Three-level rectifier open-circuit fault diagnosis method and system, and storage medium

Abstract

The disclosure provides a three-level rectifier open-circuit fault diagnosis method, system and storage medium, which uses the deviation between the actual reference voltage and the ideal reference voltage after coordinate transformation as a diagnostic variable, realizes the switch open-circuit fault diagnosis of the rectifier under the operation of unit power factor. The diagnostic threshold considering the calculation error and the counter are designed, which improves the accuracy of the diagnostic method. At the same time, the calculation of the diagnostic variable and the threshold does not involve accurate mathematical modeling, so the diagnostic method is not affected by the modeling accuracy error of the system, and has higher reliability. In addition, a unified diagnostic rule is designed to realize single switch fault and multi-switch fault diagnosis, so that the diagnostic method has the advantages of strong diagnostic ability and low diagnostic complexity.

Description

Technical Field

[0001] This disclosure relates to the field of fault diagnosis technology for power electronic equipment, and more specifically to a method, system and storage medium for diagnosing open-circuit faults in a three-level rectifier. Background Technology

[0002] Controllable three-phase rectifiers are a critical component of power systems, such as motor drives, uninterruptible power supplies (UPS) systems, and battery charging systems. Their failure can significantly impact system power quality and potentially damage other equipment, causing substantial economic and material losses. Therefore, researchers have conducted extensive studies on fault diagnosis of rectifier power switching devices. Since rectifiers primarily provide power to loads, they typically operate at unity power factor.

[0003] Compared to traditional two-level rectifiers, three-level rectifiers offer lower switching losses, better harmonic performance, and the ability to withstand higher voltage stress, making them widely used in high-power medium-voltage systems. However, the large number of power switching devices makes fault diagnosis of three-level rectifiers more challenging, especially multi-switch fault diagnosis. Currently, research on single-switch fault diagnosis methods for three-level rectifiers is relatively in-depth, but these methods cannot be directly applied to multi-switch fault diagnosis. These diagnostic methods can be improved by adding diagnostic variables and designing complex diagnostic rules to make them suitable for multi-switch fault diagnosis, but this increases the complexity and unreliability of the diagnostic algorithm.

[0004] Therefore, achieving simple and reliable multi-switch open-circuit fault diagnosis in a three-level rectifier operating at unity power factor has certain research value. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the above and / or other problems in the prior art, and to provide a method for diagnosing open-circuit faults in a three-level rectifier, which can identify and locate open-circuit faults in multiple power switching devices online, and has the characteristics of simple implementation, high reliability and low cost.

[0006] To achieve the above objectives, this disclosure provides a method for diagnosing open-circuit faults in a three-level rectifier. The three-level rectifier converts the input grid-side voltage into a DC voltage and includes three bridge arms, each including multiple switching devices. The method for diagnosing open-circuit faults in a three-level rectifier is characterized by comprising:

[0007] The first step is to obtain information related to the grid-side voltage and the DC voltage;

[0008] The second step is to calculate the diagnostic information, including reference voltage and reference current, based on the acquired information and the preset target.

[0009] The third step is to calculate the deviation between the reference voltage and the ideal reference voltage based on the phase difference between the grid-side voltage and the input side of the three-level rectifier, and obtain the reference voltage deviation.

[0010] The fourth step is to use the reference voltage deviation as a diagnostic variable and compare it with the diagnostic threshold calculated based on the phase difference.

[0011] The fifth step is to accumulate the number of times the absolute value of the diagnostic variable exceeds the diagnostic threshold, and determine whether the three-level rectifier has an open circuit fault.

[0012] The sixth step, in the presence of an open-circuit fault, is to locate the faulty bridge arm among the three bridge arms based on the diagnostic variables and the number of absolute values ​​of the diagnostic variables exceeding the diagnostic threshold; and

[0013] The seventh step involves performing fault-tolerant control by changing the reference current, and further locating the faulty switching device in the faulty bridge arm based on the diagnostic variables obtained therefrom.

[0014] In some embodiments, the three-level rectifier is a three-phase three-level rectifier that converts three-phase alternating current into direct current. The bridge arms correspond to any one of the three phases, and each phase's bridge arm includes an upper bridge arm and a lower bridge arm, each having two series-connected switching devices. The three-phase grid-side voltage is input to the connection between the upper bridge arm and the lower bridge arm of the corresponding phase. The intermediate connection of the two switching devices in each upper or lower bridge arm is connected to the midpoint of the DC side of the three-level rectifier via a clamping diode.

[0015] In some embodiments, the diagnostic information required in the second step includes: the X-phase reference voltage V. X [k]; Phase θ of the X-phase grid side voltage X [k];Grid-side voltage E in the DQ coordinate system D [k] and E Q [k]; Reference current I in the DQ coordinate system DR [k] and I QR [k]; grid-side voltage frequency f; and grid-side equivalent inductance L, where X is any one of phases A, B, and C corresponding to the three-phase AC power, and k is the sampling time.

