Three-level inverter power module detection circuit and detection method

Abstract

The invention discloses a three-level inverter power module detection circuit, including a supporting capacitor and an inverter bridge arm unit, the inverter bridge arm unit is respectively connected to the two ends of the supporting capacitor and a midpoint N, a voltage dividing unit is respectively provided between the midpoint O of the inverter bridge arm unit on the AC side and the bus positive pole and the bus negative pole of a DC power supply, a first voltage detector is provided at both ends of any one of the first voltage dividing unit and the second voltage dividing unit, and a second voltage detection element is provided between point N and the DC power supply. By providing a voltage dividing unit at the midpoint O of the AC side of the inverter bridge arm unit and the bus positive pole and the bus negative pole of the DC power supply, the first voltage detector is connected in parallel at both ends of one of the voltage dividing units, and a second voltage detector is provided between point N and the DC power supply, the power element and the voltage dividing unit are controlled to be closed or disconnected, and the detection values ​​of the two voltage detectors are compared with the theoretical voltage value when the power module is normal, to judge whether the power module is faulty, and the number of detection elements used is relatively small.

Description

Technical Field

[0001] The present invention relates to the technical field of three-level inverters, and in particular to a detection circuit and a detection method for a three-level inverter power module. Background Art

[0002] The three-level inverter is a widely used inverter system. Before connecting to the grid for power generation, the inverter usually detects the grid voltage, frequency, phase sequence and other parameters. When the inverter output parameters are synchronized with the grid parameters, it will connect to the grid for power generation. However, the detection of the power module inside the system is ignored. The power module is the core circuit of the inverter. If it is not detected, the inverter may not be able to connect to the grid for power generation normally. Summary of the invention

[0003] In view of the above analysis, the present invention proposes a three-level inverter power module detection circuit and detection method to solve the deficiencies of the prior art.

[0004] The present invention is mainly achieved through the following technical solutions:

[0005] The three-level inverter power module detection circuit provided by the present invention comprises a supporting capacitor and an inverter bridge arm unit, wherein the supporting capacitor comprises a first supporting capacitor and a second supporting capacitor, wherein the first supporting capacitor and the second supporting capacitor are connected in series and then connected in parallel on both sides of a DC power supply, wherein the inverter bridge arm unit is respectively connected to the two ends of the supporting capacitor and a midpoint N of the first supporting capacitor and the second supporting capacitor, wherein a first voltage dividing unit is provided between a midpoint O of an AC side of the inverter bridge arm unit and a positive busbar of a DC power supply, wherein a second voltage dividing unit is provided between a midpoint O of an AC side of the inverter bridge arm unit and a negative busbar of a DC power supply, wherein a first voltage detector is provided at both ends of any one of the first voltage dividing unit and the second voltage dividing unit, and wherein a second voltage detector is provided between the N point and the negative busbar or the positive busbar of the DC power supply.

[0006] Further, the inverter bridge arm unit includes a first power element, a second power element, a third power element, a fourth power element, a first diode and a second diode, the first power element, the second power element, the third power element and the fourth power element are connected in series in sequence, the first end of the first power element is connected to the first end of the first capacitor, the second end of the fourth power element is connected to the second end of the second capacitor, after the first diode and the second diode are connected in series, the cathode of the first diode is connected to the connection point of the first power element and the second power element, the anode of the second diode is connected to the connection point of the third power element and the fourth power element, and the connection point of the first diode and the second diode is connected to the midpoint N of the first support capacitor and the second support capacitor;

[0007] Alternatively, the first diode is replaced by a fifth power element, and the second diode is replaced by a sixth power element.

[0008] Further, the first voltage-dividing unit includes a first matching resistor and a first switch connected in series, the first matching resistor is connected to the first end of the first power element, the first switch is connected to the point O between the second power element and the third power element, and the second voltage-dividing unit includes a second matching resistor and a second switch connected in series, the second matching resistor is connected to the point O between the second power element and the third power element, and the second switch is connected to the second end of the fourth power element.

[0009] Furthermore, the first power element, the second power element, the third power element and the fourth power element are each an IGBT tube anti-parallel connected to a diode;

[0010] Alternatively, each of the first power element, the second power element, the third power element, the fourth power element, the fifth power element and the sixth power element is an IGBT tube connected in anti-parallel with a diode;

[0011] The IGBT tube can be replaced by MOSFET.

[0012] Furthermore, the third ends of the first power element, the second power element, the third power element and the fourth power element are all connected to the driving circuit;

[0013] Alternatively, the third ends of the first power element, the second power element, the third power element, the fourth power element, the fifth power element and the sixth power element are all connected to the driving circuit.

[0014] Further, the first switch and the second switch are respectively connected to the control unit;

[0015] Preferably, the electronic switch is an IGBT tube, a MOSFET or a triode, and the mechanical switch is a relay or a controllable contactor.

[0016] The present invention also provides a three-level inverter power module detection method, comprising the following steps:

[0017] Set the voltage value of the DC power supply to Vdc, and the voltage value of points N and O to V NO, the first supporting capacitor and the second supporting capacitor are charged to saturation. When all power elements and the voltage divider unit can work normally, the first voltage divider unit is connected in parallel with the first power element and the second power element, and other voltage divider units and power elements are disconnected. The impedance of the first voltage divider unit is matched, so that the detection value of the first voltage detector is s1*Vdc, s1∈(1 / 2, 1). The second voltage divider unit is connected in parallel with the third power element and the fourth power element, and other voltage divider units and power elements are disconnected. The impedance of the second voltage divider unit is matched, so that the detection value of the first voltage detector is s2*Vdc, s2∈(0, 1 / 2);

[0018] Respectively obtain theoretical detection values ​​of the first voltage detector and the second voltage detector under different test states when each power element and the voltage dividing unit are normally turned on;

[0019] When detecting the second power element, the first diode or the second power element, and the fifth power element, the second voltage divider unit is connected in parallel with the third power element and the fourth power element connected in series, the first voltage divider unit is disconnected, and each power element is turned off. The detection value of the first voltage detector obtained is compared with the theoretical voltage value s2*Vdc under the same detection state, and the detection value of the second voltage detector obtained is compared with the theoretical voltage value 1 / 2Vdc under the same detection state. If they are the same, proceed to the next step. If they are different, stop the detection.

