A capacitor voltage balancing method and system for a flexible DC converter valve test system

Abstract

The present invention discloses a capacitor voltage balancing method and system for a flexible direct current converter valve test system, the method comprising: obtaining a bridge arm voltage reference value, generating a first voltage control pulse, and driving a submodule semiconductor switch device of the bridge arm under test to ensure that its capacitor voltage is close to the capacitor voltage of the actual system. The capacitor voltages of the bridge arm under test and the auxiliary bridge arm are sampled to obtain sampling results; wherein the bridge arm under test and the auxiliary bridge arm are reversely connected in series, and the bridge arm under test and the auxiliary bridge arm respectively contain a plurality of flexible direct current converter valve submodules of the same number; according to the sampling results, the pulse width of the first voltage control pulse is adjusted to obtain a second voltage control pulse, and the capacitor voltage of the auxiliary bridge arm submodule is adjusted based on the second voltage control pulse to balance the capacitor voltage of the submodule of the auxiliary bridge arm. By implementing the present invention, the test current operating condition can be decoupled from the voltage operating condition of the submodule under test, thereby achieving more accurate operating condition testing.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) transmission, and in particular to a capacitor voltage balancing method and system for a flexible DC converter valve test system. Background Art

[0002] With advances in renewable energy generation technology, an increasing number of new energy systems, such as photovoltaic and wind power, are being connected to the grid via high-voltage flexible direct current (HVDC) transmission technology. As key components for energy conversion and power regulation, flexible direct current (HVDC) converter valves play a vital role in flexible HVDC transmission systems. To ensure the operational reliability of flexible direct current converter valves, comprehensive testing of key submodule components is essential before commissioning.

[0003] Currently, in the operating condition simulation test technology of the flexible direct current converter valve submodule, in order to decouple the test current operating condition from the voltage operating condition of the submodule being tested, a current generator is generally used to generate the test current, while ensuring that the switching pulses and capacitor voltage of the submodule being tested are as close as possible to its operating condition in the actual system. However, since the submodule capacitor voltage is not clamped by the DC source, the test current of the current generator may be affected by the change of the submodule capacitor voltage. In the prior art, in the process of dynamic operating condition testing, in order to maintain the balance of the submodule capacitor voltage, it is often necessary to superimpose a large additional modulation voltage component, which causes the submodule to output an additional voltage, thereby interfering with the control of the test current, causing the test current to be distorted in the dynamic operating condition, affecting the accuracy of the dynamic operating condition test. Summary of the Invention

[0004] The present invention provides a capacitor voltage balancing method and system for a flexible DC converter valve test system. The present invention can decouple the test current operating condition from the voltage operating condition of the submodule being tested, thereby achieving more accurate operating condition testing.

[0005] An embodiment of the present invention provides a capacitor voltage balancing method for a flexible DC converter valve test system, comprising:

[0006] According to the actual bridge arm voltage of the flexible DC converter valve system and the submodule capacitor voltage operating conditions, the test current reference value and the bridge arm voltage reference value are obtained;

[0007] transmitting the bridge arm voltage reference value to a voltage controller so that the voltage controller generates a first voltage control pulse;

[0008] driving the semiconductor switching device in the submodule of the bridge arm under test according to the first voltage control pulse, so that the capacitor voltage of the submodule of the bridge arm under test matches the capacitor voltage of the actual flexible direct current converter valve system;

[0009] Sampling the capacitor voltages of the measured bridge arm and the auxiliary bridge arm to obtain a first sampling result and a second sampling result, respectively; wherein the measured bridge arm and the auxiliary bridge arm are connected in reverse series, the measured bridge arm and the auxiliary bridge arm each contain a plurality of the same number of flexible direct current converter valve submodules, and the flexible direct current converter valve submodules are forward cascaded;

[0010] transmitting the first sampling result and the second sampling result to a balancing controller, so that the balancing controller adjusts the pulse width of the first voltage control pulse to obtain a second voltage control pulse;

[0011] According to the second voltage control pulse, the semiconductor switch devices in the submodules of the auxiliary bridge arm are driven to balance the capacitor voltages of the submodules of the auxiliary bridge arm.

