Fault diagnosis method of three-level active neutral point clamped rectifier based on state transfer

Abstract

The present invention provides a three-level active neutral point clamped rectifier fault diagnosis method based on state transfer, which belongs to the field of traction power supply technology, including analyzing the working principle of the three-phase three-level ANPC rectifier, and analyzing the working state of the three-phase three-level ANPC rectifier under a single-tube open circuit fault; deriving the change characteristics of the midpoint current under different switch combinations after a single-tube fault occurs; deriving the diagnosis principle of the single-tube fault; based on the phase current direction of the three-phase three-level ANPC rectifier, all fault types of double-tube faults in the same bridge arm are divided, and the fault characteristics under the corresponding double-tube faults are analyzed; the diagnosis principle of the single-tube fault is extended to the double-tube fault situation in the same bridge arm, and the double-tube fault is diagnosed. The present invention solves the problem of single-tube fault and double-tube fault of the same-phase bridge arm switch device of the three-phase three-level ANPC rectifier without adding additional sensors and other hardware costs.

Description

Technical Field

[0001] The invention belongs to the technical field of traction power supply, and in particular relates to a fault diagnosis method for a three-level active neutral point clamped rectifier based on state transfer. Background Art

[0002] The active neutral point clamp (ANPC) rectifier to which the present invention relates adopts power switching devices to replace the clamping diodes in the three-level neutral point clamp (NPC) topology structure, providing more current paths for the circuit. On the basis of inheriting the NPC topology structure, it also adds a zero-level output state commutation path, which can reduce the constraints of balanced power device losses from the hardware level and provide more flexibility. Thanks to the above advantages, the ANPC topology structure has been maturely applied to technical fields such as wind power, photovoltaic power generation, motor frequency conversion and speed regulation, and power quality management. However, due to the presence of a large number of high-power switching devices in the three-phase three-level active neutral point clamp rectifier and long-term operation in an environment with large load fluctuations and complex operating conditions, the probability of its failure will also increase accordingly. If the rectifier fails in extreme cases, it will cause problems such as overcurrent and overvoltage in the system, which will seriously affect the safe and stable operation of the entire system. Therefore, studying a fast and accurate fault diagnosis scheme is of great practical significance for ensuring the stable operation of the system and eliminating system safety hazards. The faults of the switching devices can usually be divided into short-circuit faults and open-circuit faults. Short-circuit fault is the most serious fault that endangers the stable operation of the system. Once it occurs, it will cause the instantaneous current of the converter to be too high. In actual engineering applications, short-circuit faults are generally converted into open-circuit faults for processing by adding fast fuses in the power electronic converter circuit or adding short-circuit signal blocking in the drive circuit. Therefore, the research on short-circuit faults is often unified as open-circuit faults. The fault diagnosis method based on state characteristics is one of the commonly used fault diagnosis methods in this field. It mainly extracts fault characteristics by analyzing the amplitude, variance, mean, vector trajectory, frequency characteristics, etc. of the output voltage and current of the converter to locate the fault of the device. It can be divided into fault diagnosis based on current characteristics and fault diagnosis based on voltage characteristics. For a three-phase three-level active clamp rectifier, the electrical characteristics such as the AC side voltage and current, the bridge arm output voltage and output current, the DC side upper and lower capacitor voltages, and the midpoint current can directly or indirectly provide characteristic information for fault diagnosis. Fault diagnosis methods based on current characteristics generally do not require additional sensors to extract, but because current signals are sensitive to factors such as load and noise, improving diagnostic reliability may also prolong diagnostic time; fault diagnosis methods based on voltage characteristics can be quickly acquired and have strong anti-interference capabilities, but require additional voltage sensors, which increases the design cost of the system. Existing fault diagnosis methods based on current characteristics mostly focus on studying fault diagnosis of NPC topology structures and are mainly applied to single-tube faults. Therefore, for ANPC rectifiers with many power devices and complex topology structures, how to design a fault diagnosis method with short diagnostic time, easy implementation, and low hardware cost is an urgent problem to be solved. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a three-level active neutral point clamped rectifier fault diagnosis method based on state transfer. The present invention solves the problem of single-tube fault and double-tube fault of the same-phase bridge arm switch device of the three-phase three-level ANPC rectifier without adding additional sensors and other hardware costs.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a three-level active neutral point clamped rectifier fault diagnosis method based on state transfer, comprising the following steps:

[0005] S1. Analyze the working principle of the three-phase three-level ANPC rectifier, and analyze the working state of the three-phase three-level ANPC rectifier under a single-tube open-circuit fault, and obtain the abnormal state transfer that occurs during the fault process;

[0006] S2. Analyze the midpoint current of the three-phase three-level ANPC rectifier under normal working conditions, and derive the variation characteristics of the midpoint current under different switch combinations after a single tube fault occurs;

[0007] S3. The diagnosis principle of single-tube fault is derived through the abnormal state transfer occurring during the fault process and the corresponding midpoint current change characteristics;

[0008] S4. Based on the phase current direction of the three-phase three-level ANPC rectifier, all fault types of double-tube faults in the same bridge arm are divided, and the fault characteristics under the corresponding double-tube faults are analyzed;

[0009] S5. Extend the single-tube fault diagnosis principle to the double-tube fault situation in the same bridge arm, diagnose the double-tube fault, and complete the fault diagnosis of the three-level active neutral point clamped rectifier.

[0010] Furthermore, the expression of the midpoint current of the three-phase three-level ANPC rectifier in the normal state in step S2 is as follows:

[0011] i o =(1-|S a |)i a +(1-|S b |)i b +(1-|S c |)i c

[0012]

[0013] Among them, i o Indicates the midpoint current of the DC side, i a 、i b and i c Represents the three-phase transient current, S xrepresents the switching function, v x0 Indicates the output voltage of the three-phase three-level ANPC rectifier, U dc Indicates the DC side voltage of the rectifier.

[0014] Furthermore, through the abnormal state transition that occurs during the fault process and the corresponding midpoint current change characteristics, the diagnosis principle of single-tube fault is derived, which is specifically:

[0015] Through the abnormal state transfer occurring during the fault process and the corresponding midpoint current variation characteristics, the duty cycle modulation waves of each three phases are introduced into the single-tube fault diagnosis, and the diagnosis principle of the single-tube fault is obtained.

[0016] Furthermore, the conditions for classifying all fault types of double-tube faults in the same bridge arm are as follows:

[0017] When two switching devices in the same bridge arm operate in different or the same phase current directions, the abnormal state of the bridge arm caused by their simultaneous failure is equivalent to the abnormal state transfer caused by the failure of two single tubes at different times, and is regarded as a single tube failure in the corresponding switching device.