[0020] Then the second power element is controlled to conduct, and after the voltage is balanced, the detection value of the first voltage detector is compared with the theoretical voltage value V2-V under the same detection state. NO Compare, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both less than 1 / 2Vdc, if the conditions are consistent, then the second power element, the first diode or the second power element, the anti-parallel diode on the fifth power element is normal, if they are different, then the second power element or the first diode is faulty, or the anti-parallel diode on the second power element or the fifth power element is faulty, and the detection is stopped;

[0021] On the basis that the second power element, the first diode or the second power element, and the anti-parallel diode on the fifth power element are normal, when detecting the first power element, the second voltage divider unit is disconnected, and then the first power element is controlled to be turned on, and the detection value obtained by the first voltage detector is compared with the theoretical voltage value Vdc under the same detection state. If they are the same, the first power element is normal, and if they are different, the first power element is faulty and the detection is stopped;

[0022] When detecting the third power element, the second diode or the anti-parallel diode on the third power element and the sixth power element, the first voltage divider unit is kept connected, other voltage divider units and power elements are turned off, the detection value of the first voltage detector is compared with the theoretical voltage value s1*Vdc under the same detection state, and the detection value of the second voltage detector is compared with the theoretical voltage value 1 / 2Vdc under the same detection state. If they are the same, proceed to the next step; if they are different, stop the detection;

[0023] Then the third power element is controlled to be turned on, and after the voltage is balanced, the detected value of the first voltage detector is compared with the theoretical voltage value V under the same detection state. NO +V2, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both greater than 1 / 2Vdc. If the conditions are consistent, the third power element, the second diode or the anti-parallel diode on the third power element and the sixth power element are normal. If they are different, the third power element or the second diode is faulty, or the anti-parallel diode on the third power element or the sixth power element is faulty, and the detection is stopped;

[0024] On the basis that the third power element, the second diode or the anti-parallel diode on the third power element and the sixth power element are normal, when detecting the fourth power element, the first voltage divider unit is disconnected, and then the fourth power element is controlled to be turned on, and the detection value of the first voltage detector is compared with the theoretical voltage value 0 under the same detection state. If they are the same, the fourth power element is normal. If they are different, the fourth power element is faulty and the detection is stopped.

[0025] Further, when the first diode is replaced by a fifth power element and the second diode is replaced by a sixth power element, the following steps are further included after detecting the first power element:

[0026] On the basis that the anti-parallel diodes on the second power element and the fifth power element are normal, when detecting the anti-parallel diodes on the sixth power element and the third power element, the second voltage divider unit is kept connected and the second power element is turned off.

[0027] Then the sixth power element is controlled to be turned on, and after the voltage is balanced, the detected value of the first voltage detector is compared with the theoretical voltage value V2-V under the same detection state. NO For comparison, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both less than 1 / 2Vdc. If the conditions are the same, the anti-parallel diodes on the sixth power element and the third power element are normal. If they are different, the anti-parallel diode on the sixth power element or the third power element is faulty, and detection is stopped.

[0028] Further, when the first diode is replaced by a fifth power element and the second diode is replaced by a sixth power element, the following steps are further included after the fourth power element is detected:

[0029] On the basis that the anti-parallel diodes on the third power element and the sixth power element are normal, when detecting the anti-parallel diodes on the fifth power element and the second power element, the first voltage dividing unit is kept connected and the third power element is turned off.

[0030] Then the fifth power element is controlled to be turned on, and the detected value of the first voltage detector is compared with the theoretical voltage value V under the same detection state. NO +V2 for comparison, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both greater than 1 / 2Vdc. If the conditions are consistent, the anti-parallel diodes on the fifth power element and the second power element are normal. If they are different, the anti-parallel diode on the fifth power element or the second power element is faulty, and detection stops.

[0031] Furthermore, pulse signals are applied to the power elements to be detected to turn them on.

[0032] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0033] The three-level inverter power module detection circuit and detection method provided by the present invention respectively set voltage dividing units at the midpoint O of the AC side of the inverter bridge arm unit and the bus positive pole and the bus negative pole of the DC power supply, connect a first voltage detector in parallel at both ends of at least one of the voltage dividing units, and set a second voltage detector between the point N and the bus positive pole or the bus negative pole of the DC power supply. By respectively controlling the closing or opening of the power element and the voltage dividing unit, and then comparing the detection values ​​of the two voltage detectors with the theoretical voltage value when the power module is normal, it is judged whether the power module is faulty. The number of detection elements used is small, the circuit structure is simple, and the power module can be preventively detected before the inverter is connected to the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 It is a circuit principle diagram of a three-level inverter power module detection circuit provided by an embodiment of the present invention when the power module is an NPC type;

[0036] FIG. 2( a ) is a diagram of an embodiment of the present invention. Figure 1The circuit schematic diagram when the second switch is closed;

[0037] FIG2( b ) is a pulse test diagram of the second switch in FIG2( a );

[0038] FIG. 3( a ) is a diagram of an embodiment of the present invention. Figure 1 A circuit schematic diagram when the second switch is closed and the second power element is turned on;

[0039] FIG3( b ) is a pulse test diagram of the second switch being closed and the second power element in FIG3( a );