[0012] Furthermore, after obtaining the test current reference value and the bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating condition, the method further includes:

[0013] transmitting the test current reference value to a current controller so that the current controller generates a current control pulse;

[0014] The current control pulses are sent to the current generator to match the test current with the current of the actual flexible DC converter valve system.

[0015] Furthermore, the current control pulse is generated in the following manner:

[0016] The current controller generates current control pulses based on a proportional-integral control method or a proportional-integral resonant control method.

[0017] Furthermore, transmitting the first sampling result and the second sampling result to the balancing controller so that the balancing controller adjusts the pulse width of the first voltage control pulse to obtain the second voltage control pulse includes:

[0018] The first sampling result and the second sampling result are transmitted to the balance controller, so that the balance controller calculates the average value of the capacitor voltage based on the first sampling result and the second sampling result, and adjusts the pulse width of the first voltage control pulse based on the average value of the capacitor voltage to obtain the second voltage control pulse.

[0019] Furthermore, the pulse width of the first voltage control pulse is adjusted by:

[0020] When the test current flows into the bridge arm under test, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible direct current converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the on time of the flexible direct current converter valve submodule;

[0021] When the test current flows out of the tested bridge arm, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the conduction time of the flexible DC converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible DC converter valve submodule of the auxiliary bridge arm.

[0022] Based on the above method embodiments, the present invention provides corresponding system embodiments.

[0023] An embodiment of the present invention provides a capacitor voltage balancing system for a flexible DC converter valve test system, comprising: a main control chip, a voltage controller, and a balancing controller;

[0024] The main control chip is used to obtain a test current reference value and a bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating condition, and transmit the bridge arm voltage reference value to the voltage controller;

[0025] The voltage controller is configured to generate a first voltage control pulse according to a bridge arm voltage reference value;

[0026] The main control chip is further configured to drive the semiconductor switch device in the submodule of the bridge arm under test according to the first voltage control pulse, so that the capacitor voltage of the submodule of the bridge arm under test matches the capacitor voltage of the actual flexible direct current converter valve system;

[0027] The main control chip is further used to sample the capacitor voltages of the measured bridge arm and the auxiliary bridge arm to obtain a first sampling result and a second sampling result, respectively; wherein the measured bridge arm and the auxiliary bridge arm are connected in reverse series, the measured bridge arm and the auxiliary bridge arm respectively contain a plurality of the same number of flexible direct current converter valve submodules, and the flexible direct current converter valve submodules are forward cascaded; and the first sampling result and the second sampling result are sent to the balancing controller;

[0028] The balance controller is configured to adjust the pulse width of the first voltage control pulse according to the first sampling result and the second sampling result to obtain the second voltage control pulse;

[0029] The main control chip is further configured to drive the semiconductor switch device in the submodule of the auxiliary bridge arm according to the second voltage control pulse, so as to balance the capacitor voltage of the submodule of the auxiliary bridge arm.

[0030] Furthermore, the capacitor voltage balancing system of the flexible DC converter valve test system further includes: a current controller and a current generator;

[0031] The current controller is configured to generate a current control pulse according to a test current reference value and transmit the current control pulse to the current generator;

[0032] The current generator is used to generate a test current according to the current control pulse, so that the test current matches the current of the actual flexible direct current converter valve system.

[0033] Furthermore, the balancing controller is configured to adjust the pulse width of the first voltage control pulse according to the first sampling result and the second sampling result to obtain the second voltage control pulse, including:

[0034] The balance controller calculates an average value of the capacitor voltage according to the first sampling result and the second sampling result; and then adjusts the pulse width of the first voltage control pulse according to the average value of the capacitor voltage to obtain a second voltage control pulse.

[0035] Furthermore, the method for adjusting the pulse width of the first voltage control pulse includes:

[0036] When the test current flows into the bridge arm under test, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible direct current converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the on time of the flexible direct current converter valve submodule;

