A circuit and method for direct current support capacitor discharge testing

Abstract

The application provides a direct current support capacitor discharge test loop and method, which comprises a direct current charging voltage source; the direct current charging voltage source, a current limiting resistor and a first vacuum contactor are connected in series and connected to a high voltage end of a test capacitor to form a test charging loop; the test capacitor, a thyristor, an adjustable resistor and an adjustable reactance are connected in series and connected to a high voltage end of a support capacitor to form a test discharge loop; the support capacitor, a second vacuum contactor and a discharge coil are connected in series to form a support capacitor discharge loop; a first voltage divider is connected in parallel with the test capacitor, and a second voltage divider is connected in parallel with the support capacitor; signals of the first voltage divider and the second voltage divider are led out to a measurement system; and the measurement system, the thyristor, the first vacuum contactor and the second vacuum contactor are connected to a control system. The discharge current and voltage waveform obtained by the test loop are more close to the actual working condition of the capacitor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic capacitor test, and particularly relates to a DC support capacitor discharge test loop and method. BACKGROUND

[0002] With the development and utilization of new energy, flexible and efficient flexible DC power transmission is widely used as an effective means of connecting new energy to a power grid. As a core power device in this technology, a DC support capacitor for flexible DC power transmission is subjected to a rapid 'charging-discharging-charging' cycle under actual working conditions. In each discharging process, the current waveform flowing through the capacitor is a single-polarity half wave.

[0003] In the prior art, when a ball gap is used for discharge test, it is difficult to accurately control the opening and closing of the ball gap in the millisecond-level discharge process. For the discharge current, only an under-damped waveform with multiple zero-crossing points or an over-damped waveform with a long tail can be generated, which is different from the discharge current waveform under actual working conditions. Moreover, it is difficult to accurately control the opening and closing, and the voltage on the test capacitor will be reduced to zero after each discharge, which is different from the voltage borne by the capacitor under actual working conditions. The contact point of the discharge electrode has contact resistance, which limits the adjustment of the damping parameter of the discharge loop. At the same time, due to the instability of this contact resistance in multiple discharging processes, the parameters and current waveform of the discharge current obtained by using this test method are unstable. Under a large current discharge, the copper ball contact point will be obviously worn, which leads to the degradation of the discharge loop parameters in a long-time test process, and even leads to the failure of the discharge due to the inability to contact. The discharge process is exposed to air, which will cause a large noise pollution; the flying sparks increase the unsafe factors for the test site. SUMMARY

[0004] In order to solve the problems in the prior art, the application provides a DC support capacitor discharge test loop and method to solve the above problems.

[0005] To achieve the above object, the application provides the following technical scheme:

[0006] A DC support capacitor discharge test loop, comprising a DC charging voltage source, a current-limiting resistor, a first vacuum contactor, a test capacitor, a thyristor, an adjustable resistor, an adjustable reactance, a support capacitor, a second vacuum contactor, a discharge coil, a first voltage divider, a Rogowski coil, an oscilloscope, a second voltage divider, a measurement system, and a control system.

[0007] The DC charging voltage source, the current-limiting resistor, and the first vacuum contactor are connected in series and connected to the high-voltage end of the test capacitor, forming a charging loop of the test capacitor.

[0008] The test capacitor is connected in series with the thyristor, the adjustable resistor and the adjustable reactance, and is connected to the high-voltage end of the support capacitor to form a discharge circuit of the test capacitor.

[0009] The support capacitor is connected in series with the second vacuum contactor and the discharge coil to form a discharge circuit of the support capacitor.

[0010] The first voltage divider is connected in parallel with the test capacitor, and the second voltage divider is connected in parallel with the support capacitor.

[0011] The signals of the first voltage divider and the second voltage divider are led out to the measurement system.

[0012] The measurement system, the thyristor, the first vacuum contactor and the second vacuum contactor are connected to the control system.

[0013] Preferably, the test device further comprises a Rogowski coil and an oscilloscope, the Rogowski coil is sleeved on the discharge circuit connecting line of the test capacitor, the signal of the Rogowski coil is led out to the oscilloscope, and the oscilloscope leads out waveform information to the measurement system.

