Converter Power Device Open-Circuit Fault Diagnosis Method Based on Fundamental Frequency Current Characteristics

Abstract

The present invention belongs to the technical field of converter fault diagnosis, and particularly relates to a method for diagnosing the open - circuit fault of a converter power device based on the fundamental - frequency current characteristics. Preset the operating state information of the converter to be collected; under rated operating conditions, test and obtain the initial values of the converter operating state, and calculate the initial current component eigenvalue; when the converter is put into the operating state, test and obtain the converter operating state, and calculate the current component eigenvalue in the operating state, which is used as the fault eigenvalue; based on the initial current component eigenvalue and the fault eigenvalue, calculate the change amount of the fundamental - frequency amplitude of the current; and perform a steady - state process on the change amount of the fundamental - frequency amplitude of the current to obtain the abnormal degree of the current parameters; based on the change amount of the fundamental - frequency amplitude of the current and the abnormal degree of the current parameters, judge the specific position where the converter has an open - circuit fault, assisting on - site fault troubleshooting and intelligent monitoring.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter fault diagnosis, and particularly relates to a method for diagnosing open - circuit faults of power devices in a converter based on fundamental - frequency current characteristics. Background Art

[0002] The medium - voltage DC power transmission system has developed rapidly. It has large power levels, high voltage levels, and low line losses, featuring typically high voltage and large capacity. Therefore, multilevel technologies, especially hybrid three - level technologies, have become effective means for constructing DC conversion systems and are widely used in the field of medium - voltage large - capacity drives. This structure reduces the requirement for device voltage withstand and also has advantages such as low harmonics and low voltage stress. One major problem in the application of neutral - point - clamped three - level converters is that a large number of power switching tubes are used, and the probability of open - circuit faults is relatively high. Currently, the diagnostic and location methods for the fault states and positions of switching tubes are still relatively scarce.

[0003] However, for DC converters of this type of topology, current research mainly focuses on discussing methods for achieving fault - redundant operation by selecting redundant switching states when certain power electronic devices fail, as well as aspects such as uninterrupted operation during faults. As the medium - voltage DC power transmission system is increasingly tending towards unmanned or less - manned operation, it is more important to quickly and accurately determine the fault state and position before and after a fault occurs. Therefore, there is an urgent need to conduct necessary research on intelligent methods and autonomous fault elimination for the fault states and position location of neutral - point - clamped hybrid three - level converters in this situation, so as to reduce the probability of abnormal operation or increased harmonic rate of the medium - voltage DC power transmission system caused by open - circuit faults of power devices. Summary of the Invention

[0004] In order to overcome the problems in the prior art, the present invention proposes a method for diagnosing open - circuit faults of power devices in a converter based on fundamental - frequency current characteristics.

[0005] The technical solution of the present invention to solve the above - mentioned technical problems is as follows:

[0006] The present invention provides a method for diagnosing open - circuit faults of power devices in a converter based on fundamental - frequency current characteristics, including the following steps:

[0007] Step 100: Preset the operating state information of the converter to be collected;

[0008] Step 200: Under rated operating conditions, test and obtain the initial values of the converter operating state, and calculate the initial current component characteristic values;

[0009] Step 300: When the converter is put into the operating state, test and obtain the converter operating state, and calculate the current component characteristic values in the operating state, which are used as fault characteristic values;

[0010] Step 400: Calculate the change in the fundamental frequency amplitude of the current based on the initial current component eigenvalue and the fault eigenvalue; and perform a steady-state process on the change in the fundamental frequency amplitude of the current to obtain the degree of abnormality of the current parameter.

[0011] Step 500: Determine the specific location of the open-circuit fault of the converter based on the change in the fundamental frequency amplitude of the current and the degree of abnormality of the current parameter.

