Multi-type switch open-circuit fault tolerance method for three-phase double-active-bridge direct-current transformer

Abstract

The invention discloses a multi-type switch open-circuit fault tolerance method for a three-phase dual-active-bridge direct-current transformer, and the method comprises the steps: 1), building a path electric energy model of the three-phase dual-active-bridge direct-current transformer based on the topology of the three-phase dual-active-bridge direct-current transformer, and obtaining an electric energy transmission closed-loop path composed of switches according to the electric energy transmission direction; 2) according to the number and position of fault switches of the three-phase dual-active-bridge direct-current transformer, determining electric energy transmission closed-loop path changes caused by faults, establishing a path electric energy model under multi-type switch open-circuit faults, and determining the influence of different fault types on electric energy transmission; and 3) determining the phase where the fault switch is located as a fault phase, and locking the switches except the fault switch on the secondary side of the fault phase to realize fault-tolerant operation. According to the invention, fault tolerance of all single-switch and double-switch open-circuit faults of the three-phase double-active-bridge direct-current transformer is realized, and the application range is comprehensive. Compared with a traditional switch open-circuit fault tolerance method, the method only needs to change a switch driving signal, and is simpler and more universal.

Description

Technical Field

[0001] The invention relates to the technical field of fault tolerance of a three-phase dual-active bridge DC transformer, and in particular to a multi-type switch open circuit fault tolerance method of a three-phase dual-active bridge DC transformer. Background Art

[0002] The three-phase dual active bridge DC transformer is an important form of DC transformer. It has the advantages of high energy efficiency, strong energy flow control ability, easy soft switching, modular structure, etc., and can realize bidirectional power transmission and voltage conversion. However, since the switch is a vulnerable component, the three-phase dual active bridge DC transformer is easily affected by the switch open circuit fault, which leads to overcurrent of the switch tube and transmission power loss. Therefore, it is necessary to study the fault tolerance method of multiple types of switch open circuit faults of the three-phase dual active bridge DC transformer, reduce the impact of the switch open circuit fault, and maintain the stable reliability of the operation of the three-phase dual active bridge DC transformer.

[0003] At present, there are three main types of fault tolerance methods for open-circuit switch faults of dual-active bridge DC transformers: redundant hardware method, topology transformation method, and modulation reconstruction method. In the redundant hardware method, redundant switches, bridge arms, or modules are mainly used to replace faulty modules to keep the system running normally. However, redundant hardware complicates the topology structure and increases hardware costs, which is not suitable for three-phase dual-active bridge DC transformers. The topology transformation method usually introduces a fault-tolerant unit into the original topology. When a fault occurs, the fault-tolerant unit is enabled to achieve fault-tolerant operation of the system without shutting down and maintain power transmission. Compared with the redundant hardware method, this method reduces the number of hardware, but still increases the complexity of the topology structure and the control complexity, and increases the cost. Compared with the first two methods, the modulation reconstruction method reconstructs the switch state by modulating the signal to maintain the symmetrical operation of the system under faults, without the need for high-cost redundant hardware and complex control strategies. However, the existing modulation reconstruction method ignores the impact of the power transmission path during operation on the system performance, resulting in a reduction in the power transmission path during fault-tolerant operation and limited transmission power, especially when the primary side fails, the transmission power from the primary side to the secondary side will be greatly reduced. Therefore, the existing modulation reconstruction method is not suitable for primary switch open circuit fault tolerance. In addition, the existing fault tolerance methods for three-phase dual active bridge DC transformers only consider single switch open circuit faults, and do not consider the fault situation of multiple switches being open at the same time.

[0004] Therefore, in the existing switch open circuit fault tolerance method, the transmission power of the three-phase dual active bridge DC transformer is limited, and multiple switch open circuit faults are not considered. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and to provide a more comprehensive, simple, and low-cost three-phase dual-active bridge DC transformer multi-type switch open circuit fault tolerance method, to ensure the stable and reliable operation of the three-phase dual-active bridge DC transformer, to achieve all single-switch and dual-switch open circuit fault tolerance of the three-phase dual-active bridge DC transformer, and to have a comprehensive scope of application. Compared with the traditional switch open circuit fault tolerance method, the present invention only needs to change the switch drive signal, which is simpler and more universal.

