Overcurrent trigger device and control method thereof

Abstract

The invention discloses an overcurrent trigger device, which is electrically connected between a converter and a power grid simulation device, the overcurrent trigger device comprises a control circuit and a capacitor switching device, the capacitor switching device comprises a first switching switch, a second switching switch, a fourth capacitor and a first resistor, the second switching switch is connected in series with the first resistor, and the fourth capacitor is connected in series with the second resistor. The second fling-cut switch and the first resistor which are connected in series are connected with the fourth capacitor in parallel and then connected with the first fling-cut switch in series, and the control end of the first fling-cut switch and the control end of the second fling-cut switch are connected with the control circuit. The invention further discloses a control method of the overcurrent triggering device. The operation of the capacitor switching device can be controlled to simulate that the voltage of the power grid is temporarily lowered, so as to trigger the overcurrent of the converter, thereby facilitating the subsequent triggering to judge and test the overcurrent protection function of the converter. The invention further discloses a control method of the overcurrent triggering device.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuit protection, and particularly to an overcurrent triggering device and a control method thereof. Background Art

[0002] To improve the adaptability of converter products to the power grid and protect the converter, the overcurrent protection function is widely applied to various converters. The overcurrent protection technology is widely used in converter drive protection. Since high-power devices are prone to damage under instantaneous overcurrent conditions, the overcurrent protection technology is an effective means to prevent overcurrent. However, during the production process of existing converters, no corresponding tests are carried out on whether the overcurrent protection function of the converter can work properly. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an overcurrent triggering device and a control method thereof to trigger overcurrent for facilitating subsequent judgment tests on the overcurrent protection function of the converter.

[0004] In a first aspect, the present invention provides an overcurrent triggering device electrically connected between a converter and a power grid simulation device. The overcurrent triggering device includes a control circuit and a capacitor switching device. The capacitor switching device includes a first switching switch, a second switching switch, a fourth capacitor, and a first resistor. The second switching switch and the first resistor are in series, and the series-connected second switching switch and first resistor are in parallel with the fourth capacitor and then in series with the first switching switch. The control terminals of the first switching switch and the second switching switch are connected to the control circuit.

[0005] In a second aspect, the present invention provides a control method for an overcurrent triggering device, which is applied to the above overcurrent triggering device. The control method of the overcurrent triggering device includes the following steps: obtaining a simplified equivalent model of the converter according to the converter to be tested, calculating the resistance value of the first resistor and the capacitance of the fourth capacitor of the capacitor switching device of the overcurrent triggering device to be configured, and configuring the capacitor switching device; configuring the switching trigger voltage setting value and the trigger moment; controlling the trigger enable according to the trigger moment to start overcurrent triggering.

[0006] The beneficial technical effects of the present invention are as follows: The overcurrent triggering device of the present invention is electrically connected between the converter and the power grid simulation device, and is provided with a control circuit and a capacitor switching device. The capacitor switching device includes a first switching switch, a second switching switch, a fourth capacitor, and a first resistor. The first switching switch, the first resistor, and the second switching switch are connected in series in sequence, and the first switching switch is connected in series with the fourth capacitor. The control terminals of the first switching switch and the second switching switch are connected to the control circuit to control the connection of the fourth capacitor to the converter and the power grid simulation device by controlling the on / off of the first switching switch through the control circuit. By controlling the operation of the capacitor switching device, the grid voltage is briefly pulled down to trigger the overcurrent of the converter, realizing fixed-point capacitor switching, improving the accuracy, reliability, and safety of overcurrent triggering, facilitating the subsequent triggering for the judgment and testing of the overcurrent protection function of the converter, and discharging through the first resistor to ensure that there is no residual electricity injury after the overcurrent triggering is completed, improving safety. The control method of the overcurrent triggering device of the present invention also has the above functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0008] Figure 1 It is a schematic diagram of the capacitor switching device when the overcurrent triggering device provided by the embodiment of the present invention is specifically applied;

[0009] Figure 2 It is a schematic diagram of the control circuit when the overcurrent triggering device provided by the embodiment of the present invention is specifically applied;

[0010] Figure 3 It is a schematic flow chart of the control method of the overcurrent triggering device provided by the present invention;