[0018] Furthermore, in step S5, the double-tube fault is diagnosed, which is specifically:

[0019] According to the fault characteristics of the double-tube fault obtained by analyzing step S4, a state transition diagnosis signal under different fault types is obtained;

[0020] According to whether the state transfer diagnosis signal jumps under different fault types, all faulty switch device combinations containing double-tube faults are located to complete the diagnosis of the double-tube faults.

[0021] The beneficial effects of the present invention are:

[0022] 1. The fault diagnosis method for a three-phase three-level active neutral point clamped rectifier proposed in the present invention provides more redundant states in terms of topology structure compared with the traditional three-phase three-level neutral point clamped rectifier. By utilizing the characteristics of two zero-level switching states in its own topology structure, it is easier to realize the double-tube fault location including the clamped switching device.

[0023] 2. The present invention adopts the midpoint current of each phase bridge arm of the three-phase three-level active neutral point clamped rectifier as the electrical fault feature. It can realize accurate open circuit fault positioning of the power switch device without adding additional sensors. At the same time, there is no need to compare the midpoint current and actual current corresponding to all vector states in the ANPC rectifier according to the traditional method. The faulty device can be located only based on the state transfer information of the faulty phase, which greatly improves the diagnostic efficiency.

[0024] 3. After analyzing the characteristics of single-tube faults and double-tube faults, the fault diagnosis method involved in the present invention determines the fault according to the jump of the abnormal state transfer flag bit. All fault switch device combinations including double-tube faults can be located through only one set of fault diagnosis principles, which reduces the computing power cost in the implementation process and facilitates the implementation of the programming process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a flow chart of the method of the present invention.

[0026] Figure 2 This is the topological diagram of the three-phase three-level ANPC rectifier.

[0027] Figure 3 (a) Schematic diagram of the current path in the [P] state under Sa1 open circuit fault.

[0028] Figure 3 (b) is a schematic diagram of the state switching process of the A-phase bridge arm [OU]→[P]→[OU] during normal operation.

[0029] Figure 3 (c) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under Sa1 open circuit fault.

[0030] Figure 4 (a) Schematic diagram of the current path in the [P] state under Sa2 open circuit fault.

[0031] Figure 4 (b) Schematic diagram of the current path in the [OU] state under Sa2 open circuit fault.

[0032] Figure 4 (c) is a schematic diagram of the state switching process of the A-phase bridge arm [OU]→[P]→[OU] during normal operation.

[0033] Figure 4 (d) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under Sa2 open circuit fault.

[0034] Figure 5 (a) Schematic diagram of the current path in the [N] state under Sa3 open circuit fault.

[0035] Figure 5 (b) Schematic diagram of the current path in the [OL] state under Sa3 open circuit fault.

[0036] Figure 5 (c) is a schematic diagram of the state switching process of the A-phase bridge arm [N]→[OL]→[N] during normal operation.

[0037] Figure 5(d) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A bridge arm under Sa3 open circuit fault.

[0038] Figure 6 (a) Schematic diagram of the current path in the [N] state under Sa4 open circuit fault.

[0039] Figure 6 (b) is a schematic diagram of the state switching process of the A-phase bridge arm [N]→[OL]→[N] during normal operation.

[0040] Figure 6 (c) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A bridge arm under Sa4 open circuit fault.

[0041] Figure 7 (a) Schematic diagram of the current path in the [OU] state under Sa5 open circuit fault.

[0042] Figure 7 (b) is a schematic diagram of the state switching process of the A-phase bridge arm [OU]→[P]→[OU] during normal operation.

[0043] Figure 7 (c) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under Sa5 open circuit fault.

[0044] Figure 8 (a) Schematic diagram of the current path in the [OL] state under Sa6 open circuit fault.

[0045] Figure 8 (b) is a schematic diagram of the state switching process of the A-phase bridge arm [N]→[OL]→[N] during normal operation.

[0046] Figure 8 (c) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A bridge arm under Sa6 open circuit fault.

[0047] Fig. 9 Schematic diagram of the transition process between the operating states of the A-phase bridge arm when an open-circuit fault occurs in the switching device.

[0048] Fig.10 Schematic diagram of the space vector distribution of a three-phase three-level ANPC rectifier.

[0049] Fig.11 Schematic diagram of spatial vector distribution in sector I.

[0050] Fig.12 The figure is a schematic diagram of the three-phase three-level ANPC topology structure with each phase bridge arm marked.

[0051] Fig.13 This is a flow chart of the single-tube open circuit fault diagnosis principle.

[0052] Fig.14 (a) Schematic diagram of the current path in the [P] state under the Sa1+Sa3 open circuit fault.

[0053] Fig.14 (b) Schematic diagram of the current path in the [N] state under the Sa1+Sa3 open circuit fault.

[0054] Fig.14 (c) Schematic diagram of the current path in the [OL] state under the Sa1+Sa3 open circuit fault.

[0055] Fig.14 (d) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under the Sa1+Sa3 open circuit fault.

[0056] Fig.14 (e) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A under the Sa1+Sa3 open circuit fault.

[0057] Fig.15 (a) Schematic diagram of the current path in the [P] state under the Sa1+Sa2 open circuit fault.

[0058] Fig.15 (b) Schematic diagram of the current path in the [OU] state under the Sa1+Sa2 open circuit fault.

[0059] Fig.15 (c) is a schematic diagram of the state switching process of the A-phase bridge arm [OU]→[P]→[OU] during normal operation.

[0060] Fig.15 (d) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under the Sa1+Sa2 open circuit fault.

[0061] Fig.16 (a) Schematic diagram of the current path in the [P] state under the Sa1+Sa6 open circuit fault.

[0062] Fig.16 (b) Schematic diagram of the current path in the [OL] state under the Sa1+Sa6 open circuit fault.

[0063] Fig.16 (c) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under the Sa1+Sa6 open circuit fault.

[0064] Fig.16 (d) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A under the Sa1+Sa6 open circuit fault.

[0065] Fig.17 (a) Schematic diagram of the current path in the [P] state under the Sa2+Sa6 open circuit fault.

[0066] Fig.17 (b) Schematic diagram of the current path in the [OU] state under the Sa2+Sa6 open circuit fault.

[0067] Fig.17 (c) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under the Sa2+Sa6 open circuit fault.

[0068] Fig.17 (d) Schematic diagram of the current path in the [OL] state under the Sa2+Sa6 open circuit fault.

[0069] Fig.17 (e) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A under the Sa2+Sa6 open circuit fault.