[0016] In some embodiments, in the third step, the X-phase reference voltage V is... X [k] is normalized to obtain the normalized actual reference voltage V. XN [k]; Based on the phase θ of the X-phase grid side voltage X[k] and the phase difference Δθ[k] between the grid-side voltage and the input side of the three-level rectifier, calculate the normalized ideal reference voltage under no open-circuit fault conditions. The X-phase reference voltage deviation ΔV is calculated using the following formula. XN [k]:

[0017]

[0018] In some embodiments, the phase difference Δθ[k] is calculated according to the following formula:

[0019]

[0020] In some embodiments, the ideal reference voltage Calculate according to the following formula:

[0021]

[0022] In some embodiments, in the fourth step, the X-phase reference voltage deviation ΔV is... XN [k] Perform αβ coordinate transformation to obtain the diagnostic variable ΔV as follows. αN [k] and ΔV βN [k]:

[0023]

[0024]

[0025] Where, ΔV AN [k] is the reference voltage deviation of phase A.

[0026] ΔV BN [k] is the reference voltage deviation of phase B.

[0027] ΔV CN [k] is the reference voltage deviation of phase C.

[0028] In some embodiments, in the fourth step, the diagnostic threshold ΔV is calculated according to the following formula. TH [k]:

[0029] ΔV TH [k]=2sin(Δθ Error [k] / 2)

[0030] Where, Δθ Error [k] represents the calculation error of the phase difference Δθ[k], expressed by the following formula:

[0031] Δθ Error [k]=λΔθ[k]

[0032] Wherein, λ is a proportional setting coefficient greater than 0.

[0033] In some embodiments, in the fifth step, the cumulative diagnostic variable ΔV αN [k] and ΔV βN [k] Exceeds the diagnostic threshold ΔV TH The number of [k] N α [k] and N β [k], when |ΔV αN [k]|>ΔV TH When [k], then N α The value of [k] is incremented by 1, otherwise N is incremented. α [k] value is cleared to zero; when |ΔV βN [k]|>ΔV TH When [k], then N β The value of [k] is incremented by 1, otherwise N is incremented. β The [k] value is cleared to zero.

[0034] In some embodiments, the sixth step involves locating the faulty bridge arm:

[0035] If |ΔV αN |>|ΔV βN |and ΔV αN If [k] > 0, then there is an open circuit fault in the upper arm of phase A;

[0036] If |ΔV αN |>|ΔV βN |and ΔV αN If [k] < 0, then there is an open circuit fault in the lower arm of phase A;

[0037] If |ΔV aN |<|ΔV βN |、ΔV αN [k]<0 and ΔV βN If [k] > 0, then there is an open circuit fault in the upper arm of phase B;

[0038] If |ΔN αN |<|ΔV βN |、ΔV αN [k]>0 and ΔV βN If [k] < 0, then there is an open circuit fault in the lower arm of phase B;

[0039] If |ΔV aN |<|ΔV βN |、ΔV αN [k]<0 and ΔV βN If [k] < 0, then there is an open circuit fault in the upper arm of phase C;

[0040] If |ΔV αN |<|ΔV βN |、ΔVαN [k]>0 and ΔV βN If [k] > 0, then there is an open circuit fault in the lower arm of phase C.

[0041] In some embodiments, in each upper or lower arm of the three-level rectifier, the switching device located inside the upper or lower arm is referred to as the inner switch, and the switching device located outside the upper or lower arm is referred to as the outer switch. The fault-tolerant control is achieved by changing the Q-axis reference current I. QR [k] Implement fault tolerance for external switches, and determine the actual reference voltage V. XN [k] Whether the distortion disappears is used to locate the fault switch.

[0042] In some embodiments, the Q-axis reference current I QR [k] is changed according to the following formula:

[0043] I' QR [k] = -I DR [k]tanΔθ

[0044] Based on the modified Q-axis reference current I′ QR [k], if the actual reference voltage V XN If the distortion disappears, it is determined to be an external switch fault; otherwise, it is an internal switch fault.