[0040] FIG. 4( a ) is a diagram of an embodiment of the present invention. Figure 1 The circuit schematic diagram when the first switch is closed;

[0041] FIG4( b ) is a pulse test diagram of the first switch in FIG4( a );

[0042] FIG. 5( a ) is a diagram of an embodiment of the present invention. Figure 1 The circuit schematic diagram when the first switch is closed and the third power element is turned on;

[0043] FIG5( b ) is a pulse test diagram of the first switch and the third power element in FIG5( a );

[0044] FIG. 6( a ) is a diagram of an embodiment of the present invention. Figure 1 The circuit schematic diagram when all power components and switches are disconnected;

[0045] FIG6( b ) is a pulse test diagram when all power elements and switches in FIG6( a ) are disconnected;

[0046] FIG. 7( a ) is a diagram of an embodiment of the present invention. Figure 1 A circuit schematic diagram when the first power element and the second power element are turned on;

[0047] FIG7( b ) is a pulse test diagram of the first power element and the second power element in FIG7( a );

[0048] FIG8(a) is a diagram of an embodiment of the present invention. Figure 1 The circuit schematic diagram when the third power element and the fourth power element are turned on;

[0049] FIG8( b ) is a pulse test diagram of the third power element and the fourth power element in FIG8( a );

[0050] Fig. 9 A circuit schematic diagram of a three-level inverter power module detection circuit provided in an embodiment of the present invention when the power module is an ANPC type;

[0051] FIG. 10( a ) is a diagram of an embodiment of the present invention. Fig. 9The circuit schematic diagram when the second switch is closed;

[0052] FIG10( b ) is a pulse test diagram of the second switch in FIG10( a );

[0053] FIG. 11( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram when the second switch is closed and the second power element is turned on;

[0054] FIG11( b ) is a pulse test diagram of the second switch and the second power element in FIG11( a );

[0055] FIG. 12( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram when the second switch is closed and the sixth power element is turned on;

[0056] FIG12( b ) is a pulse test diagram of the second switch and the sixth power element in FIG12( a );

[0057] FIG. 13( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram of the first switch closing test;

[0058] FIG13( b ) is a pulse test diagram of the first switch in FIG13( a );

[0059] FIG. 14( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram when the first switch is closed and the third power element is turned on;

[0060] FIG14( b ) is a pulse test diagram of the first switch and the third power element in FIG14( a );

[0061] FIG. 15( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram when the first switch is closed and the fifth power element is turned on;

[0062] FIG15( b ) is a pulse test diagram of the first switch and the fifth power element in FIG15( a );

[0063] FIG. 16( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram when all power components and switches are disconnected;

[0064] FIG16( b ) is a pulse test diagram when all power elements and switches in FIG16( a ) are disconnected;

[0065] FIG. 17( a ) is a diagram of an embodiment of the present invention. Fig. 9 A circuit schematic diagram when the first power element and the second power element are turned on;

[0066] FIG17( b ) is a pulse test diagram of the first power element and the second power element in FIG17( a );

[0067] FIG. 18( a ) is a diagram of an embodiment of the present invention. Fig. 9 The circuit schematic diagram when the third power element and the fourth power element are turned on;

[0068] FIG18( b ) is a pulse test diagram of the third power element and the fourth power element in FIG18( a ). DETAILED DESCRIPTION

[0069] In order to enable those skilled in the art to better understand the present invention, and thus to more clearly define the scope of the present invention, the present invention is described in detail with respect to some specific embodiments of the present invention. It should be noted that the following are only some specific implementation methods of the present invention, which are only part of the embodiments of the present invention, wherein the specific and direct description of the relevant structure is only for the convenience of understanding the present invention, and each specific feature does not naturally and directly limit the scope of implementation of the present invention. The conventional selection and replacement made by those skilled in the art under the guidance of the present invention should be regarded as within the scope of the present invention.

[0070] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0071] Example 1

[0072] The present invention provides a three-level inverter power module detection circuit, including a support capacitor and an inverter bridge arm unit, the support capacitor includes a first support capacitor C1 and a second support capacitor C2, the first support capacitor C1 and the second support capacitor C2 are connected in series and then connected in parallel on both sides of a direct current power supply DC, the inverter bridge arm unit is respectively connected to the two ends of the support capacitor and the midpoint N of the first support capacitor C1 and the second support capacitor C2, a first voltage divider unit is provided between the midpoint O of the AC side of the inverter bridge arm unit and the positive pole of the busbar of the direct current power supply DC, a second voltage divider unit is provided between the midpoint O of the AC side of the inverter bridge arm unit and the negative pole of the busbar of the direct current power supply DC, a first voltage detector is provided at both ends of any one of the first voltage divider unit and the second voltage divider unit, and a second voltage detector is provided between the N point and the negative pole or positive pole of the busbar of the direct current power supply. Wherein, the direct current power supply DC is an adjustable direct current power supply. The capacitance values ​​of C1 and C2 are equal.

[0073] like Figure 1As shown, preferably, the inverter bridge arm unit includes a first power element T1, a second power element T2, a third power element T3, a fourth power element T4, a first diode D1 and a second diode D2. The first power element T1, the second power element T2, the third power element T3 and the fourth power element T4 are connected in series in sequence. The first end of the first power element T1 is connected to the first end of the first capacitor, and the second end of the fourth power element T4 is connected to the second end of the second capacitor. After the first diode D1 and the second diode D2 are connected in series, the cathode of the first diode D1 is connected to the connection point of the first power element T1 and the second power element T2, the anode of the second diode D2 is connected to the connection point of the third power element T3 and the fourth power element T4, and the connection point of the first diode D1 and the second diode D2 is connected to the midpoint N of the first supporting capacitor C1 and the second supporting capacitor C2.