[0070] Fig.18 (a) Schematic diagram of the current path in the [N] state under the Sa3+Sa4 open circuit fault.

[0071] Fig.18 (b) Schematic diagram of the current path in the [OL] state under the Sa3+Sa4 open circuit fault.

[0072] Fig.18 (c) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A under the Sa3+Sa4 open circuit fault.

[0073] Fig.19 (a) Schematic diagram of the current path in the [N] state under the Sa3+Sa5 open circuit fault.

[0074] Fig.19 (b) Schematic diagram of the current path in the [OL] state under the Sa3+Sa5 open circuit fault.

[0075] Fig.19 (c) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A under the Sa3+Sa5 open circuit fault.

[0076] Fig. 20 (a) Schematic diagram of the current path in the [OU] state under the Sa3+Sa5 open circuit fault.

[0077] Fig. 20 (b) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under the Sa3+Sa5 open circuit fault.

[0078] Fig.21 (a) Schematic diagram of the current path in the [N] state under the Sa4+Sa5 open circuit fault.

[0079] Fig.21 (b) is a schematic diagram of the abnormal state transfer process of the lower bridge arm of phase A under the Sa4+Sa5 open circuit fault.

[0080] Fig. 22 (a) Schematic diagram of the current path in the [OU] state under the Sa4+Sa5 open circuit fault.

[0081] Fig. 22 (b) is a schematic diagram of the abnormal state transfer process of the upper bridge arm of phase A bridge arm under the Sa4+Sa5 open circuit fault. DETAILED DESCRIPTION

[0082] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0083] Example

[0084] like Figure 1 As shown, the present invention provides a three-level active neutral point clamped rectifier fault diagnosis method based on state transfer, and its implementation method is as follows:

[0085] S1. Analyze the working principle of the three-phase three-level ANPC rectifier, and analyze the working state of the three-phase three-level ANPC rectifier under a single-tube open-circuit fault, and obtain the abnormal state transfer that occurs during the fault process;

[0086] S2. Analyze the midpoint current of the three-phase three-level ANPC rectifier under normal working conditions, and derive the variation characteristics of the midpoint current under different switch combinations after a single tube fault occurs;

[0087] S3. The diagnosis principle of single-tube fault is derived through the abnormal state transfer occurring during the fault process and the corresponding midpoint current change characteristics;

[0088] S4. Based on the phase current direction of the three-phase three-level ANPC rectifier, all fault types of double-tube faults in the same bridge arm are divided, and the fault characteristics under the corresponding double-tube faults are analyzed;

[0089] S5. Extend the single-tube fault diagnosis principle to the double-tube fault situation in the same bridge arm, diagnose the double-tube fault, and complete the fault diagnosis of the three-level active neutral point clamped rectifier.

[0090] Through the abnormal state transition that occurs during the fault process and the corresponding midpoint current change characteristics, the diagnosis principle of single-tube fault is derived, which is as follows:

[0091] Through the abnormal state transfer occurring during the fault process and the corresponding midpoint current variation characteristics, the duty cycle modulation waves of each three phases are introduced into the single-tube fault diagnosis, and the diagnosis principle of the single-tube fault is obtained.

[0092] The conditions for classifying all fault types of double-tube faults in the same bridge arm are as follows:

[0093] When two switching devices in the same bridge arm operate in different or the same phase current directions, the abnormal state of the bridge arm caused by their simultaneous failure is equivalent to the abnormal state transfer caused by the failure of two single tubes at different times, and is regarded as a single tube failure of the corresponding switching device for processing.

[0094] In step S5, double-tube fault diagnosis is performed, which is specifically as follows:

[0095] According to the fault characteristics of the double-tube fault obtained by analyzing step S4, a state transition diagnosis signal under different fault types is obtained;

[0096] According to whether the state transfer diagnosis signal jumps under different fault types, all faulty switch device combinations containing double-tube faults are located to complete the diagnosis of the double-tube faults.

[0097] In this embodiment, Figure 2 The topology of the three-phase three-level ANPC rectifier is shown in Figure 1, where L is the filter inductor, R is the equivalent resistance of the filter inductor, and e a 、e b 、e c The three-phase AC voltage sources are A, B, and C respectively, S x1 To S x6 (x=a, b, c) are 6 fully controlled power switch devices of the three-phase bridge arms A, B, and C. In the present invention, an IGBT with an anti-parallel diode is used as an example for subsequent analysis. C1 and C2 are DC side capacitors that can stabilize the DC side voltage and store energy. a 、i b 、i c They are A, B, C three-phase current, U C1 is the voltage of capacitor C1, U C2 is the voltage of capacitor C2, U dc is the DC side voltage of the rectifier.

[0098] In this embodiment, Figure 2 — Fig. 22 As shown in the figure, the specific process of three-level ANPC rectifier fault diagnosis based on state transfer is as follows:

[0099] The working principle of the three-phase three-level ANPC rectifier is analyzed. Taking the A-phase bridge arm as an example, the working state of the three-phase three-level ANPC rectifier under a single-tube open-circuit fault is analyzed; the midpoint current of the ANPC rectifier under normal working state is analyzed, and the change characteristics of the midpoint current under different switch state combinations after a single-tube fault occurs are derived; according to the abnormal state transfer process caused by the single-tube fault, the midpoint current of the three-phase three-level ANPC rectifier is used as the criterion to derive the diagnosis principle of the single-tube fault; based on the phase current direction of the three-phase three-level ANPC rectifier, all fault types of double-tube faults in the same bridge arm are divided and the corresponding fault characteristics under the double-tube fault are analyzed; the single-tube fault diagnosis principle is extended to the double-tube fault in the same bridge arm, and the double-tube fault diagnosis method is derived.

[0100] In this embodiment, the specific process of analyzing the working state of the three-phase three-level ANPC rectifier under a single-tube open-circuit fault is as follows:

[0101] Due to the bidirectional flow of the clamping switch device in the ANPC topology, the O vector has four redundant switching states, which are defined as OU1, OU2, OL1, and OL2. x1 With S x5 Complementary conduction, S x2 With S x3 Complementary conduction, S x4 With S x6 Complementary conduction, the switching devices of complementary conduction cannot be turned on at the same time. Ideally, the voltage of the two DC side capacitors is equal, that is, U C1 =U C2 =1 / 2U dc The above six effective switching states corresponding to the level vectors are shown in Table 1. Table 1 is a table of switching states and output levels corresponding to the bridge arm vectors of the three-phase three-level ANPC rectifier.

