A method and system for low-pressure pressurization test of ultra-high voltage flexible DC converter valve

Abstract

This invention discloses a low-pressure pressurization test method and system for an ultra-high voltage flexible DC converter valve. The charging stage of the converter valve in this invention follows the following sequence: The voltage regulating transformer is adjusted to its lowest setting, the AC side switch is closed, and then the voltage of the voltage regulating transformer is gradually adjusted to the required test value; the T4 transistor of the full-bridge submodule of the converter valve is turned on; some submodules with the highest voltage are alternately disconnected for active charging; when the submodule voltage reaches the preset value and active charging is completed, the T2 transistors of all disconnected half-bridge submodules and the T2 and T4 transistors of all disconnected full-bridge submodules are disconnected. At this point, the sum of the voltages of the two full-bridge submodules and one half-bridge submodule is greater than the valve side line voltage of the converter transformer, and the starting resistor bypass switch is closed. This invention reduces the inrush current during the entire charging stage, avoiding interference with the protection operation of the input power supply.

Description

Technical Field

[0001] This invention belongs to the field of ultra-high voltage flexible DC transmission technology, specifically a method and system for low-pressure pressurization test of ultra-high voltage flexible DC converter valve. Background Technology

[0002] Ultra-high voltage flexible direct current transmission technology is a key technology for building a new power system. It can realize the ultra-long-distance and efficient transmission of large-scale renewable energy, solve the problem of cross-regional power transmission, and has the ability to support reactive power self-sufficiency, low loss and multi-terminal networking. It significantly improves the safety and stability of the power grid. By actively suppressing fault current through fully controlled IGBT devices, it avoids the commutation failure problem of traditional DC transmission and supports black start of the power grid, greatly improving transmission efficiency and land utilization.

[0003] The low-voltage pressurization test of the converter valve is conducted after the completion of the converter transformer body test, the converter valve body and valve control system joint commissioning test, the converter station control and protection device test, and the pole control and valve control joint commissioning test. Its purpose is to verify the correctness of the primary wiring of the converter transformer and converter valve. Existing technology regarding the low-voltage pressurization test of converters is simplistic and only applies to traditional UHVDC converters.

[0004] Traditional DC low-voltage pressurization test schemes, such as Figure 1 As shown, take one thyristor stage from each single valve of the converter valve, short-circuit the other thyristor stages with a temporary shorting wire, and temporarily connect them to form a 12-pulse rectifier wiring method to bring out the positive and negative voltages of the DC side. According to the calculation, connect the corresponding DC load resistor on the DC side.

[0005] (1) Disconnect the low-voltage side wiring of the step-up transformer and check whether the phase sequence of the test power supply is consistent with the phase sequence and phase angle requirements of the ignition voltage signal of the control and protection device.

[0006] (2) After checking and confirming that the synchronization signal is normal, disconnect the test power supply, adjust the voltage regulating transformer to zero position, and connect the low voltage side of the step-up transformer.

[0007] (3) Adjust the voltage regulating transformer, energize the converter transformer, unlock the converter valve, adjust the trigger angle, and record the valve side voltage and waveform at each angle. Analyze whether the control wiring of the synchronization circuit and trigger control circuit is intact.

[0008] Traditional UHVDC converters and flexible UHVDC converters differ greatly in their converter valve topology and control methods. Therefore, existing low-voltage pressurization test methods for traditional UHVDC converters cannot be used as a reference for UHVDC flexible DC transmission projects. Summary of the Invention

[0009] To address the technical problems existing in the prior art, this invention provides a low-pressure pressurization test method and system for ultra-high voltage flexible DC converter valves, which places the "closing of the starting resistor bypass switch" in the last step to reduce the inrush current during the entire charging stage and avoid affecting the protection action of the input power supply.

[0010] Therefore, the present invention adopts the following technical solution.

