 100 may have any other suitable configuration. For example, in other exemplary embodiments, the turbofan engine 100 may be configured as a turboprop engine, a turbojet engine, a turbofan engine of a different configuration, a non-ducted turbofan engine (e.g., without a nacelle 138, but including a stationary outlet guide vane 140), or any other suitable gas turbine engine. For example, the gas turbine engine may be a geared gas turbine engine (e.g., having a reduction gearbox between the LP shaft 124 and the fan 126), may have any other suitable number or configuration of shafts / spools (e.g., may include a medium speed shaft / turbine / compressor), etc.

[0058] Still reference Figure 1 and Figure 2 ,although Figure 2 140. Although not depicted in the drawings, the propulsion system 50 may additionally include an electrical connection assembly or power distribution unit 74 to allow the LP and HP motors 148, 146 to be in electrical communication with one or more other components of the propulsion system 50 and / or the aircraft 10. For the depicted embodiment, the power distribution unit 74 includes one or more cables or lines connected to the LP and HP motors 148, 146, which may extend from the LP and HP motors 148, 146 through one or more of the exit guide vanes 140. Generally, the electrical bus 72 is configured as a high voltage electrical bus such that the propulsion system 50 may generally operate at a relatively high voltage.

[0059] In addition, the depicted propulsion system 50 also includes one or more energy storage devices 62 (such as one or more batteries or other electrical energy storage devices) electrically connected to the power connection assembly 58 for providing power to the second thruster assembly 52B and / or receiving power from the generator, for example. The inclusion of one or more energy storage devices 62 can provide performance gains and can increase the propulsion capability of the propulsion system 50, for example, during transient operations. More specifically, the propulsion system 50 including one or more energy storage devices 62 can respond more quickly to speed change demands.

[0060] Now specific reference Figure 3, the power distribution system 300 will be described according to an exemplary embodiment of the present subject matter. As explained herein, the power distribution system 300 can generally be configured to regulate the power generated by the motor 302 and supplied to the electrical load 304. Although identified herein as the power distribution system 300, it should be understood that the system 300 can be alternatively referred to as, for example, a power conversion system that emphasizes the ability of the system to operate in a motor or generator mode (e.g., for regulating faults within an AC current system). For example, the power distribution system 300 can be used as part of a hybrid electric propulsion system 50 within an aircraft 10. Although the motor 302 is described herein as operating in a generator mode (e.g., using mechanical energy imparted by a prime mover to generate electricity), it should be understood that the motor 302 can alternatively operate as a motor or a combined generator / motor. In this regard, when the motor 302 operates in the generator mode, the electrical load 304 can act as an electrical load, and when the motor 302 operates as a motor, the electrical load 304 can act as a power supply. For example, the electrical load 304 can include an entire external electrical system, can include a power supply, can include a power load, or can include both a power supply and a load.

[0061] According to an exemplary embodiment, the electric machine 302 may be one or both of the first electric machine 56A and the second electric machine 56B that may be used to generate electricity during operation of the first gas turbine engine 54A and the second gas turbine engine 54B, respectively. Figure 2 , the motor 302 may be the HP motor 146 or the LP motor 148. Figure 3 As shown, during operation, the motor 302 generates three-phase AC power at its output terminals 306, which are represented herein by phases a, b, and c. For example, the output of the motor may be identified herein as a stationary three-phase power ( or and ),Voltage( or and ) and current ( or and ). For example, these terms or variables may generally refer to instantaneous sensed values ​​expressed in a stationary reference frame. It should be understood that although a three-phase AC system is described herein according to an exemplary embodiment, the subject matter may also be applied to any machine including, for example, a 1-phase, 2-phase power system, or a multi-phase power system.

[0062] In general, the power distribution system 300 includes a power converter 310 electrically coupled to the AC output terminal 306 for converting AC power to direct current (DC) power, or vice versa. In this regard, the power converter 310 may be an AC / DC converter and may include any suitable combination of power electronics or other devices suitable for conditioning AC power from the motor 302 for use as DC power by the external load 304 (or for conditioning DC power from an external electrical system (e.g., identified as the external load 304 in the figure) for use as AC power by the motor 302, for example, in an electric mode). For example, the power converter 310 may be electrically coupled to the motor 302 at an AC link 312 for receiving AC power. The power converter 310 may convert the AC power to DC power, which is output from the power converter 310 via a DC link (generally identified by reference numeral 314) to a DC power bus 316 electrically coupled to the external load 304 or other components within the power distribution system (e.g., the battery 62). According to an example embodiment, the external load 304 may be a load, another power converter, a power source, a battery, etc. Although power converter 310 is described herein and shown in the figures as an AC / DC converter, it should be understood that the present disclosure is not limited to such example embodiments. For example, according to alternative embodiments, power converter 310 may alternatively be an AC / AC converter, DC power bus 316 may be an AC power bus for conducting AC power, and external DC power source 330 may be an AC source.

[0063] According to the illustrated embodiment, the DC power bus 316 can be electrically coupled to the external load 304 (or another suitable source or electrical system) via the main contact circuit 318. In general, the main contact circuit 318 can be any suitable electrical switch or regulating device suitable for selectively coupling or disconnecting the external load 304 from the DC power bus 316. In this way, the external load 304 can be selectively isolated from the DC power bus 316. According to an exemplary embodiment, the motor power, voltage and / or current can be sensed within the power converter 310 (or at any other suitable location within the power distribution system 300). Line-to-line faults can be detected by monitoring the current in the power distribution system 300 or the vibration caused by torque pulsation. The sensed current can be only one of the power converter 310 current and the machine side current 302, or both currents.