[0012] Further, in the step 100, the converter is a three-level bidirectional DC converter, and the three-level bidirectional DC converter includes a high-voltage module, a transformer, a resonant inductor, and a low-voltage module. The high-voltage module is connected to the low-voltage module through the transformer and the resonant inductor; the high-voltage module includes a first arm and a second arm; the low-voltage module includes a third arm and a fourth arm; wherein, the upper end of the first arm, the lower end of the first arm, the upper end of the second arm, the lower end of the second arm, the third arm, and the fourth arm all include two power devices.

[0013] Further, before presetting the operating state information of the converter to be collected in the step 100, it includes: setting the key positions of the converter, and the key positions include the high-voltage input, the inverter bridge input, the inductor flow-through, the transformer secondary side output, the rectifier bridge output, and the low-voltage side output.

[0014] Further, in the step 100, preset the operating state information of the converter to be collected, and the operating state information of the converter is the current at the key positions.

[0015] Further, the step 200 includes: performing a filtering process on the initial value of the operating state of the converter to obtain the initial current component eigenvalue;

[0016] ;

[0017] In the above formula, ω represents the angular frequency; represents the initial value of the current of the operating state of the converter; represents the initial current component eigenvalue; represents the key position of the converter; ; f 0 is the operating frequency of the converter, T 0 is the single working cycle time of the power device of the converter, N represents the period, t represents the time variable of the time-domain current waveform.

[0018] Further, in the step 300, it includes: analyzing the operating state of the converter every X time, filtering the operating state of the converter, calculating the eigenvalue of the current component in the operating state, and using this as the fault eigenvalue;

[0019] ;

[0020] In the above formula, represents the x th operating state of the converter; represents the eigenvalue of the current component in the operating state, that is, the fault eigenvalue obtained by the x th sampling process.

[0021] Further, in the step 400, based on the initial eigenvalue of the current component and the fault eigenvalue, the change amount of the fundamental frequency amplitude of the current is calculated as follows:

[0022] ;

[0023] In the formula, x represents the x th fault information processing process, , is an integer; represents the fault eigenvalue of the converter obtained by the x- 1st sampling process.

[0024] Further, in the step 400, the change amount of the fundamental frequency amplitude of the current is subjected to a steady-state process to obtain the abnormal degree of the current parameter:

[0025] ;

[0026] In the formula, characterizes the abnormal degree of the monitored current parameters at each key position during the operation of the converter; x represents the x th fault information processing. When the p th fault information processing is performed, x = p .

[0027] Further, in the step 500, based on the change amount of the fundamental frequency amplitude of the current and the abnormal degree of the current parameter, the specific position where the converter has an open-circuit fault is judged, including:

[0028] When electric energy is transmitted from the high-voltage module to the low-voltage module, judge the position of the power device where the open-circuit fault occurs:

[0029] When , and , , an open - circuit fault appears at the upper end of the second bridge arm: the fifth switch tube S5 and the sixth switch tube S6;

[0030] When , and , , an open - circuit fault appears at the lower end of the first bridge arm: the third switch tube S3 and the fourth switch tube S4;

[0031] When , , , an open - circuit fault appears at the upper end of the first bridge arm: the first switch tube S1 and the second switch tube S2;

[0032] When , , , an open - circuit fault appears at the lower end of the second bridge arm: the seventh switch tube S7 and the eighth switch tube S8;

[0033] Among them, represents the abnormal degree of the current parameter at the high - voltage input, represents the abnormal degree of the current parameter at the input of the inverter bridge, represents the abnormal degree of the current parameter where the inductor passes through, Table p the change amount of the fundamental - frequency amplitude of the current passing through the inductor for the

[0034] When , and , , an open - circuit fault appears in the third bridge arm;

[0035] When , and , , an open - circuit fault appears in the fourth bridge arm;

[0036] When , and , , the fault occurs at a position outside the power device;

[0037] Among them, represents the abnormal degree of the current parameter at the output of the rectifier bridge, represents the abnormal degree of the current parameter at the low - voltage output; represents the abnormal degree of the current parameter at the output of the secondary side of the transformer; represents p the change amount of the fundamental - frequency amplitude of the current at the output of the secondary side of the transformer for the

[0038] Compared with the prior art, the present invention has the following technical effects:

[0039] (1) By monitoring and analyzing the current at key positions of the converter, extracting the fundamental frequency current characteristic values, and calculating the change in the fundamental frequency amplitude of the current, the present invention can accurately and quickly determine the open - circuit fault position of the power devices in the converter. This method not only improves the accuracy of fault diagnosis but also greatly shortens the time for fault location, helping to take timely measures to avoid the expansion of faults.