[0011] In a first aspect, the present invention provides a low-pressure pressurization test method for an ultra-high voltage flexible DC converter valve. The test circuit used in the low-pressure pressurization test includes a test power supply, a voltage regulating transformer, a step-up transformer, an AC circuit breaker, a starting resistor, a converter transformer, and a converter valve based on a hybrid half-bridge submodule and a full-bridge submodule, connected in series. The charging stages of the converter valve are as follows:

[0012] Set the voltage regulator to the lowest setting, close the AC side switch, and then gradually adjust the voltage of the voltage regulator to the required test value.

[0013] T4 tube for conducting the full-bridge submodule of the converter valve;

[0014] The submodules with the highest voltage are switched off in turn for active charging;

[0015] When the submodule voltage reaches the preset value and completes active charging, disconnect the T2 transistor of all cut-off half-bridge submodules and disconnect the T2 and T4 transistors of all cut-off full-bridge submodules. At this time, the sum of the voltage of the two bridge arm full-bridge submodules and the voltage of one bridge arm half-bridge submodule is greater than the voltage of the converter transformer valve side line, and close the starting resistor bypass switch.

[0016] Furthermore, N sub-modules are selected for low-pressure pressurization tests in each bridge arm of the converter valve, while the remaining sub-modules are bypassed using short-circuit connections. During the uncontrolled charging phase, the peak voltage of the valve side line charges M sub-modules. When the converter valve is composed entirely of half-bridge sub-modules, M=N. When the converter valve is composed of a mixture of full-bridge and half-bridge sub-modules, M= the number of full-bridge modules in the two bridge arms + the number of half-bridge modules in one bridge arm. When the converter valve is composed entirely of full-bridge sub-modules, M=2N.

[0017] Furthermore, if the threshold voltage for each submodule to enter active charging is set to V1, then the corresponding effective value of the valve-side line voltage is V1×M / kV, calculate the minimum voltage required for the primary side of the converter transformer k×V1×M / based on the transformer turns ratio k. kV;

[0018] Based on the above effective value of the valve side line voltage and the minimum voltage required for the primary side of the converter transformer, the voltage drop across the starting resistor and the margin are considered to select the converter transformer side voltage of the step-up transformer.

[0019] Furthermore, it is necessary to pre-calculate the time t1 for the submodule voltage to drop from a preset value to V1 when the converter valve unlocks, to ensure that the converter valve completes instantaneous unlocking before the submodule voltage drops to V1.

[0020] Furthermore, the starting resistor and converter transformer mentioned above are both integrated into the main circuit of the UHV flexible DC transmission project.

[0021] Furthermore, the following conditions must be met before conducting the low-pressure pressurization test:

[0022] 1) All connections between the corresponding phases and neutral line on the grid side of the converter transformer are completed; 2) The converter transformer test is completed and the test results are qualified; 3) The wiring of the converter valve and the installation and commissioning of the protection and control system are completed; 4) The converter valve equipment has completed the single valve inspection and testing, and the control and protection system has completed the test procedures and temporary settings of the protection output; 5) The switches and disconnectors related to the main circuit of the converter valve are ready for operation; 6) The converter valve sub-modules not involved in the test are reliably bypassed; 7) The converter station is isolated from the AC system, and the DC side disconnectors of the converter station are opened and in an isolated state.

[0023] Furthermore, the starting resistor is composed of multiple modules connected in series. One or more of these modules are selected and led out in series, and the resistance value of the starting resistor is adjusted according to the test results.

[0024] Furthermore, the unlocking stage of the converter valve is as follows: the AC circuit breaker is first disconnected by background sequential control, and then the converter valve is unlocked instantaneously. During unlocking, the converter valve is phase-locked according to the voltage of the first AC voltage transformer, and the converter valve adopts open-loop control; by checking whether the voltage phase sequence and phase of the first AC voltage transformer and the second AC voltage transformer are consistent, the primary wiring of the converter transformer and the converter valve is verified.

[0025] The first AC voltage transformer is located on the step-up transformer side of the AC circuit breaker, and the second AC voltage transformer is located on the starting resistor side of the AC circuit breaker.