[0102] Table 1

[0103]

[0104] According to Table 1, there are two current flow paths corresponding to the O vector. The OU1 and OU2 vectors correspond to the upper bridge arm S x2 and S x5 In the on state, the OL1 and OL2 vectors correspond to the lower bridge arm S x3 and S x6 According to the different directions of phase current, OU1 and OU2 can be defined as OU vectors, and OL1 and OL2 can be defined as OL vectors. Therefore, the working mode and corresponding output voltage V of the rectifier under different phase current directions can be further defined. xo(x=a,b,c) is summarized in Table 2, where D x1 To D x6 (x=a, b, c) are the anti-parallel diodes of the six fully controlled power switch devices in the three-phase bridge arms A, B, and C. The phase current i is defined as x (x=a, b, c) The positive direction is when the current flows from the AC side to the DC side, and the negative direction is when the current flows from the AC side to the DC side. Table 2 is the working mode table of the three-phase ANPC rectifier.

[0105] Table 2

[0106]

[0107] As shown in Table 2, there is no switch device involved in the current path under Mode I and Mode VIII, so the above two working modes are not discussed when only considering the failure of the switch device. For Mode II, Mode III and Mode IV, S x3 , S x4 , S x5 The fault will affect the current path in the corresponding working mode, and the fault of other switching devices will have no effect on the operation of the rectifier; similarly, for mode V, mode VI and mode VII, the S x1 , S x2 , S x6 The fault affects the current path in the corresponding operating mode.

[0108] When the three-level converter operates normally, each phase bridge arm switches between the three levels of "PON". However, due to the increase in redundant switch states of the ANPC topology output O level, it will increase the difficulty of rapid and effective detection and identification of device faults. Therefore, it is necessary to analyze the changes in the bridge arm operating state caused by the change in the current path before and after the single-tube open circuit fault. According to the three-phase symmetry of the three-phase three-level ANPC rectifier, the A-phase bridge arm is used as an example for subsequent fault analysis.

[0109] In this embodiment, Figures 3 to 8 They are switching devices S a1 , S a2 , S a3 , S a4 , S a5 , S a6 Schematic diagram of the current path and output level changes before and after an open-circuit fault occurs.

[0110] When S a1 After the fault, combined with the current path in Table 2, it can be seen that only working mode V will be affected by the fault. At this time, the phase current i a <0, after the fault the current flows through the anti-parallel diode D a5 , Switching device S a2 And the clamping switch device Sa6 , anti-parallel diode D a3 The two current paths continue to flow, and the bridge arm state changes from P to O.

[0111] When S a2 After the fault, combined with the current path in Table 2, it can be seen that both working mode V and working mode VI will be affected by the fault. At this time, the phase current i a <0. S in P state a2 After the fault, the current flows through the clamping switch device S a6 , anti-parallel diode D a3 The current path continues, and the bridge arm state changes from P to OL; in the OU state, S a2 After the fault, the current flows through the anti-parallel diode D a4 , anti-parallel diode D a3 The current path continues to flow, and the bridge arm state changes from OU to N.

[0112] When S a3 After the fault, combined with the current path in Table 2, it can be seen that both working mode III and working mode IV will be affected by the fault. At this time, the phase current i a >0. In N state, S a3 After the fault, the current flows through the anti-parallel diode D a2 , clamping switch device S a5 The current path continues, and the bridge arm state changes from N to OU; in the OL state, S a3 After the fault, the current flows through the anti-parallel diode D a2 , anti-parallel diode D a1 The current path continues to flow, and the bridge arm state changes from OL to P.

[0113] When S a4 After the fault, combined with the current path in Table 2, it can be seen that only working mode IV will be affected by the fault. At this time, the phase current i a >0, after the fault the current flows through the anti-parallel diode D a2 , clamping switch device S a5 And the switching device S a3 , anti-parallel diode D a6 The two current paths continue to flow, and the bridge arm state changes from N to O.

[0114] When S a5 After the fault, combined with the current path in Table 2, it can be seen that only working mode II will be affected by the fault. At this time, the phase current i a >0, after the fault the current flows through the anti-parallel diode D a2 , anti-parallel diode D a1 The current path continues to flow, and the bridge arm state changes from OU to P.

[0115] When S a6After the fault, combined with the current path in Table 2, it can be seen that only working mode VII will be affected by the fault. At this time, the phase current i a <0, after the fault the current flows through the anti-parallel diode D a4 , anti-parallel diode D a3 The current path continues to flow, and the bridge arm state changes from OL to N.

[0116] According to the above fault analysis, the impact of open circuit fault on the circuit state depends on the current direction and the level of the control system's expected output. a <0, S a1 , S a2 , S a6 When an open circuit fault occurs, the current path will change, thereby changing the output state. Other switch tube faults will not affect the normal current flow path. Similarly, S a3 , S a4 , S a5 The fault only affects i a >0 when the bridge arm state.

[0117] Therefore, the open circuit failure of the switching device will force the current to transfer from one branch to another, resulting in a change in the operating state. Taking phase A as an example, Fig. 9 The figure shows the transition between the operating states of phase A when the six switching devices have an open circuit fault, where F sax =1 (x=1,2,3,4,5,6) indicates that Sax has an open circuit fault, and [O] indicates that the output of the bridge arm including [OU] and [OL] is at zero level.

[0118] In this embodiment, from Fig. 9 It can be seen that F sa1 =1 will force the state [P] to transfer to the state [OU], [OL], and [OU] and [OL] both correspond to the bridge arm output zero level, so F sa1 =1 can be summarized as the transition from state [P] to state [O]; correspondingly, F sa4 =1 will force state [N] to move to state [O]; F sa2 =1 forces state [P] to move to state [OL], state [OU] to move to [N]; corresponding to if F sa3 =1, then force state [N] to move to state [OU], state [OL] to move to state [P]; F sa5 =1 Force state [OU] to transfer to state [P]; F sa6= 1 forces state [OL] to transfer to state [N]. It can be seen that the abnormal state transfer caused by the failure of each switch tube is unique, and the state transfer under the single tube open circuit failure can be summarized into six cases, namely [P]→[O], [N]→[O], [OU]→[P], [OU]→[N], [OL]→[P], [OL]→[N].

[0119] In this embodiment, the specific process of deriving the variation characteristics of the midpoint current under different switch combinations after a single-tube fault occurs is as follows:

[0120] According to the fault analysis in step S1, when abnormal state transfer occurs in each bridge arm of the three-phase three-level ANPC rectifier, the corresponding voltage and current signals in the circuit will also change accordingly. Therefore, as long as the electrical signal quantity reflecting the six abnormal state transfers is found, it can be used as the fault characteristic quantity, combined with the characteristics of the state transfer, to locate the faulty switching device.