[0040] (2) The present invention can comprehensively monitor the fault conditions of the power devices of the multi - level DC converter commonly used in the energy storage system. By adopting non - contact current sensing technology, direct contact with the high - voltage part is avoided, thus ensuring the safety of the operators.

[0041] (3) Through intelligent monitoring and fault warning, the present invention helps to detect potential safety hazards in advance, further improving the safe operation performance of the large - capacity DC converter in the energy storage system, extending the service life of the equipment, and reducing the maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0043] Figure 1 It is a schematic diagram of the implementation of the open - circuit fault diagnosis method for the power devices of the converter based on the fundamental frequency current characteristics of the present invention;

[0044] Figure 2 It is a schematic flowchart of the open - circuit fault diagnosis method for the power devices of the converter based on the fundamental frequency current characteristics of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following, in combination with the drawings and preferred embodiments, details the specific implementation manners, structures, features, and effects of the technical solutions proposed according to the present invention. The specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs.

[0046] In this embodiment, referring to Figure 1 , the three - level bidirectional DC converter includes a high - voltage module, a transformer, an inductor L, and a low - voltage module. The high - voltage module is connected to the low - voltage module through the transformer and the resonant inductor.

[0047] The three-level bidirectional DC converter includes a high-voltage module, a transformer, a resonant inductor, and a low-voltage module. The high-voltage module is connected to the low-voltage module through the transformer and the resonant inductor. The high-voltage module sequentially includes a first bridge arm and a second bridge arm. The low-voltage module sequentially includes a third bridge arm and a fourth bridge arm. Among them, the upper end of the first bridge arm, the lower end of the first bridge arm, the upper end of the second bridge arm, the lower end of the second bridge arm, the third bridge arm, and the fourth bridge arm all include two power devices.

[0048] Specifically, the high-voltage module includes first switch tube S1 to eighth switch tube S8. The drain of the first switch tube S1 is connected to the drain of the fifth switch tube S5. The source of the first switch tube S1 is connected to the drain of the second switch tube S2. The source of the second switch tube S2 is connected to the drain of the third switch tube S3. The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4. The source of the fourth switch tube S4 is connected to the source of the eighth switch tube S8. The drain of the eighth switch tube S8 is connected to the source of the seventh switch tube S7. The drain of the seventh switch tube S7 is connected to the source of the sixth switch tube S6. The drain of the sixth switch tube S6 is connected to the source of the fifth switch tube S5. The connection midpoint between the source of the second switch tube S2 and the drain of the third switch tube S3 is connected to one side of the inductor L. The other side of the inductor L is connected to one end of the primary side of the transformer. The other end of the primary side of the transformer is connected to the connection midpoint between the drain of the seventh switch tube S7 and the source of the sixth switch tube S6. The drains of the first switch tube S1 and the fifth switch tube S5 are connected to the DC positive busbar. The sources of the fourth switch tube S4 and the eighth switch tube S8 are connected to the DC negative busbar. The first switch tube S1 to the eighth switch tube S8 all have built-in parasitic diodes. The anode of the parasitic diode is connected to the source of the corresponding switch tube, and the cathode of the parasitic diode is connected to the drain of the corresponding switch tube. The above switch tubes are all MOSFETs.

[0049] The power devices of the above high-voltage module are divided into four groups. The power devices of the above high-voltage module form an inverter bridge. The upper end of the first bridge arm includes the first switch tube S1 and the second switch tube S2. The lower end of the first bridge arm includes the third switch tube S3 and the fourth switch tube S4. The upper end of the second bridge arm includes the fifth switch tube S5 and the sixth switch tube S6. The lower end of the second bridge arm includes the seventh switch tube S7 and the eighth switch tube S8.