[0064] As described in more detail below, for reasons described in more detail below, the power distribution system 300 may further include an external power source 330 that is generally configured to maintain the DC link 314 voltage generated by the power converter. According to an exemplary embodiment, the power source 330 may be a low voltage power source that is sized to mitigate fault currents and may be electrically coupled to the DC power bus 316. More specifically, according to the illustrated embodiment, the power source 330 may be electrically coupled to the DC power bus 316 via an auxiliary contact circuit 332. Generally, the auxiliary contact circuit 332 may be any suitable electrical switch or regulating device suitable for selectively coupling or disconnecting the power source 330 from the DC power bus 316. According to yet other embodiments, the external power source 330 may not be required and may be entirely optional or removed from the power distribution system 300. Generally, the external load 304, the power converter 310, the DC power bus 316, and / or the external DC power source 330 may be replaced by any suitable voltage source for reducing / eliminating fault currents. Therefore, these components may generally be referred to herein as a voltage source 334, such as Figure 3 According to example embodiments described herein, voltage source 334 includes DC power bus 316 and AC / DC power converter 310. However, as described above, according to alternative embodiments, voltage source 334 may alternatively include an AC power source, an AC / AC converter, an external AC power source, etc.

[0065] According to the illustrated embodiment, the power supply 330 may be a DC power supply that directly provides power to maintain the voltage of the DC power bus 316. However, it should be understood that according to other example embodiments, the power supply 330 may be any suitable AC / DC converter, DC / DC converter, battery, fuel cell, or any other suitable DC power source capable of facilitating the methods and control schemes described herein. In addition, it should be understood that according to example embodiments, the DC link voltage may be maintained by the power supply 330 and / or the external load 304, for example, such that if the external load 304 is not available, only the power supply 330 may be used to maintain the DC link voltage. It should be understood that although an external load 304 is shown in the figure, the external load 304 may include any suitable load, electrical system, AC or DC source, etc.

[0066] According to example embodiments, the DC link voltage may be maintained by the operation of the power converter 310 and / or an external power source (e.g., the power source 330 or the external load 304), for example, based on a voltage command from a system controller or a computing system. Generally, it is preferred to maintain a low value of the DC link voltage to reduce the ripple current component in the fault current, thereby reducing the losses in the power converter 310, and thus reducing the losses in the power distribution system 300. According to example embodiments, the reference value of the DC link voltage may be set to meet the commanded power converter voltage. For example, for a fault location near the power converter 310, the DC link voltage may be relatively low, and as the fault location moves closer to the terminals of the motor 302, the DC link voltage may be relatively high. According to example embodiments, the power converter 310 may determine the DC link voltage requirement based on a voltage command generated by a controller (e.g., based on any suitable predetermined algorithm, lookup table, mathematical relationship, or any other empirical, theoretical predetermined relationship, etc.).

[0067] According to example embodiments, any suitable method may be used to derive the voltage required for active mitigation of the power converter 310. For example, the required voltage may be determined based on the control of the negative sequence component of the converter three-phase current (or the machine three-phase current). In this regard, by applying a balanced converter terminal voltage, low torque oscillations and low DC link voltage oscillations may be obtained. Alternatively, the required voltage may be determined based on the control of the fault current. In this regard, by applying the line-to-line voltage only on the fault line pair (in other words, by applying an unbalanced converter terminal voltage), this may produce pulsating torque and DC link voltage oscillations.

[0068] like Figure 3 and Fig. 22 As further shown, the power distribution system 300 includes a computing system 340. The computing system 340 may include one or more processors and one or more memory devices that may be embodied in one or more computing devices. For example, the computing system 340 may include a controller associated with the power converter 340. For example, the controller may cause one or more switching devices of the power converter 310 to switch or modulate according to a switching scheme. Fig. 22 The components of computing system 340 are described in greater detail.

[0069] It is worth noting that, as described above, electrical faults occasionally occur within the power distribution system 300, and aspects of the present subject matter are directed to systems and methods for mitigating fault currents, e.g., to reduce the likelihood of a very high fault that could heat conductors in the fault path for a period of time, which could result in a complete system failure or even a fire. For purposes of explanation, Figure 3300 , a line-to-line AC fault 320 is identified between motor 302 and power converter 310 . However, it should be understood that aspects of the present subject matter are also applicable to situations where fault 320 occurs within motor 302 or at other locations within power distribution system 300 .

[0070] Specifically, Figure 3 An example fault that may occur within the power distribution system 300 is shown. For example, the fault is shown as occurring between phase a and phase b of a three-phase AC power source. However, it should be understood that the fault shown is merely exemplary and is not intended to limit the scope of the present subject matter in any way. As shown, the motor back electromotive force (EMF) is represented as E mm , the motor back EMF outside the fault is expressed as E mc (e.g., if the fault is outside the machine, it is zero), and the machine current is I m , the fault current is expressed as I f , the converter current is denoted as I c , the fault voltage is denoted as V f , the fault impedance is represented by Z f , the converter output voltage is denoted as V c , the motor side impedance is represented by Z m (for example, when the fault is inside the machine), and the converter side impedance is represented by Z c .

[0071] use Figure 3 The impedance to resolve a line-to-line (LL) fault can be modeled as follows using the model shown in FIG. 3 . Specifically, when viewed from the motor 302, the impedance during the fault (Z mL ) can be expressed as follows:

[0072] Equation 1:

[0073] In contrast, when viewed from power converter 310, the impedance (Z cL ) can be expressed as follows:

[0074] Equation 2:

[0075] Using these equations, the fault current (I f , Equation 3) and the fault voltage (V f , equation 4) can be expressed as follows:

[0076] Equation 3:

[0077] Equation 4:

[0078] As explained in more detail below, an exemplary control method for operating power converter 310 and / or other components of power distribution system 300 is provided below to mitigate fault current caused by line-to-line AC fault 320. For example, referring again to exemplary fault 320, an exemplary objective of the present disclosure may be to reduce the output voltage (V c ) is controlled to have the same internal voltage as the motor (E mm ) of the correct magnitude relative to the polarity to reduce the voltage across the fault (V f ) to reduce or eliminate the line fault current (I f ). For example, according to an example embodiment, the voltage across the fault (V f ) is equal to 0:

[0079] Equation 5:

[0080] Therefore, Equation 5 can generally provide a method for reducing or eliminating line-to-line fault current (I f ) of the power converter output voltage (V c ), output voltage (V c ) is a function of the voltage of the motor 302 and the impedance present within the power distribution system 300 (e.g., within the motor 302 or between the motor and the power converter). Therefore, the converter output voltage (V c ) may be generally referred to herein as a "fault reduction voltage", "fault elimination voltage", etc. However, it should be understood that according to alternative embodiments, the fault reduction voltage need not be applied by the power converter 310, but may instead be provided by any other suitable voltage source or electrical system. If a fault is detected, the power converter 310 may immediately apply the desired elimination voltage (V c ), since the voltage amplitude and phase angle are functions of known system parameters. As described in more detail below, aspects of the present subject matter are directed to achieving a reduction in fault current (I f ) required output voltage (e.g., “fault reduction voltage” or “fault elimination voltage”), for example, including the output voltage (V c ) and the output voltage (V c ) should be injected into the angle.