[0026] Secondly, the present invention provides a low-pressure pressurization test system for an ultra-high voltage flexible DC converter valve, comprising:

[0027] AC side switch unit: used to adjust the voltage regulator transformer to the lowest position, close the AC side switch, and then gradually adjust the voltage of the voltage regulator transformer to the required test value;

[0028] IGBT conduction unit: T4 tube used to conduct the full-bridge submodule of the converter valve;

[0029] Active charging unit: Used to alternately cut off the sub-modules with the highest voltage for active charging;

[0030] When the submodule voltage reaches the preset value and completes active charging, the T2 transistors of all cut-off half-bridge submodules and the T2 and T4 transistors of all cut-off full-bridge submodules are disconnected. At this time, the sum of the voltages of the two bridge arm full-bridge submodules and the voltage of one bridge arm half-bridge submodule is greater than the voltage of the converter transformer valve side line, and the starting resistor bypass switch is closed.

[0031] Furthermore, the ultra-high voltage flexible DC converter valve low-pressure pressurization test system also includes an unlocking unit: the AC circuit breaker is first disconnected through background sequential control, and then the converter valve is instantaneously unlocked. During unlocking, the converter valve is phase-locked according to the voltage of the first AC voltage transformer, and the converter valve adopts open-loop control; by verifying whether the voltage phase sequence and phase of the first AC voltage transformer and the second AC voltage transformer are consistent, the primary wiring of the converter transformer and the converter valve is checked.

[0032] The beneficial effects of this invention are as follows: This invention places the "starting resistor bypass switch" in the last step of the converter valve charging stage, which reduces the inrush current of the entire charging stage, avoids affecting the protection action of the input power supply, and provides a reference for the subsequent low-voltage pressurization test of UHV flexible DC projects. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 Wiring diagram for traditional DC low-voltage pressurization test;

[0035] Figure 2 Wiring diagram for low-pressure pressurization test of the ultra-high voltage flexible DC converter valve of the present invention;

[0036] Figure 3 This is a flowchart of the low-pressure pressurization test method for the ultra-high voltage flexible DC converter valve of the present invention;

[0037] Figure 4 This is a diagram showing the composition of the low-pressure pressurization test system for the ultra-high voltage flexible DC converter valve of the present invention.

[0038] Figure 2 In this context, HBSM represents a half-bridge submodule, and FBSM represents a full-bridge submodule. Detailed Implementation

[0039] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment provides a low-pressure pressurization test method for an ultra-high voltage flexible DC converter valve.

[0042] Before conducting a low-pressure pressurization test on an ultra-high voltage flexible DC converter valve, the following conditions must be met:

[0043] 1) All connections between the corresponding phases and neutral line on the grid side of the converter transformer have been completed;

[0044] 2) The converter transformer test is complete, and the test results are satisfactory;

[0045] 3) The wiring of the converter valve and the installation and commissioning of the protection and control system have been completed;

[0046] 4) The converter valve equipment completes the inspection and testing of individual valves, and the control and protection system completes the test procedures and temporary settings of the protection outlets;

[0047] 5) The switches and disconnectors related to the main circuit of the converter valve are ready for operation;

[0048] 6) The converter valve submodules not participating in the test were reliably bypassed;

[0049] 7) The converter station is isolated from the AC system. The DC side disconnectors of the converter station are opened and are in an isolated state.

[0050] like Figure 2 As shown, the test circuit used for the low-pressure pressurization test of the UHV flexible DC converter valve includes a test power supply, a voltage regulating transformer, a step-up transformer, an AC circuit breaker, an AC voltage transformer, a starting resistor, a converter transformer, and a converter valve based on a hybrid half-bridge and full-bridge submodule, connected in series. The starting resistor and converter transformer are both integrated into the main circuit of the UHV flexible DC transmission project.

[0051] (1) Test power supply

[0052] The test power supply should preferably be connected from the construction transformer to minimize the impact on operating equipment. If the capacity of the construction transformer is insufficient, consider configuring a generator power supply or connecting from the station service transformer.

