A composite voltage test device for DC support capacitors

Abstract

The present invention discloses a composite voltage test device for a DC support capacitor, which is mainly composed of a DC test circuit, a power frequency test circuit, a high frequency test circuit, a test circuit and a control circuit. The output end of the DC test circuit is connected in parallel with one end of the test circuit, and the other end of the test circuit is connected in parallel with the power frequency test circuit and one end of the high frequency test circuit, respectively. The control circuit includes signal acquisition, control output and a controller. The signal acquisition of the control circuit comes from the test circuit, and the control output of the control circuit is connected to the DC test circuit, the power frequency test circuit, the high frequency test circuit and the test circuit, respectively. The present invention has a simple structure and is easy to operate, and can meet the voltage test requirements of the DC support capacitor.

Description

Technical Field

[0001] The invention belongs to the technical field of capacitor testing, and in particular relates to a composite voltage testing device for a DC support capacitor. Background Art

[0002] The DC support capacitor is one of the important components of the converter. Its main function is to serve as an energy storage element on the DC side of the converter. Metallized film capacitors have advantages over electrolytic capacitors in terms of high voltage, high frequency, high temperature, large current, small size and long life. Therefore, metallized film DC support capacitors are widely used in high-performance converters such as rail transit, flexible DC transmission, wind power and photovoltaics, playing the role of stabilizing voltage and filtering, providing instantaneous energy exchange, and exchanging reactive power with loads and power sources.

[0003] When the traditional DC capacitor is working, the current is zero. The DC support capacitor is different from the traditional DC capacitor. In actual operation, in addition to the DC voltage applied to the DC support capacitor, the ripple voltage is also applied to the DC support capacitor, thus generating ripple current.

[0004] The voltage breakdown and insulation characteristics of capacitors under DC and AC voltage conditions are different, and the working field strength is also very different. The working field strength of AC capacitors is 40~60V / μm. The working field strength of DC capacitors is above 200V / μm.

[0005] Important voltage test items for capacitors: thermal stability test, durability test, and inter-electrode withstand voltage test.

[0006] At present, most capacitor test devices can only use a single DC voltage source, power frequency voltage source or variable frequency power source. Therefore, the DC support capacitor test can only reflect the characteristics of the capacitor under a single DC voltage, power frequency voltage source or variable frequency voltage, and cannot reflect the working characteristics of the DC support capacitor under actual working conditions.

[0007] In order to better design a reasonable DC support capacitor, it is necessary to accurately understand the insulation characteristics and life characteristics of the DC support capacitor under actual working conditions.

[0008] Therefore, it is necessary to design a new DC support capacitor voltage test device that can solve the technology of superposition of different types of voltage sources to meet the test requirements of DC support capacitors. Summary of the invention

[0009] In order to overcome the shortcomings of existing test devices that most of them can only have a single DC voltage source, industrial frequency voltage source or variable frequency power supply, the present invention proposes a composite voltage test device for DC support capacitors.

[0010] The technical solution adopted by the present invention is as follows.

[0011] The invention provides a composite voltage test device for a DC support capacitor.

[0012] The composite voltage test device is mainly composed of a DC test circuit, a power frequency test circuit, a high frequency test circuit, a test circuit and a control circuit.

[0013] The output end of the DC test circuit is connected in parallel with one end of the test circuit.

[0014] The other end of the test circuit is connected in parallel with the power frequency test circuit and the high frequency test circuit respectively.

[0015] The control loop includes signal acquisition, control output, and controller. The signal acquisition of the control loop comes from the test loop. The control output of the control loop is connected to the DC test loop, power frequency test loop, high frequency test loop, and test loop respectively. The controller gives the control output instruction based on the signal acquisition calculation.

[0016] The DC test circuit includes a first power supply, a first switch, a first voltage regulator, a first step-up transformer, a high-voltage silicon stack, a current limiting resistor, a DC filter capacitor, a DC filter resistor, and an AC isolation inductor.

[0017] The power frequency test circuit includes a second power supply, a second switch, a second voltage regulator, a second step-up transformer, a power frequency compensation reactor, a third switch, and a power frequency DC blocking capacitor.

[0018] The high-frequency test circuit includes a third power supply, a fourth switch, a high-frequency power supply, a filter, a high-frequency compensation reactor, a fifth switch, and a high-frequency DC blocking capacitor.