[0074] Specifically, the first power element T1, the second power element T2, the third power element T3 and the fourth power element T4 are each an IGBT tube connected in anti-parallel with a diode. The IGBT tube can be replaced by a MOSFET.

[0075] Specifically, the third ends of the first power element T1 , the second power element T2 , the third power element T3 , and the fourth power element T4 are all connected to the driving circuit.

[0076] like Fig. 9 As shown, preferably, the first diode D1 in the above-mentioned inverter bridge arm unit is replaced by a fifth power element T5, and the second diode D2 is replaced by a sixth power element T6.

[0077] Specifically, the first power element T1, the second power element T2, the third power element T3, the fourth power element T4, the fifth power element T5 and the sixth power element T6 are each an IGBT tube connected in anti-parallel with a diode. The IGBT tube can be replaced by a MOSFET.

[0078] Specifically, the third ends of the first power element T1 , the second power element T2 , the third power element T3 , the fourth power element T4 , the fifth power element T5 , and the sixth power element T6 are all connected to the driving circuit.

[0079] Preferably, the first voltage divider unit includes a first matching resistor R1 and a first switch K1 connected in series, the first matching resistor R1 is connected to the first end of the first power element T1, the first switch K1 is connected to the point O between the second power element T2 and the third power element T3, and the second voltage divider unit includes a second matching resistor R2 and a second switch K2 connected in series, the second matching resistor R2 is connected to the point O between the second power element T2 and the third power element T3, and the second switch K2 is connected to the second end of the fourth power element T4.

[0080] Preferably, the first switch K1 and the second switch K2 are electronic switches or mechanical switches.

[0081] Furthermore, the electronic switch is an IGBT tube or a MOSFET or a triode, and the mechanical switch is a relay or a controllable contactor.

[0082] Specifically, the first switch K1 and the second switch K2 are respectively connected to the control unit to control the switches to be turned on.

[0083] As shown in Figure 2-8, when the power module is an NPC type, the self-test steps are as follows:

[0084] 1) Set the DC power supply voltage to Vdc, and the voltage values ​​at points N and O to V NO , the first supporting capacitor C1 and the second supporting capacitor C2 are charged to saturation, and the theoretical values ​​of the first voltage detector V1 and the second voltage detector V2 when each power element and the voltage dividing unit are normally turned on are respectively obtained, and the impedance of the first matching resistor R1 and the second matching resistor R2 are matched according to the actual situation. For the specific matching steps, please refer to the content of the detection method;

[0085] 2) IGBT tube (T2) and diode (D1) self-test:

[0086] The switch (K2) is closed, the IGBT tubes (T1, T2, T3, T4) are turned off, and the switch (K1) is opened. If the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value, and a=s2*Vdc, s2∈(0, 1 / 2), the voltage value detected by the second voltage detector V2 is the same as the theoretical voltage value, which is 1 / 2Vdc; under the above conditions, the IGBT tube (T2) is turned on again, and after voltage balance is achieved, if the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value b, and is V2-V NO At this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2Vdc. If the conditions are consistent, the IGBT tube (T2) and the diode (D1) are intact; otherwise, the IGBT tube (T2) or the diode (D1) is faulty and the detection is stopped.

[0087] 3) Perform a self-test of the IGBT tube (T1) when the IGBT tube (T2) and diode (D1) are in good condition:

[0088] Under the conditions of step 2), the switch (K2) is turned off, and then the IGBT tube (T1) is controlled to be turned on. At this time, the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value f of V1, and is Vdc; that is, the IGBT tube (T1) is intact; otherwise, the IGBT tube (T1) is faulty and the detection is stopped.

[0089] 4) IGBT tube (T3) and diode (D2) self-test:

[0090] The switch (K1) is closed, the IGBT tubes (T1, T2, T3, T4) are turned off, and the switch (K2) is opened. If the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value, and is c=s1*Vdc, s1∈(1 / 2, 1), the detection value of the second voltage detector V2 is the same as the theoretical voltage value, which is 1 / 2Vdc; under the above conditions, the IGBT tube (T3) is turned on again. After the voltage balance is achieved, if the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value d, and is V NO +V2, at this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc. If the conditions are consistent, the IGBT tube (T3) and the diode (D2) are intact; otherwise, the IGBT tube (T3) or the diode (D2) is faulty and the detection is stopped.

[0091] 5) If the IGBT tube (T3) and diode (D2) are in good condition, perform self-test on the IGBT tube (T4):

[0092] Under the conditions of step 4), the switch (K1) is turned off and the IGBT tube (T4) is turned on. At this time, the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value g of V1 and is 0; that is, the IGBT tube (T4) is intact; otherwise, the IGBT tube (T4) is faulty and the detection is stopped.

[0093] As shown in Figure 10-18, when the power module is ANPC type, the self-test steps are as follows:

[0094] 1) Set the DC power supply voltage to Vdc, and the voltage values ​​at points N and O to V NO , the first supporting capacitor C1 and the second supporting capacitor C2 are charged to saturation, and the theoretical values ​​of the first voltage detector V1 and the second voltage detector V2 when each power element and the voltage dividing unit are normally turned on are respectively obtained, and the impedance of the first matching resistor R1 and the second matching resistor R2 are matched according to the actual situation. For the specific matching steps, please refer to the content of the detection method;

[0095] 2) Self-test of IGBT tube (T2) and IGBT tube (T5) anti-parallel diodes:

[0096] The switch (K2) is closed, the IGBT tubes (T1, T2, T3, T4, T5, T6) are turned off, and the switch (K1) is opened. If the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value, and a=s2*Vdc, s2∈(0, 1 / 2), the voltage value detected by the second voltage detector V2 is the same as the theoretical voltage value, which is 1 / 2Vdc; under the above conditions, the IGBT tube (T2) is turned on again, and after voltage balance is achieved, if the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value b, and is V2-V NOAt this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2Vdc. If the conditions are consistent, that is, the anti-parallel diodes of the IGBT tube (T2) and the IGBT tube (T5) are intact; otherwise, the anti-parallel diode of the IGBT tube (T2) or the IGBT tube (T5) is faulty and the detection is stopped.