[0006] To achieve the above object, the technical solution provided by the present invention is: a multi-type switch open circuit fault tolerance method for a three-phase dual active bridge DC transformer, comprising the following steps:

[0007] 1) According to the topology of the three-phase dual active bridge DC transformer, a path power model of the three-phase dual active bridge DC transformer is established. The transmitted power in the three-phase dual active bridge DC transformer is regarded as being carried by the switch and its anti-parallel diode in the path. Then, according to the power transmission direction of the three-phase dual active bridge DC transformer, a closed-loop power transmission path composed of the switch and its anti-parallel diode is obtained;

[0008] 2) According to the number and position of faulty switches in the three-phase dual-active bridge DC transformer, determine the changes in the closed-loop path of power transmission caused by multiple types of switch open-circuit faults, establish a path power model under multiple types of switch open-circuit faults, and clarify the impact of different fault types on the operation and power transmission of the three-phase dual-active bridge DC transformer, wherein the multiple types of switch open-circuit faults include single switch open-circuit faults and double switch open-circuit faults;

[0009] 3) For the faulty switch of the three-phase dual-active bridge DC transformer, the phase where the faulty switch is located is determined to be the faulty phase, and the remaining switches on the secondary side of the faulty phase except the faulty switch are locked. The anti-parallel diode of the secondary side locking switch is used to reconstruct the closed-loop path of power transmission to achieve fault-tolerant operation.

[0010] Further, in step 2), since the three-phase dual active bridge DC transformer has a primary side and a secondary side, according to the different number and position of the faulty switches in the three-phase dual active bridge DC transformer, the multi-type switch open circuit faults include 2 single switch open circuit faults and 5 double switch open circuit faults, namely: a single switch open circuit fault occurring on the primary side, a single switch open circuit fault occurring on the secondary side, a double switch open circuit fault occurring on the same phase primary side, a double switch open circuit fault occurring on the same phase secondary side, a double switch open circuit fault occurring on the same phase different sides, a double switch open circuit fault occurring on different same sides, and a double switch open circuit fault occurring on different phases different sides; after determining the number and position information of the faulty switches, based on the power transmission closed-loop path obtained in step 1), the power transmission closed-loop path associated with the faulty switch is deleted, and the remaining power transmission closed-loop path is the power transmission closed-loop path under the current fault. Based on this, a path power model under multi-type switch open circuit faults is established to determine the impact of different fault types on the operation and power transmission of the three-phase dual active bridge DC transformer.

[0011] Further, in step 3), for the faulty switch of the three-phase dual active bridge DC transformer, the phase where the faulty switch is located is determined to be the faulty phase, the remaining switches on the secondary side of the faulty phase except the faulty switch are locked, and the anti-parallel diode of the secondary side locking switch is used to construct a closed-loop path for power transmission. The specific fault-tolerant operation is as follows:

[0012] ① If a single switch on the primary side fails to open circuit and there is a faulty phase, the two switches on the secondary side of the faulty phase are locked to achieve fault-tolerant operation;

[0013] ② If a single switch on the secondary side fails to open circuit and there is a faulty phase, the remaining switch on the secondary side of the faulty phase is locked to achieve fault-tolerant operation;

[0014] ③ If the dual switches on the primary side of the same phase are open circuit faults and there is a faulty phase, the two switches on the secondary side of the faulty phase are locked to achieve fault-tolerant operation; then adjust the angle between the non-faulty phases to 180° to achieve three-phase balanced operation;

[0015] ④ If the double switches on the same-phase secondary side have an open circuit fault, there is a faulty phase, and both switches on the secondary side of the faulty phase are locked, no operation is required, and fault-tolerant operation can be directly achieved;

[0016] ⑤ If the double switches on the same phase but different sides have an open circuit fault, there is a faulty phase, one faulty switch is on the primary side of the faulty phase, and the other faulty switch is on the secondary side of the faulty phase, the remaining switch on the secondary side of the faulty phase is locked to achieve fault-tolerant operation;

[0017] ⑥ If the double switches on different sides have open circuit faults, there are two fault phases; if the two fault switches are both on the primary side of the two fault phases, the four switches on the secondary side of the two fault phases are locked to achieve fault-tolerant operation; if the two fault switches are both on the secondary side of the two fault phases, the remaining two switches on the secondary side of the two fault phases are locked to achieve fault-tolerant operation;

[0018] ⑦ If the double switches on different phases and different sides have open circuit faults, there are two fault phases, one fault switch is on the primary side of one fault phase, and the other fault switch is on the secondary side of the other fault phase, thus locking the remaining three switches on the secondary sides of the two fault phases to achieve fault-tolerant operation.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1. The present invention establishes a complete path power model and a closed-loop power transmission path of a three-phase dual-active bridge DC transformer. By determining the changes in the closed-loop power transmission path caused by the faulty switch of the three-phase dual-active bridge DC transformer, the influence of different fault types on power transmission is judged. The analysis process is simple and intuitive.