[0053] (2) Voltage regulating transformer

[0054] The voltage regulating transformer is specially configured for testing. By adjusting the voltage of the voltage regulating transformer, the inrush current at the moment of closing the AC circuit breaker can be reduced, and the AC voltage can be regulated to meet the test requirements.

[0055] (3) Step-up transformer

[0056] The step-up transformer is specially configured for testing. It boosts the test power supply to ensure that the submodule voltage is charged to the preset value during the converter valve charging stage, thus laying the foundation for reliable unlocking of the converter valve.

[0057] (4) AC circuit breaker

[0058] The AC circuit breaker is specially configured for testing. When the AC circuit breaker is closed, the converter valve begins charging. After the converter valve completes active charging (the submodule voltage reaches the preset value), the AC circuit breaker is opened, and the converter valve is momentarily unlocked for passive phase verification. At this time, because the converter valve is unlocked while the AC circuit breaker is open, it avoids affecting the AC system and also prevents the AC system from inputting energy to the converter valve, ensuring the safety of the converter valve submodule.

[0059] (5) Voltage transformer

[0060] AC voltage transformers are installed on both sides of the AC circuit breaker. When the converter valve is instantaneously unlocked, the converter valve is phase-locked according to the voltage of the first AC voltage transformer PT1 and uses open-loop control. By verifying the phase sequence and phase of the first AC voltage transformer PT1 and the second AC voltage transformer PT2, the primary wiring of the converter transformer and the converter valve can be verified. The first AC voltage transformer PT1 is located on the step-up transformer side of the AC circuit breaker, and the second AC voltage transformer PT2 is located on the starting resistor side of the AC circuit breaker.

[0061] (6) Starting resistor

[0062] The starting resistor is integrated into the main circuit of the UHV flexible DC transmission project. Because the voltage and current during the low-voltage pressurization test are much lower than the rated operating values, the starting resistor value is too high, which can easily cause the submodule voltage to fail to reach the preset value during the charging phase. Since the starting resistor is usually composed of multiple modules connected in series, one or more modules can be selected for series connection to reduce the starting resistor value. The starting resistor value can be adjusted according to the test results. Furthermore, it is necessary to verify the energy of the starting resistor during the charging phase to prevent it from exceeding the design value and causing resistor burnout.

[0063] (7) Converter transformer

[0064] The converter transformer is integrated into the main circuit of the UHV flexible DC transmission project.

[0065] (8) Converter valve

[0066] A small subset (N) of the submodules in each arm of the converter valve are selected for low-voltage pressurization testing, while the remaining submodules are bypassed using short-circuit connections. During the uncontrolled charging phase, the peak line voltage charges M submodules (M=N when all are half-bridge submodules; M=the number of full-bridge modules in two arms + the number of half-bridge modules in one arm when all are half-bridge submodules; M=2N when all are half-bridge submodules). The threshold voltage for each submodule to enter active charging is V1. From this, the corresponding effective value of the valve-side line voltage can be calculated as V1×M / 1.414kV. Based on the converter transformer's turns ratio k, the minimum voltage required on the primary side of the converter transformer is calculated as k×V1×M / 1.414kV. Considering the voltage drop across the starting resistor and the margin, the converter transformer-side voltage of the step-up transformer is selected.

[0067] The aforementioned low-pressure pressurization test method for ultra-high voltage flexible DC converter valves consists of a charging phase and an unlocking phase for the converter valves, such as... Figure 3 As shown.

[0068] The charging process of the converter valve consists of four stages: closing the AC side switch, turning on the full-bridge submodule T4, closing the starting resistor bypass switch, and active charging. All four stages are prone to inrush current, which may affect the protection operation of the input power supply. To prevent these problems, the charging strategy of the converter valve during the low-voltage pressurization test needs to be optimized.

[0069] To reduce the inrush current during the entire charging process, the "closing the start-up resistor bypass switch" is implemented as the final step. The optimized charging strategy is as follows:

[0070] Set the voltage regulator to the lowest setting, close the AC side switch, and then gradually adjust the voltage of the voltage regulator to the required test value.