[0014] Preferably, the measurement system and the control system are connected for data interaction.

[0015] Preferably, the direct-current charging voltage source comprises an alternating-current voltage source and a rectifier silicon stack, and the alternating-current voltage source and the rectifier silicon stack are connected in series.

[0016] Preferably, the ground ends of the test capacitor and the support capacitor are grounded.

[0017] A method for discharging test of a direct-current support capacitor, characterized in that the method is based on the discharge test circuit for the direct-current support capacitor according to any one of the preceding claims, and comprises the following steps,

[0018] Step 1: the control system triggers the first vacuum contactor and the thyristor to be turned on; the direct-current charging voltage source charges the test capacitor and the support capacitor, the voltages between the test capacitor and the support capacitor are measured by the first voltage divider and the second voltage divider respectively, and are transmitted to the measurement system in real time, and the measurement system transmits to the control system.

[0019] Step 2: when the voltage between the support capacitor reaches the reference level preset in the control system, the charging of the support capacitor is stopped.

[0020] Step 3: the control system triggers the first vacuum contactor again to continue charging the test capacitor, and when the voltage between the test capacitor reaches the discharge voltage preset in the control system, the control system stops triggering the first vacuum contactor to be turned off, at this time, the charging of the test capacitor is stopped, and the voltage on the test capacitor is higher than the voltage on the support capacitor.

[0021] Step 4, the control system triggers the thyristor to conduct under forward bias, and the support capacitor is discharged by the test capacitor, and the current waveform is controlled by the adjustable resistance, the adjustable reactance, the capacitance of the support capacitor and the pre-charging voltage thereof;

[0022] Step 5, when the positive half-wave of the discharge current decays to be lower than the conducting maintaining current of the thyristor, the thyristor is turned off, the control system counts the current discharge test and starts timing, and when the timing time reaches the preset discharge interval time, the next discharge test process is started;

[0023] Step 6, the first vacuum contactor and the second vacuum contactor are triggered by the control system, at this time, the support capacitor is discharged through the discharge coil, and the test capacitor is continuously charged by the DC charging voltage source;

[0024] Step 7, when the voltage across the support capacitor decreases to the preset reference level in the control system, the control system stops triggering the second vacuum contactor, at this time, the support capacitor stops discharging through the discharge coil;

[0025] Step 8, the test process of steps 3-7 is repeated until the discharge times reach the expected times, and the discharge test is terminated by the control system, at the same time, the thyristor and the second vacuum contactor are triggered to make the test capacitor and the support capacitor discharge through the discharge coil until the voltage decreases to zero, the thyristor and the second vacuum contactor are stopped, and the discharge test is completed.

[0026] Preferably, in step 1, the AC voltage generated by the AC voltage source is converted into DC voltage by the rectifier silicon stack to charge the test capacitor and the support capacitor.

[0027] Preferably, in step 5, the discharge current waveform is collected by the Rogowski coil, transmitted to the oscilloscope for further processing, and then transmitted to the measurement system for recording, storage and visualization.

[0028] Preferably, in step 5, the discharge current waveform is a unipolar half-wave discharge waveform.

[0029] Compared with the prior art, the present application has the following beneficial technical effects:

[0030] The present application provides a kind of discharge test loop for DC support capacitor, by using thyristor instead of discharge sphere gap, by utilizing the conduction characteristic of thyristor, when the circulating current is lower than the conduction maintenance current, thyristor is automatically turned off, so as to intercept the discharge current waveform of oscillation attenuation, form only unipolar half-wave discharge current waveform, more close to the discharge current waveform of such capacitor in engineering practice.The support capacitor is added in the discharge loop, when discharging, when the voltage of test capacitor is reduced to be close to the support capacitor, the current in the discharge loop is lower than the conduction maintenance current of thyristor, thyristor is turned off to stop discharging, so as to control the voltage drop of test capacitor during discharging, and the voltage waveform of test capacitor during discharging is more close to engineering practice.The present application is used for the discharge test of DC support capacitor, and during discharging, the test capacitor discharges to another capacitor with lower voltage in the discharge loop.The discharge current and voltage waveform obtained by the test loop are more close to the actual working condition of such capacitor. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a wiring schematic diagram of the discharge test loop for DC support capacitor of the present application;

