METHOD AND SYSTEM FOR DIAGNOSING OPEN-CIRCUIT FAULT OF POWER SWITCHING DEVICE OF THREE-PHASE THREE-LEVEL RECTIFIER

Abstract

A method and a system for diagnosing a fault of a three-phase three-level rectifier are relate to the technical field of fault diagnosis of power electronic equipment, and provided to implement identification and location of an open-circuit fault of a power switching device thereof. A deviation between an expected value and an actual value of a phase-to-phase voltage is adopted as a diagnosis variable. The diagnosis variable is calculated by adopting a screening technique, thereby reducing calculation error to ensure accuracy of diagnosis. Only existing voltage current signals in a control system of the rectifier are required to calculate the diagnosis variable, so no additional hardware is required and low-cost fault diagnosis can be implemented. Different voltage thresholds are adopted for different fault characteristic sections, and the voltage thresholds are updated in real time according to a direct current side voltage, which improves diagnosis speed while ensuring higher robustness.

Claims

1. A method for diagnosing an open-circuit fault of a power switching device of a three-phase three-level rectifier, comprising: Step (1) of selecting an expected value of a phase-to-phase voltage between an X-phase and a Y-phase of the rectifier at a current time and an actual value of the phase-to-phase voltage, and using a deviation between the two as a diagnosis variable; Step (2) of obtaining voltage current information required for diagnosis from a control system of the rectifier, and calculating the diagnosis variable by adopting a screening technique; Step (3) of classifying fault sections according to fault characteristics of faulty switches at different times, and updating a diagnosis threshold at the current time for a current fault section; Step (4) of judging whether the diagnosis variable exceeds a threshold range and a polarity thereof according to the diagnosis variable and the diagnosis threshold; Step (5) of identifying and locating a fault of an internal switching transistor according to the judgment result; and Step (6) of checking a diagnosis result of the fault to verify whether the diagnosis result is correct, and correcting the diagnosis result of a fault of an external switching transistor that is misdiagnosed as the fault of the internal switching transistor to implement identification and location of an external switching fault.

2. The method according to claim 1, comprising: obtaining the expected value V.sub.XY*(k) of the phase-to-phase voltage from V.sub.XY*(k)=½V.sub.DC(k)(S.sub.X(k)−S.sub.Y(k)), and obtaining the actual value V.sub.XY(k) of the phase-to-phase voltage $V_{XY}\left(k\right)=\left(E_X\left(k\right)-E_Y\left(k\right)\right)-R\left(I_X\left(k\right)-I_Y\left(k\right)\right)-\frac{L}{T}\left[\left(I_X\left(k\right)-I_X\left(k-1\right)\right)-\left(I_Y\left(k\right)-I_Y\left(k-1\right)\right)\right],$ from where V.sub.DC(k) is a direct current side voltage of the rectifier at the current time; S.sub.X(k) and S.sub.Y(k) are respectively switching control signals of the X-phase and the Y-phase of the rectifier, S.sub.X(k)=1 represents that switches S.sub.X1 and S.sub.X2 are turned on and switches S.sub.X3 and S.sub.X4 are turned off, S.sub.X(k)=0 represents that the switches S.sub.X2 and S.sub.X3 are turned on and the switches S.sub.X1 and S.sub.X4 are turned off, and S.sub.X(k)=−1 represents that the switches S.sub.X3 and S.sub.X4 are turned on and the switches S.sub.X1 and S.sub.X2 are turned off; E.sub.X(k) and E.sub.Y(k) are respectively alternating current side voltages of the X-phase and the Y-phase of the rectifier; I.sub.X(k) and I.sub.Y(k) are respectively alternating current side currents of the X-phase and the Y-phase of the rectifier; R is an alternating current side equivalent resistance of the rectifier; L is an alternating current side inductance of the rectifier; T is a sampling interval time, k represents a sampling point at the current time, k−1 represents a sampling point at a previous time, and X and Y=A and B, B and C, or C and A.

3. The method according to claim 2, wherein Step (2) comprises: ΔV.sub.XY(k)=V.sub.XY*(k)−V.sub.XY(k) when there is no switching of three-phase switching control signals between the sampling points k and k−1, that is, when S.sub.A(k)=S.sub.A(k−1), S.sub.B(k)=S.sub.B(k−1), and S.sub.C(k)=S.sub.C(k−1) are satisfied; and not calculating ΔV.sub.XY(k), and regarding ΔV.sub.XY(k) at the current time as zero when one of S.sub.A(k)=S.sub.A(k−1), S.sub.B(k)=S.sub.B(k−1), and S.sub.C(k)=S.sub.C(k−1) is not satisfied, where ΔV.sub.XY(k) represents the deviation between the expected value of the phase-to-phase voltage between the X-phase and the Y-phase and the actual value of the phase-to-phase voltage.