[0121] Before analyzing the fault characteristic quantity, it is necessary to derive the vector of the three-phase three-level ANPC rectifier for subsequent analysis.

[0122] For a three-phase three-level ANPC rectifier, in one switching cycle, the switching between the vectors of the single-phase bridge arm should consider the four defined states [P], [OU], [OL], and [N]. Therefore, there are 4×4×4=64 three-phase state combinations in its switching state. The corresponding vector distribution diagram is shown in Fig.10 As shown. This area can be divided into 6 large sectors, namely sector I, sector II, sector III, sector IV, sector V, and sector VI; and each large sector can be divided into 6 small sectors 1, 2, 3, 4, 5, and 6. Therefore, there are a total of 19 spatial voltage vectors of the three-phase three-level ANPC rectifier, distributed in the vector space composed of 36 small sectors. Among them, due to the redundant nature of the ANPC topology structure, the [O] state can correspond to the [OL] and [OU] states. In the following, L and U are used to represent the bridge arm [OL] and [OU] states. According to Fig.10 The vector size in the vector set can be divided into four categories: zero vector (V0), small vector (V1~V6), medium vector (V7~V8), and 12 ) and large vector (V 13 ~V 18 ), and there are more redundancies in the zero vector, small vector, and medium vector, while the vector corresponding to the large vector is unique. According to the above analysis, the vector table shown in Table 3 can be summarized. Table 3 is the vector table of the three-phase three-level ANPC rectifier.

[0123] Table 3

[0124]

[0125] Under normal conditions, the relationship between the midpoint current of the three-phase three-level ANPC rectifier and the three-phase switch state and the three-phase current can be expressed as:

[0126] i o =-(|S a |i a +|S b |i b +|S c |i c )

[0127] Among them, i o Indicates the midpoint current of the DC side, i a 、i b 、i c is the three-phase transient current, S x (x=a,b,c) is the switching function, and its value is shown in the following formula:

[0128]

[0129] like Fig.11 As shown, the corresponding midpoint current is analyzed by taking all the vectors in the first largest sector as an example. When the rectifier is operating normally, the three-phase current is balanced and satisfies i a +i b +i c = 0. According to the expression of midpoint current, the midpoint current i under zero vector o =0; the small vector V1 corresponds to the output switching function S x They can be expressed as 0-1-1 and 100 respectively, and the midpoint currents are i a , -i a ; The midpoint current formed by the switch state corresponding to the small vector V2 is i c 、-i c ; The vector V7 is -i a ; Large vector V 13 、V 14 is 0.

[0130] In order to understand the expression of midpoint current more intuitively, Fig.12 The topological structure of each phase bridge arm of the three-phase three-level ANPC rectifier is marked in FIG. Fig.12 It can be seen that when the switch function S x When the switching function S is 0, there is current flowing between the bridge arm and the DC side midpoint O, so the midpoint current is the phase current of a certain phase during normal operation; on the contrary, when the switching function S x When it is 1 or -1, there is no connection between the bridge arm and the DC side midpoint O, which has no effect on the value of the midpoint current expression. Therefore, the above midpoint current expression can also be written as:

[0131] io =(1-|S a |)i a +(1-|S b |)i b +(1-|S c |)i c

[0132] Taking the A-phase bridge arm as an example, the variation characteristics of the midpoint current under a single-tube open-circuit fault are analyzed. b and S c When the absolute value of is 1 or 0, according to the above formula, the value of the midpoint current is only related to the switching function S of the A phase bridge arm. a And the phase current i a Therefore, for the characteristic changes caused by the open circuit fault of the phase A bridge arm, the 64 switch state combinations can be divided into two categories:

[0133] 1) The switching functions of the bridge arms of phases B and C are both 1 or -1. At this time, the midpoint current i o It can be expressed as:

[0134] i0=(1-|S a |)i a

[0135] When S a1 After an open circuit fault occurs, the state of the bridge arm changes from [P] to [O], i o From 0 to i a ; When the switch tube S a2 Open circuit, state [P] changes to [OL], i o From 0 to i a , the state [OU] changes to [N], i o By i a becomes 0; S a6 The fault will only force the state [OL] to transition to [N], i o by i a Similarly, when the outputs of the B and C bridge arms are both 1 or -1, the failure of other switch tubes in the A bridge arm will cause the midpoint current to be a Varies between 0 and 0.

[0136] 2) The switching functions of the bridge arms of phases B and C are both 0. At this time, the midpoint current i o It can be expressed as:

[0137] i0=-(|S a |)i a

[0138] When S a1 After an open circuit fault occurs, the state of the bridge arm changes from [P] to [O], then io by -i a becomes 0; when the switch tube S a2 Open circuit, state [P] changes to [OL], at this time i o Also by -i a becomes 0, the state [OU] becomes [N], i o Then it changes from 0 to -i a ; S a6 The fault will only force the state [OL] to transition to [N], i o Changed from 0 to -i a Similarly, when the outputs of the B and C bridge arms are both 0, the failure of other switch tubes in the A bridge arm will cause the midpoint current to be -i a Varies between 0 and 0.

[0139] In summary, the fault characteristic analysis of the midpoint current under the single-tube open-circuit fault of phase A is shown in Table 4, where the constraints in brackets are the midpoint current i after the switching functions of phases B and C satisfy a certain relationship. o , "|S b |=1&&|S c |=1" indicates the switch function S b and S c The absolute value of "|S b |=0&&|S c |=0" indicates the switch function S b and S c The absolute values ​​of are all 0. Table 4 is the midpoint current analysis table under specific switch combinations under single-tube fault of phase A.

[0140] Table 4

[0141]

[0142] The analysis of the midpoint current under a specific switch combination under a single-tube fault on phase A shows from Table 4 that the midpoint current under a specific switch combination after a single-tube fault occurs is different from the midpoint current during the corresponding normal operation. The values ​​of the affected midpoint current under the fault have been marked in bold italic font in Table 4. The midpoint current change characteristics when a single-tube fault occurs on phases B and C are similar to the above analysis. For the B-phase fault, the 64 switch state combinations can be analyzed to find that the output absolute values ​​of the A and C bridge arms are 1 and 0. Then the midpoint current caused by the switch tube fault on the B bridge arm is between 0 and ±i b For a phase C fault, all switch state combinations are divided into two categories: the output absolute values ​​of the A and B bridge arms are 1 and 0, and the midpoint current under the fault is between 0 and ±i c Changes between.

[0143] In this embodiment, the specific process of deriving the single-tube fault diagnosis principle in step S3 is as follows:

[0144] After the fault phase analysis in step S2, the midpoint current before and after the fault is detected to be 0 or i x (x=a,b,c) can accurately obtain the relevant information of state transfer.