[0019] The test circuit includes a sixth switch, a discharge resistor, a voltage measurement, a current measurement, and a DC support capacitor to be tested.

[0020] One end of the first power supply is connected to one end of the first switch. The other end of the first switch is connected to one end of the primary side of the first voltage regulator. The other end of the first power supply is connected to the other end of the primary side of the first voltage regulator. The secondary side of the first voltage regulator is connected in parallel with the primary side of the first step-up transformer. One end of the secondary side of the first step-up transformer is connected in series with a high-voltage silicon stack and a current-limiting resistor in sequence. One end of the current-limiting resistor is connected in parallel with a DC filter capacitor, and a DC filter resistor and an AC isolation inductor are connected in series at the same time. One end of the AC isolation inductor is connected to the high-voltage end of the test loop. The other end of the secondary side of the first step-up transformer is connected in parallel with the other end of the DC filter capacitor and the low-voltage end of the test loop, and is grounded.

[0021] One end of the second power supply is connected to one end of the second switch. The other end of the second switch is connected to one end of the primary side of the second voltage regulator. The other end of the second power supply is connected to the other end of the primary side of the second voltage regulator. The secondary side of the second voltage regulator is connected in parallel with the primary side of the second step-up transformer. The secondary side of the second step-up transformer is connected in parallel with the power frequency compensation reactor. The high voltage end of the power frequency compensation reactor is connected in series with the third switch and the power frequency DC blocking capacitor in sequence. The other end of the power frequency DC blocking capacitor is connected to the high voltage end of the test circuit. The low voltage end of the power frequency compensation reactor is connected in parallel with the low voltage end of the test circuit and is grounded.

[0022] The third power supply is connected to the fourth switch and the high-frequency power supply in sequence. The output end of the high-frequency power supply is connected to the input end of the filter. The output end of the filter is connected in parallel with the high-frequency compensation reactor. The high-voltage end of the high-frequency compensation reactor is connected in series with the fifth switch and the high-frequency DC blocking capacitor in sequence. The other end of the high-frequency DC blocking capacitor is connected to the high-voltage end of the test circuit. The low-voltage end of the high-frequency compensation reactor is connected in parallel with the low-voltage end of the test circuit and is grounded.

[0023] The sixth switch is connected in series with the discharge resistor and then connected in parallel with the voltage measurement. The DC support capacitor to be tested is connected in series with the current measurement and then connected in parallel with the voltage measurement.

[0024] Signal acquisition includes voltage signals, current signals, and other signals, including temperature, pressure, etc.

[0025] The control output includes a first output, a second output, a third output, and a fourth output.

[0026] The DC filter capacitor and the DC filter resistor form an RC filter, which can stabilize the DC voltage applied to the DC support capacitor to be tested.

[0027] When the first switch is in the closed state, and the second switch and the fourth switch are both in the open state, the output voltage of the composite voltage test device is only a DC voltage, and a DC withstand voltage test and a DC durability test can be performed.

[0028] When the second switch is in the closed state, and the first switch and the fourth switch are both in the open state, the output voltage of the composite voltage test device is only the power frequency voltage, and the power frequency thermal stability test can be carried out.

[0029] When the fourth switch is in the closed state and the first switch and the second switch are both in the open state, the output voltage of the composite voltage test device is only a high-frequency voltage, and a high-frequency thermal stability test can be performed.

[0030] When the first switch, the second switch and the third switch are all in the closed state and the fourth switch is in the open state, the output voltage of the composite voltage test device is a DC voltage superimposed on an industrial frequency voltage, and thermal stability tests and durability tests can be carried out.

[0031] When the first switch, the fourth switch and the fifth switch are all in the closed state and the second switch is in the open state, the composite voltage test device outputs a DC voltage superimposed with a high-frequency voltage, and thermal stability tests and durability tests can be performed.

[0032] When the second switch, the third switch, the fourth switch and the fifth switch are all in the closed state and the first switch is in the open state, the composite voltage test device outputs the industrial frequency voltage superimposed on the high frequency voltage, and the thermal stability test can be carried out.