[0071] T4 tube for conducting the full-bridge submodule of the converter valve;

[0072] The submodules with the highest voltage are switched off in turn for active charging;

[0073] Once the submodule voltage reaches the preset value and active charging is complete, disconnect the T2 transistors of all disconnected half-bridge submodules and the T2 and T4 transistors of all disconnected full-bridge submodules. At this point, the sum of the voltages of the two full-bridge submodules and one half-bridge submodule is greater than the converter transformer valve side line voltage. Then, close the starting resistor bypass switch. It is necessary to pre-calculate the time t1 it takes for the submodule voltage to drop from the preset value to V1 when the converter valve unlocks, ensuring that the converter valve instantaneously unlocks before the submodule voltage drops to V1.

[0074] The unlocking phase of the converter valve is as follows: the AC circuit breaker is disconnected first through background sequential control, and then the converter valve is unlocked instantaneously. During unlocking, the converter valve is phase-locked according to the voltage of the first AC voltage transformer, and the converter valve adopts open-loop control. By checking whether the voltage phase sequence and phase of the first AC voltage transformer and the second AC voltage transformer are consistent, the primary wiring of the converter transformer and the converter valve is verified.

[0075] The following simulation was conducted using the low-pressure pressurization test method for the ultra-high voltage flexible DC converter valve in this embodiment.

[0076] The simulation parameters are as follows:

[0077] 1. Voltage regulating transformer

[0078] Rated voltage is 400V / 0-400V, Y / Y connection, capacity is 630kVA.

[0079] 2. Step-up transformer

[0080] Rated voltage is 35kV / 0.4kV, Dyn connection, capacity is 630kVA.

[0081] 3. Starting resistor

[0082] The starting resistor is 2166.66Ω.

[0083] 4. Converter transformer

[0084] Table 1. Converter Transformer Parameter Table

[0085]

[0086] 5. Flow converter valve

[0087] Fifteen submodules (nine full-bridge and six half-bridge) were selected for low-voltage pressurization testing in each bridge arm, while the remaining submodules were bypassed using short-circuit connections. The T4 transistor was activated at 500V for the full-bridge submodules, and three submodules were deactivated during the active charging phase.

[0088] The simulation results are as follows:

[0089] 1. Waveform during charging phase

[0090] Simulation results of submodule voltage, bridge arm current, and 400V side current waveforms during the start-up charging process show that the peak inrush current during the start-up charging process occurs when the AC circuit breaker is closed, at which point the peak current flowing through the 400V side of the construction transformer is approximately 1100A. When the T4 tube of the full-bridge submodule is closed, the peak inrush current flowing through the 400V side of the construction transformer is approximately 750A. After bypassing the last submodule during the active voltage equalization stage, the peak inrush current flowing through the 400V side of the construction transformer is approximately 300A. In steady state, the submodule capacitor voltage is approximately 1.5kV.

[0091] The simulation results of the starting resistor current, the effective value of the starting resistor current, and the energy waveform of the starting resistor show that the maximum inrush current flowing through the starting resistor occurs when the AC circuit breaker is closed. At this time, the peak current is 13A, the effective value is 9A, and the steady-state effective value is about 0.2A.

[0092] 2. Waveform of the instantaneous unlocking phase

[0093] The simulation results show that the voltage phase sequence of PT1 and PT2 on both sides of the AC circuit breaker is consistent, which can be used to determine the correctness of the primary wiring of the converter transformer and converter valve.

[0094] Example 2

[0095] This embodiment provides a low-pressure pressurization test system for an ultra-high voltage flexible DC converter valve, used to implement the low-pressure pressurization test method for the ultra-high voltage flexible DC converter valve described in Embodiment 1, such as... Figure 4 As shown, it consists of an AC side switch unit, an IGBT turn-on unit, an active charging unit, a start-up resistor bypass switch unit, and an unlocking unit.