4. The method according to claim 1, wherein Step (3) comprises: dividing the fault sections into a current zero zone and a current non-zero zone, and setting different diagnosis thresholds TH.sub.XY(k) for different sections: $T{H}_{XY}\left(k\right)=\{\begin{array}{cc}\frac{V_{\mathrm{DC}}\left(k\right)}{4}-V,& I_{XY}\left(k\right)=0\\ \frac{V_{\mathrm{DC}}\left(k\right)}{2}-V,& I_{XY}\left(k\right)=1\end{array}$ for a fault diagnosis of the internal switching transistor, where V is a preset value, which is a constant; I.sub.XY(k)=0 represents that I.sub.X or I.sub.Y is in the current zero zone, I.sub.XY(k)=1 represents that I.sub.X and I.sub.Y are both in the current non-zero zone, and V.sub.DC(k) is a direct current side voltage of the rectifier at the current time; and providing a following definition: $I_{XY}\left(k\right)=\{\begin{array}{cc}0,& .Math.I_X\left(k\right).Math.\le I_{TH}\mathrm{or}.Math.I_Y\left(k\right).Math.\le I_{TH}\\ 1,& .Math.I_X\left(k\right).Math.>I_{TH}\mathrm{and}.Math.I_Y\left(k\right).Math.>I_{TH}\end{array}$ for the definition of the current zero zone and the current non-zero zone, considering noise and fluctuations of current, where I.sub.TH is a current threshold.

5. The method according to claim 4, wherein Step (4) comprises: obtaining a variable F.sub.XY(k) indicating whether the diagnosis variable exceeds a threshold range [−TH.sub.XY(k),TH.sub.XY(k)] and the polarity thereof from $F_{XY}\left(k\right)=\{\begin{array}{cc}1,& \Delta V_{XY}\left(k\right)>T{H}_{XY}\left(k\right)\\ 0,& .Math.\Delta V_{XY}\left(k\right).Math.\le {\mathrm{TH}}_{XY}\left(k\right)\\ -1,& \Delta V_{XY}\left(k\right)<-T{H}_{XY}\left(k\right)\end{array}.$

6. The method according to claim 5, wherein Step (5) comprises: a corresponding relationship between the fault of the internal switching transistor and the variable F.sub.XY(k) being: when S.sub.A2 is faulty, F.sub.AB=1, F.sub.BC=0, F.sub.CA=−1; when S.sub.A3 is faulty, F.sub.AB=−1, F.sub.BC=0, F.sub.CA=1; when S.sub.B2 is faulty, F.sub.AB=−1, F.sub.BC=1, F.sub.CA=0; when S.sub.B3 is faulty, F.sub.AB=1, F.sub.BC=−1, F.sub.CA=0; when S.sub.C2 is faulty, F.sub.AB=0, F.sub.BC=−1, F.sub.CA=1; and when S.sub.C3 is faulty, F.sub.AB=0, F.sub.BC=1, F.sub.CA=−−1.

7. The method according to claim 6, wherein Step (6) comprises: the diagnosis result being correct and being represented by F.sub.check=1 when at least one value of three diagnosis variables ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) is greater than a threshold TH(k) at a certain time during a preset current cycle after completing the fault diagnosis; and conversely, the diagnosis result being wrong and being represented by F.sub.check=0 when values of all sampling points of ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) all do not exceed the threshold TH(k) during the preset current cycle after completing the fault diagnosis, where the threshold TH(k) is set to V.sub.DC(k)/2+V.