[0145] From the perspective of the entire vector space, it is necessary to further divide the A, B, and C phases of the ANPC rectifier to form a specific vector state set.

[0146] From the analysis of the working principle in step S1, it can be seen that the state transitions that occur under a single-tube open-circuit fault include six abnormal situations: [P]→[O], [N]→[O], [OU]→[P], [OU]→[N], [OL]→[P], and [OL]→[N]. Define F xP =1(x=A,B,C) indicates that [P]→[O] is detected; F xN =1 indicates that [N]→[O] is detected; F xO1 =1 indicates that [OU]→[P] or [N] is detected; F xO2 =1 indicates that [OL]→[P] or [N] is detected; [OU]→[P] is detected by F xO1P =1 means [OU]→[N] uses F xO1N =1 means [OL]→[P] uses F xO2P =1 means [OL]→[N] uses F xO2N =1 indicates that. The specific vector sets and state abnormality judgment rules corresponding to the single-tube open-circuit faults in the three bridge arms A, B, and C are shown in Table 5, Table 6, and Table 7, respectively. The expressions involved in the form of "expression 1? expression 2: expression 3" are question mark expressions, and the judgment rules are: if expression 1 is true, the value of the question mark expression is the value of expression 2; if expression 1 is not true, the value of the question mark expression is expression 3. Table 5 is a state transition abnormality judgment rule table under the A phase vector set, Table 6 is a state transition abnormality judgment rule table under the B phase vector set, and Table 7 is a state transition abnormality judgment rule table under the C phase vector set.

[0147] Table 5

[0148]

[0149] In Table 5, the P-type redundant state of V1 and the N-type redundant state of V4 in the zero vector and the small vector meet the second case analyzed in the previous section, that is, the switch functions of the two bridge arms B and C are both 0. The zero vector is mainly used to judge the abnormal transfer of the states [OU] and [OL]. Under normal operation, the midpoint current corresponding to the zero vector should be 0. In the single-tube open circuit fault type, S a2 , S a3 , S a5 , S a6The fault will force [OU] or [OL] to transfer to [P] or [N], and the actual midpoint current becomes -i a . In case of single tube open circuit fault, S a1 , S a2 A fault will cause the P level to change to the O level, and the actual midpoint current changes from -i a becomes 0, so the vector state V 1P It can be used to determine whether the P level of phase A is forced to transfer to the O level; among the small vectors, the N-type of V1 and the P-type of V4 satisfy the first case analyzed in the previous section: that is, the switch states of the two bridge arms B and C are both 1 or -1. At this time, the midpoint current is only related to the switch state of phase A and the current of phase A. By detecting whether the actual midpoint current is zero, it can be determined whether the V 1N 、V 4P In the state, it is determined whether the [O] state of phase A is transferred to [P] or [N]; the vector V8, V 11 With V 1N 、V 4P Similarly, this is the first case in the A-phase characteristic vector set; the large vector is divided into A-phase P and A-phase N. In the normal state, the corresponding midpoint current is 0. When the P level or N level is transferred to the O level, the actual output midpoint current is i a , by judging whether the midpoint current is i a The characteristic vector sets selected by phases B and C are the same as those of phase A.

[0150] Table 6

[0151]

[0152]

[0153] Table 7

[0154]

[0155]

[0156] Since both paths [OU] and [OL] are at zero level, and i o is about the switching function S x The absolute value function, [P] and [N] two states in i o The above table shows that oOnly the information of the transition from zero level to high (low level) can be obtained, and the specific state cannot be distinguished. Therefore, in order to further obtain the specific path transfer information, it is necessary to consider the generation method of PWM pulse signal by the same phase carrier stacking modulation. According to the working principle analysis in step S1, the switching mode of the switch sequence satisfies [OU]→[P]→[OU], [N]→[OL]→[N]. If the duty cycle modulation wave v of the three phases A, B, and C is introduced in the single-tube fault diagnosis a *、v b *、v c *, then within the unit switching cycle, the position (i.e. polarity) of the duty cycle modulation wave can be judged to determine whether the modulation wave is compared with the upper carrier or the lower carrier within this cycle: if it is compared with the upper carrier, then the commutation mode of the bridge arm is [OU]→[P]→[OU]; if it is compared with the lower carrier, then the commutation mode of the bridge arm is [N]→[OL]→[N]. On this basis, referring to the state switching mode of normal operation of each phase bridge arm, combined with the fault characteristics of the above midpoint current under the vector set, the specific state transfer mode (i.e. one of [OU]→[P], [OU]→[N], [OL]→[P], [OL]→[N]) can be inferred.

[0157] In summary, the principle and process of single-tube fault diagnosis of three-phase three-level ANPC rectifier based on state transfer is as follows: Fig.13 After the abnormal state transfer information is obtained by comparing the reference midpoint current with the actual midpoint current, the corresponding relationship between the state transfer and the switch device diagnosis result is: F AP =1 is judged as S a1 Fault, diagnostic signal F a1 =1; F AN =1 is judged as S a4 Fault, diagnostic signal F a4 =1; F AO1N =1 is judged as S a2 Fault, diagnostic signal F a2 =1; F AO2P =1 is judged as S a3 Fault, diagnostic signal F a3 =1; F AO1P =1 is judged as S a5 Fault, diagnostic signal F a5 =1; F AO2N =1 is judged as S a6 Fault, diagnostic signal F a6 =1.

[0158] In this embodiment, the specific process of classifying the fault types and analyzing the fault characteristics in step S4 is as follows:

[0159] There are 6 switching devices in each bridge arm of the three-phase three-level ANPC rectifier. Therefore, there are There are various permutations and combinations. The following also takes the A-phase bridge arm as an example to analyze the characteristics under double-tube fault.

[0160] First, the two switching devices work in different phase current directions. Fig.14 As shown, Fig.14 For S a1 +S a3 The changes of current flow path and output level under double-tube open circuit fault, where S a1 Fault-affected phase current i a <0 [P] state, S a3 Fault-affected phase current i a >0 when [N] state and [OL] state.

[0161] when i a <0, S a3 The fault will not cause the normal working state of the circuit to change abnormally, so only S a1 The open circuit fault causes the current in the normal [P] state to flow through S a6 , anti-parallel diode D a3 and anti-parallel diode D a5 , S a2 Two current paths, state [P] changes to [O].