[0032] Figure 2 It is a discharge current waveform diagram of the discharge test loop for DC support capacitor of the present application;

[0033] Figure 3 It is a discharge voltage waveform diagram of the discharge test loop for DC support capacitor of the present application;

[0034] Figure 4 It is a schematic diagram of the discharge loop in the embodiment of the present application;

[0035] Figure 5 It is a schematic diagram of the equivalent discharge loop in the embodiment of the present application;

[0036] In the drawings: 1 is an AC voltage source; 2 is a rectifier silicon stack; 3 is a current-limiting resistor; 4 is a first vacuum contactor; 5 is a test capacitor; 6 is a thyristor; 7 is an adjustable resistor; 8 is an adjustable reactance; 9 is a support capacitor; 10 is a second vacuum contactor; 11 is a discharge coil; 12 is a first voltage divider; 13 is a Rogowski coil; 14 is an oscilloscope; 15 is a second voltage divider; 16 is a measurement system; 17 is a control system. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below in combination with specific embodiments, which are an explanation of the present application rather than a limitation.

[0038] As Figure 1As shown, one kind for direct current support capacitor discharge test loop of the present application, including AC voltage source 1, rectifier silicon stack 2, current-limiting resistance 3, first vacuum contactor 4, test capacitor 5, thyristor 6, adjustable resistance 7, adjustable reactance 8, support capacitor 9, second vacuum contactor 10, discharge coil 11, first voltage divider 12, Rogowski coil 13, oscilloscope 14, second voltage divider 15, measurement system 16, control system 17 and copper wire and copper bar connected to each part of the loop.

[0039] The outgoing line end of AC voltage source 1, first vacuum contactor 4, current-limiting resistance 3, rectifier silicon stack 2 are connected in series to the high-voltage end of test capacitor 5, forming a test charging circuit. AC voltage source 1 cooperates with rectifier silicon stack 2 to provide a DC charging voltage source for test capacitor 5 and support capacitor 9; current-limiting resistance 3 is used to limit the charging current and protect AC voltage source 1 and rectifier silicon stack 2; first vacuum contactor 4 is used to control the start and stop of the charging process. The ground end of AC voltage source 1 is grounded.

[0040] The high-voltage end of test capacitor 5 is connected to the high-voltage end of support capacitor 9 through series-connected thyristor 6, adjustable resistance 7 and adjustable reactance 8, forming a test discharge circuit. Thyristor 6 is used to control the start and stop of the discharge process; adjustable resistance 7 and adjustable reactance 8 are used to adjust the damping parameters of the discharge circuit to obtain the required current waveform; support capacitor 9 is used to control the voltage drop of test capacitor during discharge, indirectly controlling the waveform parameters of the discharge current. The ground end of test capacitor 5 and support capacitor 9 is grounded.

[0041] Support capacitor 9 is connected in series with second vacuum contactor 10 and discharge coil 11, forming a discharge circuit for support capacitor 9. Second vacuum contactor 10 is used to control the discharge process of the support capacitor, and discharge coil 11 is used to limit the discharge current of support capacitor 9.

[0042] First voltage divider 12 and second voltage divider 15 are connected in parallel to test capacitor 5 and support capacitor 9 respectively, and Rogowski coil 13 is sleeved on the discharge circuit connection line. The signals of first voltage divider 12 and second voltage divider 15 are led out to measurement system 16, providing real-time voltage across test capacitor 5 and support capacitor 9; the signal of Rogowski coil 13 is led out to oscilloscope 14, which in turn leads the waveform information to measurement system 16, collecting and recording the discharge current waveform and parameter information. Measurement system 16 integrates the test status, parameters and data and displays them in real time, and stores the necessary information.

[0043] The sleeved part of Rogowski coil 13 is on both the discharge circuit of support capacitor 14 and the discharge circuit of test capacitor 5, and the main function of Rogowski coil 13 is to measure the discharge waveform of test capacitor 5.