[0097] 3) Perform self-test of IGBT tube (T1) when the anti-parallel diodes of IGBT tube (T2) and IGBT tube (T5) are intact:

[0098] Under the conditions of step 2), the switch (K2) is turned off, and then the IGBT tube (T1) is controlled to be turned on. At this time, the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value h of V1, and is Vdc; that is, the IGBT tube (T1) is intact; otherwise, the IGBT tube (T1) is faulty and the detection is stopped.

[0099] 4) Self-test of IGBT tube (T6) and IGBT tube (T3) anti-parallel diode:

[0100] Under the conditions of step 2), the IGBT tube (T2) is turned off, and the IGBT tube (T6) is turned on. After the voltage balance is achieved, if the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value c, and is V2-V NO At this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2Vdc. If the conditions are consistent, that is, the anti-parallel diodes of the IGBT tube (T6) and the IGBT tube (T3) are intact; otherwise, the anti-parallel diode of the IGBT tube (T6) or the IGBT tube (T3) is faulty and the detection is stopped.

[0101] 5) Self-test of IGBT tube (T3) and IGBT tube (T6) anti-parallel diodes:

[0102] The switch (K1) is closed, the IGBT tubes (T1, T2, T3, T4, T5, T6) are turned off, and the switch (K2) is opened. If the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value, and is d=s1*Vdc, s1∈(1 / 2, 1), the detection value of the second voltage detector V2 is the same as the theoretical voltage value, which is 1 / 2Vdc; under the above conditions, the IGBT tube (T3) is turned on again. After the voltage balance is achieved, if the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value e, and is V NO +V2, at this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc. If the conditions are consistent, that is, the anti-parallel diodes of the IGBT tube (T3) and the IGBT tube (T6) are intact; otherwise, the anti-parallel diodes of the IGBT tube (T3) or the IGBT tube (T6) are faulty and the detection is stopped.

[0103] 6) Perform self-test of IGBT tube (T4) when the anti-parallel diodes of IGBT tube (T3) and IGBT tube (T6) are intact:

[0104] Under the conditions of step 5), the switch (K1) is turned off and the IGBT tube (T4) is turned on. At this time, the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value i of V1 and is 0; that is, the IGBT tube (T4) is intact; otherwise, the IGBT tube (T4) is faulty and the detection is stopped.

[0105] 7) Self-test of IGBT tube (T5) and IGBT tube (T2) anti-parallel diodes:

[0106] Under the conditions of step 5), the IGBT tube (T3) is turned off, and then the IGBT tube (T5) is turned on. After the voltage balance is achieved, if the voltage value detected by the first voltage detector V1 is the same as the theoretical voltage value f, and is V NO +V2, at this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc. If the conditions are consistent, that is, the anti-parallel diodes of the IGBT tube (T5) and the IGBT tube (T2) are intact; otherwise, the anti-parallel diode of the IGBT tube (T5) or the IGBT tube (T2) is faulty and the detection is stopped.

[0107] If any IGBT tube fails, detection will be stopped.

[0108] The present invention also provides a three-level inverter power module detection method, comprising the following steps:

[0109] Set the voltage value of the DC power supply DC to Vdc, and the voltage value of the N and O points to V NO , the first supporting capacitor C1 and the second supporting capacitor C2 are charged to saturation. When all power elements and voltage divider units can work normally, the first voltage divider unit is connected in parallel with the first power element T1 and the second power element T2, and other voltage divider units and power elements are disconnected. The impedance of the first voltage divider unit is matched, so that the detection value of the first voltage detector V1 is s1*Vdc, s1∈(1 / 2, 1). The second voltage divider unit is connected in parallel with the third power element and the fourth power element T4, and other voltage divider units and power elements are disconnected. The impedance of the second voltage divider unit is matched, so that the detection value of the first voltage detector V1 is s2*Vdc, s2∈(0, 1 / 2);

[0110] Respectively obtain theoretical detection values ​​of the first voltage detector V1 and the second voltage detector V2 under different test states when each power element and the voltage dividing unit are normally turned on;

[0111] When detecting the second power element T2, the first diode or the second power element T2, and the fifth power element T5, the second voltage divider unit is connected in parallel with the third power element T3 and the fourth power element T4 connected in series, the first voltage divider unit is disconnected, and each power element is turned off. The detection value of the first voltage detector V1 obtained is compared with the theoretical voltage value s2*Vdc under the same detection state, and the detection value of the second voltage detector obtained is compared with the theoretical voltage value 1 / 2Vdc under the same detection state. If they are the same, proceed to the next step. If they are different, stop the detection.