[0162] when i a >0, S a1 The fault will not cause the normal working state of the circuit to change abnormally. If the bridge arm output [N] is normally controlled, then S a3 The fault causes the current to flow through S in the [N] state. a5 , anti-parallel diode D a2 The state [N] changes to [OU], and according to the switching principle, the next normal state is [OL], at which time the current is forced to pass through the anti-parallel diode D a1 and D a2 Outflow, state [OL] changes to [P].

[0163] It can be seen that S a1 and S a3 The fault affects the normal operation of the bridge arm in the negative half cycle and the positive half cycle respectively. When the two switching devices in the same bridge arm work in different phase current directions, the abnormal state of the bridge arm caused by the simultaneous fault is equivalent to the abnormal state transfer caused by the failure of two single tubes at different times, that is, it can be regarded as a single tube fault of the corresponding switching device for processing. The double tube fault types that meet the above conditions are S a1 +Sa3 Fault, S a1 +S a4 Fault, S a1 +S a5 Fault, S a2 +S a3 Fault, S a2 +S a4 Fault, S a2 +S a5 Fault, S a3 +S a6 Fault, S a4 +S a6 Fault, S a5 +S a6 There are 9 types of faults in total.

[0164] S a1 +S a2 Fault, S a1 +S a6 Fault, S a2 +S a6 Fault, S a3 +S a4 Fault, S a3 +S a5 Fault, S a4 +S a5 All faults occur when two switching devices operate in the same phase current direction. Each fault type will be analyzed one by one below.

[0165] like Fig.15 Shown is S a1 +S a2 The current flow path and output level change under open circuit fault. a <0, if the output state of the A-phase bridge arm is normally controlled to be [P], then S a1 +S a2 After an open circuit fault occurs, the current cannot flow from the upper half bridge arm and can only flow through S a6 , anti-parallel diode D a3 The state [P] changes to [OL]; the output state of the A-phase bridge arm under normal control is [OU], S a1 +S a2 The open circuit fault causes the current to flow through the anti-parallel diode D a3 and D a4 The actual output state of the bridge arm is [N]. a >0, due to S a1 , S a2 It only participates in the commutation between the bridge arm [OU]-[P]-[OU], during which the current mainly flows through the anti-parallel diode D a1 and D a2 , Sa1 +S a2 An open circuit fault will not cause the bridge arm output to deviate from the normal value. a1 +S a2 The impact of open circuit fault on rectifier output and S a2 Same as open circuit fault.

[0166] like Fig.16 Shown is S a1 +S a6 The current flow path and output level change under open circuit fault. a <0, S a1 Open circuit fault makes the current unable to flow through S in the normal [P] state. a1 , S a2 Circulation, plus S a6 Fault, the current can only flow through S a2 , anti-parallel diode D a5 Freewheeling, the normal switching process within a unit switching cycle is destroyed, the actual output of the bridge arm is 0; S a6 Open circuit faults disrupt the switching process In state [OL], the current can only flow through the anti-parallel diode D a3 and D a4 The actual output of the bridge arm in a unit switching cycle is -U dc / 2.

[0167] like Fig.17 Shown is S a2 +S a6 The current flow path and output level change under open circuit fault. a <0, if the normal control bridge arm is in the [P] state, S a2 The fault makes the A bridge arm unable to connect to the DC bus, and due to S a6 Also fault, the current can only flow through the anti-parallel diode D a3 and D a4 Continue current, the operating state [P] changes to [N], and when the next state in the unit switching cycle is normally controlled to [OU], the operating state changes from [OU] to [N]; if the bridge arm in the normal control state is Switching, in the [OL] state, negative current can still only pass through the anti-parallel diode D a3 and D a4 The [OL] state is replaced by the [N] state. a2 +S a6 Under fault conditions, the faulty bridge arm cannot output positive and zero levels normally. a <0 when the bridge arm output voltage is always -U dc / 2.

[0168] like Fig.18 Shown is S a3 +S a4 The current flow path and output level change under open circuit fault. a >0, if the normal control A bridge arm output state is [N], then S a3 +S a4 After an open circuit fault occurs, the current cannot flow from the lower half bridge arm, and the current flows through S a5 , anti-parallel diode D a2 The state [N] changes to [OU]; when the normal output state of bridge arm A is [OL], S a3 The open circuit fault causes the current to flow through S a1 and S a2 The anti-parallel diode of the bridge arm actually outputs the state [P]. a <0, due to S a3 , S a4 It only participates in the commutation between the bridge arm [N]-[OL]-[N], during which the current mainly flows through the anti-parallel diode D a3 and D a4 , S a3 +S a4 An open circuit fault will not cause the bridge arm output to deviate from the normal value. a3 +S a4 The impact of open circuit fault on rectifier output and S a3 Same as open circuit fault.

[0169] like Fig.19 , Fig. 20 Shown is S a3 +S a5 The current flow path and output level change under open circuit fault. a >0, if the normal control bridge arm is in [N] state, S a3 The fault makes the A phase bridge arm unable to connect to the DC bus, and due to S a5 If a fault occurs, the current can only flow through the anti-parallel diode D a1 and D a2 The running state [N] changes to [P] when the next state in the unit switching cycle is normally controlled to [OL], and the running state changes from [OL] to [P]. If the bridge arm in the normal control state is in Switching, in the [OU] state, the forward current can still only pass through the anti-parallel diode D a1 and D a2 The [OU] state is replaced by the [P] state. a3 +S a5 Under fault conditions, the fault phase bridge arm cannot output negative level and zero level normally. When the phase current i a<0 when the bridge arm output voltage is always U dc / 2.

[0170] like Fig.21 , Fig. 22 Shown is S a4 +S a5 The current flow path and output level change under open circuit fault. a >0, S a4 The open circuit fault causes the bridge arm to actually output zero level in the normal [N] state, but at this time due to S a5 Also faulty, current can only flow through S a3 , anti-parallel diode D a6 , the normal switching process within a unit switching cycle is destroyed, the actual output of the bridge arm is 0; S a5 Open circuit faults disrupt the switching process In state [OU], the current flows through the anti-parallel diode D a1 and D a2 The actual output of the bridge arm in a unit switching cycle is U dc / 2.

[0171] In this embodiment, the diagnosis principle of the double-tube open circuit fault in step S5 is as follows:

[0172] From the fault analysis in step S4, it can be seen that 9 fault types among the 15 double-tube fault combinations can be equivalent to single-tube faults for fault location. Therefore, the following only analyzes the diagnosis principle of 6 double-tube fault types working in the same current direction.

[0173] According to the characteristic analysis of the above six fault types in step S4, the transfer process of the corresponding bridge arm state is determined when the phase current direction is fixed. Therefore, the state transfer diagnostic signals under different fault types can be summarized as shown in Table 8. Table 8 is a single-phase double-tube fault state transfer table.