[0021] 2. The present invention realizes for the first time the mechanism analysis and fault-tolerant operation of multiple types of switch open-circuit faults of a three-phase dual-active bridge DC transformer. The multiple types of switch open-circuit faults cover all single-switch open-circuit faults and double-switch open-circuit faults in the three-phase dual-active bridge DC transformer, and has a comprehensive scope of application.

[0022] 3. In the present invention, the fault tolerance of multiple types of switch open-circuit faults of the three-phase dual-active bridge DC transformer can be achieved by locking the remaining switches on the secondary side of the faulty phase except the faulty switch, which has universality.

[0023] 4. The fault-tolerant method proposed in the present invention only needs to change the secondary switch driving signal of the fault phase. The fault-tolerant operation is simple and convenient, and there is no need to modify the topology, add high-cost redundant hardware, or design complex control strategies. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 4 is an analysis flow chart of the method of the present invention.

[0025] Figure 2 This is the topology diagram of the three-phase dual active bridge DC transformer based on YY connection.

[0026] Figure 3 This is the path power model diagram of the three-phase dual active bridge DC transformer.

[0027] Figures 4a to 4g This is the path power model diagram of the three-phase dual active bridge DC transformer under multiple types of switch open circuit faults.

[0028] Figures 5a to 5gThis is the path power model diagram of the three-phase dual active bridge DC transformer under multi-type switch open circuit fault tolerance.

[0029] Figure 6a~6g This is the current waveform experimental diagram of the three-phase dual active bridge DC transformer under multi-type switch open circuit fault tolerance. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0031] like Figures 1 to 6g As shown, this embodiment discloses a method for multi-type switch open circuit fault tolerance of a three-phase dual active bridge DC transformer, and the specific situation is as follows:

[0032] 1) According to the topology of the three-phase dual active bridge DC transformer, the path power model of the three-phase dual active bridge DC transformer is established. The transmitted power in the three-phase dual active bridge DC transformer is regarded as being carried by the switches and their anti-parallel diodes in the path. Then, according to the power transmission direction of the three-phase dual active bridge DC transformer, the power transmission closed-loop path composed of the switches and their anti-parallel diodes is obtained.

[0033] The three-phase dual active bridge DC transformer topology based on YY connection provided in this embodiment is as follows Figure 2 As shown, it includes input and output DC voltages V1 and V2, a primary three-phase bridge and a secondary three-phase bridge, and a high-frequency transformer. The three phases are "Aa phase", "Bb phase", and "Cc phase", where phase A, phase B, and phase C are located on the primary side, and phase a, phase b, and phase c are located on the secondary side. The primary three-phase bridge includes switches S1-S6 and their anti-parallel diodes D1-D6, and the secondary three-phase bridge includes switches S7-S 12 and its anti-parallel diode D7-D 12 The turns ratio of the high-frequency transformer is n:1, the primary star point is N, and the secondary star point is M. A , L B , L C is the transformer equivalent inductance, L A =L B =L C ≈L. i A 、i B 、i C Indicates the three-phase high-frequency link current. In a three-phase dual active bridge DC transformer based on YY connection, the three-phase high-frequency link current can always maintain automatic balance:

[0034] i A (t)+i B (t)+i C (t)=0 (1)

[0035] In the formula, i A (t), i B (t), i C (t) represents the instantaneous value of the three-phase high-frequency link current. During operation, the three-phase dual active bridge DC transformer transmits power W per phase. x (x=Aa, Bb, Cc) is expressed as follows:

[0036]

[0037] Where V AN (t), V BN (t) and V CN (t) is the instantaneous value of the primary three-phase voltage, and T is a switching cycle. The total power transmitted by the three-phase dual active bridge DC transformer is the sum of the three-phase power transmission. During normal operation, the three-phase current and voltage waveforms are the same and symmetrical without bias. Therefore, the power transmitted by each phase is equal, which is 1 / 3 of the total power transmission.