[0037] When the test current flows out of the tested bridge arm, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the conduction time of the flexible DC converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible DC converter valve submodule of the auxiliary bridge arm.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention calculates and generates a first voltage control pulse based on a bridge arm voltage reference value; the first voltage control pulse drives the semiconductor switching device in the submodule of the bridge arm under test, ensuring that the capacitor voltage of the submodule of the bridge arm under test is close to the capacitor voltage of the actual flexible direct current converter valve system at this time, so that the submodule in the bridge arm under test has a test operating condition similar to that of the submodule in the actual flexible direct current converter valve; because the output voltage of the submodule of the bridge arm under test will interfere with the test current, the bridge arm under test and the auxiliary bridge arm are reversely connected in series in the test circuit, and the capacitor voltage of the submodule of the auxiliary bridge arm is balanced by the second voltage control pulse, so that the output voltage of the submodule of the auxiliary bridge arm is the same as the output voltage of the submodule of the bridge arm under test, so that the output voltage of the submodule of the bridge arm under test is always in a state of cancellation, and will not interfere with the control of the test current. By implementing the present invention, the test current operating condition can be decoupled from the voltage operating condition of the submodule under test, thereby achieving more accurate operating condition testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a flow chart of a capacitor voltage balancing method for a flexible DC converter valve test system provided by one embodiment of the present invention.

[0041] Figure 2 It is a structural diagram of a capacitor voltage balancing system of a flexible DC converter valve test system provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] like Figure 1 As shown, an embodiment of the present invention provides a capacitor voltage balancing method for a flexible DC converter valve test system, comprising at least the following steps:

[0044] Step S1: obtaining a test current reference value and a bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating conditions;

[0045] Specifically, in a preferred embodiment, after obtaining the test current reference value and the bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating conditions, the method further includes:

[0046] transmitting the test current reference value to a current controller so that the current controller generates a current control pulse;

[0047] The current control pulses are sent to the current generator to match the test current with the current of the actual flexible DC converter valve system.

[0048] Exemplarily, the current control pulse is generated in the following manner:

[0049] The current controller generates current control pulses based on a proportional-integral control method or a proportional-integral resonant control method.

[0050] Optionally, the test current reference value and the bridge arm voltage reference value are obtained by simulating and analyzing the bridge arm voltage and submodule capacitor voltage operating conditions of the actual flexible DC converter valve system.

[0051] It should be noted that the current controller consists of a DC power supply and a bridge inverter. During the above process, the current controller generates a modulation voltage based on the test current reference value, and then generates control pulses for the bridge inverter based on the modulation voltage, namely current control pulses. The current control pulses are then sent to the current generator, driving it to output the required test current, thereby ensuring that the test current approximates the actual bridge arm current of the flexible DC converter valve in the main circuit.

[0052] It is understandable that obtaining the test current reference value and the bridge arm voltage reference value through the actual bridge arm voltage of the flexible DC converter valve system and the submodule capacitor voltage operating conditions can more accurately reflect the actual operating status of the system, thereby improving the accuracy and credibility of the operating condition test results. By transmitting the test current reference value to the current controller and generating a current control pulse, the test current can be effectively controlled to ensure that it matches the test current, thereby achieving more accurate current control. At the same time, the method of generating current control pulses based on the proportional integral control method or the proportional integral resonant control method can improve the stability and response speed of the system and further optimize the current control effect.

[0053] Step S2: transmitting the bridge arm voltage reference value to a voltage controller, so that the voltage controller generates a first voltage control pulse.

[0054] Specifically, in a preferred embodiment, the first voltage control pulse is generated in the following manner:

[0055] The voltage controller generates a first voltage control pulse based on a proportional-integral control method or a proportional-integral resonant control method.

[0056] It is understandable that by transmitting the bridge arm voltage reference value to the voltage controller so that the voltage controller generates a first voltage control pulse based on the proportional-integral control method or the proportional-integral resonant control method, the voltage control effect can be further optimized. The proportional-integral control method can take into account the magnitude and duration of the voltage error and make the system response smoother and faster by adjusting the amplitude and width of the control signal. The proportional-integral resonant control method can control the bridge arm voltage while also taking into account the influence of the resonant frequency, making the voltage control of the system near the resonant frequency more accurate and stable.

[0057] Step S3: driving the semiconductor switch device in the submodule of the bridge arm under test according to the first voltage control pulse, so that the capacitor voltage of the submodule of the bridge arm under test matches the capacitor voltage of the actual flexible direct current converter valve system.

[0058] It can be understood that precisely driving semiconductor switching devices helps to achieve precise control of the flexible DC converter valve system, and can match the capacitor voltage of the measured bridge arm sub-module with the capacitor voltage of the actual system, so that the system can better adapt to the actual working environment and load changes, and improve the stability and reliability of the power grid.