8. The method according to claim 7, wherein when F.sub.check=0, a corresponding relationship between the diagnosis result, F.sub.check, and a checking result is: $S_{A2}\mathrm{fault}\{\begin{array}{c}1,\mathrm{correct},S_{A2}\mathrm{fault}\\ 0,\mathrm{wrong},S_{A1}\mathrm{fault}\end{array};S_{A3}\mathrm{fault}\{\begin{array}{c}1,\mathrm{correct},S_{A3}\mathrm{fault}\\ 0,\mathrm{wrong},S_{A4}\mathrm{fault}\end{array};S_{B2}\mathrm{fault}\{\begin{array}{c}1,\mathrm{correct},S_{B2}\mathrm{fault}\\ 0,\mathrm{wrong},S_{B1}\mathrm{fault}\end{array};S_{B3}\mathrm{fault}\{\begin{array}{c}1,\mathrm{correct},S_{B3}\mathrm{fault}\\ 0,\mathrm{wrong},S_{B4}\mathrm{fault}\end{array};S_{C2}\mathrm{fault}\{\begin{array}{c}1,\mathrm{correct},S_{C2}\mathrm{fault}\\ 0,\mathrm{wrong},S_{C1}\mathrm{fault}\end{array};\mathrm{and}{S}_{C3}\mathrm{fault}\{\begin{array}{c}1,\mathrm{correct},S_{C3}\mathrm{fault}\\ 0,\mathrm{wrong},S_{C4}\mathrm{fault}\end{array}.$

9. A system for diagnosing an open-circuit fault of a power switching device of a three-phase three-level rectifier, comprising: a diagnosis variable determination module, configured to select an expected value of a phase-to-phase voltage between an X-phase and a Y-phase of the rectifier at a current time and an actual value of the phase-to-phase voltage, and use a deviation between the two is as a diagnosis variable; a diagnosis variable calculation module, configured to obtain voltage current information required for diagnosis from a control system of the rectifier, and calculate the diagnosis variable by adopting a screening technique; a diagnosis threshold determination module, configured to classify fault sections according to fault characteristics of faulty switches at different times, and update a diagnosis threshold at the current time for a current fault section; a polarity determination module, configured to judge whether the diagnosis variable exceeds a threshold range and a polarity thereof according to the diagnosis variable and the diagnosis threshold; a diagnosis module, configured to identify and locate a fault of an internal switching transistor according to the judgment result; a correction module, configured to check a diagnosis result of the fault to verify whether the diagnosis result is correct, and correct the diagnosis result of a fault of an external switching transistor that is misdiagnosed as the fault of the internal switching transistor to implement identification and location of an external switching fault.

10. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 1 are implemented.

11. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 2 are implemented.

12. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 3 are implemented.

13. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 4 are implemented.

14. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 5 are implemented.

15. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 6 are implemented.

16. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 7 are implemented.

17. A computer-readable storage medium stored with a computer program, wherein when the computer program is executed by a processor, steps of the method according to claim 8 are implemented.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a topological structure diagram of a three-phase three-level rectifier and a flowchart of a method for diagnosing an open-circuit fault of a power switching device thereof according to an embodiment of the disclosure.

[0047] FIG. 2 is a diagram of a diagnosis result of an open-circuit fault of an internal switching transistor of a three-phase three-level rectifier according to an embodiment of the disclosure.

[0048] FIG. 3 is a diagram of a diagnosis result of an open-circuit fault of an external switching transistor of a three-phase three-level rectifier according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0049] In order for the objectives, technical solutions, and advantages of the disclosure to be clearer, the following further describes the disclosure in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the disclosure, but not to limit the disclosure. In addition, the technical features involved in the various embodiments of the disclosure described below may be combined with each other as long as there is no conflict therebetween.

[0050] FIG. 1 shows a method for diagnosing an open-circuit fault of a power switching device of a three-phase three-level rectifier according to an embodiment of the disclosure, which includes the following steps.

[0051] In Step S1, information required for diagnosis is obtained from a control system of a rectifier.

[0052] Alternating current side three-phase voltages (E.sub.A(k), E.sub.B(k), E.sub.C(k)), three-phase currents (I.sub.A(k), I.sub.B(k), I.sub.C(k)), and a direct current side voltage (V.sub.DC(k)) obtained by the three-phase three-level rectifier through sampling are sent to the control system. According to information such as the above signals and the stored alternating current side inductance (L) and equivalent resistance (R), the control system obtains control signals (S.sub.A(k), S.sub.B(k), S.sub.C(k)) of each phase power switching device through calculation and sends the same to the rectifier, so that the rectifier runs according to a control target. Therefore, the control system has all the information required for diagnosis. The information is used to calculate a diagnosis variable and update a threshold.

[0053] For an X-phase of the rectifier, X=A, B, C, four power switching transistors thereof are classified into two outer switching transistors S.sub.X1 and S.sub.X4 and two inner switching transistors S.sub.X2 and S.sub.X3. Therefore, the rectifier consists of six outer switching transistors and six inner switching transistors in total.