[0050] The high-voltage module also includes a first support capacitor C1, a second support capacitor C2, a first clamping diode D1, and a second clamping diode D2. The first support capacitor C1 and the second support capacitor C2 are connected in series and then connected to the DC positive / negative busbars respectively. After the first clamping diode D1 and the second clamping diode D2 are connected in series, the negative pole of the first clamping diode D1 is connected between the source of the first switch tube S1 and the drain of the second switch tube S2, and the positive pole of the second clamping diode D2 is connected between the source of the third switch tube S3 and the drain of the fourth switch tube D4.

[0051] The connection point between the first clamping diode D1 and the second clamping diode D2 is connected to the connection point between the first support capacitor C1 and the second support capacitor C2; after the third clamping diode D3 and the fourth clamping diode D4 are connected in series, the negative electrode of the fourth clamping diode D4 is connected between the source electrode of the fifth switching tube S5 and the drain electrode of the sixth switching tube S6, and the positive electrode of the fourth clamping diode D4 is connected between the source electrode of the seventh switching tube S7 and the drain electrode of the eighth switching tube S8; the connection point between the third clamping diode D3 and the fourth clamping diode D4 is connected to the connection point between the first support capacitor C1 and the second support capacitor C2.

[0052] The low-voltage module consists of four switching devices Q1, Q2, Q3, Q4 and a third support capacitor C3. Among them, the source electrode of the first switching device Q1 is connected to the drain electrode of the second switching device Q2, and the source electrode of the third switching device Q3 is connected to the drain electrode of the fourth switching device Q4; the third support capacitor C3 is connected across the DC positive / negative bus. One end of the secondary side of the transformer is connected to the midpoint between the source electrode of the first switching device Q1 and the drain electrode of the second switching device Q2, and the other end of the secondary side of the transformer is connected to the midpoint between the source electrode of the third switching device Q3 and the drain electrode of the fourth switching device Q4. The drain electrodes of the first switching device Q1 and the third switching device Q3 are connected to the DC positive bus, and the source electrodes of the second switching device Q2 and the fourth switching device Q4 are connected to the DC negative bus. The low-voltage module also includes a third support capacitor C3, one end of which is connected to the drain electrode of the third switching device Q3 and the other end is connected to the source electrode of the fourth switching device Q4.

[0053] The above low-voltage module is divided into two groups, and the power devices of the above low-voltage module form a rectifier bridge. The third bridge arm includes the first switching device Q1 and the second switching device Q2, and the fourth bridge arm includes the third switching device Q3 and the fourth switching device Q4.

[0054] Based on the above three-level bidirectional DC converter, referring to Figure 1 - Figure 2 , a fault diagnosis method for the open-circuit fault of the converter power device based on the fundamental frequency current characteristics is proposed, including the following steps:

[0055] Step 100: Preset the operating state information of the converter to be collected;

[0056] Step 200: Under rated operating conditions, test and obtain the initial value of the operating state of the three-level bidirectional DC converter, and filter the initial value to obtain the initial current component characteristic value;

[0057] Step 300: Test and obtain the operating state of the three-level bidirectional DC converter when the converter is put into operation, calculate the current component characteristic value in the operating state, and use this as the fault characteristic value;

[0058] Step 400: Calculate the change in the fundamental frequency amplitude of the current based on the initial current component eigenvalue and the fault eigenvalue; and perform a steady-state process on the change in the fundamental frequency amplitude of the current to obtain the abnormal degree of the current parameter.

[0059] Step 500: Determine the specific location of the open circuit fault in the three-level bidirectional DC converter based on the change in the fundamental frequency amplitude of the current and the abnormal degree of the current parameter.

[0060] The above steps will be elaborated in detail as follows:

[0061] Step 100: Preset the operating state information of the converter to be collected.