[0059] Step S4: Sampling the capacitor voltages of the measured bridge arm and the auxiliary bridge arm to obtain a first sampling result and a second sampling result, respectively; wherein the measured bridge arm and the auxiliary bridge arm are connected in reverse series, the measured bridge arm and the auxiliary bridge arm each contain a plurality of the same number of flexible direct current converter valve submodules, and the flexible direct current converter valve submodules are forward cascaded;

[0060] In an optional embodiment, since the measured bridge arm and the auxiliary bridge arm contain multiple identical numbers of flexible DC converter valve sub-modules, the functions of the measured bridge arm and the auxiliary bridge arm can be interchanged. The auxiliary bridge arm can be used as the measured bridge arm, and the measured bridge arm can be used as the auxiliary bridge arm accordingly.

[0061] It can be understood that by reversely connecting the measured bridge arm and the auxiliary bridge arm in series, and using the second voltage control pulse to balance the sub-module capacitor voltage of the auxiliary bridge arm, the sub-module output voltage of the auxiliary bridge arm is made the same as the sub-module output voltage of the measured bridge arm, thereby eliminating the interference of the output voltage of the sub-module of the measured bridge arm on the test current, ensuring the stability and accuracy of the test current control during the operating condition test, and thereby improving the reliability of the test results of the operating condition test.

[0062] Step S5: transmitting the first sampling result and the second sampling result to the balance controller, so that the balance controller adjusts the pulse width of the first voltage control pulse to obtain a second voltage control pulse;

[0063] Specifically, transmitting the first sampling result and the second sampling result to the balancing controller so that the balancing controller adjusts the pulse width of the first voltage control pulse to obtain the second voltage control pulse includes:

[0064] The first sampling result and the second sampling result are transmitted to the balance controller, so that the balance controller calculates the average value of the capacitor voltage based on the first sampling result and the second sampling result, and adjusts the pulse width of the first voltage control pulse based on the average value of the capacitor voltage to obtain the second voltage control pulse.

[0065] In an optional embodiment, the pulse width of the first voltage control pulse is adjusted by:

[0066] When the test current flows into the bridge arm under test, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible direct current converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the on time of the flexible direct current converter valve submodule;

[0067] When the test current flows out of the tested bridge arm, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the conduction time of the flexible DC converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible DC converter valve submodule of the auxiliary bridge arm.

[0068] Optionally, calculate the average capacitor voltage using the following formula:

[0069]

[0070] Among them, V avg is the average value of the capacitor voltage; is the capacitance voltage of the i-th submodule of the measured bridge arm m; is the capacitor voltage of the i-th submodule of the auxiliary bridge arm n; k is the number of flexible direct current valve submodules of the same number contained in the measured bridge arm and the auxiliary bridge arm.

[0071] It is understandable that the pulse width adjustment of the second voltage control pulse is limited to the dead zone level, and the bridge arm output pulse difference caused by the pulse adjustment has no obvious interference with the control of the current generator, and therefore does not increase the ripple of the test current.

[0072] Step S6: driving the semiconductor switch devices in the submodules of the auxiliary bridge arm according to the second voltage control pulse, so as to balance the capacitor voltages of the submodules of the auxiliary bridge arm.

[0073] It can be understood that by driving the semiconductor switching device of the auxiliary bridge arm sub-module according to the second voltage control pulse, the capacitor voltage balance of the auxiliary bridge arm sub-module can be achieved, which helps to reduce the difference between the capacitor voltages, reduce the capacitor imbalance in the system, and thereby reduce the interference of capacitor voltage fluctuations on the test current, thereby improving the stability and reliability of the test system.

[0074] Based on the above method embodiments, the present invention provides corresponding system embodiments.