[0045] In some embodiments, when an open-circuit fault exists in the upper arm of phase A, if |ΔV αN [k]|≤ΔV TH [k] indicates that the external switch of the upper bridge arm of phase A has an open circuit fault;

[0046] When there is an open circuit fault in the upper arm of phase A, if |ΔV αN [k]|>ΔV TH [k] indicates that the switch inside the upper arm of phase A has an open circuit fault;

[0047] When there is an open circuit fault in the lower arm of phase A, if |ΔV αN [k]|>ΔV TH [k] indicates that there is an open circuit fault in the switch of the lower bridge arm of phase A;

[0048] When there is an open circuit fault in the lower arm of phase A, if |ΔV αN [k]|≤ΔV TH [k] indicates that the external switch of the lower bridge arm of phase A has an open circuit fault;

[0049] When there is an open circuit fault in the upper arm of phase B, if |ΔV βN [k]|≤ΔV TH [k] indicates that the external switch of the upper bridge arm of phase B has an open circuit fault;

[0050] When there is an open circuit fault in the upper arm of phase B, if |ΔV βN [k]|>ΔV TH [k] indicates that the switch inside the upper arm of phase B has an open circuit fault;

[0051] When there is an open circuit fault in the lower arm of phase B, if |ΔV βN [k]|>ΔV TH [k] indicates that there is an open circuit fault in the switch inside the lower arm of phase B;

[0052] When there is an open circuit fault in the lower arm of phase B, if |ΔV βN [k]|≤ΔV TH [k] indicates that the external switch of the lower bridge arm of phase B has an open circuit fault;

[0053] When there is an open circuit fault in the upper arm of phase C, if |ΔV βN [k]|≤ΔV TH [k] indicates that the external switch of the upper bridge arm of phase C has an open circuit fault;

[0054] When there is an open circuit fault in the upper arm of phase C, if |ΔV βN [k]|>ΔV TH [k] indicates that the switch inside the upper arm of phase C has an open circuit fault;

[0055] When there is an open circuit fault in the lower arm of phase C, if |ΔV βN [k]|>ΔV TH [k] indicates that the switch in the lower arm of phase C has an open circuit fault;

[0056] When there is an open circuit fault in the lower arm of phase C, if |ΔV βN [k]|≤ΔV TH [k] indicates an open circuit fault in the external switch of the lower arm of phase C.

[0057] In some embodiments, an eighth step is also included, which involves determining the fault range of the faulty switch and repeating steps three through seven outside the fault range to locate other faulty switches.

[0058] In some embodiments, the fault range of the fault switch is pre-stored in the form of a mapping table.

[0059] In another aspect, this disclosure provides a three-level rectifier open-circuit fault diagnosis system. The three-level rectifier converts an input grid-side voltage into a DC voltage and includes three bridge arms, each including multiple switching devices. The system is characterized by comprising: an information acquisition module for acquiring information related to the grid-side voltage and the DC voltage; an information preprocessing module, which calculates diagnostic information including a reference voltage and a reference current based on the information and a preset target; and a calculation module that calculates the phase difference between the grid-side voltage and the input side of the three-level rectifier, and calculates a diagnostic threshold and the relationship between the reference voltage and an ideal reference voltage based on the phase difference. The deviation is the reference voltage deviation, which is used as a diagnostic variable; an open-circuit fault determination module accumulates the number of times the absolute value of the diagnostic variable exceeds the diagnostic threshold to determine whether an open-circuit fault exists in the three-level rectifier; a fault arm location module locates the faulty arm among the three arms based on the diagnostic variable and the number of times the absolute value of the diagnostic variable exceeds the diagnostic threshold; and a fault switch location module performs fault-tolerant control by changing the reference current, and further locates the faulty switching device, i.e., the fault switch, in the faulty arm based on the diagnostic variable obtained therefrom.

[0060] In another aspect, this disclosure provides a computer-readable storage medium storing a computer program, characterized in that the three-level rectifier open-circuit fault diagnosis method described in any of the preceding claims is implemented by executing the computer program.

[0061] Compared with the prior art, this disclosure has the following beneficial technical effects:

[0062] (1) The signals required for the calculation of diagnostic variables and diagnostic thresholds in this disclosure are all from the existing voltage, current and switching signals in the three-level rectifier system, and do not involve precise mathematical modeling. Therefore, compared with the traditional diagnostic method that uses additional sensors, the diagnostic method proposed in this disclosure is lower in cost. Compared with the traditional model-based diagnostic method, the diagnostic method proposed in this disclosure is not affected by the system modeling accuracy error and has higher reliability.

[0063] (2) By using the fault range of the known fault switch in the eighth step, the interference of multiple switch faults on diagnostic variables can be eliminated. Therefore, the diagnosis of multiple switch faults can be achieved by using the same steps as the diagnosis of single switch faults. Compared with the existing multiple switch fault diagnosis methods, fewer diagnostic variables are required and the diagnostic rules are simpler. Attached Figure Description

[0064] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the embodiments of the present disclosure to explain the disclosure and do not constitute a limitation thereof. In the drawings:

[0065] Figure 1 This is a topology diagram of a three-phase three-level rectifier according to an embodiment of this disclosure;

[0066] Figure 2 This is a flowchart of an open-circuit fault diagnosis method for a three-phase three-level rectifier according to an embodiment of this disclosure;

[0067] Figure 3 This is a diagnostic result diagram of a double-switch open-circuit fault in a three-phase three-level rectifier with unity power factor according to an embodiment of this disclosure.