[0062] Set the key positions of the three-level bidirectional DC converter, and the key positions include the high-voltage input, the inverter bridge input, the inductor L flow-through, the output of the secondary side of the transformer, the output of the rectifier bridge, and the low-voltage side output.

[0063] The high-voltage input is the input side of the high-voltage module, and a current sensor is set here i , and the high-voltage side input DC current is obtained through the current sensor i ; the inverter bridge input is specifically between the drain of the first clamping diode D1 and the first switching transistor S1, and a current sensor is set here j , and the inverter bridge input current is obtained through the current sensor j ; the inductor L flow-through is specifically between the source of the second switching transistor S2 and the inductor L, and a current sensor is set here k k , and the AC current flowing through the inductor L is obtained through the current sensor ; the output of the secondary side of the transformer is specifically between one end of the secondary side of the transformer and the source of the first switching device Q1, and a current sensor is set here l， l , and the output current of the secondary side of the transformer is obtained through the current sensor m ; the output of the rectifier bridge is specifically between the drain of the third switching device Q3 and the third support capacitor C3, and a current sensor is set here m , and the output current of the rectifier bridge is obtained through the current sensor ; the low-voltage side output is specifically the output side of the low-voltage module, and a current sensor is set here n n , and the current at the low-voltage output is obtained through the current sensor

[0064] ​​​​​​​Record it N the current waveforms within cycles, and sequentially denote them as , , , , , where:

[0065] ;

[0066] In the formula, f f0 is the operating frequency of the converter, T T0 is the single operating cycle time of the power device of the converter.

[0067] Step 200: Under rated operating conditions, test and obtain the initial values of the operating state of the three-level bidirectional DC converter, and perform filtering processing on the initial values to obtain the initial current component eigenvalue.

[0068] As an example, this step 200 may include the following sub-steps:

[0069] Step 210: Before the three-level bidirectional DC converter is put into operation, under rated operating conditions, test the current waveforms at each key position of the three-level bidirectional DC converter as the initial values of the operating state of the three-level bidirectional DC converter.

[0070] The initial values of the operating state of the three-level bidirectional DC converter include: the initial value of the high-voltage side input DC current , the initial value of the input current of the inverter bridge , the initial value of the AC current flowing through the inductor L , the initial value of the output current of the secondary side of the transformer , the initial value of the output current of the rectifier bridge , the initial value of the current at the low-voltage output .

[0071] Step 220: Perform filtering processing on the initial value waveforms to obtain the fundamental frequency amplitude of the current of the initial values, that is, the initial current component eigenvalues at each key position.

[0072] ;

[0073] In the above formula, ω represents the angular frequency; represents the initial value of the current of the operating state of the converter; represents the initial current component eigenvalue; y represents the key position of the converter.

[0074] In a specific embodiment, the initial current component eigenvalues at each key position specifically include:

[0075] ;

[0076] In the above formula, ω represents the angular frequency, and the calculation formula is ω = 2π f 0; represents the eigenvalue of the initial current component at the high-voltage input; represents the eigenvalue of the initial current component at the input of the inverter bridge; represents the inductor L eigenvalue of the initial current component flowing through; represents the eigenvalue of the initial current component at the output of the secondary side of the transformer; represents the eigenvalue of the initial current component at the output of the rectifier bridge; represents the eigenvalue of the initial current component at the low-voltage output.

[0077] Step 300: When the converter is in the operating state, test to obtain the operating state of the three-level bidirectional DC converter, calculate the eigenvalue of the current component in the operating state, and use this as the fault eigenvalue.

[0078] For the three-level bidirectional DC converter in the operating state, perform periodic sampling and judgment on its operating state. Analyze the collected data of the above monitoring current sensors every X time, where X can be set as needed. Repeat the above process. At the x th sampling, obtain the operating state of the converter at the x th time, perform filtering processing on the operating state of the converter, calculate the eigenvalue of the current component in the operating state, and use this as the fault eigenvalue;

[0079] ;

[0080] In the above formula, represents the operating state of the converter at the x th time; represents the eigenvalue of the current component in the operating state, that is, the fault eigenvalue obtained by the x th sampling process.