[0038] On this basis, the path power model of the three-phase dual active bridge DC transformer is established as follows: Figure 3 As shown, the transmitted power of the three-phase dual active bridge DC transformer is regarded as being carried by the switches in the path and their anti-parallel diodes. Figure 3 The path energy model shown consists of 2 total energy blocks W and 12 switch energy blocks S1-S 12 The arrow indicates the direction of power transmission. The total power block W indicates the total power transmitted during operation. The switch power block S1-S 12 Respectively represent switches S1-S 12 and its anti-parallel diode D1-D 12 The transmitted power carried. When the three-phase dual active bridge DC transformer operates normally, the transmitted power carried by each switch power block is equal, and their sum is equal to the total power block W. In the switch power block S1, the arrow from node 1 to A indicates the direction of power transmission of switch S1, and the arrow from node A to 1 indicates the direction of power transmission of anti-parallel diode D1. The same applies to the other switch power blocks.

[0039] Therefore, according to the power transmission direction of the three-phase dual active bridge DC transformer, the closed-loop power transmission path of each phase of the three-phase dual active bridge DC transformer composed of the switch and its anti-parallel diode can be obtained, as shown in Table 1. When the current path in the working mode of the three-phase dual active bridge DC transformer can form a complete power transmission closed-loop path under the corresponding current direction, power can be transmitted between the primary and secondary sides in this mode.

[0040] Table 1 Closed-loop path of power transmission of each phase of three-phase dual active bridge DC transformer

[0041]

[0042] 2) According to the number and position of the faulty switches in the three-phase dual active bridge DC transformer, the multi-type switch open circuit fault includes 2 single switch open circuit faults and 5 double switch open circuit faults, namely: single switch open circuit fault occurring on the primary side, single switch open circuit fault occurring on the secondary side, double switch open circuit fault occurring on the same phase primary side, double switch open circuit fault occurring on the same phase secondary side, double switch open circuit fault occurring on the same phase but different sides, double switch open circuit fault occurring on different same sides, and double switch open circuit fault occurring on different phases but different sides. In addition, the phase where the faulty switch in the three-phase dual active bridge DC transformer is located is the faulty phase, and the phase without fault is the non-faulty phase.

[0043] After determining the number and location information of the faulty switches of the three-phase dual-active bridge DC transformer, based on the closed-loop power transmission path in Table 1, the closed-loop power transmission path associated with the faulty switch is deleted, and the remaining closed-loop power transmission path is the closed-loop power transmission path under the current fault. On this basis, a path power model under multi-type switch open-circuit faults is established to clarify the impact of different fault types on the operation and power transmission of the three-phase dual-active bridge DC transformer. The specific analysis is as follows:

[0044] When a single switch on the primary side fails, the closed-loop power transmission path associated with the faulty switch is deleted, and only a single high-frequency link current direction, i.e., positive or negative, remains in the fault phase. Therefore, the path power model under the single switch open-circuit fault on the primary side is as follows: Figure 4a As shown, the faulty switch cannot transmit power, and only 5 switch power blocks are left in the primary side to maintain the original transmission power, which causes overstress of the normal switch, complete bias of the high-frequency link current in the faulty phase, and bias of the high-frequency link current in the non-faulty phase.

[0045] When a single switch on the secondary side fails, the closed-loop power transmission path associated with the faulty switch is deleted, and in the non-fault phase, the closed-loop power transmission path with a positive or negative direction of the high-frequency link current is reduced. The path power model under the open-circuit fault of a single switch on the secondary side is as follows: Figure 4b As shown, the faulty switch cannot transmit power, and only 5 switch energy blocks are left in the secondary side to maintain the original transmission power, which causes overstress on the normal switch and bias of the three-phase high-frequency link current.

[0046] When the same-phase primary dual switch open circuit fault occurs, the power transmission closed-loop path associated with the faulty switch is deleted, and there is no power transmission closed-loop path in the faulty phase. The path power model under the same-phase primary dual switch open circuit fault is as follows: Figure 4c As shown, only four switch energy blocks are left in the primary side to carry the transmitted energy, there is no transmitted energy in the fault phase, the transmitted energy is limited, and the three-phase balance is destroyed.