[0081] Additionally, as described in more detail below, aspects of the present subject matter also relate to setting the appropriate / optimal value of the DC link voltage to be low enough to reduce the AC line current ripple (and fault current ripple), but high enough to produce the desired AC side terminal voltage. It is worth noting that it is apparent from the above equation that if the fault is closer to the motor 302, then Z m Z c , and the expected V cThe amplitude can be high so that a higher DC link voltage (V dc ). However, if the fault is inside the machine winding, then E mc The presence of c On the contrary, if the fault is closer to the power converter 310, then Z m >>Z c , and the expected V c The amplitude can be low so that a lower converter DC link voltage (V dc ). It is worth noting that the selection of the optimal DC link voltage / low DC link voltage can help reduce the fault current ripple and system loss, especially when the fault location is closer to the power converter 310.

[0082] Now briefly refer to Figure 4 , example electromotive force (EMF) vector (where the rotor emf vector (e m ) and the scalar along the Δ axis exist Figure 4 ) are shown in various reference frames, such as a stationary reference frame (denoted by a superscript “s”), a rotating reference frame (denoted by a superscript “r”), and a line-to-line fault reference frame (denoted by a superscript Δ). Figure 4 Also shown in FIG. 1 is the converter voltage vector (v c ), which eliminates the fault current (I f ) required. As explained in more detail below, the representation of these vectors in these reference frames is useful in determining the line-to-line fault current cancellation voltage (FCCV) (also referred to herein as the "fault reduction voltage," "fault cancellation voltage," etc.). Mathematical derivations and equations for determining FCCV are provided herein, but it should be understood that certain steps may be omitted for the sake of brevity. In addition, it should be understood that the methods described herein are exemplary only and are not intended to limit the scope of the present subject matter, as variations and modifications may be made to the methods and equations while remaining within the scope of the present subject matter.

[0083] The back EMF vector of the motor 302 in the stationary reference frame can be expressed as follows:

[0084] Equation 6:

[0085] The back EMF vector of the motor 302 appearing in two fault lines (eg, in the line-to-line fault reference frame Δ) may be expressed as follows:

[0086] Equation 7:

[0087] In Equation 7, the fault current cancellation angle (φ) is defined as follows, where when φ = 0, the back EMF is at -d Δ On the line fault reference system at:

[0088] Equation 8:

[0089] The back EMF can also be expressed as a single-phase quantity as follows:

[0090] Equation 9: E m =-E m .

[0091] If the fault is inside the motor 302, the back EMF can be approximately divided into components of the machine-side EMF (Equation 10) and the converter-side EMF (Equation 11), where ∈ is a scaling factor that can take values ​​from 0 to 1 based on the location of the fault, as shown below:

[0092] Equation 10: E mm =(1-∈)E m

[0093] Equation 11: E mc =∈E m .

[0094] Ideally, the power converter 310 is operated to control the output voltage (V c ) will eliminate the fault current between lines:

[0095] Equation 12:

[0096] Fault current elimination voltage ratio (K c ) can be defined as follows:

[0097] Equation 13:

[0098] Use this fault current elimination voltage ratio (K c , also abbreviated as FCCVR), Fault Current Cancellation Voltage (FCCV or Converter Voltage, V c ) can be expressed as follows:

[0099] Equation 14: V c =-K c E m =K c e jα E m .

[0100] By appropriately adjusting the fault current elimination voltage ratio (K) in the line voltage of the power converter 310, c )(where the amplitude is K c, angle α) will achieve control of the line fault current as follows:

[0101] Equation 15:

[0102] The measured fault current can be used to adjust the FCCV. If the measured fault current is of magnitude (I f ) and the sinusoidal curve of the phase angle (γ), it can be expressed as shown in Equation 16:

[0103] Equation 16:

[0104] Various control methods can be used to regulate the fault current to zero, such as various sliding mode control methods, synchronous system regulation, complex vector regulation, etc. Even if the line voltage and fault current are scalars, the AC component can be effectively controlled using a vector control method.

[0105] Now briefly refer to Figure 5 , a vector representation of line-to-line fault current is shown according to an example embodiment. Differential current measurement is a direct way to obtain the fault current, where the fault current can be defined as the difference between the converter side current vector and the machine side current vector, such as Figure 3 It can be seen in and is expressed as follows:

[0106] Equation 17A:

[0107] Equation 17B:

[0108] For example, Figure 5 As shown in Figure 2, when the line-to-line AC fault is between phase A and phase B, the fault current in the stationary reference frame can be expressed as follows:

[0109] Equation 18:

[0110] Equation 19:

[0111] The complex vector representation of the fault current can be derived as follows, where Δ can be defined as the fault angle or the angle of the fault line-to-line angle, as Figure 6 Specifically, the fault angle (Δ) for all three line-to-line fault conditions may be -30° / 150° for an AB phase fault, -90° / 90° for a BC phase fault, and -150° / 30° for a CA phase fault.

[0112] Reference now Figure 7, a fault system phasor diagram for mixed positive sequence injection and negative sequence injection of FCCV is provided. FCCV is expected to provide line-to-line voltage, but it can be generalized as a complex voltage vector and extended to mixed injection of positive and negative sequences for line-to-line phase compensation as shown below to provide additional control paths to the system. Specifically, Equation 20A represents the complex voltage vector FCCV, Equation 20B represents the positive sequence FCCV, and Equation 20C represents the negative sequence FCCV.