[0011] Figure 4 It is a schematic circuit connection diagram of the capacitor switching device of the overcurrent triggering device provided by the present invention and the equivalent model of the converter. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] Please refer to Figure 1 ,Figure 1 FIG. 1 is a schematic diagram of a capacitor switching device in the specific application of the overcurrent trigger device provided by an embodiment of the present invention. The overcurrent trigger device is electrically connected between a converter 20 and a power grid simulation device 30. The overcurrent trigger device includes a control circuit and a capacitor switching device 11. The capacitor switching device 11 includes a first switching switch CB1, a second switching switch CB2, a fourth capacitor C4, and a first resistor R1. The second switching switch CB2 and the first resistor R1 are connected in series. The series-connected second switching switch CB2 and first resistor R1 are connected in parallel with the fourth capacitor C4 and then connected in series with the first switching switch CB1. Then, the first switching switch CB1, the first resistor R1, and the second switching switch CB2 are connected in series in sequence, and the first switching switch CB1 is connected in series with the fourth capacitor C4. The control terminal TCB1 of the first switching switch CB1 and the control terminal TCB2 of the second switching switch CB2 are connected to the control circuit.

[0014] Among them, the overcurrent trigger device is electrically connected between the converter 20 and the power grid simulation device 30, and is provided with a control circuit and a capacitor switching device 11. The capacitor switching device 11 includes a first switching switch CB1, a second switching switch CB2, a fourth capacitor C4, and a first resistor R1. The first switching switch CB1, the first resistor R1, and the second switching switch CB2 are connected in series in sequence, and the first switching switch CB1 is connected in series with the fourth capacitor C4. The control terminal TCB1 of the first switching switch CB1 and the control terminal TCB2 of the second switching switch CB2 are connected to the control circuit. By using the control circuit to control the on / off of the first switching switch CB1, the connection between the fourth capacitor C4 and the converter 20 and the power grid simulation device 30 is controlled. By controlling the operation of the capacitor switching device 11, the overcurrent of the converter is triggered, realizing fixed-point capacitor switching, improving the accuracy, reliability, and safety of overcurrent triggering, facilitating the subsequent triggering for the judgment and test of the overcurrent protection function of the converter, and discharging through the first resistor R1 to ensure that there is no residual electricity to hurt people after the overcurrent trigger is completed, improving safety.

[0015] Preferably, the common terminal of the first switching switch CB1 is connected to the converter 20 and the power grid simulation device 30. The normally open terminal of the first switching switch CB1 is connected to one end of the first resistor R1. The other end of the first resistor R1 is connected to the normally open terminal of the second switching switch CB2. The common terminal of the second switching switch CB2 is connected to the converter 20 and the power grid simulation device 30. One end of the fourth capacitor C4 is connected to the first switching switch CB1 and the first resistor R1. The other end of the fourth capacitor C4 is connected to the common terminal of the second switching switch CB2.

[0016] Among them, the connection mode of the overcurrent trigger device can be single-phase connection or two-phase connection.

[0017] Specifically, the power grid simulation device 30 includes a three-phase AC power supply, which includes a first-phase AC power supply A, a second-phase AC power supply B, and a third-phase AC power supply C. The common terminal of the first switching switch CB1 is connected to one phase of the three-phase AC power supply, and the common terminal of the second switching switch CB2 is connected to another phase of the three-phase AC power supply.

[0018] The three-phase AC power supply further includes an N phase. When connected in single-phase: the common terminal of the first switching switch CB1 is connected to one of the first-phase AC power supply A, the second-phase AC power supply B, and the third-phase AC power supply C, and the common terminal of the second switching switch CB2 is connected to the N phase of the three-phase AC power supply. Specifically, the common terminal of the second switching switch CB2 can be connected to the phase that needs to trigger overcurrent in the three-phase AC power supply, and the common terminal of the first switching switch CB1 is connected to the N phase in the three-phase AC power supply.

[0019] When connected in two-phase: the common terminal of the first switching switch CB1 is connected to one of the first-phase AC power supply A, the second-phase AC power supply B, and the third-phase AC power supply C, and the common terminal of the second switching switch CB2 is connected to another of the first-phase AC power supply A, the second-phase AC power supply B, and the third-phase AC power supply C. Specifically, the common terminal of the second switching switch CB2 can be connected to the phase that needs to trigger overcurrent in the three-phase AC power supply, and the common terminal of the first switching switch CB1 is connected to any one of the other two-phase AC power supplies in the three-phase AC power supply.