[0081] In a specific embodiment, the operating state of the converter at the x th time includes: the high-voltage side input DC current at the x th time , the input current of the inverter bridge at the x th sampling , the AC current flowing through the inductor L at the x th sampling , the output current of the secondary side of the transformer at the x th sampling , the output current of the rectifier bridge at the xSub-sampled rectifier bridge output current and the current at the low-voltage output of the x th sub-sampling , the fault eigenvalue of the three-level bidirectional DC converter obtained by processing:

[0082] ;

[0083] In the above formula, represents the current component eigenvalue at the high-voltage input obtained by the x th sub-sampling during operation, that is, the fault eigenvalue at the high-voltage input; represents the component eigenvalue of the current at the input of the inverter bridge obtained by the x th sub-sampling during operation, that is, the fault eigenvalue at the input of the inverter bridge; represents the current component eigenvalue flowing through the inductor x obtained by the L th sub-sampling during operation, that is, the fault eigenvalue at the position where the inductor L flows through; represents the current component eigenvalue at the output of the secondary side of the transformer obtained by the x th sub-sampling during operation, that is, the fault eigenvalue at the output of the secondary side of the transformer; represents the current component eigenvalue at the output of the rectifier bridge obtained by the x th sub-sampling during operation, that is, the fault eigenvalue at the output of the rectifier bridge; represents the current component eigenvalue at the low-voltage output obtained by the x th sub-sampling during operation, that is, the fault eigenvalue at the low-voltage output.

[0084] Step 400: Based on the initial current component eigenvalue and the fault eigenvalue, calculate the change in the fundamental frequency amplitude of the current; and perform steady-state processing on the change in the fundamental frequency amplitude of the current to obtain the abnormal degree of the current parameter.

[0085] As an example, this step 400 may include the following sub-steps:

[0086] Step 410: Analyze the change in the fundamental frequency amplitude of the current based on the initial current component eigenvalue at each key position and the converter fault eigenvalue to obtain the change in the fundamental frequency amplitude of the current :

[0087] ;

[0088] In the formula, x represents the x th fault information processing process, , is an integer; represents thex- Fault eigenvalue of the three-level bidirectional DC converter obtained by the first sampling process; Denote the x fault eigenvalue of the three-level bidirectional DC converter obtained by the th sampling process; .

[0089] Step 420: Further eliminate the interference of sampling errors, etc., and perform a steady-state process on the above x change amount of the fundamental frequency parameters of the current for

[0090] times, and we can obtain:

[0091] In the formula, x denotes the x th fault information process. When the p th fault information process is performed, x = p ; characterizes the abnormal degree of the monitored current parameters at various positions during the operation of the three-level bidirectional DC converter, which can be used to reflect whether the converter has an open-circuit fault of the power device. At the same time, through the steady-state process, the interference caused by mode switching or control instability to the result can be avoided.

[0092] Step 500: Based on the change amount of the fundamental frequency amplitude of the current and the abnormal degree of the current parameters, determine the specific position where the three-level bidirectional DC converter has an open-circuit fault.

[0093] By comparing and analyzing the change amount of the fundamental frequency amplitude of the current in step 300 and the abnormal degree of the current parameters in step 400, determine the specific position where the open-circuit fault occurs in the primary side of the three-level bidirectional DC converter:

[0094] If the abnormal degree of the current parameters at the high-voltage input is equal to the abnormal degree of the current parameters at the input of the inverter bridge , and the abnormal degree of the current parameters at the position where the inductor L flows through is greater than the first threshold, and the change amount p of the fundamental frequency amplitude of the current at the position where the L th inductor flows through is less than or equal to the second threshold, the open-circuit fault appears at the upper end of the second bridge arm: the fifth switch tube S5 and the sixth switch tube S6. Here, the first threshold is 0.2 and the second threshold is 0.