[0113] Equation 20A:

[0114] Equation 20B:

[0115] Equation 20C:

[0116] According to an example embodiment, this mixed injection voltage will result in a desired line-to-line FCCV. The resulting complex vector voltage at the converter output terminal is expressed as follows:

[0117] Equation 21:

[0118] The fault system FCCV d-axis voltage can be derived as:

[0119] Equation 22:

[0120] This enables independent control of the positive sequence angle μβ while achieving line-to-line FCCV v c cos(φ+α), resulting in a fault current (using v c and α) and decoupled control of converter power (using μ and β). The conversion to the stationary frame voltage vector (i.e., the voltage that the power converter will achieve at its output terminals) can be performed using the following equation:

[0121] Equation 23:

[0122] Reference now Figure 8 , a control block diagram of mixed positive sequence injection and negative sequence injection of FCCV is provided. Specifically, Figure 8 The unified control block diagram for FCCV generation by mixing positive and negative sequence voltages is shown. The goal of the control scheme is to independently control the fault current and converter power. The fault current is minimized by adjusting the magnitude and phase angle of the fault current cancellation voltage. For example, the vector PI controller can be used to adjust v cThe input to the control may be the sequence component of the fault current in the fault current system. This may be derived from the fault current measurement or from the machine side / converter side current measurement, which will be explained in more detail below.

[0123] For standalone operation of power converter 310, the DC link voltage is given by Figure 8 The V-reg controller shown is maintained at a required minimum value, which in turn generates a power command for the power converter 310. In some cases where there is an external source to maintain the DC link, the power regulator can bypass V-reg and take commands directly from the local / supervisory controller. Power control is achieved by adjusting the negative sequence voltage to positive sequence voltage ratio (μ) and the phase angle (β) between the positive sequence voltage and the negative sequence voltage. The μ value is adjusted to the minimum value while satisfying the power command. This will help reduce machine torque, converter power, and ripple in the DC link voltage. If β exceeds its defined boundaries, the μ value is increased to maintain the DC link, where the ripple in the converter power and other quantities discussed above are increased. According to v c ,α,β,μ values, calculate the reference voltage in the Δ system and the reference voltage in the rotor system and then transform to the stationary reference frame

[0124] Now generally refer to Fig. 9 and Fig.10 , P is shown for the changing values ​​of β and μ. c and P c Plot of the ripple (%). Figure 8 The control discussed in enables the power converter 310 to minimize / eliminate fault current while achieving different operating modes, such as power neutral mode, power flow mode (sinking or exporting several kilowatts (kW) of power), or zero power ripple mode, by appropriate selection of β and μ values. These operating modes can be selected from Fig. 9 and Fig.10 The power neutral mode is the situation when the power drawn or supplied by the power converter 310 is zero at the DC link, while in the generation mode several kW of power is fed to the connected DC load, and in the power consumption mode several kW of power is drawn from the DC side to the AC side. When operating in the power neutral mode, as Fig. 9 and Fig.10As can be seen in , the ripple in the converter power is reduced relative to the generating mode. The power ripple is higher in the power neutral case compared to the power consuming mode. The power ripple is higher relative to the power consuming case because the lowest μ value corresponding to the 3% power consuming case is lower than the minimum μ value required for the power neutral operation and generating case. Therefore, while achieving fault current elimination, the best system performance in terms of machine torque ripple, DC link voltage ripple, etc. is for the power consuming case (for example, there is a DC side load or power source that can be regenerated). Even if the system performance is compromised in the case shown, it will enable the power converter 310 to serve small loads that are critical to the system, such as control power, cooling pumps, etc., by injecting more negative sequence voltage.

[0125] Zero ripple operation is achieved using a zero μ value. This is a special case where the power converter 310 injects only positive sequence voltage. Fig. 9 As can be seen in , power neutral mode and fault current cancellation cannot be achieved simultaneously by keeping μ = 0. In order to achieve fault current cancellation with zero power ripple, the power converter 310 will operate in power consumption mode using power drawn from the DC bus. Its control logic is in Fig.17 When μ = 0, the power neutral mode and the power flow mode can only be achieved by compromising the fault current control performance. In this case, fault current reduction is feasible, but complete elimination is not feasible. The control logic of this case is Fig.19 The positive sequence voltage injection of the power converter in power neutral mode and power flow mode and Fig.17 and Fig.19 are covered in a later section of this document.

[0126] If the power converter 310 has an external source to maintain the DC link, the power converter 310 can also operate in a power control mode that ignores the outer voltage loop. The power command can come from the converter controller or any external controller including a supervisory controller. Fig. 9 and Fig.10 , multiple values ​​of μ can give the same P c The control logic is set to output the minimum μ value to ensure that P c The ripple is minimal.

[0127] Fig.11 Shown in the implementation Figure 8 The plot obtained after the control discussed in . 0 to 1 , the power converter 310 is in an unloaded state, and at time t 1 Simulate an AC LL fault in AB. This condition may trip the power converter 310, resulting in an open circuit. Fig.11It can be seen that the fault current rises to 1.149 per unit (pu), creating a significant imbalance in the machine current. The machine will continue to feed the fault with zero contribution from the power converter 310 until t 2 .from Fig.11 It can be seen that the machine torque oscillates due to the unbalanced current flow in the machine. 2 , enabling the fault current mitigation control discussed in this application. 2 , the power converter 310 starts to regulate its terminal voltage to or FCCV, which reduces the fault current and the imbalance in the machine and converter currents to zero. As the machine currents become balanced, the machine torque oscillations will also drop to zero. The DC link voltage, which was maintained at 1 p.u before the fault, is reduced to the minimum required value just enough to establish FCCV at the converter terminals. In this particular example, the DC link voltage is reduced to 0.125 pu. In this particular case, since the load on the power converter 310 is zero, only approximately 0.018 pu of power converter 310 losses are drawn from the machine, making it a power neutral system. The β value saturates to its limit because the power converter 310 power cannot be reduced to zero by either zero negative sequence injection or a μ value of zero. Therefore, the control increases the μ value from its desired value of 0 to 0.15 to maintain the DC link voltage to its reference value. These details are captured in Fig.11 middle.