[0020] The converter 20 is connected to the first-phase AC power supply A, the second-phase AC power supply B, and the third-phase AC power supply C. Specifically, in this embodiment, the power grid simulation device 30 is connected to the converter 20 and the overcurrent trigger device through an inductor. Among them, since the power grid simulation device 30 includes a three-phase AC power supply, each phase of the AC power supply can be connected to the converter 20 and the overcurrent trigger device through a corresponding inductor to reduce the influence of the power grid simulation device on the overcurrent trigger device and the converter 20.

[0021] Combined with Figure 2, specifically, the control circuit includes a controller and a first switching control circuit. The first switching control circuit includes a first operational amplifier U1, a second operational amplifier U2, an AND gate &, a first delay unit YT1, a buffer, a second delay unit YT2, and a NOT gate. The input terminal of the first operational amplifier U1 is connected to the power grid simulation device 30. The output terminal of the first operational amplifier U1 is connected to an input terminal of the second operational amplifier U2. The other input terminal of the second operational amplifier U2 is connected to a reference voltage Uref. The output terminal of the second operational amplifier U2 is connected to the first input terminal of the AND gate &. The second input terminal of the AND gate & is connected to the trigger enable terminal EN of the controller. The output terminal of the AND gate & is connected to the control terminal TCB1 of the first switching switch CB1 after passing through the first delay unit YT1 and the buffer. The second delay unit YT2 and the NOT gate are connected in series in sequence, and the input terminal of the second delay unit YT2 is connected to the connection node between the buffer and the control terminal TCB1 of the first switching switch CB1. The output terminal of the NOT gate is connected to the third input terminal of the AND gate &. By setting the first delay unit YT1 and the second delay unit YT2, it can more accurately ensure that the capacitor is switched in at the required time node to achieve overcurrent triggering according to the required trigger moment.

[0022] Refer to Figure 3 , Figure 3 FIG. is a schematic flow chart of the control method of the overcurrent triggering device provided by the present invention. The control method of the overcurrent triggering device is applied to the above-mentioned overcurrent triggering device, and the control method includes the following steps:

[0023] Step S10: Obtain a simplified equivalent model of the converter according to the converter to be tested, calculate the resistance value of the first resistor and the capacitance of the fourth capacitor of the capacitor switching device of the overcurrent triggering device to be configured, and configure the capacitor switching device;

[0024] Step S20: Configure the switching trigger voltage setting value and the trigger moment;

[0025] Step S30: Control the trigger enable according to the trigger moment to start overcurrent triggering.

[0026] Among them, the control method of the overcurrent triggering device calculates and configures the overcurrent triggering device through the simplified equivalent model of the converter obtained according to the converter to be tested, and can realize voltage magnitude adjustment, fixed-point capacitor switching, and improve the accuracy, reliability, and safety of overcurrent triggering by configuring the switching trigger voltage setting value and the trigger moment. The equivalent model of the converter is as Figure 4 shown, Figure 4 FIG. shows a schematic circuit diagram of the connection between the capacitor switching device of the overcurrent triggering device and the equivalent model of the converter, Figure 4In it, the DC bus of the converter can be an ideal voltage source, denoted as the first capacitor C1 and the second capacitor C2 connected in series. The DC bus of the converter is connected to the AC port through the inverter LC filter circuit 21. The inverter LC filter circuit 21 includes a first inductor L1, a third capacitor C3, and a second inductor L2. The DC bus of the converter, the first inductor L1, the third capacitor C3, and the second inductor L2 are connected in series in sequence to form a loop. One end of the first switching switch CB1 of the capacitor switching device 11 is connected to the series node of the first inductor L1 and the third capacitor C3, and the other end of the first switching switch CB1 is connected to one end of the fourth capacitor C4. The other end of the fourth capacitor C4 is connected to the series node of the second inductor L2 and the third capacitor C3, so as to adjust the voltage of the AC port of the converter 20 by controlling the on / off of the first switching switch CB1, thereby realizing the voltage mutation of the AC port of the converter 20, increasing the voltages at both ends of the first inductor L1 and the second inductor L2, increasing the change rate of the inductor current, thereby realizing overcurrent, and then triggering the overcurrent protection of the converter 20, which is convenient for subsequent judgment and testing of the overcurrent protection function of the converter 20. Figure 4 The resistor R connected in parallel with the third capacitor C3 is equivalent to the operating load of the converter 20.