[0044] The measuring system 16, the gate of the thyristor 6, the first vacuum contactor 4 and the second vacuum contactor 10 are connected to the control system 17, and the control system 17 controls the gate of the thyristor 6, the first vacuum contactor 4 and the second vacuum contactor 10 to carry out the charging and discharging process according to the real-time voltage collected by the measuring system 16 and the system parameters set in advance.

[0045] Embodiment

[0046] The method for discharging test loop of DC support capacitor provided by the application comprises the following processes,

[0047] Step 1: when the first discharging test starts, the control system 17 triggers the first vacuum contactor 4 and the thyristor 6 to be turned on, at this time, the AC voltage from the AC voltage source 1 is converted into DC voltage by the rectifier silicon stack 2 to charge the test capacitor 5 and the support capacitor 9, and the voltage between the test capacitor 5 and the support capacitor 9 is measured by the first voltage divider 12 and the second voltage divider 15 respectively and transmitted to the measuring system 16 in real time, and then provided to the control system 17.

[0048] Step 2: when the voltage between the support capacitor 9 reaches the reference level preset in the control system 17, the control system 17 stops triggering the thyristor 6 and the first vacuum contactor 4, and the first vacuum contactor 4 is turned off, and the thyristor 6 is also turned off in the absence of the turn-on maintaining current, at this time, the charging of the support capacitor 9 is stopped.

[0049] Step 3: the control system 17 triggers the first vacuum contactor 4 again to continue charging the test capacitor 5, and when the voltage between the test capacitor 5 reaches the discharging voltage preset in the control system 17, the control system 17 stops triggering the first vacuum contactor 4 to be turned off, at this time, the charging of the test capacitor 5 is stopped, and the voltage on the test capacitor 5 should be higher than the voltage on the support capacitor 9.

[0050] Step 4: the control system 17 triggers the thyristor 6 to be turned on under the forward bias, and the test capacitor 5 discharges the support capacitor 9, and the current waveform is controlled by the adjustable resistance 7, the adjustable reactance 8, the capacitance of the support capacitor 9 and the pre-charging voltage thereof.

[0051] Step 5: when the positive half wave of the discharging current decays to be lower than the turn-on maintaining current of the thyristor 6, the thyristor 6 is turned off, at this time, the discharging current is a unipolar half wave discharging waveform, the discharging current waveform is collected by the Rogowski coil 13, transmitted to the oscilloscope 14 for further processing, and then transmitted to the measuring system 16 for recording, storage and visualization, the control system 17 counts the discharging test and starts timing, and when the timing time reaches the preset discharging interval time, the next discharging test process starts; the waveforms of the discharging current and the discharging voltage are as shown in Figure 2 ,Figure 3 as shown.

[0052] Step 6, in the second and subsequent discharge tests, since the support capacitor 9 has voltage before the discharge test starts, and is higher than its preset reference level, therefore at the start of the second and subsequent discharge tests, the first vacuum contactor 4 and the second vacuum contactor 10 are triggered by the control system 17, at this time, the support capacitor 9 is discharged through the discharge coil 11, and at the same time, the AC voltage source 1 converts the AC voltage into DC voltage through the rectifier silicon stack 2, to continue charging the test capacitor 5;

[0053] Step 7, when the voltage across the support capacitor 9 decreases to the reference level preset in the control system 17, the control system 17 stops triggering the second vacuum contactor 10, at this time the support capacitor 9 stops discharging through the discharge coil 11;

[0054] Step 8, repeat the test process of steps 3-7 until the discharge times reach the expected number, the discharge test is terminated by the control system 17, and the thyristor 6 and the second vacuum contactor 10 are triggered, so that the test capacitor 5 and the support capacitor 9 are discharged through the discharge coil 11 until the voltages of both are reduced to zero, the thyristor 6 and the second vacuum contactor 10 are stopped, the second vacuum contactor 10 is turned off, and the thyristor 6 is also turned off in the absence of conduction maintenance current, and the discharge test is completed.

[0055] Through preliminary calculation and numerical simulation, the theoretical values of the discharge loop damping parameters, the discharge voltage and the pre-charge voltage of the support capacitor are calculated as a reference from the required discharge current parameters and the required residual voltage, and the appropriate type of support capacitor 9 is selected;

[0056] The preliminary calculation method of the loop parameters is as follows: when the test capacitor is discharged, the discharge loop can be simplified as Figure 4 the circuit shown.