[0128] Reference now Fig.12 , shows the machine torque, converter power and DC voltage ripple performance of the system for varying the DC power injection into the DC link of the power converter 310. 0 to 1 ,t 1 to 2 ,t 2 to 3 Moment period capture Fig. 9 and Fig.10 The power consumption, power neutrality and power generation discussed in Fig.12 As shown in Figure 2, the fault current is eliminated in all cases except for the switching ripple flowing toward the fault. Fig.12 When moving from left to right, the ripple performance deteriorates. Fig.12 An increase in ripple in the DC link voltage, converter power, and machine torque can be seen in Figure 1. This is because the required μ value or negative sequence voltage mix in the FCCV is increasing as we move from a power consumption case to a generation case. Fig.12 Changes in the values ​​of β and μ are captured while maintaining the residual fault current seen by the power converter 310 to its desired value of 0 p.u.

[0129] According to an example embodiment, a single location current measurement may be used to achieve fault current estimation, while the algorithm may be adjusted depending on the sensor location, as will be described in more detail below. Specifically, Equation 24A represents the converter side current in the sequence phasor component, and Equation 24B represents the machine side current in the sequence phasor component:

[0130] Equation 24A:

[0131] Equation 24B:

[0132] Equation 25 provides the fault current sequence phasor components:

[0133] Equation 25:

[0134] If the fault current is removed and if the system is balanced, the negative sequence current on both the converter side and the machine side should be zero ( and ). Therefore, the fault current can be indirectly controlled by controlling the negative sequence current on the converter side or the machine side.

[0135] Reference now Fig.13 and Fig.14 , a more direct control scheme will be derived to mitigate the fault current in the fault system from the negative sequence converter side or machine side current. Specifically, Fig.13 and Fig.14 The converter side and machine side currents ( and ) Extract the positive sequence of the fault current in the fault system Negative sequence extraction box extraction and The negative sequence component ( and ). The mixed positive and negative sequence injection of power converter 310 is represented by Equation 26 (below), where and Due to the negative sequence voltage The injection and have components due to the fault. Therefore, Fig.13 and Fig.14 Provides a Fig.13 ) or machine side ( Fig.14 ) estimates the fault current. Therefore, these plots generate The input includes and θ:

[0136] Equation 26:

[0137] The negative sequence of the converter current under the ideal fault current elimination state can be expressed by Equation 27:

[0138] Equation 27:

[0139] This will give the residual negative sequence current, or in other words, the negative sequence converter current caused by the line-to-line fault, as shown in Equation 28:

[0140] Equation 28:

[0141] If the system has unbalanced current under normal operation due to imbalance in the system The negative sequence current can be measured from This current is further subtracted from the current, as shown in Equation 29:

[0142] Equation 29:

[0143] Using the same method, you can Fig.14 The residual negative sequence current on the machine side is estimated as The residual negative sequence current is a measure of the fault current and is expressed by the factor (K cf and K mf ) is scaled to derive the negative sequence of the fault current like Fig.15 shown.

[0144] according to Figure 3 , the negative sequence voltage and current vectors can be related by:

[0145] Equation 30:

[0146] For balancing machines, And considering the case where the negative sequence voltage injected by the power converter 310 is minimal or even zero, the above equation will be:

[0147] Equation 31:

[0148] Equation 32:

[0149] According to equations 25 and 32, the fault current negative sequence vector can be written as:

[0150] Equation 33:

[0151] Equation 34:

[0152] therefore, Fig.13 and Fig.14 K used in cf and Kmf Given by Equations 35 and 36, it is as follows:

[0153] Equation 35:

[0154] Equation 36:

[0155] according to Figure 8 In the control block diagram shown in Figure 1, the fault current in the fault system is used to derive the converter voltage reference in the fault system. The following transformation will help to get the Export The fault current with phase angle γ represented by equation 16 can be expressed as a fault current complex vector in the fault system, such as:

[0156] Equation 37:

[0157] The fault current can be expressed in terms of sequence components with respect to the FCC angle φ as:

[0158] Equation 38:

[0159] Equation 39A:

[0160] Equation 39B:

[0161] In Equation 38-39B, and represents the complex vector in the positive sequence fault system and the negative sequence fault system. In order to derive the sequence component about the rotor angle θ, the fault system complex vector is rotated by Δ, as shown in Equation 40:

[0162] Equation 40A:

[0163] Equation 40B:

[0164] Equation 40C:

[0165] According to equation 40, the positive sequence component (equation 41) and negative sequence component (equation 42) of the fault current in the rotor system can be derived as follows:

[0166] Equation 41:

[0167] Equation 42:

[0168] According to equation 42, the negative sequence component of the fault current in the fault system is given by:

[0169] Equation 43:

[0170] According to equations 41 and 42, the positive sequence component of the fault current in the fault system is given as follows, where ()* represents the complex conjugate of the complex vector:

[0171] Equation 44:

[0172] The two rotor sequence components given by equations 41 and 42 include the fault current amplitude information (I f ). The phase angle γ can be measured from the positive sequence, and the fault phase angle Δ can be measured from both sequences. The sequence components can be extracted using phase transformation and appropriate filtering, including methods such as SOGI (Second Order Generalized Integrator). The control scheme can be implemented using a fault current regulator that receives or As feedback, and use and as output.

[0173] Reference now Fig.16 , showing fault current measurement at a single location. Specifically, the location of the three-phase current sensor can be anywhere between the converter output terminals and the machine neutral terminal. Based on the location of the fault relative to the sensor, the fault detection and mitigation strategy may be different. For example, two cases can be considered, including: Case 1 - line-to-line fault on the AC terminal outside the sensor, and Case 2 - line-to-line fault between the sensor and the power converter 310.

[0174] First consider case 1, where the AC line fault occurs at Fig.16 Outside the current sensor in (labeled L1), the sensed current may be higher than the set protection limit and the power converter 310 may trip. Depending on the location and impedance of the fault and the voltage level across the faulted line, the fault current may increase quickly to a detectable level, or even to a level requiring overcurrent protection, or it may increase slowly to a detectable level. This may take less than one control cycle, or it may take multiple control cycles. The sensed current can be used not only for the detection of the fault, but also to determine the line where the fault occurred, and therefore Δ, which is based on Figure 8 required for control. If the fault current is large enough, the deviation of the measured current compared to the predicted current (commanded or expected) can be used to detect the fault line. However, if the fault current is not large enough, some signal processing may be desired. Once the fault line is detected, the Δ value (as provided above) can be used for control. The tripped converter can be reset and active fault current mitigation control can be initiated.