[0068] Figure 4 This is a block diagram of the control system of a three-phase three-level rectifier according to an embodiment of this disclosure;

[0069] Figure 5 This is a block diagram of the hardware structure of a control system for a three-phase three-level rectifier according to an embodiment of this disclosure. Detailed Implementation

[0070] The following describes specific embodiments of this disclosure. It should be noted that, in order to provide a concise description, this specification cannot exhaustively describe all features of the actual embodiments. It should be understood that, in the actual implementation of any embodiment, just as in any engineering or design project, various specific decisions are often made to achieve the developer's specific goals and to meet system-related or business-related constraints, and this can change from one embodiment to another. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this disclosure, changes in design, manufacturing, or production based on the technical content disclosed in this disclosure are merely conventional technical means and should not be construed as insufficient content of this disclosure.

[0071] Unless otherwise defined, the technical or scientific terms used in the claims and description shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar words used in this patent disclosure and the claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. The terms “an” or “a” and similar words do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar words mean that the element or object preceding “comprising” or “including” encompasses the element or object listed following “comprising” or “including” and its equivalents, and do not exclude other elements or objects. The terms “connected,” “coupled,” or “linked” and similar words are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections.

[0072] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions. Similarly, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0073] In the description of the embodiments of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0074] The following describes in detail, with reference to the accompanying drawings, a method for diagnosing open-circuit faults in a three-level rectifier according to embodiments of the present disclosure.

[0075] The embodiments disclosed herein are illustrated using a three-phase three-level rectifier as an example.

[0076] Figure 1 This is a topology diagram of a three-phase three-level rectifier according to an embodiment of this disclosure. This three-level rectifier is a neutral point clamped (NPC) type three-level rectifier, used to convert input AC power into DC power. In this circuit diagram, each phase of the three-phase bridge arm consists of four switching devices S. X1 S X2 S X3 S X4The four switching devices are connected in series (X = A, B, C). The midpoint of the connection between them serves as the input terminal for the three-phase grid voltage. The midpoints of the two switching devices in each phase's upper and lower arms are each connected to the DC-side midpoint via a clamping diode to output a 0-level voltage. By controlling the on and off times of the 12 switching devices, real-time control of the DC-side voltage can be achieved.

[0077] exist Figure 1 In the middle, E A [k]、E B [k]、E C [k] represents the grid-side three-phase voltage, I A [k]、I B [k]、I C [k] represents the three-phase AC current, L represents the grid-side equivalent inductance, C1 and C2 represent the DC-side upper and lower capacitances, and V DC1 [k]、V DC2 [k] represents the voltage across the upper and lower capacitors C1 and C2 on the DC side. S A1 S A2 S A3 S A4 S B1 S B2 S B3 S B4 S C1 S C2 S C3 S C4 The 12 switching devices that make up the three bridge arms of this three-level rectifier are S A1 S A2 Forming the upper arm of phase A, S A3 S A4 Forming the lower arm of phase A, S B1 S B2 Forming the upper arm of phase B, S B3 S B4 Forming the lower arm of phase B, S C1 S C2 Forming the upper arm of phase C, S C3 S C4 It forms the lower arm of phase C.

[0078] In a three-level rectifier, each bridge arm includes switching devices. Switches located inside the bridge arm are designated as inner switches, and those located outside the bridge arm are designated as outer switches. Specifically, the uppermost switch S in the bridge arm... X1 and the bottommost switching transistor S X4 For external switching devices, the switching transistor S in the middle of the bridge arm X2 and switching transistor S X3 It is an internal switching device.

[0079] D A1 D A2 D A3 D A4 D B1 D B2 D B3 D B4 D C1 D C2 D C3 D C4 D represents the clamping diode corresponding to each switching device. CA1 D CA2 D CB1 D CB2 D CC1 D CC2 This indicates that the clamping diode at the midpoint of the connection between the two switching devices in the upper and lower arms of each phase is connected to the DC side midpoint.

[0080] Figure 2 This is a flowchart of an open-circuit fault diagnosis method for a three-phase three-level rectifier according to an embodiment of this disclosure.

[0081] The open-circuit fault diagnosis method for three-level rectifiers of the present invention mainly includes the following steps:

[0082] The first step, S1, is to obtain information related to grid-side voltage and DC voltage.

[0083] Using a sampling circuit, the three-phase three-level rectifier is sampled at sampling time k to obtain the grid-side three-phase voltage E obtained from the sampling of the three-phase three-level rectifier. A [k]、E B [k]、E C [k], AC three-phase current I A [k]、I B [k]、I C [k] and DC side upper and lower capacitor voltages V DC1 [k]、V DC2 [k], and the equivalent inductance L on the grid side are fed into the voltage-current dual closed-loop control system (hereinafter referred to as the control system).