[0027] Specifically, after the step S30, it further includes:

[0028] After the preset time for overcurrent triggering is completed, close the second switching switch to release the remaining electricity of the capacitor switching device.

[0029] Specifically, before the step S30, it further includes:

[0030] Calculate the trigger delay and trigger level, adjust the trigger delay and trigger level according to the required simulated grid voltage sag moment and the preset grid voltage sag value, and update the trigger moment. By calculating the trigger delay and trigger level, it is possible to more accurately ensure that the capacitor is inserted at the required time node to realize overcurrent triggering according to the required trigger moment.

[0031] In the first example, there is no DC charging device to charge the capacitor switching device of the overcurrent triggering device. When the capacitor needs to be switched in at the voltage peak and the voltage reaches 0, if the equivalent capacitance of the AC port filter capacitor of the converter equivalent model, i.e., the third capacitor, is 50 μF, and the rated line voltage of the AC port of the converter is 690 V, the control process of the overcurrent triggering device can be as follows: Since there is no DC voltage to adjust the initial value of the switched capacitor, the switched-in capacitor is set according to the requirement of 0.1Umax. The capacitance of the fourth capacitor of the capacitor switching device of the overcurrent triggering device can be set to nine times the capacitance of the third capacitor, i.e., 450 μF, so as to configure the capacitor switching device according to the obtained capacitance of the fourth capacitor, calculate the trigger delay and trigger level, and verify whether it meets the requirements according to the required simulated grid voltage sag moment and the preset grid voltage sag value. If the trigger moment lags behind the target value, the trigger delay time can be adjusted to adjust the trigger delay and trigger level, and the trigger moment is updated to ensure that the trigger moment reaches the target value. Configure the switching trigger voltage setting value and trigger moment; Control the trigger enable according to the trigger moment to start the overcurrent trigger; After the preset time of the overcurrent trigger is completed, close the second switching switch to release the remaining power of the capacitor switching device. The trigger delay time is the set value of the first delay unit.

[0032] Preferably, after the step of configuring the capacitor switching device in step S10, it further includes:

[0033] Equivalently calculate the initial voltage of the preset switched capacitor according to the cut-set charge conservation principle.

[0034] Specifically, after the step of equivalently calculating the initial voltage of the preset switched capacitor according to the cut-set charge conservation principle, it further includes:

[0035] Charge the fourth capacitor of the capacitor switching device according to the required simulated grid voltage sag moment and characteristics in combination with the initial voltage of the preset switched capacitor.

[0036] In the second example, a DC charging device charges a capacitor switching device of an overcurrent triggering device. When the capacitor needs to be connected at the voltage peak and the voltage reaches 0, if the equivalent capacitance of the AC port filtering capacitor of the converter equivalent model, i.e., the third capacitor, is 50 μF, and the rated line voltage of the AC port of the converter is 690 V, the control process of the overcurrent triggering device can be as follows: The capacitance of the fourth capacitor of the capacitor switching device of the overcurrent triggering device can be set to three times the capacitance of the third capacitor, i.e., 150 μF. According to the principle of cut-set charge conservation, the initial voltage of the preset switching capacitor is equivalently calculated, that is, the voltage required to charge the fourth capacitor to obtain the fourth capacitor, so as to configure the capacitor switching device according to the obtained capacitance of the fourth capacitor. According to the grid voltage sag moment and characteristics to be simulated and combined with the initial voltage of the preset switching capacitor, the fourth capacitor of the capacitor switching device is charged, the trigger delay and trigger level are calculated, and whether the requirements are met is verified according to the grid voltage sag moment to be simulated and the preset grid voltage sag value. If the trigger moment lags behind the target value, the trigger delay time can be adjusted to adjust the trigger delay and trigger level, and the trigger moment is updated to ensure that the trigger moment reaches the target value, and the switching trigger voltage setting value and trigger moment are configured; According to the trigger moment, the trigger enable is controlled to start the overcurrent trigger; After the preset time of the overcurrent trigger is completed, the second switching switch is closed to release the remaining power of the capacitor switching device. The trigger delay time is the set value of the first delay unit. Wherein, the line voltage of the AC port before the capacitor is connected is the peak voltage U C3(0-) , U C3(0-) = 975.8 V. After the capacitor is connected, the line voltage of the AC port needs to reach 0 voltage, denoted as U C3(0+) . Then the initial voltage of the preset switching capacitor, that is, the voltage required to charge the fourth capacitor to obtain the fourth capacitor, is denoted as U C4(0-) , and can be calculated by formula (1):