[0047] When the same-phase secondary dual switch open circuit fault occurs, the power transmission closed-loop path associated with the faulty switch is deleted, and the power transmission closed-loop paths under the positive and negative high-frequency link currents in the non-fault phase are reduced by the same amount. Therefore, the path power model under the same-phase secondary dual switch open circuit fault is as follows: Figure 4d As shown in the figure, the anti-parallel diode of the fault switch replaces the fault switch in the positive and negative current directions to re-construct the closed-loop path of power transmission, and the six switch power blocks in the secondary side can still transmit power. Therefore, the current value of the three-phase high-frequency chain is reduced but the current is not biased, and the power transmitted by each phase is reduced but equal.

[0048] When the double switches on the same phase but different sides are open circuit fault, the power transmission closed loop path associated with the faulty switch is deleted, and only a single high-frequency link current direction, that is, a positive or negative downward power transmission closed loop path, remains in the fault phase. Therefore, the path power model under the double switches on the same phase but different sides are open circuit fault is as follows: Figure 4e As shown, the faulty switch cannot transmit power, and only 10 switch power blocks are left on the primary and secondary sides of the three-phase dual active bridge DC transformer to maintain power transmission, resulting in overstress of the normal switch, complete bias of the high-frequency link current in the faulty phase, and bias of the high-frequency link current in the non-faulty phase.

[0049] When a double switch open circuit fault occurs on different sides or different phases, the power transmission closed-loop path associated with the faulty switch is deleted, which is equivalent to the superposition of two single switch open circuit faults. The power transmission closed-loop path in the three-phase dual active bridge DC transformer consists of two phases with single switch faults and one non-fault phase. Therefore, the path power models under double switch open circuit faults on different sides or different phases are as follows: Figure 4f , Figure 4g As shown in Figure 1, the faulty switch cannot transmit power, and the remaining switch power blocks maintain the original transmission power, causing overstress on the normal switch and high-frequency link current bias in the faulty phase.

[0050] 3) According to the fault mechanism analysis, for the open-circuit fault of multiple types of switches in the three-phase dual-active bridge DC transformer, the phase where the faulty switch is located is determined as the faulty phase, and the phase without fault is the non-faulty phase. The remaining switches on the secondary side of the faulty phase except the faulty switch are locked, and the anti-parallel diode of the secondary side locking switch is used to reconstruct the closed-loop path of power transmission. The specific fault-tolerant operations are as follows:

[0051] If a single switch on the primary side fails to open, there is a fault phase, and the two switches on the secondary side of the fault phase are locked to achieve fault-tolerant operation and ensure power transmission. Taking the open circuit failure of the primary side switch S1 of phase Aa as an example, the secondary side switches S7 and S8 of the fault phase Aa are locked. Figure 5a As shown in Figure 1, the primary switch S2 of the fault phase Aa and the secondary diodes D7-D8 are used to build a closed-loop path for power transmission. The experimental diagram of the three-phase high-frequency link current waveform under S1 open-circuit fault tolerance operation is shown in Figure 1. Figure 6a As shown, the three-phase high-frequency link current bias is alleviated and the current stress is reduced.

[0052] If a single switch on the secondary side fails to open, there is a fault phase, and the remaining switch on the secondary side of the fault phase is locked to achieve fault-tolerant operation and ensure power transmission. Taking the open circuit failure of the secondary side switch S7 of phase Aa as an example, the remaining switch S8 on the secondary side of the fault phase Aa is locked. Figure 5b As shown in Figure 1, the primary switch S1-S2 of the fault phase Aa and the secondary diode D7-D8 are used to build a closed-loop path for power transmission. The experimental diagram of the three-phase high-frequency link current waveform under S7 open-circuit fault tolerance operation is shown in Figure 1. Figure 6b As shown, the three-phase high-frequency link current bias is eliminated and the current stress is reduced.

[0053] If the two switches on the same phase primary side open circuit fault, there is a faulty phase, the two switches on the secondary side of the faulty phase are locked to achieve fault-tolerant operation and ensure power transmission; then adjust the angle between the non-faulty phases to 180° to achieve balanced operation. Taking the open circuit fault of the primary side switches S1 and S2 of phase Aa as an example, lock the secondary side switches S7 and S8 of the faulty phase Aa, and then adjust the angle between the Bb phase and the Cc phase to 180°, as shown in Figure 1. Figure 5c As shown in Figure 1, the switches and diodes of phases Bb and Cc are used to reconstruct the closed-loop path of power transmission. The experimental diagram of the three-phase high-frequency link current waveform under S1S2 open-circuit fault tolerance operation is shown in Figure 1. Figure 6c As shown, the three-phase dual active bridge DC transformer is in balanced single-phase operation, and the high-frequency link current has no bias.