[0112] Then the second power element T2 is controlled to be turned on. After the voltage is balanced, the detected value of the first voltage detector V1 is compared with the theoretical voltage value V2-V under the same detection state. NO Compare, at this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2Vdc, if the conditions are consistent, then the second power element T2, the first diode or the second power element T2, the anti-parallel diode on the fifth power element T5 are normal, if they are different, then the second power element T2 or the first diode is faulty, or the anti-parallel diode on the second power element T2 or the fifth power element T5 is faulty, and the detection is stopped;

[0113] On the basis that the second power element T2, the first diode or the second power element T2, and the anti-parallel diode on the fifth power element T5 are normal, when detecting the first power element T1, the second voltage divider unit is disconnected, and then the first power element T1 is controlled to be turned on, and the detection value of the first voltage detector V1 is obtained and compared with the theoretical voltage value Vdc under the same detection state. If they are the same, the first power element T1 is normal, and if they are different, the first power element T1 is faulty, and the detection is stopped;

[0114] When detecting the third power element T3, the second diode or the anti-parallel diode on the third power element T3 and the sixth power element T6, the first voltage divider unit is kept connected, other voltage divider units and power elements are turned off, the detection value of the first voltage detector V1 obtained is compared with the theoretical voltage value s1*Vdc under the same detection state, and the detection value of the second voltage detector V2 obtained is compared with the theoretical voltage value 1 / 2Vdc under the same detection state. If they are the same, proceed to the next step, and if they are different, stop the detection;

[0115] Then the third power element T3 is controlled to be turned on. After the voltage is balanced, the detected value of the first voltage detector V1 is compared with the theoretical voltage value V under the same detection state. NO+V2, at this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc. If the conditions are consistent, the third power element T3, the second diode or the anti-parallel diode on the third power element T3 and the sixth power element T6 are normal. If they are different, the third power element T3 or the second diode is faulty, or the anti-parallel diode on the third power element T3 or the sixth power element T6 is faulty, and the detection is stopped;

[0116] On the basis that the third power element T3, the second diode or the third power element T3, and the anti-parallel diode on the sixth power element T6 are normal, when detecting the fourth power element T4, the first voltage divider unit is disconnected, and then the fourth power element T4 is controlled to be turned on, and the detection value of the first voltage detector V1 is compared with the theoretical voltage value under the same detection state. If they are the same, the fourth power element T4 is normal; if they are different, the fourth power element T4 is faulty and the detection is stopped.

[0117] Wherein, S1 and S2 are both voltage coefficients. S1 and S2 will change according to the resistance value of the first distribution resistor R1 and the second distribution resistor R2. The impedance of the voltage dividing branch is different, and the voltage shared by the corresponding parallel power elements is also different.

[0118] Preferably, pulse signals are applied to the power elements to be detected to turn them on.

[0119] When the power module is an NPC type, specifically, obtaining the theoretical values ​​of the first voltage detector V1 and the second voltage detector V2 under different test states when each power element and the voltage dividing branch are normally turned on includes the following steps:

[0120] Control the second voltage divider circuit to access the circuit, disconnect the power elements and other voltage divider branches, match the impedance of the second matching resistor R2, so that the detection value of the first voltage detector V1 is the theoretical voltage value a=s2*Vdc under the current test state, s2∈(0,1 / 2), and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, which is 1 / 2Vdc;

[0121] Under the conditions of the previous step, the second power element T2 is controlled to be turned on. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value b under the current test state. Since b will gradually increase from a, and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, this theoretical voltage value will gradually decrease from 1 / 2Vdc until V1=V2-V NO The voltage balance is reached, at which time the theoretical voltage values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2 Vdc;

[0122] Control the first voltage divider circuit to access the circuit, disconnect the power elements and other voltage divider branches, match the impedance of the first matching resistor R1, so that the detection value of the first voltage detector V1 is the theoretical voltage value c=s1*Vdc under the current test state, s1∈(1 / 2,1), and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, which is 1 / 2Vdc;

[0123] Under the conditions of the previous step, the third power element T3 is controlled to be turned on. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value d under the current test state. Since d will gradually decrease from c, and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, this theoretical voltage value will gradually increase from 1 / 2Vdc until V1=V NO +V2 reaches voltage balance, at which point the theoretical voltage values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc;

[0124] Disconnect each power element and the voltage dividing branch. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value e=1 / 2Vdc under the current test state;

[0125] The first power element T1 and the second power element T2 are controlled to be turned on, and other power elements and the voltage dividing branch are turned off. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value f=Vdc under the current test state;

[0126] The third power element T3 and the fourth power element T4 are controlled to be turned on, and other power elements and the voltage dividing branch are turned off. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value g=0 in the current test state.

[0127] When the first diode is replaced by the fifth power element T5 and the second diode is replaced by the sixth power element T6, preferably, after detecting the first power element T1, the following steps are further included:

[0128] On the basis that the anti-parallel diodes on the second power element T2 and the fifth power element T5 are normal, when detecting the anti-parallel diodes on the sixth power element T6 and the third power element T3, the second voltage divider unit is kept connected, the second power element T2 is turned off, and the sixth power element T6 is controlled to be turned on. After the voltage balance is achieved, the detection value of the first voltage detector V1 is obtained and compared with the theoretical voltage value V2-V under the same detection state. NO For comparison, at this time, the detection values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2Vdc. If the conditions are consistent, the anti-parallel diodes on the sixth power element T6 and the third power element T3 are normal. If they are different, the anti-parallel diodes on the sixth power element T6 or the third power element T3 are faulty, and detection is stopped.

[0129] When the first diode is replaced by the fifth power element T5, and the second diode is replaced by the sixth power element T6, preferably, after detecting the fourth power element T4, the following steps are further included:

[0130] On the basis that the anti-parallel diodes on the third power element T3 and the sixth power element T6 are normal, when detecting the anti-parallel diodes on the fifth power element T5 and the second power element T2, the connection state of the first voltage divider unit is maintained, the third power element is turned off, and the fifth power element T5 is controlled to be turned on, and the detection value of the first voltage detector V1 obtained is compared with the theoretical voltage value V under the same detection state. NO +V2 for comparison, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both greater than 1 / 2Vdc. If the conditions are consistent, the anti-parallel diodes on the fifth power element T5 and the second power element T2 are normal. If they are different, the anti-parallel diodes on the fifth power element T5 or the second power element T2 are faulty, and detection is stopped.