[0175] Now consider case 2, where Fig.16In the case of an AC line fault (marked as L2) between the sensor and the power converter 310, the power converter 310 may trip instantaneously before the sensed current reaches a detectable level, or may trip when the sensed current reaches a detectable level. This depends on the location of the fault and the sensor. If the fault occurs within the power converter 310, regardless of the sensor location (machine side / converter side), the sensed current will not have information about the fault or Δ before tripping. Once tripped, there will be a fault current flowing in the fault phase, so we can directly determine the line in which the fault occurs. If the fault is far away from the power converter 310 and the current sensor location is anywhere between the fault and the machine neutral, the sensed current may have information about the fault location and Δ, as discussed in the previous section.

[0176] In the case where the power converter 310 trips before Δ is detected, after the trip reset, the power converter 310 can first enter the three-phase short circuit mode to reduce the fault current. The effectiveness of the three-phase SC can be determined by monitoring the negative sequence component of the sensed current. For the case where the fault is within the power converter 310, the negative sequence component of the sensed current will drop to zero. For the case where the negative sequence component of the sensed current is not zero, active mitigation control can be initiated after Δ detection.

[0177] Fig.17 shows that only the positive sequence voltage is injected This is achieved by keeping μ = 0 (e.g., since there is no power control loop, μ = 0 and the required power is taken from the DC source) from Figure 8 In other words, Fig.17 A control method is shown in which the power control loop is removed and negative sequence injection is eliminated. Here, the DC link is controlled by Figure 3 The external source connected to contactor 1 or contactor 2 shown remains. Injecting the positive sequence voltage alone has the advantage of making the fault current zero and no ripple in the torque / converter power. But in this case, the converter losses will come from the DC link (connected external source) and will operate in power dissipation mode.

[0178] Fig.18 Shown according to Fig.17 Simulation results after control is implemented. During the pre-fault state and until time t 2 Behavior and Fig.11 Same. Fig.18 It can be seen that the fault current mitigation control using this scheme produces zero ripple in torque and converter power. The machine current and converter current are balanced and equal, which will make them positive sequence components in the rotor system. equal, while the negative sequence component in the rotor system The DC link is maintained by an external source with a command voltage of 0.125 pu, with converter losses of 0.018 pu.

[0179] Now briefly refer to Fig.19 , a closed-loop feedback control algorithm, such as the minimum fault current tracking (MFCT) control method for fault current control using positive sequence voltage injection, will be described. The MFCT algorithm can generate a voltage amplitude (v c ) to reduce the fault current, by Specifically, in order to obtain a power-neutral system with only positive sequence injection, Figure 8 The DC link voltage regulator V-reg gives the angle (α) of the fault current elimination voltage. In this case, μβ=0, and the only control path for regulating the fault current is the converter voltage (v c ) magnitude. Fault current The amplitude is changed by changing v c And minimize. Fig.19 The MFCT control box shown in the figure perturbs v c And observe The amplitude of the disturbance and observation logic is implemented. It will eventually stabilize to the v that produces the minimum fault current. c It should be understood that any other suitable search algorithm may be used to determine v c If the DC link voltage is maintained by an external supply / system, the power conditioner may bypass the voltage regulator output command and obtain the power command directly from the converter controller or any external controller including a supervisory controller. In this case, the power converter 310 may also operate in a power flow mode of receiving or outputting power.

[0180] Fig. 20 Shown in the implementation Fig.19 Simulation results after control in . Similar to the previous case, during the pre-fault state and until time t 2 Behavior and Fig.11 Once at t 2 Starting the fault current reduction control, the fault current drops from 1.149 pu to 0.36 pu, because it is impossible to completely eliminate the fault current here. Therefore, the imbalance of machine and converter currents will continue to exist, making the negative sequence component is not zero, the machine torque, converter power and DC link voltage continue to oscillate. Fig.21 The control variable v c and the change of α and V dc Once α stabilizes to its final value by regulating the DC bus to a command value of 0.125 pu, the control will gradually perturb vc To reduce fault current.

[0181] Fig. 22 Shows Figure 3 3. System diagram of computing system 340 of power distribution system 300 of FIG. 3. The computing elements described herein may include one, some, or all of the components of computing system 340 and may perform the operations described below.

[0182] like Fig. 22 As shown, the computing system 340 includes one or more computing devices 350. The computing devices, controllers, etc. described herein may embody one or more of the components of the computing device 350. The computing device 350 may include one or more processors 350A and one or more memory devices 350B. The one or more processors 350A may include any processing device, such as a microprocessor, a microcontroller, an integrated circuit, a logic device, and / or other suitable processing device. The one or more memory devices 350B may include one or more computer-readable media, including but not limited to non-transitory computer-readable media, RAM, ROM, hard disk drives, flash drives, and / or other memory devices.

[0183] One or more memory devices 350B may store information accessible by one or more processors 350A, including computer executable or computer readable instructions 350C that may be executed by one or more processors 350A. Instructions 350C may be any set of instructions that cause one or more processors 350A to operate when executed by one or more processors 350A. In some embodiments, instructions 350C may be executed by one or more processors 350A to cause one or more processors 350A to operate, such as any operation and function that computing system 340 and / or computing device 350 are constructed for. Instructions 350C may be software written in any programming language or may be implemented in hardware. Additionally and / or alternatively, instructions 350C may be executed in logically and / or virtually separate threads on processor 350A. Memory device 350B may further store data 350D that may be accessed by processor 350A.

[0184] Computing device 350 may also include a network interface 350E for communicating (e.g., via a network) with other components of system 340, for example. Network interface 350E may include components for interfacing with one or more networks, including, for example, transmitters, receivers, ports, controllers, antennas, and / or other suitable components.

[0185] The technology discussed herein refers to computer-based systems, actions taken by computer-based systems, information sent to computer-based systems, and information from computer-based systems. Those of ordinary skill in the art will recognize that the inherent flexibility of computer-based systems allows for a variety of possible configurations, combinations, and divisions of tasks and functions between and within components. For example, the processing discussed herein can be implemented using a single computing device or multiple computing devices working in combination. Databases, memories, instructions, and applications can be implemented on a single system or distributed on multiple systems. Distributed components can operate sequentially or in parallel.