[0174] Table 8

[0175]

[0176] As can be seen from Table 8, the abnormal state transfer combinations caused by the six fault types are all different, so the fault diagnosis method based on state transfer will not cause misdiagnosis. And because the fault occurs in the same bridge arm, the fault characteristics based on the midpoint current can still distinguish the abnormal state transfer caused by these fault types. Unlike single-tube faults, double-tube faults often cause multiple state transfers, so the fault location process is not determined by a single state transfer diagnostic signal.

[0177] The phase current i a <0 time Sa1 +S a6 Taking the double-tube fault as an example, this type of fault will produce two abnormal state transition processes: [P]→[OU] and [OL]→[N]. The state transition of [P]→[OU] belongs to the F of the corresponding [P]→[O]. AP A diagnostic signal, so if F is detected AP =1, it is judged that an abnormal state transition from [P] to [OU] occurs, S a1 Failure; Similarly, the [OL]→[N] state transition process uniquely corresponds to F AO2N Diagnostic signal, if F is detected AO2N =1, it is judged that an abnormal state transition from [OL] to [N] occurs, S a6 Fault.

[0178] It is worth noting that although the two switching devices fail at the same time, the fault location process is also carried out one by one under the same current direction in the same bridge arm, that is, the diagnostic signals F of the two switching devices are AP and F AO2N The jump time of the fault signal is different, so it is feasible to adopt the above diagnostic method. The diagnostic methods of the other five fault types are the same. It is only necessary to locate the faulty device according to whether the diagnostic signal corresponding to the abnormal state transition jumps.

[0179] In summary, the present invention takes the A-phase bridge arm as an example to analyze the working state of the three-phase three-level active midpoint clamped rectifier under a single-tube open-circuit fault; analyzes the midpoint current of a specific switch combination under a single-tube fault, and then obtains the corresponding fault characteristics; derives the single-tube fault diagnosis principle through the abnormal state transfer occurring during the fault process and the corresponding midpoint current change; divides and analyzes the double-tube fault type according to the influence of the phase current direction on the double-tube fault; and derives the double-tube fault diagnosis result according to the influence of the double-tube fault on the switch state. The present invention uses the midpoint current of the ANPC rectifier as the fault characteristic quantity, and on the basis of analyzing the existing diagnostic strategy, studies a three-phase three-level active midpoint clamped rectifier fault diagnosis including a double-tube open-circuit fault, associates various fault conditions with the abnormal transfer of the switch state under the fault, and makes full use of the state transfer characteristics of the ANPC topology structure. Without adding additional sensors, the single-tube fault and the double-tube fault are quickly and effectively located, and the hardware cost is low and easy to implement.

Claims

1. A three-level active neutral point clamped rectifier fault diagnosis method based on state transfer, characterized in that: The following steps are involved: S1. Analyze the working principle of the three-phase three-level ANPC rectifier, and analyze the working state of the three-phase three-level ANPC rectifier under a single-tube open-circuit fault, and obtain the abnormal state transfer that occurs during the fault process. The abnormal state transfer includes [P]→[O], [N]→[O], [OU]→[P], [OU]→[N], [OL]→[P], [OL]→[N]; The specific circumstances of abnormal state transfer are as follows: F sa1 =1 will force the state [P] to transfer to the state [OU], [OL], and [OU] and [OL] both correspond to the bridge arm output zero level, so F sa1 =1 can be summarized as the transition from state [P] to state [O]; F sa4 =1 will force state [N] to move to state [O]; F sa2 =1 Force state [P] to state [OL], state [OU] to [N]; F sa3 =1, then force state [N] to move to state [OU], state [OL] to move to state [P]; F sa5 =1 Force state [OU] to transfer to state [P]; F sa6 =1 forces state [OL] to transition to state [N], where F sax =1 indicates that Sax has an open circuit fault, x=1,2,3,4,5,6, state [O] indicates that the bridge arm output including state [OU] and state [OL] is zero level; Sax indicates that the switch device x=1,2,3,4,5,6; S2. Analyze the midpoint current of the three-phase three-level ANPC rectifier under normal working conditions, and derive the variation characteristics of the midpoint current under different switch combinations after a single tube fault occurs; S3. The diagnosis principle of single-tube fault is derived through the abnormal state transfer occurring during the fault process and the corresponding midpoint current change characteristics; S4. Based on the phase current direction of the three-phase three-level ANPC rectifier, all fault types of double-tube faults in the same bridge arm are divided, and the fault characteristics under the corresponding double-tube faults are analyzed; S5. Extend the single-tube fault diagnosis principle to the double-tube fault in the same bridge arm, diagnose the double-tube fault, and complete the fault diagnosis of the three-level active neutral point clamped rectifier; In step S5, double-tube fault diagnosis is performed, which is specifically as follows: According to the fault characteristics of the double-tube fault obtained by analyzing step S4, a state transition diagnosis signal under different fault types is obtained; According to whether the state transfer diagnosis signal jumps under different fault types, all faulty switch device combinations containing double-tube faults are located to complete the diagnosis of the double-tube faults.

2. The fault diagnosis method of a three-level active neutral point clamped rectifier based on state transfer according to claim 1, characterized in that: The expression of the midpoint current of the three-phase three-level ANPC rectifier in the normal state in step S2 is as follows: i o =(1-|S a |)i a +(1-|S b |)i b +(1-|S c |)i c Among them, i o Indicates the midpoint current of the DC side, i a 、i b and i c Represents the three-phase transient current, S x represents the switching function, v x0 Indicates the output voltage of the three-phase three-level ANPC rectifier, U dc Indicates the DC side voltage of the rectifier.

3. The fault diagnosis method of a three-level active neutral point clamped rectifier based on state transfer according to claim 1, characterized in that: Through the abnormal state transition that occurs during the fault process and the corresponding midpoint current change characteristics, the diagnosis principle of single-tube fault is derived, which is as follows: Through the abnormal state transfer occurring during the fault process and the corresponding midpoint current variation characteristics, the duty cycle modulation waves of each three phases are introduced into the single-tube fault diagnosis, and the diagnosis principle of the single-tube fault is obtained.

4. The three-level active neutral point clamped rectifier fault diagnosis method based on state transfer according to claim 1, characterized in that: The conditions for classifying all fault types of double-tube faults in the same bridge arm are as follows: When two switching devices in the same bridge arm operate in different or the same phase current directions, the abnormal state of the bridge arm caused by their simultaneous failure is equivalent to the abnormal state transfer caused by the failure of two single tubes at different times, and is regarded as a single tube failure in the corresponding switching device.

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