[0095] That is, when , and , , the open-circuit fault appears at the upper end of the second bridge arm: the fifth switch tube S5 and the sixth switch tube S6.

[0096] If the abnormal degree of the current parameter at the high-voltage input is equal to the abnormal degree of the current parameter at the input of the inverter bridge , and the abnormal degree of the current parameter at the place where the inductor L flows through is greater than the first threshold, and the change amount of the fundamental frequency amplitude of the current at the place where the p th inductor L flows through is greater than the third threshold, the open-circuit fault appears at the lower end of the first bridge arm: the third switch tube S3 and the fourth switch tube S4. Wherein, the third threshold is 0.5.

[0097] That is, when , and , , the open-circuit fault appears at the lower end of the first bridge arm: the third switch tube S3 and the fourth switch tube S4.

[0098] If the abnormal degree of the current parameter at the high-voltage input is greater than the second threshold and less than the first threshold, and the abnormal degree of the current parameter at the high-voltage input is equal to the abnormal degree of the current parameter at the place where the inductor L flows through is less than or equal to the fourth threshold, and the change amount of the fundamental frequency amplitude of the current at the place where the p th inductor L flows through is greater than the third threshold, the open-circuit fault appears at the upper end of the first bridge arm: the first switch tube S1 and the second switch tube S2.

[0099] That is, when , , , the open-circuit fault appears at the upper end of the first bridge arm: the first switch tube S1 and the second switch tube S2.

[0100] If the abnormal degree of the current parameter at the high-voltage input is greater than the second threshold and less than the first threshold, and the abnormal degree of the current parameter at the high-voltage input is equal to the abnormal degree of the current parameter at the place where the inductor L flows through is less than or equal to the fourth threshold, and the change amount of the fundamental frequency amplitude of the current at the place where the p th inductor L flows through is less than or equal to the second threshold, the open-circuit fault appears at the lower end of the second bridge arm: the seventh switch tube S7 and the eighth switch tube S8.

[0101] That is, when , , , an open - circuit fault appears at the lower end of the second bridge arm: the seventh switch tube S7 and the eighth switch tube S8.

[0102] Similarly, the position of the power device with an open - circuit fault on the secondary side can be judged:

[0103] If the abnormal degree of the current parameter at the output of the rectifier bridge is equal to the abnormal degree of the current parameter at the low - voltage output , that is:

[0104] When , and , , an open - circuit fault appears in the third bridge arm: the first switching device Q1 and the second switching device Q2;

[0105] When , and , , an open - circuit fault appears in the fourth bridge arm: the third switching device Q3 and the fourth switching device Q4;

[0106] When , and , , the fault occurs at a position outside the power device.

[0107] In addition, the present invention can also achieve the following functions:

[0108] When electric energy is transmitted from the low - voltage module to the high - voltage module, for the current value of the open - circuit fault of the converter, regardless of its direction, the calculation process of the above - mentioned step 100 to step 500 can be carried out again, and the judgment basis is consistent with that in step 500.