[0131] When the power module is of ANPC type, specifically, obtaining theoretical values ​​of the first voltage detector V1 and the second voltage detector V2 under different test states when each power element and the voltage dividing branch are normally turned on includes the following steps:

[0132] 1) Control the second voltage divider circuit to access the circuit, disconnect the power elements and other voltage divider branches, match the impedance of the second matching resistor R2, so that the detection value of the first voltage detector V1 is the theoretical voltage value a=s2*Vdc under the current test state, s2∈(0,1 / 2), and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, which is 1 / 2Vdc;

[0133] 2) Under the condition of step 1), the second power element T2 is controlled to be turned on. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value b under the current test state. Since b will gradually increase from a, the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state. This theoretical voltage value will gradually decrease from 1 / 2Vdc until V1=V2-V NO The voltage balance is reached, at which time the theoretical voltage values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2 Vdc;

[0134] 3) Under the condition of step 1), the sixth power element T6 is controlled to be turned on. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value c under the current test state. Since c will gradually increase from a, and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, this theoretical voltage value will gradually decrease from 1 / 2Vdc until V1=V2-V NOThe voltage balance is reached, at which time the theoretical voltage values ​​of the first voltage detector V1 and the second voltage detector V2 are both less than 1 / 2 Vdc;

[0135] 4) Control the first voltage divider circuit to access the circuit, disconnect the power elements and other voltage divider branches, match the impedance of the first matching resistor R1, so that the detection value of the first voltage detector V1 is the theoretical voltage value d=s1*Vdc, s1∈(1 / 2,1), and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, which is 1 / 2Vdc;

[0136] 5) Under the condition of step 4), the third power element T3 is controlled to be turned on. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value e under the current test state. Since e will gradually decrease from d, and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, this theoretical voltage value will gradually increase from 1 / 2Vdc until V1=V NO +V2 reaches voltage balance, at which point the theoretical voltage values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc;

[0137] 6) Under the condition of step 4), the fifth power element T5 is controlled to be turned on. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value f under the current test state. Since f will gradually decrease from d, and the detection value of the second voltage detector V2 is the theoretical voltage value under the current test state, this theoretical voltage value will gradually increase from 1 / 2Vdc until V1=V NO +V2 reaches voltage balance, at which point the theoretical voltage values ​​of the first voltage detector V1 and the second voltage detector V2 are both greater than 1 / 2Vdc;

[0138] 7) Disconnect all power components and voltage-dividing branches. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value g=1 / 2Vdc under the current test state;

[0139] 8) Control the first power element T1 and the second power element T2 to be turned on, and other power elements and the voltage dividing branch to be turned off. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value h=Vdc under the current test state;

[0140] 9) The third power element T3 and the fourth power element T4 are controlled to be turned on, and other power elements and the voltage dividing branch are turned off. At this time, the detection value of the first voltage detector V1 is the theoretical voltage value i=0 in the current test state.

[0141] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A three-level inverter power module detection circuit, characterized in that: It includes a supporting capacitor and an inverter bridge arm unit, the supporting capacitor includes a first supporting capacitor and a second supporting capacitor, the first supporting capacitor and the second supporting capacitor are connected in series and then connected in parallel on both sides of a DC power supply, the inverter bridge arm unit is respectively connected to the two ends of the supporting capacitor and the midpoint N of the first supporting capacitor and the second supporting capacitor, a first voltage dividing unit is provided between the midpoint O of the AC side of the inverter bridge arm unit and the positive pole of the busbar of the DC power supply, a second voltage dividing unit is provided between the midpoint O of the AC side of the inverter bridge arm unit and the negative pole of the busbar of the DC power supply, a first voltage detector is provided at both ends of any one of the first voltage dividing unit and the second voltage dividing unit, and a second voltage detector is provided between the N point and the negative pole or positive pole of the busbar of the DC power supply; The inverter bridge arm unit includes a first power element, a second power element, a third power element, a fourth power element, a first diode and a second diode, wherein the first power element, the second power element, the third power element and the fourth power element are connected in series in sequence, the first end of the first power element is connected to the first end of the first capacitor, the second end of the fourth power element is connected to the second end of the second capacitor, after the first diode and the second diode are connected in series, the cathode of the first diode is connected to the connection point of the first power element and the second power element, the anode of the second diode is connected to the connection point of the third power element and the fourth power element, and the connection point of the first diode and the second diode is connected to the midpoint N of the first support capacitor and the second support capacitor; The first voltage dividing unit includes a first matching resistor and a first switch connected in series, the first matching resistor is connected to the first end of the first power element, and the first switch is connected to the O point between the second power element and the third power element. The second voltage dividing unit includes a second matching resistor and a second switch connected in series, the second matching resistor is connected to the O point between the second power element and the third power element, and the second switch is connected to the second end of the fourth power element.

2. The three-level inverter power module detection circuit according to claim 1, characterized in that: The first diode is replaced by a fifth power element, and the second diode is replaced by a sixth power element.

3. The three-level inverter power module detection circuit according to claim 1 or 2, characterized in that: The first power element, the second power element, the third power element and the fourth power element are each an IGBT tube connected in anti-parallel with a diode; Alternatively, each of the first power element, the second power element, the third power element, the fourth power element, the fifth power element and the sixth power element is an IGBT tube connected in anti-parallel with a diode; Alternatively, the IGBT tube is replaced by a MOSFET.

4. The three-level inverter power module detection circuit according to claim 3, characterized in that: The third ends of the first power element, the second power element, the third power element and the fourth power element are all connected to the driving circuit; Alternatively, the third ends of the first power element, the second power element, the third power element, the fourth power element, the fifth power element and the sixth power element are all connected to the driving circuit.

5. The three-level inverter power module detection circuit according to claim 1, characterized in that: The first switch and the second switch are connected to the control unit respectively.