[0037]

[0038] In the formula, U C4(0-) represents the initial voltage of the preset switching capacitor, C 3 represents the capacitance of the third capacitor, C 4 represents the capacitance of the fourth capacitor, U C3(0-) represents the line voltage of the AC port before the capacitor is connected as the peak voltage. The value of the initial voltage U C4(0-) of the preset switching capacitor can be obtained as -243.95 V.

[0039] In the third example, a DC charging device charges a capacitor switching device of an overcurrent triggering device. It is necessary to input the capacitor at the voltage peak and when the voltage reaches the negative voltage peak. If the equivalent capacitance of the AC port filtering capacitor of the converter equivalent model, that is, the capacitance of the third capacitor, is 50 μF, and the rated line voltage of the AC port of the converter is 690 V, the control process of the overcurrent triggering device can be as follows: The capacitance of the fourth capacitor of the capacitor switching device of the overcurrent triggering device can be set to ten times the capacitance of the third capacitor, that is, 500 μF. According to the principle of cut-set charge conservation, the initial voltage of the preset switching capacitor is equivalently calculated, that is, the voltage required to charge the fourth capacitor to obtain the fourth capacitor, so as to configure the capacitor switching device according to the obtained capacitance of the fourth capacitor. Charge the fourth capacitor of the capacitor switching device according to the required simulated grid voltage sag moment and characteristics combined with the initial voltage of the preset switching capacitor, calculate the trigger delay and trigger level, verify whether the requirements are met according to the required simulated grid voltage sag moment and the preset grid voltage sag value. If the trigger moment lags behind the target value, the trigger delay time can be adjusted to adjust the trigger delay and trigger level, and update the trigger moment to ensure that the trigger moment reaches the target value, configure the switching trigger voltage setting value and trigger moment; Control the trigger enable according to the trigger moment to start the overcurrent trigger; After the preset time of the overcurrent trigger is completed, close the second switching switch to release the remaining power of the capacitor switching device. The trigger delay time is the set value of the first delay unit. Among them, the line voltage of the AC port before the capacitor is input is the peak voltage, and the peak voltage can be set to 975.8 V, denoted as U C3(0-) , after the capacitor is input, the line voltage of the AC port needs to reach the negative peak voltage, then the negative peak voltage can be -975.8 V, denoted as U C3(0+) , then the initial voltage of the preset switching capacitor, that is, the voltage required to charge the fourth capacitor to obtain the fourth capacitor, is denoted as U C4(0-) , and can be calculated by formula (2):

[0040]

[0041] In the formula, U C4(0-) represents the initial voltage of the preset switching capacitor, C 3 represents the capacitance of the third capacitor, C 4 represents the capacitance of the fourth capacitor, U C3(0-) represents the line voltage of the AC port before the capacitor is input is the peak voltage, and the initial voltage U C4(0-) of the preset switching capacitor can be obtained as -1219.76 V.

[0042] In summary, the overcurrent triggering device of the present invention is electrically connected between the converter and the power grid simulation device, and is provided with a control circuit and a capacitor switching device. The capacitor switching device includes a first switching switch, a second switching switch, a fourth capacitor and a first resistor. The first switching switch, the first resistor and the second switching switch are connected in series in sequence, and the first switching switch is connected in series with the fourth capacitor. The control terminals of the first switching switch and the second switching switch are connected to the control circuit to control the connection of the fourth capacitor to the converter and the power grid simulation device by controlling the on / off of the first switching switch with the control circuit. By controlling the operation of the capacitor switching device to trigger the overcurrent of the converter, fixed-point capacitor switching is realized, the accuracy, reliability and safety of overcurrent triggering are improved, which is convenient for subsequent triggering to judge and test the overcurrent protection function of the converter, and the first resistor is used to discharge to ensure that there is no residual electricity injury after the overcurrent triggering is completed, thus improving safety. The control method of the overcurrent triggering device of the present invention also has the above functions.