[0054] In Step S2, a deviation of a phase-to-phase voltage is calculated.

[0055] Taking an AB phase-to-phase voltage as an example, an expected value V.sub.AB*(k) of the AB phase-to-phase voltage is:

V.sub.AB*(k)=½V.sub.DC(k)(S.sub.A(k)−S.sub.B(k)),

[0056] where k represents a k-th sampling.

[0057] An actual value V.sub.AB(k) of the AB phase-to-phase voltage is:

[00006]$V_{AB}\left(k\right)=\left(E_A\left(k\right)-E_B\left(k\right)\right)-R\left(I_A\left(k\right)-I_B\left(k\right)\right)-\frac{L}{T}\left[\left(I_A\left(k\right)-I_A\left(k-1\right)\right)-\left(I_B\left(k\right)-I_B\left(k-1\right)\right)\right]$

[0058] where T is a sampling interval time.

[0059] For a deviation ΔV.sub.AB(k) of the AB phase-to-phase voltage, when conditions S.sub.A(k)=S.sub.A(k−1), S.sub.B(k)=S.sub.B(k−1), and S.sub.C(k)=S.sub.C(k−1) are satisfied, ΔV.sub.AB(k)=V.sub.AB*(k)−V.sub.AB(k); and when one of the conditions S.sub.A(k)=S.sub.A(k−1), S.sub.B(k)=S.sub.B(k−1), and S.sub.C(k)=S.sub.C(k−1) is not satisfied, ΔV.sub.AB(k)=0.

[0060] By analogy, a deviation ΔV.sub.BC(k) of a BC phase-to-phase voltage and a deviation ΔV.sub.CA(k) of a CA phase-to-phase voltage are calculated.

[0061] In Step S3, fault sections are determined and the threshold is updated in real time.

[0062] In Step S3, fault characteristics of different faulty switches at different times are analyzed. If errors are not considered, when the rectifier is working normally, three diagnosis variables ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) are all zero; and when an open-circuit fault of a switch occurs, the diagnosis variables have different values according to different faulty switches, currents, and switching control signals, as shown in Table 1 below.

TABLE-US-00001 TABLE 1 Current Faulty switch S.sub.X ΔV.sub.XY ΔV.sub.YZ ΔV.sub.ZX i.sub.x < 0 S.sub.x1 1 V.sub.DC/2 0 −V.sub.DC/2 i.sub.x > 0 S.sub.x2 1 V.sub.DC 0 −V.sub.DC 0 V.sub.DC/2 0 −V.sub.DC/2 S.sub.x3 0 −V.sub.DC/2 0 V.sub.DC/2 −1 −V.sub.DC 0 V.sub.DC S.sub.x4 −1 −V.sub.DC/2 0 V.sub.DC/2 i.sub.x = 0 S.sub.x2 1 [0, V.sub.DC] 0 [−V.sub.DC, 0] 0 [0, V.sub.DC/2] 0 [−V.sub.DC/2 0] S.sub.x3 0 [−V.sub.DC/2, 0] 0 [0, V.sub.DC/2] −1 [−V.sub.DC, 0] 0 [0, V.sub.DC]

[0063] For the fault diagnosis of the internal switching transistor, the specific method for determining the threshold is as follows.

[0064] Taking the AB phase as an example, a current zero zone and a current non-zero zone are determined.

[00007]$I_{AB}\left(k\right)=\{\begin{array}{cc}0,& .Math.I_A\left(k\right).Math.\le I_{TH}\mathrm{or}.Math.I_B\left(k\right).Math.\le I_{TH}\\ 1,& .Math.I_A\left(k\right).Math.>I_{TH}\mathrm{and}.Math.I_B\left(k\right).Math.>I_{TH}\end{array}$

[0065] where I.sub.AB(k)=0 represents I.sub.A or I.sub.B is in the current zero zone, I.sub.AB(k)=1 represents that I.sub.A or I.sub.B are both in the current non-zero zone, I.sub.TH is a current threshold, and a current amplitude may be 5%.

[0066] By analogy, current zero zones and current non-zero zones of the BC phase and the CA phase are determined.

[0067] Taking the AB phase as an example, a main threshold is updated.