[0033] When the first switch, the second switch, the third switch, the fourth switch and the fifth switch are all in the closed state, the composite voltage test device outputs a DC voltage superimposed on an industrial frequency voltage and a high frequency voltage, and a thermal stability test and a durability test can be performed.

[0034] The instructions of the first output, the second output) and the third output correspond to the first switch, the second switch and the fourth switch respectively. When the measurement signal is abnormal, the controller gives a corresponding instruction.

[0035] When the test is finished or the test is abnormal, the controller gives a fourth output instruction, and after the sixth switch is closed, the energy on the DC support capacitor to be tested is released through the discharge resistor.

[0036] Furthermore, the first power supply is usually 220V AC, the second power supply is usually 380V AC, and the third power supply is usually 380V AC.

[0037] Furthermore, the capacity of the first step-up transformer is 30KVA and the transformation ratio is 0.4 / 7kV.

[0038] Furthermore, the capacity of the second step-up transformer is 100KVA and the transformation ratio is 0.4 / 3kV.

[0039] Furthermore, the frequency range of the variable frequency power supply is 100~2500HZ and the power is 100KVA.

[0040] Furthermore, the voltage is measured using a voltage measuring meter.

[0041] Furthermore, other signals (temperature, pressure, etc.) are connected by placing relevant sensors on the DC support capacitor (Cx) under test.

[0042] Furthermore, the industrial frequency DC blocking capacitor and high frequency DC blocking capacitor are selected to be the largest 10mF currently.

[0043] Furthermore, the inductive reactance of the power frequency compensation reactor is adjustable, and the sum of the capacitive reactances of the power frequency DC blocking capacitor and the DC support capacitor to be tested matches the inductive reactance of the power frequency compensation reactor, at which time the output power of the second step-up transformer is minimum.

[0044] Furthermore, the inductive reactance of the high-frequency compensation reactor is adjustable, and the sum of the capacitive reactance of the high-frequency DC blocking capacitor and the DC support capacitor to be tested matches the inductive reactance of the high-frequency compensation reactor (under the test frequency conditions), at which time the output power of the high-frequency power supply is minimum.

[0045] The beneficial effects of the present invention are: it can realize various voltage forms, can realize AC and DC withstand voltage tests, thermal stability tests, and durability tests, which conforms to the actual working conditions of DC support capacitors, and the test operation is simple, easy to maintain, highly reliable, and safe.

[0046] The invention has a simple structure and is easy to operate, and can meet the requirements of a DC support capacitor voltage test. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the structure of the present invention;

[0048] Figure 2 A schematic diagram of the wiring for the implementation of the present invention;

[0049] In the figure, 1-DC test circuit; 2-power frequency test circuit; 3-high frequency test circuit; 4-test circuit; 5-control circuit;

[0050] 51-signal acquisition; 52-control output; 52-controller;

[0051] 511-voltage signal; 512-current signal; 513-other signals;

[0052] 521-first output; 522-second output; 523-third output; 523-fourth output;

[0053] Us1-first power supply; S1-first switch; BT1-first voltage regulator; T1-first step-up transformer; D-high voltage silicon stack; R1-current limiting resistor; C1-DC filter capacitor; R2-DC filter resistor; L-isolation inductor 1;

[0054] Us2-second power supply; S2-second switch; BT2-second voltage regulator; T2-second step-up transformer; L2-power frequency compensation reactor; S3-third switch; C2-power frequency DC blocking capacitor;

[0055] Us3-third power supply; S4-fourth switch; BP-high frequency power supply; LB-filter; L3-high frequency compensation reactor; S5-fifth switch; C3-high frequency DC blocking capacitor; GND-ground;

[0056] S6 - the sixth switch; R3 - the discharge resistor; V - voltage measurement; TA - current measurement; Cx - the DC support capacitor to be tested. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0058] exist Figure 1 It can be seen that the composite voltage test device of the present invention mainly comprises a DC test circuit (1), an industrial frequency test circuit (2), a high frequency test circuit (3), a test circuit (4) and a control circuit (5).