[0186] As described in this article, an AC line-to-line fault between a power converter and a permanent magnet synchronous generator (PMSG) (or within the machine itself) may cause a fault current to flow between the fault terminals. This may result in heating of the conductors in the fault path for a period of time, which may lead to a complete system failure or even a fire. One way to overcome this dangerous situation is to mechanically disconnect the generator shaft from the prime mover, as this prevents the PMSG from feeding the fault. This can be achieved, for example, by disconnecting the motor terminals from the cables using a switch (such as a contactor or circuit breaker) (which does not mitigate internal faults of the motor). In a multi-channel generator system, mechanical disconnection of the shaft may reduce the reliability of the system because the fault tolerance provided by other winding groups may also be affected.

[0187] Thus, aspects of the present subject matter are directed to a control solution that can reduce fault current to an acceptable value (or even eliminate fault current) without mechanically disconnecting the engaging shaft (shaft cutters, clutches, etc.). This can reduce the number of fault conditions that necessitate mechanical disconnection of the engagement. A variety of control schemes are proposed, each providing certain technical and commercial advantages over prior art solutions. Examples of such advantages are provided below, but it should be understood that other advantages of the present subject matter will be apparent to those of ordinary skill in the art.

[0188] Example advantages of the present subject matter may include reducing or completely eliminating problems associated with AC side line-to-line faults, such as heating, arcing, fire, and explosion. In addition, the number of fault conditions that may require mechanical disconnection may be reduced. When the imbalance in the machine current is reduced, the machine torque oscillation may be reduced in the steady state. Furthermore, the proposed system and method may not require any additional sensors, and the dual channel operation of the motor and power converter may ensure that the redundancy provided by the second set of windings is not affected even in the presence of a fault.

[0189] Now briefly refer to Fig.23, describes an exemplary method 700 for regulating the operation of the power converter 310 in the event of a line-to-line AC fault 320. It is noteworthy that the method 800 may include many steps similar to those described above with respect to the methods 400, 500, and 600. Therefore, for the sake of brevity, repeated discussion of these steps is omitted here. However, it should be understood that parts of the methods 400, 500, 600, and 700 may be interchanged to form further operating methods that are considered to fall within the scope of the present subject matter.

[0190] As mentioned above, Fig.23 A method 700 of operating a power conversion system is shown, the power conversion system including an alternating current (AC) source or motor for generating or receiving AC power, a direct current (DC) power bus, and a power converter electrically coupling the AC source or motor and the DC power bus. The method 800 includes, at step 710, measuring an AC line fault current (I f ).

[0191] Step 720 includes determining to reduce the AC line fault current (I f ) of the converter output voltage (V c ), which is based at least in part on a closed-loop feedback algorithm and an AC line fault current (I f ) to determine the converter output voltage (V c According to an example embodiment, it is determined that the AC line fault current (I f ) of the converter output voltage (V c ) includes: AC line fault current (I f ) Determine the measured fault current vector Based at least in part on the measured fault current vector To determine the positive sequence fault converter voltage and negative sequence fault converter voltage determining a fault frame angle (Δ) measured between a stationary reference frame and a fault reference frame; and determining a fault frame angle (Δ) based at least in part on a positive sequence fault frame converter voltage Negative sequence fault is the converter voltage and the fault phase angle (Δ) to determine the target positive sequence converter voltage and the target negative sequence converter voltage

[0192] Step 730 includes operating the voltage source to apply a voltage at the AC terminals to reduce the AC line fault current (I f ) of a fault reduction voltage, for example, by operating a power converter to apply the fault reduction voltage.

[0193] Further aspects are provided by the subject matter of the following clauses:

[0194] A power conversion system, comprising: an alternating current (AC) source, the AC source comprising a plurality of AC terminals for conducting AC power; a voltage source electrically coupled to the AC terminals; and a controller operably coupled to the voltage source, the controller being configured to: operate the voltage source to apply a reduced AC line fault current (I f ) fault reduces the voltage.

[0195] A power conversion system according to any preceding clause, wherein the voltage source comprises: a power bus for conducting bus power; and a power converter comprising an AC link electrically connected to the AC terminals of the AC source and a bus link electrically connected to the power bus, the power converter being constructed to convert between the AC power and the bus power.

[0196] A power conversion system as described in any preceding clause, wherein operating the voltage source to apply the fault reduction voltage comprises operating the power converter to apply the fault reduction voltage.

[0197] The power conversion system according to any of the preceding clauses, further comprising an external power supply electrically connected to the power bus and the power converter, wherein the controller is further constructed to: operate the external power supply to provide a bus voltage at the bus link of the power converter 310, thereby allowing the power converter to maintain the fault reduction voltage at the AC link of the power converter.

[0198] A power conversion system according to any preceding clause, wherein the controller is in operative communication with the external power source, the controller being configured to: operate the power converter and the external power source to independently manipulate the AC line fault current (I f ) and the input power to the power converter.

[0199] A power conversion system according to any preceding clause, wherein the controller is operably coupled to the power converter, the controller being further configured to: measure the AC line fault current (I f ); and determine to reduce the AC line fault current (I f ) of the converter output voltage (V c ), wherein the fault reduction voltage is the converter output voltage (V c ).

[0200] A power conversion system according to any preceding clause, wherein the converter output voltage (V c ) is based at least in part on a closed-loop feedback algorithm and the AC line fault current (I f ) to determine.

[0201] A power conversion system according to any preceding clause, wherein reducing the AC line fault current (I f ) of the converter output voltage (V c ) is determined using the following equation:

[0202]

[0203] Where: E mc is the fault voltage outside the motor;

[0204] E mm is the internal voltage or back EMF of the motor;

[0205] Z c is the electrical converter side impedance; and

[0206] Z m is the motor side impedance.