[0096] AC side switch unit with starting resistor: used to adjust the voltage regulator transformer to the lowest position, close the AC side switch, and then gradually adjust the voltage of the voltage regulator transformer to the value required for the test;

[0097] IGBT conduction unit: T4 tube used to conduct the full-bridge submodule of the converter valve;

[0098] Active charging unit: Used to alternately cut off the sub-modules with the highest voltage for active charging;

[0099] When the submodule voltage reaches the preset value and completes active charging, the T2 transistors of all cut-off half-bridge submodules and the T2 and T4 transistors of all cut-off full-bridge submodules are disconnected. At this time, the sum of the voltage of the two bridge arm full-bridge submodules and the voltage of one bridge arm half-bridge submodule is greater than the voltage of the converter transformer valve side line, and the starting resistor bypass switch is closed.

[0100] Unlocking unit: The AC circuit breaker is disconnected first through background sequential control, and then the converter valve is unlocked instantaneously. During unlocking, the converter valve is phase-locked according to the voltage of the first AC voltage transformer. The converter valve adopts open-loop control. By checking whether the voltage phase sequence and phase of the first AC voltage transformer and the second AC voltage transformer are consistent, the primary wiring of the converter transformer and the converter valve is verified.

[0101] It should be noted that each unit in the aforementioned low-pressure pressurization test system for an ultra-high voltage flexible DC converter valve can be implemented entirely or partially through software, hardware, or a combination thereof. These units can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each unit. For specific limitations regarding the low-pressure pressurization test system for an ultra-high voltage flexible DC converter valve, please refer to the limitations of the low-pressure pressurization test method for an ultra-high voltage flexible DC converter valve (i.e., Example 1) above; both have the same function and effect, and will not be repeated here.

[0102] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for low-voltage voltage boosting test of an extra-high voltage flexible DC converter valve, wherein a test circuit used for the low-voltage voltage boosting test comprises, in series, a test power supply, a voltage regulating transformer, a voltage boosting transformer, an AC circuit breaker, a starting resistor, a converter transformer, and a converter valve based on a hybrid of half-bridge sub-modules and full-bridge sub-modules, and characterized in that, The charging phase of the converter valve is in the following order: The voltage regulating transformer is adjusted to the lowest gear, the AC side switch is closed, and then the voltage of the voltage regulating transformer is gradually adjusted to the required value for the test; The T4 tube of the full-bridge sub-module of the conducting converter valve is turned on; The sub-modules with the highest voltage are cut off in turn for active charging; When the sub-module voltage reaches the preset value to complete active charging, the T2 tube of all cut-off half-bridge sub-modules and the T2 tube and T4 tube of all cut-off full-bridge sub-modules are disconnected, at this time, the sum of the voltage of the two bridge arm full-bridge sub-modules and the voltage of the half-bridge sub-module of one bridge arm is greater than the valve side line voltage of the converter transformer, and the starting resistance bypass switch is closed.

2. The method of claim 1, wherein, N sub-modules are selected for each bridge arm of the converter valve to carry out low-voltage voltage boosting test, and the remaining sub-modules are bypassed by short-circuit wires; in the uncontrolled charging phase, the peak value of the valve side line voltage charges M sub-modules, M=N when the converter valve is composed of half-bridge sub-modules, M=the number of full-bridge modules of two bridge arms+the number of half-bridge modules of one bridge arm when the converter valve is composed of mixed full-bridge and half-bridge sub-modules, and M=2N when the converter valve is composed of full-bridge sub-modules.

3. The UHV DC valve low voltage pressurization test method of claim 2, wherein, The threshold voltage of each sub-module entering active charging is set as VI, and the corresponding effective value of the valve side line voltage is VI x M kV, the minimum voltage required by the primary side of the converter transformer is k x VI x M according to the transformation ratio k of the converter transformer kV; The voltage of the converter transformer side of the voltage regulating transformer is selected based on the above-mentioned effective value of the valve side line voltage and the minimum voltage required for the primary side of the converter transformer, considering the voltage drop on the starting resistor and the margin.