[0059] from Figure 2 visible:

[0060] The output end of the DC test circuit (1) is connected in parallel with one end of the test circuit (4);

[0061] The other end of the test circuit (4) is connected in parallel with one end of the power frequency test circuit (2) and the high frequency test circuit (3);

[0062] The control circuit (5) includes a signal acquisition circuit (51), a control output circuit (52), and a controller (53); the signal acquisition circuit (51) of the control circuit (5) comes from the test circuit (4); the control output circuit (5) is respectively connected to the DC test circuit (1), the power frequency test circuit (2), the high frequency test circuit (3), and the test circuit (4); the controller (53) calculates and gives an instruction for the control output circuit (52) according to the signal acquisition circuit (51);

[0063] The DC test circuit (1) comprises a first power supply (Us1), a first switch (S1), a first voltage regulator (BT1), a first step-up transformer (T1), a high-voltage silicon stack (D), a current limiting resistor (R1), a DC filter capacitor (C1), a DC filter resistor (R2), and an AC isolation inductor (L1);

[0064] The power frequency test circuit (2) comprises a second power supply (Us2), a second switch (S2), a second voltage regulator (BT2), a second step-up transformer (T2), a power frequency compensation reactor (L2), a third switch (S3), and a power frequency DC blocking capacitor (C2);

[0065] The high-frequency test circuit (3) comprises a third power supply (Us3), a fourth switch (S4), a high-frequency power supply (BP), a filter (LB), a high-frequency compensation reactor (L3), a fifth switch (S5), and a high-frequency DC blocking capacitor (C3);

[0066] The test circuit (4) comprises a sixth switch (S6), a discharge resistor (R3), a voltage measurement (V), a current measurement (TA), and a DC support capacitor (Cx) to be tested;

[0067] One end of the first power supply (Us1) is connected to one end of the first switch (S1); the other end of the first switch (S1) is connected to one end of the primary side of the first voltage regulator (BT1); the other end of the first power supply (Us1) is connected to the other end of the primary side of the first voltage regulator (BT1); the secondary side of the first voltage regulator (BT1) is connected in parallel to the primary side of the first step-up transformer (T1); one end of the secondary side of the first step-up transformer (T1) is connected in series with a high-voltage silicon stack (D) and a current limiting resistor (R1); one end of the current limiting resistor (R1) is connected in parallel with a DC filter capacitor (C1), and is connected in series with a DC filter resistor (R2) and an AC isolation inductor (L1); one end of the AC isolation inductor (L1) is connected to a high-voltage end of a test loop (4); the other end of the secondary side of the first step-up transformer (T1) is connected in parallel with the other end of the DC filter capacitor (C1) and a low-voltage end of the test loop (4), and is grounded (GND);

[0068] One end of the second power supply (Us2) is connected to one end of the second switch (S2); the other end of the second switch (S2) is connected to one end of the primary side of the second voltage regulator (BT2); the other end of the second power supply (Us2) is connected to the other end of the primary side of the second voltage regulator (BT2); the secondary side of the second voltage regulator (BT2) is connected in parallel with the primary side of the second step-up transformer (T2); the secondary side of the second step-up transformer (T2) is connected in parallel with the power frequency compensation reactor (L2); the high voltage end of the power frequency compensation reactor (L2) is connected in series with the third switch (S3) and the power frequency DC blocking capacitor (C2) in sequence; the other end of the power frequency DC blocking capacitor (C2) is connected to the high voltage end of the test loop (4); the low voltage end of the power frequency compensation reactor (L2) is connected in parallel with the low voltage end of the test loop (4) and is grounded (GND);

[0069] The third power supply (Us3) is connected to the fourth switch (S4) and the high-frequency power supply (BP) in sequence; the output end of the high-frequency power supply (BP) is connected to the input end of the filter (LB); the output end of the filter (LB) is connected in parallel to the high-frequency compensation reactor (L3); the high-voltage end of the high-frequency compensation reactor (L3) is connected in series to the fifth switch (S5) and the high-frequency DC blocking capacitor (C3) in sequence; the other end of the high-frequency DC blocking capacitor (C3) is connected to the high-voltage end of the test loop (4); the low-voltage end of the high-frequency compensation reactor (L3) is connected in parallel to the low-voltage end of the test loop (4) and is grounded (GND);

[0070] The sixth switch (S6) is connected in series with the discharge resistor (R3) and then connected in parallel with the voltage measurement (V); the DC support capacitor (Cx) to be tested is connected in series with the current measurement (TA) and then connected in parallel with the voltage measurement (V);

[0071] The signal acquisition (51) includes a voltage signal (511), a current signal (512), and other signals (513), and the other signals (513) include temperature, pressure, etc.;

[0072] The control output (52) includes a first output (521), a second output (522), a third output (53), and a fourth output (524).