[0084] The second step, S2, involves calculating the diagnostic information, including reference voltage and reference current, based on the acquired information and the preset target.

[0085] The control system performs calculations based on the given control objective, and can obtain the phase θ of the three-phase grid-side voltage. A [k]、θ B [k]、θ C [k], angular velocity of grid-side voltage ω=2πf, grid-side voltage E in DQ coordinate system D [k] and EQ Reference AC current I in [k], DQ coordinate system DR [k] and I QR [k], and output the three-phase reference voltage V A [k]、V B [k]、V C [k] to the Space Vector Pulse Width Modulation (SVPWM) module. Here, "grid side" refers to the side of the power grid. The DQ coordinate system is a two-phase rotating coordinate system that follows the rotation of the rectifier's internal structure, with the electromagnetic field direction as the D-axis and the armature magnetic field direction as the Q-axis. The D-axis and Q-axis are orthogonal to each other. The Space Vector Pulse Width Modulation (SVPWM) module is a modulation strategy widely used in three-level NPC topologies. It uses the power switching devices of the three-phase motor to form a specific switching pattern, making the three-phase current waveform as close as possible to an ideal sine wave, thereby maximizing the stability of the output DC voltage. The modulation module calculates the duty cycle of the switching signal of each power switching device based on a given switching cycle to control the on and off of all switches, thus enabling the rectifier to operate according to the control objective. The control system uses the diagnostic information obtained to calculate diagnostic variables and diagnostic thresholds.

[0086] In the third step S3, based on the phase difference between the grid-side voltage and the input side of the three-level rectifier, the deviation between the reference voltage and the ideal reference voltage is calculated to obtain the reference voltage deviation.

[0087] Taking phase A as an example, first, the reference voltage V of phase A is... A [k] Normalize its amplitude to obtain the normalized actual reference voltage V. AN [k].

[0088] Then calculate the normalized ideal reference voltage for phase A without an open-circuit fault.

[0089]

[0090] Where Δθ[k] is the phase difference between the grid-side voltage and the rectifier input voltage, calculated by the following formula:

[0091]

[0092] Then according to V AN [k] and Calculate the reference voltage deviation ΔV of phase A. AN [k]:

[0093]

[0094] Similarly, calculate the reference voltage deviation ΔV of phase B.BN [k] and C-phase reference voltage deviation ΔV CN [k].

[0095] In the fourth step S4, the reference voltage deviation is used as a diagnostic variable and compared with the diagnostic threshold calculated based on the phase difference.

[0096] Specifically, the diagnostic variable ΔV in the αβ coordinate system is calculated. αN [k] and ΔV βN [k]:

[0097]

[0098]

[0099] In this system, the αβ coordinate system refers to a two-phase stationary coordinate system, where the α-axis and β-axis are orthogonal to each other, and the positive direction of the α-axis is in the same direction as the A-direction in the ABC three-phase stationary coordinate system. The coefficients of the coordinate transformation are derived from the well-known Clarke transformation to ensure that the transformation is of equal amplitude. Applying this transformation to use the transformed reference voltage deviation as a diagnostic variable reduces the number of variables and the amount of subsequent calculations.

[0100] Diagnostic threshold ΔV TH [k] = 2sin(λΔθ[k] / 2). Where λ is a proportional setting coefficient greater than 0, which is 1 in this example.

[0101] In the fifth step S5, the number of diagnostic variables whose absolute values ​​exceed the diagnostic threshold is accumulated to determine whether the three-level rectifier has an open-circuit fault.

[0102] Using counter N α [k] and N β [k] The number of samples where the cumulative diagnostic variable exceeds the threshold. When |ΔV αN [k]|>ΔV TH When [k], then N α The value of [k] is incremented by 1, otherwise N is incremented. α [k] value is cleared to zero; when |ΔV βN [k]|>ΔV TH When [k], then N β The value of [k] is incremented by 1, otherwise N is incremented. β The [k] value is cleared to zero.

[0103] In the sixth step S6, in the case of an open circuit fault, based on the diagnostic variables and the number of times the absolute value of the diagnostic variables exceeds the diagnostic threshold, the faulty bridge arm is located among the three bridge arms.

[0104] If the counter N α [k] < N and N βIf [k] < N, it indicates that the rectifier does not have an open circuit fault; if N α [k]≥N or N β If [k] ≥ N, it indicates that the rectifier has an open-circuit fault. Here, N is the counter threshold, which is 3 in this example. After determining that the rectifier has an open-circuit fault, the faulty bridge arm can be located according to Table 1, and a fault indicator can be set for the faulty bridge arm. In this embodiment, the fault indicator for the faulty bridge arm is set to 1.