[0057] Figure 4 wherein C1 is the test capacitor 5, U1 is the voltage applied to the test capacitor 5 during discharge;

[0058] R is the resistance value set by the adjustable resistor 7;

[0059] L is the reactance set by the adjustable reactance 8;

[0060] C2 is the support capacitor 9, U2 is the voltage applied to the support capacitor 9 during discharge;

[0061] I is the discharge current.

[0062] ① For the discharge test of the test capacitor, first of all, attention is paid to the peak value of the current in this process, when calculating the peak value of the discharge current, the Figure 4The capacitances C1 and C2 in the figure are equivalent to a capacitance C S The initial voltage of the capacitance C S is ΔU.

[0063] Where C S =1 / (1 / C1+1 / C2), ΔU=U1-U2.

[0064] The equivalent discharge circuit is shown in the figure Figure 5 .

[0065] It is easy to know that the discharge circuit is a RLC series second-order circuit at this time, and the zero-input response process is discussed, in which the initial voltage of the capacitance C S is ΔU. The two cases of under-damped discharge and over-damped discharge of this circuit are discussed below.

[0066] A. Under-damped discharge

[0067] In the case of under-damped discharge, an oscillatory discharge process occurs. Due to the characteristics of thyristor discharge, the discharge waveform will be truncated before the first zero-crossing point.

[0068] Let

[0069] The time-domain expression of the discharge current is ⑴

[0070] Let

[0071] The first extreme point of the discharge current , substitute formula 1 to calculate the first peak value of the discharge current.

[0072] B. Over-damped discharge

[0073] In the case of over-damped discharge, a non-oscillatory discharge process occurs.

[0074] The time-domain expression of the discharge current is ⑵

[0075] Where,

[0076] The maximum point of the discharge current , substitute formula 2 to calculate the peak value of the discharge current.

[0077] ② For the discharge test of the test capacitor, there are corresponding requirements for the residual voltage on the test capacitor 5 after the discharge is completed. The calculation method of the residual voltage after the discharge is completed is as follows.

[0078] A. Under-damped discharge

[0079] According to the discharge current, the initial voltage and the time of the discharge, the voltage on the capacitor C1 after the discharge can be calculated.

[0080]

[0081] wherein, V0 is the voltage on the capacitor C1 before the discharge

[0082] V1 is the voltage on the capacitor C1 after the discharge

[0083] t is the time of the discharge,

[0084] I is the discharge current described by the equation 1

[0085] B. Over-damped discharge

[0086] In the case of over-damped discharge, the voltages on the capacitors C1 and C2 at the end of the discharge are approximately equal, and the voltage on the capacitor C1 after the discharge can be calculated according to the law of conservation of charge.

[0087] Before the discharge, the amount of charge on the capacitor C1 is

[0088] The amount of charge on the capacitor C2 is

[0089] At the end of the discharge process, the discharge process ends when the voltages on the two capacitors are approximately equal, and this voltage (i.e. the remaining voltage of C1) is recorded as V1.

[0090] After the discharge, the amount of charge on the capacitor C1 is

[0091] The amount of charge on the capacitor C2 is

[0092] According to the law of conservation of charge,

[0093] i.e.

[0094] Thus,

[0095] When calculating the loop parameters, first give a set of R, L, C2, U2 within a certain range, calculate the corresponding current peak and the remaining voltage on the sample capacitor by the above method, compare with the required value, and then adjust the size of R, L, C2, U2 according to the deviation, and repeat the adjustment until the deviation of the calculated current peak and the remaining voltage from the required value reaches an acceptable range.

[0096] Check the test loop, confirm that the equipment is in good condition and correctly connected, and connect the test capacitor 5 to the test loop as shown in the figure. Figure 1 Connect the loop as shown in the figure.

[0097] Pre-test the discharge at a reduced test voltage, based on the theoretical value calculated in ⑴, adjust the adjustable reactance 8, the adjustable resistance 7, the discharge voltage, and the pre-charge voltage of the support capacitor 9 (if necessary, the type of support capacitor can also be adjusted), so that the obtained discharge current parameters and waveforms meet the requirements.