[0073] The DC filter capacitor (C1) and the DC filter resistor (R1) form an RC filter, which can stabilize the DC voltage applied to the DC support capacitor (Cx) to be tested.

[0074] When the first switch (S1) is in the closed state, and the second switch (S2) and the fourth switch (S4) are both in the open state, the output voltage of the composite voltage test device is only a DC voltage, and a DC withstand voltage test and a DC durability test can be performed.

[0075] When the second switch (S2) is in the closed state, and the first switch (S1) and the fourth switch (S4) are both in the open state, the output voltage of the composite voltage test device is only the power frequency voltage, and the power frequency thermal stability test can be carried out.

[0076] When the fourth switch (S4) is in the closed state and the first switch (S1) and the second switch (S2) are both in the open state, the output voltage of the composite voltage test device is only a high-frequency voltage, and a high-frequency thermal stability test can be performed.

[0077] When the first switch (S1), the second switch (S2), and the third switch (S3) are all in the closed state, and the fourth switch (S4) is in the open state, the output voltage of the composite voltage test device is a DC voltage superimposed on an industrial frequency voltage, and thermal stability tests and durability tests can be performed.

[0078] When the first switch (S1), the fourth switch (S4), and the fifth switch (S5) are all in the closed state, and the second switch (S2) is in the open state, the composite voltage test device outputs a DC voltage superimposed with a high-frequency voltage, and thermal stability tests and durability tests can be performed.

[0079] When the second switch (S2), the third switch (S3), the fourth switch (S4), and the fifth switch (S5) are all in the closed state, and the first switch (S1) is in the open state, the composite voltage test device outputs a power frequency voltage superimposed on a high frequency voltage, and a thermal stability test can be performed.

[0080] When the first switch (S1), the second switch (S2), the third switch (S3), the fourth switch (S4), and the fifth switch (S5) are all in the closed state, the composite voltage test device outputs a DC voltage superimposed on an industrial frequency voltage and a high-frequency voltage, and a thermal stability test and a durability test can be performed.

[0081] The instructions of the first output (521), the first output (522), and the third output (523) correspond to the first switch (S1), the second switch (S2), and the fourth switch (S3) respectively. When the measurement signal is abnormal, the controller (53) gives the instructions of the first output (521), the first output (522), and the third output (523) accordingly.

[0082] When the test is finished or the test is abnormal, the controller (53) gives an instruction of the fourth output (524), at which time the sixth switch (S6) is closed, and the discharge resistor (R3) and the DC support capacitor (Cx) to be tested form a discharge circuit to release the energy stored in the DC support capacitor (Cx) to be tested.

[0083] Furthermore, the inductive reactance value of the power frequency compensation reactor (L2) is adjustable, and the sum of the capacitive reactances of the power frequency DC blocking capacitor (C2) and the DC support capacitor (Cx) to be tested matches the inductive reactance of the power frequency compensation reactor (L2), at which time the output power of the second step-up transformer (T2) is minimum.

[0084] Furthermore, the inductive reactance value of the high-frequency compensation reactor (L3) is adjustable, and the sum of the capacitive reactance of the high-frequency DC blocking capacitor (C3) and the DC support capacitor (Cx) to be tested matches the inductive reactance of the high-frequency compensation reactor (L3) (under the test frequency condition), at which time the output power of the high-frequency power supply (BP) is minimum.