[0075] like Figure 2 As shown, an embodiment of the present invention provides a capacitor voltage balancing system of a flexible DC converter valve test system, comprising: a main control chip 101, a voltage controller 102 and a balancing controller 103;

[0076] The main control chip 101 is used to obtain a test current reference value and a bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating conditions, and transmit the bridge arm voltage reference value to the voltage controller;

[0077] The voltage controller 102 is configured to generate a first voltage control pulse according to a bridge arm voltage reference value;

[0078] The main control chip 101 is further configured to drive the semiconductor switch device in the submodule of the bridge arm under test according to the first voltage control pulse, so that the capacitor voltage of the submodule of the bridge arm under test matches the capacitor voltage of the actual flexible direct current converter valve system;

[0079] The main control chip 101 is further configured to sample the capacitor voltages of the measured bridge arm and the auxiliary bridge arm to obtain a first sampling result and a second sampling result, respectively; wherein the measured bridge arm and the auxiliary bridge arm are connected in reverse series, the measured bridge arm and the auxiliary bridge arm each contain a plurality of the same number of flexible direct current converter valve submodules, and the flexible direct current converter valve submodules are forward cascaded; and the first sampling result and the second sampling result are sent to the balancing controller;

[0080] The balance controller 103 is configured to adjust the pulse width of the first voltage control pulse according to the first sampling result and the second sampling result to obtain a second voltage control pulse;

[0081] The main control chip 101 is further configured to drive the semiconductor switch device in the submodule of the auxiliary bridge arm according to the second voltage control pulse, so as to balance the capacitor voltage of the submodule of the auxiliary bridge arm.

[0082] In this embodiment, a capacitor voltage balancing system of a flexible DC converter valve test system further includes: a current controller 104 and a current generator 105;

[0083] The current controller 104 is configured to generate a current control pulse according to a test current reference value and transmit the current control pulse to the current generator;

[0084] According to the current generator 105, it is used to generate a test current according to the current control pulse, so that the test current matches the current of the actual flexible direct current converter valve system.

[0085] In an optional embodiment, the balancing controller 103 is configured to adjust the pulse width of the first voltage control pulse according to the first sampling result and the second sampling result to obtain the second voltage control pulse, including:

[0086] The balance controller calculates an average value of the capacitor voltage according to the first sampling result and the second sampling result; and then adjusts the pulse width of the first voltage control pulse according to the average value of the capacitor voltage to obtain a second voltage control pulse.

[0087] Specifically, the method for adjusting the pulse width of the first voltage control pulse includes:

[0088] When the test current flows into the bridge arm under test, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible direct current converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the on time of the flexible direct current converter valve submodule;

[0089] When the test current flows out of the tested bridge arm, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the conduction time of the flexible DC converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible DC converter valve submodule of the auxiliary bridge arm.

[0090] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A capacitor voltage balancing method for a flexible DC converter valve test system, characterized in that: include: According to the actual bridge arm voltage of the flexible DC converter valve system and the submodule capacitor voltage operating conditions, the test current reference value and the bridge arm voltage reference value are obtained; transmitting the bridge arm voltage reference value to a voltage controller so that the voltage controller generates a first voltage control pulse; driving the semiconductor switching device in the submodule of the bridge arm under test according to the first voltage control pulse, so that the capacitor voltage of the submodule of the bridge arm under test matches the capacitor voltage of the actual flexible direct current converter valve system; Sampling the capacitor voltages of the measured bridge arm and the auxiliary bridge arm to obtain a first sampling result and a second sampling result, respectively; wherein the measured bridge arm and the auxiliary bridge arm are connected in reverse series, the measured bridge arm and the auxiliary bridge arm each contain a plurality of the same number of flexible direct current converter valve submodules, and the flexible direct current converter valve submodules are forward cascaded; transmitting the first sampling result and the second sampling result to a balancing controller, so that the balancing controller adjusts the pulse width of the first voltage control pulse to obtain a second voltage control pulse; According to the second voltage control pulse, the semiconductor switch devices in the submodules of the auxiliary bridge arm are driven to balance the capacitor voltages of the submodules of the auxiliary bridge arm.

2. The capacitor voltage balancing method of a flexible DC converter valve test system according to claim 1, characterized in that: After obtaining the test current reference value and the bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating conditions, the following steps are also included: transmitting the test current reference value to a current controller so that the current controller generates a current control pulse; The current control pulses are sent to the current generator to match the test current with the current of the actual flexible DC converter valve system.

3. The capacitor voltage balancing method of a flexible DC converter valve test system according to claim 2, characterized in that: The current control pulse is generated in the following manner: The current controller generates current control pulses based on a proportional-integral control method or a proportional-integral resonant control method.