[0098] Set the expected number of discharges, the expected discharge voltage, and the discharge interval time in the control system, and confirm the data that need to be collected and stored in the measurement system, and start the continuous discharge test.

[0099] The application utilizes the conduction characteristics of thyristors, and the thyristors are automatically turned off when the circulating current is lower than the conduction maintenance current, thereby intercepting the oscillation decay discharge current waveform and forming a discharge current waveform with only unipolar half waves, which is closer to the discharge current waveform that such capacitors bear in engineering practice, thereby improving the test quality.

[0100] The application adds a support capacitor in the discharge loop, and when the voltage of the test capacitor decreases to be close to the voltage of the support capacitor during discharge, the current in the discharge loop decreases to be lower than the conduction maintenance current of the thyristor, the thyristor is turned off to stop the discharge, thereby controlling the voltage drop of the test capacitor during discharge and making the voltage waveform on the test capacitor during discharge closer to the engineering practice.

[0101] The application adopts thyristors to discharge the test capacitor, and the inherent resistance is the conduction resistance of the thyristor, which can remain relatively stable in the long-time and multiple-time discharge test process, is conducive to the adjustment of the damping parameters of the discharge loop, and reduces the uncertainty of the discharge process from the direction of the loop parameters.

[0102] The application adopts thyristors to discharge the test capacitor, and the discharge process does not cause explosion or impact, can reduce noise pollution in the discharge process, and reduces the unsafe factors in the test site.

[0103] The application adopts thyristors to discharge the test capacitor, and the thyristors in the test device are used as consumables and are easy to replace, thereby improving the convenience of maintenance of the test system.

[0104] The application adopts thyristors to discharge the test capacitor, which is equivalent to directly controlling the discharge process by a gate trigger signal, has the advantages of small delay, direct action of the trigger signal, and no mechanical failure compared with mechanical structures, and increases the stability of the system.

[0105] In the present application, the DC charging voltage source can be provided in a manner other than the combination of an AC voltage source and a rectifying silicon stack. The discharge current waveform can be collected, recorded and stored using a waveform recording and collecting device other than the combination of a Rogowski coil and an oscilloscope. The discharge is performed in a discharge circuit without connecting an adjustable resistance, an adjustable reactance or connecting a fixed resistance or a fixed reactance.

Claims

1. A test circuit for discharging a DC-supported capacitor, characterized in that, Includes a DC charging voltage source, a current-limiting resistor (3), a first vacuum contactor (4), a test sample capacitor (5), a thyristor (6), an adjustable resistor (7), an adjustable reactance (8), a supporting capacitor (9), a second vacuum contactor (10), a discharge coil (11), a first voltage divider (12), a Rogowski coil (13), an oscilloscope (14), a second voltage divider (15), a measurement system (16), and a control system (17); The DC charging voltage source, the current limiting resistor (3) and the first vacuum contactor (4) are connected in series and connected to the high voltage end of the test capacitor (5) to form a charging circuit for the test capacitor (5). The test capacitor (5) is connected in series with the thyristor (6), the adjustable resistor (7), and the adjustable reactance (8), and is connected to the high voltage end of the supporting capacitor (9) to form the discharge circuit of the test capacitor (5). The supporting capacitor (9) is connected in series with the second vacuum contactor (10) and the discharge coil (11) to form the discharge circuit of the supporting capacitor (9); The first voltage divider (12) is connected in parallel with the test capacitor (5), and the second voltage divider (15) is connected in parallel with the support capacitor (9); The signals from the first voltage divider (12) and the second voltage divider (15) are led out to the measurement system (16). The measurement system (16), thyristor (6), first vacuum contactor (4), and second vacuum contactor (10) are connected to the control system (17). During discharge, when the voltage of the test capacitor drops to nearly equal that of the supporting capacitor, the current in the discharge circuit drops below the thyristor's conduction sustaining current, and the thyristor turns off, stopping the discharge.