[0085] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A composite voltage test device for DC support capacitors, characterized in that: The composite voltage test device is mainly composed of a DC test circuit, a power frequency test circuit, a high-frequency test circuit, a test circuit and a control circuit. The output end of the DC test circuit is connected in parallel with one end of the test circuit, and the other end of the test circuit is connected in parallel with one end of the power frequency test circuit and the high-frequency test circuit respectively. The control circuit includes signal acquisition, control output and a controller. The controller of the control circuit gives a control output instruction according to the signal acquisition calculation result. The signal acquisition of the control circuit comes from the test circuit. The control output of the control circuit is connected to the DC test circuit, the power frequency test circuit, the high-frequency test circuit and the test circuit respectively. The DC test circuit includes a first power supply, a first switch, a first voltage regulator, a first step-up transformer, a high-voltage silicon stack, a current limiting resistor, a DC filter capacitor, a DC filter resistor, and an AC isolation inductor; The power frequency test circuit includes a second power supply, a second switch, a second voltage regulator, a second step-up transformer, a power frequency compensation reactor, a third switch, and a power frequency DC blocking capacitor; The high-frequency test circuit includes a third power supply, a fourth switch, a high-frequency power supply, a filter, a high-frequency compensation reactor, a fifth switch, and a high-frequency DC blocking capacitor; When the first switch is in the closed state, and the second switch and the fourth switch are both in the open state, the output voltage of the composite voltage test device is only a DC voltage at this time, and a DC withstand voltage test and a DC durability test can be performed; when the second switch is in the closed state, and the first switch and the fourth switch are both in the open state, the output voltage of the composite voltage test device is only a power frequency voltage at this time, and a power frequency thermal stability test can be performed; when the fourth switch is in the closed state, and the first switch and the second switch are both in the open state, the output voltage of the composite voltage test device is only a high-frequency voltage at this time, and a high-frequency thermal stability test can be performed; When the first switch, the second switch, and the third switch are all in the closed state, and the fourth switch is in the open state, the composite voltage test device outputs a DC voltage superimposed on a power frequency voltage, and can perform a thermal stability test and a durability test; when the first switch, the fourth switch, and the fifth switch are all in the closed state, and the second switch is in the open state, the composite voltage test device outputs a DC voltage superimposed on a high-frequency voltage, and can perform a thermal stability test and a durability test; when the second switch, the third switch, the fourth switch, and the fifth switch are all in the closed state, and the first switch is in the open state, the composite voltage test device outputs a power frequency voltage superimposed on a high-frequency voltage, and can perform a thermal stability test; When the first switch, the second switch, the third switch, the fourth switch and the fifth switch are all in the closed state, the composite voltage testing device outputs a DC voltage superimposed on an industrial frequency voltage and a high frequency voltage, and can perform thermal stability tests and durability tests.

2. The composite voltage test device according to claim 1, characterized in that: One end of the first power supply is connected to one end of the first switch, the other end of the first switch is connected to one end of the primary side of the first voltage regulator, the other end of the first power supply is connected to the other end of the primary side of the first voltage regulator, the secondary side of the first voltage regulator is connected in parallel with the primary side of the first step-up transformer, one end of the secondary side of the first step-up transformer is connected in series with a high-voltage silicon stack and a current limiting resistor in sequence, one end of the current limiting resistor is connected in parallel with a DC filter capacitor, and a DC filter resistor and an AC isolation inductor are connected in series at the same time, and the other end of the secondary side of the first step-up transformer is connected in parallel with the other end of the DC filter capacitor and is grounded.

3. The composite voltage test device according to claim 1, characterized in that: One end of the second power supply is connected to one end of the second switch, the other end of the second switch is connected to one end of the primary side of the second voltage regulator, the other end of the second power supply is connected to the other end of the primary side of the second voltage regulator, the secondary side of the second voltage regulator is connected in parallel with the primary side of the second step-up transformer, the secondary side of the second step-up transformer is connected in parallel with the power frequency compensation reactor, and the high voltage end of the power frequency compensation reactor is connected in series with the third switch and the power frequency DC blocking capacitor in sequence.

4. The composite voltage test device according to claim 1, characterized in that: The third power supply is connected to the fourth switch and the high-frequency power supply in sequence, the high-frequency power supply output end is connected to the filter input end, the filter output end is connected in parallel with the high-frequency compensation inductor, and the high-voltage end of the high-frequency compensation inductor is connected in series with the fifth switch and the high-frequency DC blocking capacitor in sequence.

5. The composite voltage test device according to claim 1, characterized in that: The test circuit includes a sixth switch, a discharge resistor, a voltage measurement, a current measurement, and a DC support capacitor to be tested; The sixth switch is connected in series with the discharge resistor and then connected in parallel with the voltage measurement, and the DC support capacitor to be tested is connected in series with the current measurement and then connected in parallel with the voltage measurement.

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