4. The capacitor voltage balancing method for a flexible DC converter valve test system according to claim 1, characterized in that: The first voltage control pulse generation method is specifically as follows: The voltage controller generates a first voltage control pulse based on a proportional-integral control method or a proportional-integral resonant control method.

5. The capacitor voltage balancing method of a flexible DC converter valve test system according to claim 1, characterized in that: Transmitting the first sampling result and the second sampling result to a balancing controller so that the balancing controller adjusts the pulse width of the first voltage control pulse to obtain a second voltage control pulse, including: The first sampling result and the second sampling result are transmitted to the balance controller, so that the balance controller calculates the average value of the capacitor voltage based on the first sampling result and the second sampling result, and adjusts the pulse width of the first voltage control pulse based on the average value of the capacitor voltage to obtain the second voltage control pulse.

6. The capacitor voltage balancing method of a flexible DC converter valve test system according to claim 5, characterized in that: The method for adjusting the pulse width of the first voltage control pulse includes: When the test current flows into the bridge arm under test, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible direct current converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the on time of the flexible direct current converter valve submodule; When the test current flows out of the tested bridge arm, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the conduction time of the flexible DC converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible DC converter valve submodule of the auxiliary bridge arm.

7. A capacitor voltage balancing system for a flexible DC converter valve test system, characterized in that: include: Main control chip, voltage controller and balance controller; The main control chip is used to obtain a test current reference value and a bridge arm voltage reference value according to the actual bridge arm voltage of the flexible direct current converter valve system and the submodule capacitor voltage operating condition, and transmit the bridge arm voltage reference value to the voltage controller; The voltage controller is configured to generate a first voltage control pulse according to a bridge arm voltage reference value; The main control chip is further configured to drive the semiconductor switch device in the submodule of the bridge arm under test according to the first voltage control pulse, so that the capacitor voltage of the submodule of the bridge arm under test matches the capacitor voltage of the actual flexible direct current converter valve system; The main control chip is further used to sample the capacitor voltages of the measured bridge arm and the auxiliary bridge arm to obtain a first sampling result and a second sampling result, respectively; wherein the measured bridge arm and the auxiliary bridge arm are connected in reverse series, the measured bridge arm and the auxiliary bridge arm respectively contain a plurality of the same number of flexible direct current converter valve submodules, and the flexible direct current converter valve submodules are forward cascaded; and the first sampling result and the second sampling result are sent to the balancing controller; The balance controller is configured to adjust the pulse width of the first voltage control pulse according to the first sampling result and the second sampling result to obtain the second voltage control pulse; The main control chip is further configured to drive the semiconductor switch device in the submodule of the auxiliary bridge arm according to the second voltage control pulse, so as to balance the capacitor voltage of the submodule of the auxiliary bridge arm.

8. The capacitor voltage balancing system of the flexible DC converter valve test system according to claim 7, characterized in that: Also includes: Current controller and current generator; The current controller is configured to generate a current control pulse according to a test current reference value and transmit the current control pulse to the current generator; The current generator is used to generate a test current according to the current control pulse, so that the test current matches the current of the actual flexible direct current converter valve system.

9. The capacitor voltage balancing system of the flexible DC converter valve test system according to claim 7, characterized in that: The balancing controller is configured to adjust the pulse width of the first voltage control pulse according to the first sampling result and the second sampling result to obtain the second voltage control pulse, including: The balance controller calculates an average value of the capacitor voltage according to the first sampling result and the second sampling result; and then adjusts the pulse width of the first voltage control pulse according to the average value of the capacitor voltage to obtain a second voltage control pulse.

10. The capacitor voltage balancing system of the flexible DC converter valve test system according to claim 9, characterized in that: The method for adjusting the pulse width of the first voltage control pulse includes: When the test current flows into the bridge arm under test, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible direct current converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the on time of the flexible direct current converter valve submodule; When the test current flows out of the tested bridge arm, determine whether the average value of the capacitor voltage exceeds the preset upper limit; if the average value of the capacitor voltage exceeds the preset upper limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the conduction time of the flexible DC converter valve submodule of the auxiliary bridge arm; if the average value of the capacitor voltage is less than the preset lower limit, adjust the pulse width of the reference control pulse of the auxiliary bridge arm to increase the off time of the flexible DC converter valve submodule of the auxiliary bridge arm.

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