4. The UHV DC valve low voltage pressurization test method of claim 3, wherein, The time t1 for the sub-module voltage to decrease from the preset value to V1 when the converter valve is unlocked needs to be calculated in advance to ensure that the converter valve is unlocked instantaneously before the sub-module voltage decreases to V1.

5. The method of claim 1, wherein the low voltage pressurization test is performed at a voltage of 100 kV or less. The starting resistor and the converter transformer are both provided in the main circuit of the ultra-high voltage flexible DC power transmission project.

6. The method of claim 1, wherein, Before the low-voltage voltage boosting test is carried out, the following conditions need to be met: 1) The connection between the corresponding phase and neutral line of the converter transformer grid side is completed; 2) The test of the converter transformer is completed, and the test result is qualified; 3) The wiring and protection control system of the converter valve are installed and debugged; 4) The single valve inspection test of the converter valve equipment is completed, and the test program and protection outlet of the control protection system are temporarily set; 5) The switches and breakers related to the main circuit of the converter valve have operating conditions; 6) The sub-modules of the converter valve not participating in the test are reliably bypassed; 7) The converter station is isolated from the AC system, the DC side of the converter station is isolated, and the isolation state is in the isolation state. The starting resistor is composed of multiple modules connected in series, and one or more modules connected in series are selected for introduction, and the resistance value of the starting resistor is adjusted according to the test situation.

7. The method of claim 1, wherein the method further comprises, The unlocking phase of the converter valve is: the AC circuit breaker is disconnected first and then the converter valve is unlocked instantaneously through background sequential control, the converter valve is phase-locked according to the voltage of the first AC voltage transformer during unlocking, and the converter valve adopts open-loop control; whether the phase sequence and phase of the voltage of the first AC voltage transformer and the second AC voltage transformer are consistent is checked to realize the checking of the primary wiring of the converter transformer and the converter valve; 8. The method of claim 1, wherein, The first AC voltage transformer is arranged on the side of the voltage regulating transformer of the AC circuit breaker, and the second AC voltage transformer is arranged on the side of the starting resistor of the AC circuit breaker. It comprises:

9. An ultra-high voltage (UHV) flexible converter valve low-voltage withstand test system, wherein a test circuit for low-voltage withstand test comprises, in series, a test power supply, a voltage regulating transformer, a step-up transformer, an AC circuit breaker, a starting resistor, a converter transformer, and a converter valve based on a hybrid of half-bridge sub-modules and full-bridge sub-modules, characterized in that, The AC side switch unit is used to adjust the voltage regulating transformer to the lowest gear, close the AC side switch, and then gradually adjust the voltage of the voltage regulating transformer to the required value for the test; The IGBT conduction unit is used to turn on the T4 tube of the full-bridge sub-module of the conducting converter valve; ​ Active charging unit: used to cut off part of the highest voltage sub-modules in turn, and perform active charging; Combined start-up resistance bypass switch unit: when the voltage of the sub-modules reaches the preset value to complete the active charging, disconnect the T2 tubes of all cut-off half-bridge sub-modules and the T2 and T4 tubes of all cut-off full-bridge sub-modules, at this time, the sum of the voltages of the two bridge arms of the full-bridge sub-modules and the voltage of the half-bridge sub-module is greater than the valve side line voltage of the converter transformer, and the start-up resistance bypass switch is closed.

10. The UHV DC valve low voltage pressurization test system of claim 9, wherein, Further comprising an unlocking unit: through background sequential control, first disconnect the AC circuit breaker, and then instantaneously unlock the converter valve; when unlocking, the converter valve is phase-locked according to the voltage of the first AC voltage transformer, and the converter valve adopts open-loop control; through checking whether the voltage phase sequence and phase of the first AC voltage transformer and the second AC voltage transformer are consistent, the primary wiring of the converter transformer and the converter valve is checked; The first AC voltage transformer is arranged on the step-up transformer side of the AC circuit breaker, and the second AC voltage transformer is arranged on the start-up resistance side of the AC circuit breaker.

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