[0105] Table 1 Locating the Faulty Bridge Arm

[0106]

[0107] In step S7, fault-tolerant control is performed by changing the reference current, and the faulty switching device is further located in the faulty bridge arm based on the diagnostic variables obtained therefrom.

[0108] After obtaining the faulty bridge arm information, the Q-axis reference current I is... QR [k] is modified to:

[0109] I' QR [k] = -I DR [k]tanΔθ

[0110] The fault switch can then be located according to Table 2, and a fault indicator can be set for the fault switch. In this embodiment, the fault indicator of the fault switch is set to 1.

[0111] Table 2 Fault Location Switches

[0112]

[0113] Step S8: Determine the fault range of the faulty switch, and repeat steps three through seven outside the fault range to locate other faulty switches.

[0114] When a faulty switch is detected, the fault range of the faulty switch is determined according to Table 3. Table 3 can be pre-stored in the form of a mapping table.

[0115] Table 3. Fault range of known fault switches

[0116]

[0117] Based on the known fault range of the faulty switch, if the fault is outside the range, the aforementioned steps can be repeated to diagnose multiple faulty switches.

[0118] To describe this embodiment more clearly, Figure 3 The diagnostic results for this example are presented, and the parameters used are shown in Table 4.

[0119] Table 4 shows the parameters used in the examples.

[0120]

[0121] like Figure 3 As shown, under unity power factor, S A1 and S C3 in i A An open circuit fault occurred simultaneously during the negative half-cycle.

[0122] After the fault occurs, |ΔV αN [k]|>ΔV TH [k] makes N α [k] is accumulated, and N is added after 3 switching cycles. α [k] = 3. In this example, the counter N... α The threshold for [k] is set to 3, indicating that there is an open circuit fault in the rectifier.

[0123] At the same time, the diagnostic variables satisfy |ΔV αN |>|ΔV βN |and ΔV αN The condition [k] > 0 is met, therefore, according to Table 1, it can be determined that there is an open circuit fault in the upper arm of phase A (step S6).

[0124] Reset Q-axis reference current I QR After [k], it was found that |ΔV αN [k]|≤ΔV TH [k] indicates the actual reference voltage V. XN [k] The distortion has disappeared, and the fault-tolerant control is effective. Therefore, the fault is an open-circuit fault in the external switch of the upper bridge arm of phase A. That is, S A1 An open circuit fault exists; fault flag F. A1 [k] = 1 (Step S7).

[0125] Subsequently, S was determined according to Table 3. A1 The fault range, outside of which N was found β [k]≥3, and simultaneously satisfy |ΔV αN |<|ΔV βN |、ΔV αN [k]>0 and ΔV βN [k] > 0, according to Table 1, there is an open circuit fault in the lower arm of phase C. Because in S... A1 The Q-axis reference current has already been reset during fault diagnosis, so this step does not need to be repeated. (The information can be found via |ΔV...) βN [k]|>ΔV TH [k] indicates that the fault-tolerant control is ineffective, and the actual reference voltage V XN [k] The distortion did not disappear, thus determining that an open-circuit fault occurred in the switch within the lower arm of phase C, enabling the control of S. C3Fault diagnosis (step S8).

[0126] According to the three-level rectifier open-circuit fault diagnosis method of this embodiment, the signals required for calculating the diagnostic variables and diagnostic thresholds all come from the existing voltage, current, and switching signals within the three-level rectifier system, and do not involve precise mathematical modeling. Therefore, compared with traditional diagnostic methods that use additional sensors, the diagnostic method proposed in this disclosure has lower costs. Compared with traditional model-based diagnostic methods, the diagnostic method proposed in this disclosure is not affected by system modeling accuracy errors and has higher reliability. Moreover, through the eighth step, the interference of multiple switch faults on diagnostic variables is eliminated by utilizing the fault range of the known faulty switch. Therefore, multi-switch fault diagnosis can be implemented using the same steps as single-switch fault diagnosis. Compared with existing multi-switch fault diagnosis methods, fewer diagnostic variables are required, and the diagnostic rules are simpler.