[00008]$T{H}_{AB}\left(k\right)=\{\begin{array}{cc}\frac{V_{DC}\left(k\right)}{4}-V,& I_{AB}\left(k\right)=0\\ \frac{V_{DC}\left(k\right)}{2}-V,& I_{AB}\left(k\right)=1\end{array}$

[0068] where V is a relatively small constant, which may be 2% times of V.sub.DC.

[0069] By analogy, main thresholds of the BC phase and the CA phase are updated.

[0070] The threshold required for diagnosis result checking is updated.

[00009]$\mathrm{TH}\left(k\right)=\frac{V_{DC}\left(k\right)}{2}+V$

[0071] In Step S4, whether the diagnosis variable exceeds a main threshold range and a polarity thereof is judged.

[0072] Taking the AB phase as an example, a variable F.sub.AB(k) indicating whether ΔV.sub.AB(k) exceeds a range [−TH.sub.AB(k),TH.sub.AB(k)] and the polarity thereof is:

[00010]$F_{AB}\left(k\right)=\{\begin{array}{cc}1,& \Delta V_{AB}\left(k\right)>T{H}_{AB}\left(k\right)\\ 0,& .Math.\Delta V_{AB}\left(k\right).Math.\le {\mathrm{TH}}_{AB}\left(k\right)\\ -1,& \Delta V_{AB}\left(k\right)<-T{H}_{AB}\left(k\right)\end{array}$

[0073] By analogy, indicating variables F.sub.BC(k) and F.sub.CA(k) of the BC phase and the CA phase are determined.

[0074] In Step S5, the fault of the internal switching transistor is identified and located.

[0075] After obtaining F.sub.AB(k), F.sub.BC(k), and F.sub.CA(k), the fault of the internal switching transistor may be located according to Table 2.

TABLE-US-00002 TABLE 2 Fault diagnosis of internal switching transistor Faulty switch F.sub.AB F.sub.BC F.sub.CA S.sub.A2 1 0 −1 S.sub.A3 −1 0 1 S.sub.B2 −1 1 0 S.sub.B3 1 −1 0 S.sub.C2 0 −1 1 S.sub.C3 0 1 −1

[0076] In Step S6, the diagnosis result is checked (a fault of an external switching transistor is identified and located).

[0077] After obtaining the diagnosis result of Step S5, whether ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) are greater than the threshold TH(k) is judged. During ⅛ of a current cycle, if a value of at least one sampling point of any of the variables ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) is greater than the threshold TH(k), the diagnosis result is correct and is represented by F.sub.check=1. Conversely, during ⅛ of the current cycle, if values of all sampling points of ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) do not exceed the threshold TH(k), the diagnosis result is wrong and is represented by F.sub.check=0. When F.sub.check=0, the diagnosis result is corrected to a fault of a corresponding external switching transistor, as shown in Table 3. Taking the diagnosis result of Step S5 being S.sub.A2 open-circuit fault as an example, if F.sub.check=1, it represents that the diagnosis result is correct and it is S.sub.A2 open-circuit fault; and if F.sub.check=0, it represents that the diagnosis result is wrong and is corrected to S.sub.A1 open-circuit fault.

TABLE-US-00003 TABLE 3 Correction of diagnosis result (fault diagnosis of external switching transistor) Diagnosis result F.sub.check Checking result S.sub.A2 fault 1 Correct, S.sub.A2 fault 0 Wrong, S.sub.A1 fault S.sub.A3 fault 1 Correct, S.sub.A3 fault 0 Wrong, S.sub.A4 fault S.sub.B2 fault 1 Correct, S.sub.B2 fault 0 Wrong, S.sub.B1 fault S.sub.B3 fault 1 Correct, S.sub.B3 fault 0 Wrong, S.sub.B4 fault S.sub.C2 fault 1 Correct, S.sub.C2 fault 0 Wrong, S.sub.C1 fault S.sub.C3 fault 1 Correct, S.sub.C3 fault 0 Wrong, S.sub.C4 fault

[0078] In order to describe the example more clearly, FIG. 2 and FIG. 3 provide the diagnosis result of the example, and the parameters used are shown in Table 4.