[0054] If the same-phase secondary dual switches open circuit fault, there is a fault phase, and the two switches on the secondary side of the fault phase are locked, fault-tolerant operation can be achieved directly without operation to ensure power transmission. Take the Aa phase secondary switch S7 and S8 open circuit fault as an example. Figure 5d As shown in the figure, without changing the on / off state of other switches, the primary switches S1-S2 and secondary diodes D7-D8 of the fault phase Aa can reconstruct the closed-loop path of power transmission. The experimental figure of the three-phase high-frequency link current waveform under the open-circuit fault of S7S8 is as follows Figure 6d , the three-phase high-frequency link current is unbiased.

[0055] If the two switches on the same phase but different sides are open-circuited, there is a fault phase, one fault switch is on the primary side of the fault phase, and the other fault switch is on the secondary side of the fault phase. The remaining switch on the secondary side of the fault phase is locked to achieve fault-tolerant operation and ensure power transmission. Taking the open-circuit failure of the primary switch S1 and the secondary switch S8 of the Aa phase as an example, the remaining switch S7 on the secondary side of the fault phase Aa is locked, as shown in Figure 5e As shown in Figure 1, the primary switch S2 of the fault phase Aa and the secondary diodes D7-D8 are used to build a closed-loop path for power transmission. The experimental diagram of the three-phase high-frequency link current waveform under the S1S8 open-circuit fault tolerance operation is shown in Figure 1. Figure 6eAs shown, the three-phase high-frequency link current bias is alleviated and the current stress is reduced.

[0056] If two switches on different sides are open-circuited, there are two fault phases. If both faulty switches are on the primary side of the two faulty phases, the four switches on the secondary side of the two faulty phases are locked to achieve fault tolerance; if both faulty switches are on the secondary side of the two faulty phases, the remaining two switches on the secondary side of the two faulty phases are locked to achieve fault tolerance. Taking the open-circuit fault of the primary switch S1 of the Aa phase and the primary switch S4 of the Bb phase as an example, the secondary switches S7-S8 of the faulty phase Aa and the secondary switches S9-S 10 ,like Figure 5f As shown, the primary switches S2-S3 and the secondary diodes D7-D of the two fault phases Aa and Bb are used. 10 Construct a closed-loop path for power transmission. The experimental diagram of the three-phase high-frequency link current waveform under S1S4 open-circuit fault tolerance operation is as follows Figure 6f As shown, the high-frequency link current bias of the fault phases Aa and Bb is alleviated, the high-frequency link current bias of the non-fault phase Cc is eliminated, and the current stress is reduced.

[0057] If the double switches on different sides of different phases are open circuit fault, there are two fault phases, one fault switch is on the primary side of one fault phase, and the other fault switch is on the secondary side of the other fault phase, thus locking the remaining three switches on the secondary sides of the two fault phases to achieve fault-tolerant operation and ensure power transmission. 10 Taking an open circuit fault as an example, the secondary switches S7-S8 of the faulty phase Aa and the remaining secondary switch S9 of the faulty phase Bb are locked. Figure 5g As shown, the two fault phase primary switches S2-S4 and secondary diodes D7-D 10 Build a closed loop of power transmission. S1S 10 The experimental diagram of the three-phase high-frequency link current waveform under open circuit fault tolerance operation is as follows: Figure 6g As shown, the high-frequency link current bias of the fault phases Aa and Bb is alleviated, the high-frequency link current bias of the non-fault phase Cc is eliminated, and the current stress is reduced.