[0207] A power conversion system according to any preceding clause, wherein determining to reduce the AC line fault current (I f ) of the converter output voltage (V c ) includes: according to the AC line fault current (I f ) Determine the measured fault current vector Based at least in part on the measured fault current vector To determine the positive sequence fault converter voltage and negative sequence fault converter voltage determining a fault frame angle (Δ) measured between a stationary reference frame and a fault reference frame; and determining a positive sequence fault frame converter voltage based at least in part on the positive sequence fault frame converter voltage The negative sequence fault is the converter voltage and the fault phase angle (Δ) to determine the target positive sequence converter voltage and the target negative sequence converter voltage

[0208] A power conversion system as described in any preceding clause, further comprising: a load electrically coupled to the power bus for conducting the bus power from the power bus.

[0209] An electric power conversion system according to any preceding clause, wherein the power bus is a direct current (DC) power bus for conducting DC power, and the bus link is a DC link electrically connected to the DC power bus, and the power converter is constructed to convert between the AC power and the DC power.

[0210] A power conversion system as claimed in any preceding clause, wherein the fault reduction voltage is a positive sequence voltage and the voltage source regulates the amplitude and angle of the positive sequence voltage.

[0211] A power conversion system as described in any preceding clause wherein the fault reduction voltage is a negative sequence voltage.

[0212] A power conversion system as described in any preceding clause, wherein the fault reduction voltages are positive sequence voltages and negative sequence voltages, and wherein the voltage source adjusts the ratio (μ) of the negative sequence voltage to the positive sequence voltage, and the phase angle (β) between the positive sequence voltage and the negative sequence voltage.

[0213] A power conversion system as claimed in any preceding clause, wherein the phase angle (β) and the ratio of the negative sequence voltage to the positive sequence voltage (μ) are determined using a power control loop comprising using a bus side converter voltage and a converter power (p c ) input of the power control regulator.

[0214] A power conversion system as described in any preceding clause, wherein the power control loop drives the ratio of the negative sequence voltage to the positive sequence voltage (μ) to zero.

[0215] A power conversion system as claimed in any preceding clause wherein the AC source is an electric machine operable in a motoring mode and a generating mode.

[0216] A method of operating a power conversion system, the power conversion system comprising an alternating current (AC) source and a voltage source, the AC source comprising a plurality of AC terminals for conducting AC power, the voltage source being electrically coupled to the AC terminals, the method comprising: operating the voltage source to apply a voltage at the AC terminals to reduce an AC line fault current (I f ) fault reduces the voltage.

[0217] A method according to any preceding clause, wherein the voltage source includes a power bus and a power converter, the power bus is used to conduct bus power, the power converter includes an AC link electrically connected to the AC terminals of the AC source and a bus link electrically connected to the power bus, the power converter is constructed to convert between the AC power and the bus power, and wherein operating the voltage source to apply the fault reduction voltage includes operating the power converter to apply the fault reduction voltage.

[0218] A method according to any preceding clause, further comprising: measuring the AC line fault current (I f ); and determining to reduce the AC line fault current (I f ) of the converter output voltage (V c ), wherein the fault reduction voltage is the converter output voltage (V c ).

[0219] This written description uses examples to disclose the present disclosure, including the best mode, and also to enable any person skilled in the art to practice the present disclosure, including making and using any device or system and performing any combined method. The patentable scope of the present disclosure is defined by the claims and may include other examples that occur to those skilled in the art. These other examples are intended to fall within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ substantially from the literal language of the claims.

Claims

1. A power conversion system, characterized in that: include: an alternating current (AC) source comprising a plurality of AC terminals for conducting AC power; a voltage source electrically coupled to the AC terminal; as well as a controller operably coupled to the voltage source, the controller being configured to: The voltage source is operated to apply a reduced AC line fault current (I f ) fault reduces the voltage.

2. The power conversion system according to claim 1, characterized in that: in, The voltage source comprises: a power bus configured to conduct bus power; and A power converter includes an AC link electrically coupled to the AC terminals of the AC source and a bus link electrically coupled to the power bus, the power converter being configured to convert between the AC power and the bus power.

3. The power conversion system according to claim 2, characterized in that: in, Operating the voltage source to apply the fault reduction voltage includes operating the power converter to apply the fault reduction voltage.

4. The power conversion system according to claim 2, characterized in that: further comprising an external power source electrically coupled to the power bus and the power converter, wherein the controller is further configured to: The external power source is operated to provide a bus voltage at the bus link of the power converter, thereby allowing the power converter to maintain the fault reducing voltage at the AC link of the power converter.

5. The power conversion system according to claim 4, characterized in that: in, The controller is in operative communication with the external power source, the controller being configured to: The power converter and the external power supply are operated to independently control the AC line fault current (I f ) and the input power to the power converter.

6. The power conversion system according to claim 2, characterized in that: in, The controller is operably coupled to the power converter, the controller being further configured to: Measuring the AC line fault current (I f );and Determine the reduction of the AC line fault current (I f ) of the converter output voltage (V c ), wherein the fault reduction voltage is the converter output voltage (V c ).

7. The power conversion system according to claim 6, characterized in that: in, The converter output voltage (V c ) is based at least in part on a closed-loop feedback algorithm and the AC line fault current (I f ) to determine.

8. The power conversion system according to claim 6, characterized in that: in, Reduce the AC line fault current (I f ) of the converter output voltage (V c ) is determined using the following equation: Where: E mc is the fault voltage outside the motor; E mm is the internal voltage or back EMF of the motor; Z c is the electrical converter side impedance; and Z m is the motor side impedance.

9. The power conversion system according to claim 6, characterized in that: in, Determine the reduction of the AC line fault current (I f ) of the converter output voltage (V c )include: According to the AC line fault current (I f ) Determine the measured fault current vector Based at least in part on the measured fault current vector To determine the positive sequence fault converter voltage and negative sequence fault converter voltage determining a fault frame angle (Δ) measured between a stationary reference frame and a fault reference frame; and Based at least in part on the positive sequence fault system converter voltage The negative sequence fault is the converter voltage and the fault phase angle (Δ) to determine the target positive sequence converter voltage and the target negative sequence converter voltage 10. The power conversion system according to claim 2, characterized in that: Further including: A load is electrically coupled to the power bus for conducting the bus power from the power bus.

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