TABLE-US-00004 TABLE 4 Parameters used in example Alternating current side voltages E.sub.A, E.sub.B, E.sub.C 110 V(rms), 50 Hz Sampling interval T 25 μs Switching frequency f 5 kHz Alternating current side inductance L 5 mH Direct current side given voltage V 400 V Direct current side resistance R.sub.L 200 Ω

[0079] As shown in FIG. 2, the open-circuit fault of the switch S.sub.A2 occurs at 1.03 s. After the fault, ΔV.sub.AB(k) rapidly increases to ΔV.sub.AB(k)>TH.sub.AB(k), so that F.sub.AB(k)=1; ΔV.sub.CA(k) rapidly decreases to ΔV.sub.CA(k)<−TH.sub.CA(k), so that F.sub.CA(k)=−1; and ΔV.sub.BC(k) is always within the threshold range, F.sub.BC(k)=0. Therefore, according to Table 2, the switch S.sub.A2 is diagnosed as the open-circuit fault, and the diagnosis time is about 0.3 ms. Also, during ⅛ of the current cycle after identifying S.sub.A2 open-circuit fault, that is F.sub.check=1, the diagnosis may be verified as correct according to Table 3.

[0080] As shown in FIG. 3, the open-circuit fault of the switch S.sub.A1 occurs at 1.03 s. After the fault, ΔV.sub.AB(k) rapidly increases to ΔV.sub.AB(k)>TH.sub.AB(k), so that F.sub.AB(k)=1; ΔV.sub.CA(k) rapidly decreases to ΔV.sub.CA(k)<−TH.sub.CA(k), so that F.sub.CA(k)=−1; and ΔV.sub.BC(k) is always within the threshold range, F.sub.BC(k)=0. Therefore, according to Table 2, the switch S.sub.A2 is diagnosed as the open-circuit fault. However, during ⅛ of the current cycle after identifying S.sub.A2 open-circuit fault, ΔV.sub.AB(k), ΔV.sub.BC(k), and ΔV.sub.CA(k) are all within the threshold range [−TH(k),TH(k)], so F.sub.check=0. According to Table 3, the diagnosis result is corrected to S.sub.A1 open-circuit fault, and the diagnosis time is about 3 ms.

[0081] The above results prove that the disclosure can implement the open-circuit fault diagnosis of all power switching devices of the three-phase three-level rectifier and ensure the speed and the accuracy of the fault diagnosis of the internal switching transistor that has a greater impact on the system, and the overall diagnosis speed is faster.

[0082] The disclosure also provides a system for diagnosing an open-circuit fault of a power switching device of a three-phase three-level rectifier, which includes the following.

[0083] A diagnosis variable determination module is configured to select an expected value V.sub.XY*(k) of a phase-to-phase voltage between an X-phase and a Y-phase of a rectifier k at the current time and an actual value V.sub.XY(k) of the phase-to-phase voltage, and use a deviation ΔV.sub.XY(k) between the two is as a diagnosis variable, where XY=AB,BC,CA.

[0084] A diagnosis variable calculation module is configured to obtain voltage current information required for diagnosis from a control system of the rectifier, and calculate the diagnosis variable ΔV.sub.XY(k) by adopting a screening technique.

[0085] A diagnosis threshold determination module is configured to classify fault sections according to fault characteristics of faulty switches at different times, and update a diagnosis threshold TH.sub.XY(k) at the current time for a current fault section.

[0086] A polarity determination module is configured to judge whether the diagnosis variable exceeds a threshold range and a polarity thereof according to the diagnosis variable ΔV.sub.XY(k) and the diagnosis threshold TH.sub.XY(k).

[0087] A diagnosis module is configured to identify and locate a fault of an internal switching transistor according to the above judgment result.

[0088] A correction module is configured to check a diagnosis result of the fault to verify whether the diagnosis result is correct, and correct the diagnosis result of a fault of an external switching transistor that may be misdiagnosed as the fault of the internal switching transistor to implement identification and location of an external switching fault.

[0089] For the specific implementation of each module, reference may be made to the description of the foregoing embodiment of the method, which will not be repeated in the embodiment of the disclosure.

[0090] The disclosure also provides a computer-readable storage medium stored with a computer program. When the program is executed by a processor, the method for diagnosing the open-circuit fault of the power switching device of the three-phase three-level rectifier in the embodiment of the method is implemented.

[0091] It should be noted that according to implementation requirements, each step/component described in the disclosure may be split into more steps/components or two or more steps/components or partial operation of a step/component may be combined into a new step/component to implement the objective of the disclosure.

[0092] Persons skilled in the art may easily understand that the above are only preferred embodiments of the disclosure and are not intended to limit the disclosure. Any modification, equivalent replacement, improvement, etc., made within the spirit and principle of the disclosure should be included in the protection scope of the disclosure.