6. The three-level inverter power module detection circuit according to claim 1, characterized in that: The first switch and the second switch are electronic switches or mechanical switches; The electronic switch is an IGBT tube or a MOSFET or a triode, and the mechanical switch is a relay or a controllable contactor.

7. A detection method for a three-level inverter power module detection circuit according to any one of claims 1 to 6, characterized in that: The steps include: Set the voltage value of the DC power supply to Vdc, and the voltage value of points N and O to V NO , the first supporting capacitor and the second supporting capacitor are charged to saturation. When all power elements and the voltage divider unit can work normally, the first voltage divider unit is connected in parallel with the first power element and the second power element, and other voltage divider units and power elements are disconnected. The impedance of the first voltage divider unit is matched, so that the detection value of the first voltage detector is s1*Vdc, s1∈(1 / 2, 1). The second voltage divider unit is connected in parallel with the third power element and the fourth power element, and other voltage divider units and power elements are disconnected. The impedance of the second voltage divider unit is matched, so that the detection value of the first voltage detector is s2*Vdc, s2∈(0, 1 / 2); Respectively obtain theoretical detection values ​​of the first voltage detector and the second voltage detector under different test states when each power element and the voltage dividing unit are normally turned on; When detecting the second power element, the first diode or the second power element, and the fifth power element, the second voltage divider unit is connected in parallel with the third power element and the fourth power element connected in series, the first voltage divider unit is disconnected, and each power element is turned off. The detection value of the first voltage detector obtained is compared with the theoretical voltage value s2*Vdc under the same detection state, and the detection value of the second voltage detector obtained is compared with the theoretical voltage value 1 / 2Vdc under the same detection state. If they are the same, proceed to the next step. If they are different, stop the detection. Then the second power element is controlled to conduct, and after the voltage is balanced, the detection value of the first voltage detector is compared with the theoretical voltage value V2-V under the same detection state. NO Compare, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both less than 1 / 2Vdc, if the conditions are consistent, then the second power element, the first diode or the second power element, the anti-parallel diode on the fifth power element is normal, if they are different, then the second power element or the first diode is faulty, or the anti-parallel diode on the second power element or the fifth power element is faulty, and the detection is stopped; On the basis that the second power element, the first diode or the second power element, and the anti-parallel diode on the fifth power element are normal, when detecting the first power element, the second voltage divider unit is disconnected, and then the first power element is controlled to be turned on, and the detection value of the first voltage detector is compared with the theoretical voltage value Vdc under the same detection state. If they are the same, the first power element is normal, and if they are different, the first power element is faulty and the detection is stopped; When detecting the third power element, the second diode or the anti-parallel diode on the third power element and the sixth power element, the first voltage divider unit is kept connected, other voltage divider units and power elements are turned off, the detection value of the first voltage detector is compared with the theoretical voltage value s1*Vdc under the same detection state, and the detection value of the second voltage detector is compared with the theoretical voltage value 1 / 2Vdc under the same detection state. If they are the same, proceed to the next step; if they are different, stop the detection; Then the third power element is controlled to be turned on, and after the voltage is balanced, the detected value of the first voltage detector is compared with the theoretical voltage value V under the same detection state. NO +V2, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both greater than 1 / 2Vdc. If the conditions are consistent, the third power element, the second diode or the anti-parallel diode on the third power element and the sixth power element are normal. If they are different, the third power element or the second diode is faulty, or the anti-parallel diode on the third power element or the sixth power element is faulty, and the detection is stopped; On the basis that the third power element, the second diode or the anti-parallel diode on the third power element and the sixth power element are normal, when detecting the fourth power element, the first voltage divider unit is disconnected, and then the fourth power element is controlled to be turned on, and the detection value of the first voltage detector is compared with the theoretical voltage value 0 under the same detection state. If they are the same, the fourth power element is normal. If they are different, the fourth power element is faulty and the detection is stopped.

8. The three-level inverter power module detection method according to claim 7, characterized in that: When the first diode is replaced by the fifth power element and the second diode is replaced by the sixth power element, the following steps are further included after detecting the first power element: On the basis that the anti-parallel diodes on the second power element and the fifth power element are normal, when detecting the anti-parallel diodes on the sixth power element and the third power element, the second voltage divider unit is kept connected, the second power element is turned off, and the sixth power element is controlled to be turned on. After the voltage balance is achieved, the detection value of the first voltage detector is obtained and compared with the theoretical voltage value V2-V under the same detection state. NO For comparison, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both less than 1 / 2Vdc. If the conditions are the same, the anti-parallel diodes on the sixth power element and the third power element are normal. If they are different, the anti-parallel diode on the sixth power element or the third power element is faulty, and detection is stopped.

9. The three-level inverter power module detection method according to claim 7 or 8, characterized in that: When the first diode is replaced by a fifth power element and the second diode is replaced by a sixth power element, the following steps are further included after detecting the fourth power element: On the basis that the anti-parallel diodes on the third power element and the sixth power element are normal, when detecting the anti-parallel diodes on the fifth power element and the second power element, the connection state of the first voltage divider unit is maintained, the third power element is turned off, and the fifth power element is controlled to be turned on, and the detection value of the first voltage detector obtained is compared with the theoretical voltage value V under the same detection state. NO +V2 for comparison, at this time, the detection values ​​of the first voltage detector and the second voltage detector are both greater than 1 / 2Vdc. If the conditions are consistent, the anti-parallel diodes on the fifth power element and the second power element are normal. If they are different, the anti-parallel diode on the fifth power element or the second power element is faulty, and detection stops.

10. The three-level inverter power module detection method according to claim 7, characterized in that: A pulse signal is applied to each power element to be detected to turn it on.

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