2. The discharge test circuit for a DC-supported capacitor according to claim 1, characterized in that, It also includes a Rogowski coil (13) and an oscilloscope (14). The Rogowski coil (13) is connected to the discharge circuit connection line of the test capacitor (5). The signal of the Rogowski coil (13) is led out to the oscilloscope (14), and the oscilloscope (14) leads out the waveform information to the measurement system (16).

3. The discharge test circuit for a DC-supported capacitor according to claim 1, characterized in that, The measurement system (16) and the control system (17) are connected for data interaction.

4. The discharge test circuit for a DC-supported capacitor according to claim 1, characterized in that, The DC charging voltage source includes an AC voltage source (1) and a rectifier silicon stack (2), which are connected in series.

5. A test circuit for discharging a DC-supported capacitor according to claim 1, characterized in that, The grounding terminals of the test capacitor (5) and the supporting capacitor (9) are both grounded.

6. A method for testing the discharge of a DC-supported capacitor, characterized in that, A discharge test circuit for a DC-supported capacitor according to any one of claims 1 to 5 includes the following process. Step 1: The control system (17) triggers the first vacuum contactor (4) and thyristor (6) to conduct; the DC charging voltage source charges the test capacitor (5) and the support capacitor (9). The voltages across the test capacitor (5) and the support capacitor (9) are measured by the first voltage divider (12) and the second voltage divider (15) respectively, and transmitted in real time to the measurement system (16). The measurement system (16) transmits the data to the control system (17). Step 2: When the voltage across the supporting capacitor (9) reaches the preset reference level in the control system (17), the charging of the supporting capacitor (9) is stopped. Step 3: The control system (17) triggers the first vacuum contactor (4) again to continue charging the sample capacitor (5). When the voltage across the sample capacitor (5) reaches the preset discharge voltage in the control system (17), the control system (17) stops triggering the first vacuum contactor (4) to turn it off. At this time, the charging of the sample capacitor (5) stops, and the voltage on the sample capacitor (5) is higher than the voltage on the supporting capacitor (9). Step 4: The control system (17) triggers the thyristor (6) to conduct under forward bias, and the test capacitor (5) discharges the support capacitor (9). The current waveform is controlled by the pre-adjusted adjustable resistor (7), adjustable reactance (8), and the capacitance and pre-charge voltage of the support capacitor (9). Step 5: When the positive half-wave of the discharge current decays to below the conduction sustaining current of the thyristor (6), the thyristor (6) is turned off, the control system (17) counts the current discharge test and starts timing, and when the timing reaches the preset discharge interval time, the next discharge test process begins. Step 6: The first vacuum contactor (4) and the second vacuum contactor (10) are triggered by the control system (17). At this time, the supporting capacitor (9) discharges through the discharge coil (11), and the DC charging voltage source continues to charge the test capacitor (5). Step 7: When the voltage across the supporting capacitor (9) drops to the preset reference level in the control system (17), the control system (17) stops triggering the second vacuum contactor (10), and at this time the supporting capacitor (9) stops discharging through the discharge coil (11). Step 8: Repeat the test process from Step 3 to Step 7 until the number of discharges reaches the expected number. The discharge test is terminated by the control system (17). At the same time, the thyristor (6) and the second vacuum contactor (10) are triggered to discharge the test sample capacitor (5) and the supporting capacitor (9) through the discharge coil (11) until the voltage drops to zero. Then, the triggering of the thyristor (6) and the second vacuum contactor (10) is stopped, and the discharge test is completed.

7. A method for testing the discharge of a DC-supported capacitor according to claim 6, characterized in that, In step 1, the AC voltage generated by the AC voltage source (1) is converted into DC voltage by the rectifier silicon stack (2) to charge the test capacitor (5) and the support capacitor (9).

8. A method for testing the discharge of a DC-supported capacitor according to claim 6, characterized in that, In step 5, the discharge current waveform is acquired by the Rogowski coil (13), transmitted to the oscilloscope (14) for further processing, and then transmitted to the measurement system (16) for recording, storage and visualization.

9. A method for testing the discharge of a DC-supported capacitor according to claim 6, characterized in that, In step 5, the discharge current waveform is a unipolar half-wave discharge waveform.

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