[0109] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A fault diagnosis method for open - circuit faults of converter power devices based on fundamental - frequency current characteristics, characterized in that, It includes the following steps: Step 100: Preset the operating state information of the converter to be collected; Step 200: Under rated operating conditions, test to obtain the initial value of the converter operating state, and calculate the initial current component eigenvalue; Step 300: When the converter is put into the operating state, test to obtain the converter operating state, calculate the current component eigenvalue in the operating state, and use this as the fault eigenvalue; Step 400: Based on the initial current component eigenvalue and the fault eigenvalue, calculate the change in the fundamental frequency amplitude of the current; And perform a steady-state process on the change in the fundamental frequency amplitude of the current to obtain the abnormal degree of the current parameter; Step 500: Based on the change in the fundamental frequency amplitude of the current and the abnormal degree of the current parameter, determine the specific location of the open-circuit fault in the converter; In Step 100, before presetting the operating state information of the converter to be collected, it includes: setting the key positions of the converter, and the key positions include the high-voltage input, the inverter bridge input, the inductor flow-through, the transformer secondary side output, the rectifier bridge output, and the low-voltage side output; In step 400, based on the initial current component eigenvalue and the fault eigenvalue, the change amount of the fundamental current amplitude is calculated : ； In the formula, represents the eigenvalue of the current component in the operating state, that is, the fault eigenvalue obtained by the x -th sampling process; represents the converter fault eigenvalue obtained by the x- -th sampling process; represents the initial current component eigenvalue; x represents the process of the x -th fault information processing, , where is an integer; represents the key position of the converter; In Step 400, perform a steady-state process on the change in the fundamental frequency amplitude of the current to obtain the abnormal degree of the current parameter: ； In the formula, characterizes the abnormal degree of the monitored current parameters at each key position during the operation of the converter; x represents the x times of fault information processing. When p times of fault information processing are performed, x = p ; In Step 500, based on the change in the fundamental frequency amplitude of the current and the abnormal degree of the current parameter, determine the specific location of the open-circuit fault in the converter, including: When electric energy is transmitted from the high-voltage module to the low-voltage module, judge the location of the power device with the open-circuit fault; When and , a break fault appears at the upper end of the second arm When and , a break fault appears at the lower end of the arm of the first arm When , , , an open-circuit fault appears at the upper end of the first arm of the bridge arm; When , , , an open - circuit fault appears at the lower end of the second bridge arm. Among them, represents the abnormal degree of the current parameter at the high-voltage input, represents the abnormal degree of the current parameter at the input of the inverter bridge, represents the abnormal degree of the current parameter where the inductor passes through, Table p the change amount of the fundamental frequency amplitude of the current passing through the inductor for the When and , a break fault appears in the third bridge arm; When and , , an open-circuit fault appears in the fourth arm; When and , the fault occurs at a location outside the power device; Among them, represents the abnormal degree of the current parameter at the output of the rectifier bridge, represents the abnormal degree of the current parameter at the low-voltage output; represents the abnormal degree of the current parameter at the output of the secondary side of the transformer; represents the p change amount of the fundamental frequency amplitude of the current at the output of the secondary side of the transformer for the th time.

2. The method for diagnosing the open - circuit fault of the converter power device based on the fundamental - frequency current characteristics according to claim 1, wherein, In Step 100, the converter is a three-level bidirectional DC converter, and the three-level bidirectional DC converter includes a high-voltage module, a transformer, a resonant inductor, and a low-voltage module. The high-voltage module is connected to the low-voltage module through the transformer and the resonant inductor; the high-voltage module includes a first arm and a second arm; the low-voltage module includes a third arm and a fourth arm; among them, the upper end of the first arm, the lower end of the first arm, the upper end of the second arm, the lower end of the second arm, the third arm, and the fourth arm all include two power devices.

3. The method for diagnosing the open - circuit fault of the converter power device based on the fundamental - frequency current characteristics according to claim 2, wherein In Step 100, preset the operating state information of the converter, and the operating state information of the converter is the current at the key position.

4. A method for diagnosing an open-circuit fault of a converter power device based on fundamental frequency current characteristics according to claim 3, characterized in that In Step 200, it includes: filtering the initial value of the converter operating state to obtain the initial current component eigenvalue; ； In the above formula, ω represents the angular frequency; represents the initial value of the current indicating the operating state of the converter; ; f f₀ is the operating frequency of the converter, T T₀ is the single working cycle time of the power device of the converter, N T represents the period, t t represents the time variable of the time-domain current waveform.

5. The method for diagnosing the open - circuit fault of a converter power device based on the fundamental - frequency current characteristics according to claim 4, wherein In Step 300, it includes: analyzing the converter operating state every X time, filtering the converter operating state, and calculating the current component eigenvalue in the operating state, and using this as the fault eigenvalue; ； In the above formula, represents the x th operating state of the converter.

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