[0058] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A multi-type switch open circuit fault tolerance method for a three-phase dual active bridge DC transformer, characterized in that: The following steps are involved: 1) According to the topology of the three-phase dual active bridge DC transformer, a path power model of the three-phase dual active bridge DC transformer is established. The transmitted power in the three-phase dual active bridge DC transformer is regarded as being carried by the switch and its anti-parallel diode in the path. Then, according to the power transmission direction of the three-phase dual active bridge DC transformer, a closed-loop power transmission path composed of the switch and its anti-parallel diode is obtained; 2) According to the number and position of faulty switches in the three-phase dual-active bridge DC transformer, determine the changes in the closed-loop path of power transmission caused by multiple types of switch open-circuit faults, establish a path power model under multiple types of switch open-circuit faults, and clarify the impact of different fault types on the operation and power transmission of the three-phase dual-active bridge DC transformer, wherein the multiple types of switch open-circuit faults include single switch open-circuit faults and double switch open-circuit faults; 3) For the faulty switch of the three-phase dual-active bridge DC transformer, the phase where the faulty switch is located is determined to be the faulty phase, and the remaining switches on the secondary side of the faulty phase except the faulty switch are locked. The anti-parallel diode of the secondary side locking switch is used to reconstruct the closed-loop path of power transmission to achieve fault-tolerant operation.

2. The method for tolerant multiple types of switch open circuit faults of a three-phase dual active bridge DC transformer according to claim 1, characterized in that: In step 2), since the three-phase dual active bridge DC transformer has a primary side and a secondary side, according to the different number and position of the faulty switches in the three-phase dual active bridge DC transformer, the multi-type switch open circuit faults include 2 single switch open circuit faults and 5 double switch open circuit faults, namely: a single switch open circuit fault occurring on the primary side, a single switch open circuit fault occurring on the secondary side, a double switch open circuit fault occurring on the same phase primary side, a double switch open circuit fault occurring on the same phase secondary side, a double switch open circuit fault occurring on the same phase different sides, a double switch open circuit fault occurring on different same sides, and a double switch open circuit fault occurring on different phases different sides; after determining the number and position information of the faulty switches, based on the power transmission closed-loop path obtained in step 1), the power transmission closed-loop path associated with the faulty switch is deleted, and the remaining power transmission closed-loop path is the power transmission closed-loop path under the current fault. Based on this, a path power model under multi-type switch open circuit faults is established to determine the impact of different fault types on the operation and power transmission of the three-phase dual active bridge DC transformer.

3. The method for tolerant multiple types of switch open circuit faults of a three-phase dual active bridge DC transformer according to claim 2, characterized in that: In step 3), for the faulty switch of the three-phase dual active bridge DC transformer, the phase where the faulty switch is located is determined to be the faulty phase, the remaining switches on the secondary side of the faulty phase except the faulty switch are locked, and the anti-parallel diode of the secondary side locking switch is used to construct a closed-loop path for power transmission. The specific fault-tolerant operation is as follows: ① If a single switch on the primary side fails to open circuit and there is a faulty phase, the two switches on the secondary side of the faulty phase are locked to achieve fault-tolerant operation; ② If a single switch on the secondary side fails to open circuit and there is a faulty phase, the remaining switch on the secondary side of the faulty phase is locked to achieve fault-tolerant operation; ③ If the dual switches on the primary side of the same phase are open circuit faults and there is a faulty phase, the two switches on the secondary side of the faulty phase are locked to achieve fault-tolerant operation; then adjust the angle between the non-faulty phases to 180° to achieve three-phase balanced operation; ④ If the double switches on the same-phase secondary side have an open circuit fault, there is a faulty phase, and both switches on the secondary side of the faulty phase are locked, no operation is required, and fault-tolerant operation can be achieved directly; ⑤ If the double switches on the same phase but different sides have an open circuit fault, there is a faulty phase, one faulty switch is on the primary side of the faulty phase, and the other faulty switch is on the secondary side of the faulty phase, the remaining switch on the secondary side of the faulty phase is locked to achieve fault-tolerant operation; ⑥ If the double switches on different sides have open circuit faults, there are two fault phases; if the two fault switches are both on the primary side of the two fault phases, the four switches on the secondary side of the two fault phases are locked to achieve fault-tolerant operation; if the two fault switches are both on the secondary side of the two fault phases, the remaining two switches on the secondary side of the two fault phases are locked to achieve fault-tolerant operation; ⑦ If the double switches on different phases and different sides have open circuit faults, there are two fault phases, one fault switch is on the primary side of one fault phase, and the other fault switch is on the secondary side of the other fault phase, thus locking the remaining three switches on the secondary sides of the two fault phases to achieve fault-tolerant operation.

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