[0043] As described above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An overcurrent triggering device, characterized in that: The overcurrent trigger device is electrically connected between the converter and the power grid simulation device, and includes a control circuit and a capacitor switching device. The capacitor switching device includes a first switching switch, a second switching switch, a fourth capacitor and a first resistor. The second switching switch and the first resistor are connected in series. The second switching switch and the first resistor connected in series are connected in parallel with the fourth capacitor and then connected in series with the first switching switch. The control end of the first switching switch and the control end of the second switching switch are connected to the control circuit.

2. The overcurrent triggering device according to claim 1, characterized in that: The common end of the first switching switch is connected to the converter and the power grid simulation device, the normally-open end of the first switching switch is connected to one end of the first resistor, the other end of the first resistor is connected to the normally-open end of the second switching switch, the common end of the second switching switch is connected to the converter and the power grid simulation device, one end of the fourth capacitor is connected to the first switching switch and the first resistor, and the other end of the fourth capacitor is connected to the common end of the second switching switch.

3. The overcurrent triggering device according to claim 2, characterized in that: The power grid simulation device includes a three-phase AC power supply, the common end of the first switching switch is connected to one phase of the three-phase AC power supply, and the common end of the second switching switch is connected to another phase of the three-phase AC power supply.

4. The overcurrent triggering device according to claim 3, characterized in that: The control circuit includes a controller and a first switching control circuit, wherein the first switching control circuit includes a first operational amplifier, a second operational amplifier, an AND gate, a first delay unit, a buffer, a second delay unit and a NOT gate, wherein the input end of the first operational amplifier is connected to the power grid simulation device, the output end of the first operational amplifier is connected to an input end of the second operational amplifier, the other input end of the second operational amplifier is connected to a reference voltage, the output end of the second operational amplifier is connected to the first input end of the AND gate, the second input end of the AND gate is connected to the trigger enable end of the controller, the output end of the AND gate is connected to the control end of the first switching switch after passing through the first delay unit and the buffer, the second delay unit and the NOT gate are connected in series in sequence, and the input end of the second delay unit is connected to the connection node between the buffer and the control end of the first switching switch, and the output end of the NOT gate is connected to the third input end of the AND gate.

5. The overcurrent triggering device according to claim 3, characterized in that: The power grid simulation device is connected to the converter and the overcurrent triggering device through an inductor.

6. A control method for an overcurrent trigger device, characterized in that: Applied to the overcurrent triggering device according to any one of claims 1 to 5, the control method of the overcurrent triggering device comprises the following steps: Obtain a simplified converter equivalent model according to the converter to be tested, calculate the resistance value of the first resistor and the capacity of the fourth capacitor of the capacitor switching device of the overcurrent trigger device to be configured, and configure the capacitor switching device; Configure the switching trigger voltage setting value and trigger time; The trigger enable is controlled according to the triggering time to start the overcurrent triggering.

7. The control method of the overcurrent trigger device according to claim 6, characterized in that: After the step of configuring the capacitor switching device, the method further includes: The preset initial value voltage of the switched capacitor is calculated based on the charge conservation principle of the cut set.

8. The control method of the overcurrent trigger device according to claim 7, characterized in that: After the step of equivalently calculating the preset initial value voltage of the switching capacitor according to the cut-set charge conservation principle, the method further includes: The fourth capacitor of the capacitor switching device is charged according to the grid sag time and characteristics to be simulated and the preset initial value voltage of the switching capacitor.

9. The control method of the overcurrent trigger device according to claim 6, characterized in that: Before the step of controlling the triggering enable to start the overcurrent triggering according to the triggering moment, the method further includes: Calculate the trigger delay and trigger level, adjust the trigger delay and trigger level according to the simulated grid sag moment and the preset grid sag voltage value, and update the trigger moment.

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