[0127] This disclosure also provides a three-level rectifier open-circuit fault diagnosis system, such as Figure 4 As shown, the three-level rectifier open-circuit fault diagnosis system 10 includes: an information acquisition module 100 that acquires information related to grid-side voltage and DC voltage; an information preprocessing module 200 that calculates diagnostic information including reference voltage and reference current based on the information acquired by the information acquisition module 100 and preset targets; a calculation module 300 that calculates the phase difference between the grid-side voltage and the input side of the three-level rectifier, and calculates a diagnostic threshold and the deviation between the reference voltage and the ideal reference voltage, i.e., the reference voltage deviation, based on the phase difference, and uses the reference voltage deviation as a diagnostic variable; an open-circuit fault determination module 400 that determines whether an open-circuit fault exists in the three-level rectifier by accumulating the number of diagnostic variables whose absolute values ​​exceed the diagnostic threshold; a fault arm location module 500 that locates the faulty arm among the three arms based on the diagnostic variables and the number of diagnostic variables whose absolute values ​​exceed the diagnostic threshold; and a fault switch location module 600 that performs fault-tolerant control by changing the reference current, and further locates the faulty switching device, i.e., the fault switch, among the faulty arms based on the diagnostic variables obtained therefrom. The specific implementation methods of each module can be referred to the description of the above method embodiments, and will not be repeated in this disclosure.

[0128] This disclosure also provides a computer-readable storage medium on which a computer program is stored, such as... Figure 5 As shown, the reference voltage-based three-level rectifier power open-circuit fault diagnosis method in this embodiment is implemented by executing the computer program.

[0129] It should be understood that the above description is illustrative and not restrictive. For example, the above embodiments (and / or aspects thereof) can be used in combination with each other. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the various embodiments of this disclosure without departing from the scope of this disclosure. While the dimensions and types of materials described herein are used to define parameters of the various embodiments of this disclosure, the embodiments are not intended to be restrictive but are exemplary. Many other embodiments will become apparent to those skilled in the art upon reading the above description. Therefore, the scope of the various embodiments of this disclosure should be determined by reference to the appended claims and the full scope of their equivalents.

Claims

1. A method for diagnosing open-circuit faults in a three-level rectifier, wherein the three-level rectifier converts the input grid-side voltage into a DC voltage, includes three bridge arms, each bridge arm including multiple switching devices, and the method for diagnosing open-circuit faults in the three-level rectifier is characterized by comprising: The first step is to obtain information related to the grid-side voltage and the DC voltage; The second step is to calculate the diagnostic information, including reference voltage and reference current, based on the acquired information and the given control target. The third step is to calculate the deviation between the reference voltage and the ideal reference voltage based on the phase difference between the grid-side voltage and the input side of the three-level rectifier, and obtain the reference voltage deviation. The fourth step is to use the reference voltage deviation as a diagnostic variable and compare it with the diagnostic threshold calculated based on the phase difference. The fifth step is to accumulate the number of times the absolute value of the diagnostic variable exceeds the diagnostic threshold, and determine whether the three-level rectifier has an open circuit fault. The sixth step is to locate the faulty bridge arm among the three bridge arms based on the diagnostic variables and the number of absolute values ​​of the diagnostic variables exceeding the diagnostic threshold in the case of an open circuit fault. as well as The seventh step involves performing fault-tolerant control by changing the reference current, and further locating the faulty switching device in the faulty bridge arm based on the diagnostic variables obtained therefrom.

2. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 1, characterized in that, The three-level rectifier is a three-phase three-level rectifier that converts three-phase alternating current into direct current. The bridge arms correspond to any one of the three phases, and each phase's bridge arm includes an upper bridge arm and a lower bridge arm, each having two series-connected switching devices. The three-phase grid-side voltage is input to the connection point of the upper bridge arm and the lower bridge arm of the corresponding phase. The middle connection point of the two switching devices in each upper or lower bridge arm is connected to the midpoint of the DC side of the three-level rectifier via a clamping diode.

3. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 2, characterized in that, The diagnostic information required in the second step includes: X-phase reference voltage ; X-phase grid-side voltage phase ; Grid-side voltage in DQ coordinate system and ; Reference current in the DQ coordinate system and ; Grid-side voltage frequency ;as well as Network-side equivalent inductance , Where X represents any one of phases A, B, and C in a three-phase alternating current circuit. k The sampling time.

4. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 3, characterized in that, In the third step, the X-phase reference voltage is... Normalization is performed to obtain the normalized actual reference voltage. ; Based on the phase of the X-phase grid side voltage and the phase difference between the grid-side voltage and the input side of the three-level rectifier. Calculate the normalized ideal reference voltage under no open-circuit fault conditions. ; The X-phase reference voltage deviation is calculated using the following formula. : 。 5. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 4, characterized in that, The phase difference Calculate according to the following formula: 。 6. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 5, characterized in that, The ideal reference voltage Calculate according to the following formula: 。 7. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 4, characterized in that, In the fourth step, the X-phase reference voltage deviation is... Performing an αβ coordinate transformation yields the following diagnostic variables. and : in, It is the reference voltage deviation of phase A. It is the reference voltage deviation of phase B. It is the reference voltage deviation of phase C.

8. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 4, characterized in that, In the fourth step, the diagnostic threshold is calculated according to the following formula. : in, Phase difference The calculation error is expressed by the following formula: Wherein, λ is a proportional setting coefficient greater than 0.

9. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 7, characterized in that, In the fifth step, the diagnostic variables are accumulated. and Exceeding the diagnostic threshold Number of and , when At times The value is incremented by 1, otherwise... Value cleared to zero; when At times The value is incremented by 1, otherwise... The value is reset to zero.

10. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 8, characterized in that, In the sixth step, the faulty bridge arm is located: like and If so, then there is an open circuit fault in the upper arm of phase A; like and If so, there is an open circuit fault in the lower arm of phase A; like , and If so, there is an open circuit fault in the upper arm of phase B; like , and If so, there is an open circuit fault in the lower arm of phase B; like , and If so, then there is an open circuit fault in the upper arm of phase C; like , and If so, then there is an open circuit fault in the lower arm of phase C.

11. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 10, characterized in that, In each upper or lower bridge arm of the three-level rectifier, the switching device located inside the upper or lower bridge arm is referred to as the internal switch. The switching device located on the outside of the upper or lower bridge arm is referred to as the external switch. The fault-tolerant control is achieved by changing the Q-axis reference current. To achieve fault tolerance for external switches, and by judging the actual reference voltage Whether the distortion disappears can help locate the fault switch.

12. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 11, characterized in that, The Q-axis reference current Make the changes according to the following formula: in, This is the reference current for the D-axis. Based on the modified Q-axis reference current If the actual reference voltage If the distortion disappears, the fault is determined to be an external switch; otherwise, it is determined to be an internal switch fault.

13. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 12, characterized in that, When there is an open circuit fault in the upper arm of phase A, if If so, the external switch of the upper bridge arm of phase A has an open circuit fault; When there is an open circuit fault in the upper arm of phase A, if If so, the switch inside the upper arm of phase A has an open circuit fault; When there is an open circuit fault in the lower arm of phase A, if If so, the switch in the lower arm of phase A has an open circuit fault; When there is an open circuit fault in the lower arm of phase A, if If so, the external switch of the lower bridge arm of phase A has an open circuit fault; When there is an open circuit fault in the upper arm of phase B, if If so, the external switch of the upper bridge arm of phase B has an open circuit fault; When there is an open circuit fault in the upper arm of phase B, if If so, the switch inside the upper arm of phase B has an open circuit fault; When there is an open circuit fault in the lower arm of phase B, if If so, the switch in the lower arm of phase B has an open circuit fault; When there is an open circuit fault in the lower arm of phase B, if If so, the external switch of the lower bridge arm of phase B has an open circuit fault; When there is an open circuit fault in the upper arm of phase C, if If so, the external switch of the upper bridge arm of phase C has an open circuit fault; When there is an open circuit fault in the upper arm of phase C, if If so, the switch inside the upper arm of phase C has an open circuit fault; When there is an open circuit fault in the lower arm of phase C, if If so, the switch in the lower arm of phase C has an open circuit fault; When there is an open circuit fault in the lower arm of phase C, if If so, then the external switch of the lower bridge arm of phase C has an open circuit fault.

14. The method for diagnosing open-circuit faults in a three-level rectifier as described in any one of claims 1 to 13, characterized in that, It also includes an eighth step, which determines the fault range of the faulty switch, and repeats the third to seventh steps outside the fault range to locate other faulty switches.

15. The method for diagnosing open-circuit faults in a three-level rectifier as described in claim 11, characterized in that, The fault range of the fault switch is pre-stored in the form of a mapping table.

16. A three-level rectifier open-circuit fault diagnosis system, wherein the three-level rectifier converts the input grid-side voltage into a DC voltage, includes three bridge arms, each bridge arm including multiple switching devices, and the three-level rectifier open-circuit fault diagnosis system is characterized in that it includes: An information acquisition module that acquires information related to the grid-side voltage and the DC voltage; An information preprocessing module calculates diagnostic information, including reference voltage and reference current, based on the information and the given control target. The calculation module calculates the phase difference between the grid-side voltage and the input side of the three-level rectifier, and calculates the diagnostic threshold and the deviation between the reference voltage and the ideal reference voltage, i.e., the reference voltage deviation, based on the phase difference, and uses the reference voltage deviation as a diagnostic variable. An open-circuit fault determination module is used to determine whether an open-circuit fault exists in the three-level rectifier by accumulating the number of times the absolute value of the diagnostic variable exceeds the diagnostic threshold. The faulty bridge arm location module locates the faulty bridge arm among the three bridge arms based on the diagnostic variables and the number of times the absolute value of the diagnostic variables exceeds the diagnostic threshold. as well as The fault switch location module performs fault-tolerant control by changing the reference current, and further locates the faulty switching device, i.e., the fault switch, in the faulty bridge arm based on the diagnostic variables obtained therefrom.

17. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 15.

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