A flexible direct current transmission converter valve section operation test loop and a control method thereof

Abstract

The application discloses a flexible direct current transmission converter valve section operation test loop and a control method thereof, and belongs to the technical field of power electronics. The test loop comprises: at least two test units, each test unit being composed of a first test valve section and a second test valve section in series, and each of the first test valve section and the second test valve section being composed of n sub-modules in series; one single-phase alternating current power supply comprising a diode, one loop inductance and a plurality of load inductances, the first test valve section and the second test valve section of any one or more test units being connected with one load inductance in series respectively, and the connection points of the load inductances being electrically connected with intermediate nodes of other test units; and the single-phase alternating current power supply being connected to all the test units through the loop inductance and the diode respectively, and used for initial charging of all the first test valve sections and the second test valve sections and supplementing of energy in a test process. The application can simultaneously perform operation tests on multiple valve sections, improves test efficiency, simplifies design and reduces cost.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a test circuit for the operation of a flexible DC transmission converter valve section and its control method. Background Technology

[0002] Flexible High Voltage Direct Current (Flexible HVDC) is a new generation of HVDC transmission technology composed of fully controlled power electronic devices. This technology features independent control of active and reactive power, no commutation failure issues, the ability to supply power to passive networks, and good harmonic performance. Therefore, it is suitable for applications such as distributed renewable energy grid connection, asynchronous interconnection of AC grids, and supplying power to weak or isolated networks. Compared to two-level and three-level converters, the Modular Multi-level Converter (MMC) offers advantages such as suitability for high-voltage, high-capacity transmission, low power device losses, and high waveform quality. The introduction of this topology has greatly promoted the engineering application of flexible HVDC technology.

[0003] The MMC converter valve is a core component of a flexible DC transmission system, and its safety and reliability directly affect the reliability of the flexible DC transmission project. Before the MMC converter valve is put into formal operation, type tests, including insulation tests and operational tests, are required. The valve section operational test, in particular, examines the operating characteristics of each key component of the converter valve under actual operating conditions according to standard test conditions. Currently, commonly used operational test circuit topologies include... Figure 1 As shown, it mainly consists of one test valve section, one valve section under test, multiple power supply circuits, and one load inductor. Both the test valve section and the valve section under test are composed of n sub-modules (the number of n can be determined according to engineering test requirements, generally not exceeding 8) connected in series. Each sub-module of the test valve section is connected to the power supply circuit, and the test valve section and the valve section under test are connected through the load inductor. The power supply circuit is mainly used to charge the test valve section and the valve section under test in the initial stage of the test, and to replenish the electrical energy consumed by the power modules and the load during the test. At the beginning of the module bypass test, the power supply circuit first charges the module capacitor of the test valve section. When the module capacitor voltage of the test valve section reaches the rated value, the test valve section pulses through the test valve section, causing the module capacitor voltage of the valve section under test to rise in a stepwise manner. When the module capacitor voltage of the valve section under test reaches the rated value, all power modules are unlocked, and the test valve section and the valve section under test operate according to their respective modulation waves. By adjusting the amplitude and phase of the modulation wave, the module voltage and valve current of the tested valve section can be made to be basically consistent with those of the actual engineering, thereby achieving the purpose of verifying the module's stress resistance capability.

[0004] However, the existing operational test circuits can only test two valve sections at a time. Taking the ±800kV / 8GW flexible DC transmission project currently under construction as an example, a single converter valve contains as many as 360 valve sections, and all valve sections require long-term (e.g., 8 hours) operational tests. Using the existing operational test circuits would result in extremely low testing efficiency and excessively long total time, making it difficult to meet project schedule requirements. Secondly, the power supply circuits in the existing operational test circuits require multiple DC voltage sources, the same number as the sub-modules, leading to extremely complex design of the entire test device and high hardware costs. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the prior art by providing a flexible DC transmission converter valve section operation test circuit and its control method, which can simultaneously conduct operation tests on multiple valve sections, improve test efficiency, simplify design, and reduce costs.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Firstly, a test circuit for the operation of a flexible DC transmission converter valve section is provided, comprising: At least two test units, each test unit consisting of a first test valve section and a second test valve section connected in series, and both the first test valve section and the second test valve section consisting of n sub-modules connected in series; A single-phase AC power supply containing diodes, a loop inductor, and multiple load inductors are provided. The first and second test valve sections of any one or more test units are connected in series with one of the load inductors, and the connection points of the load inductors are electrically connected to the intermediate nodes of other test units. The single-phase AC power supply is connected to all test units through the loop inductor and the diode, respectively, for initial charging of all first and second test valve sections and replenishment of energy during the test.

[0007] As a preferred embodiment, the test unit is provided in two parts, namely a first test unit and a second test unit. The first test valve section and the second test valve section of the first test unit are each connected in series with a load inductor. The connection point of the load inductor of the first test unit is electrically connected to the intermediate node of the second test unit.

[0008] As a preferred embodiment, the test circuit for the operation of the flexible DC transmission converter valve section further includes a start-up control device. The start-up control device is used to control the number of sub-modules to be put into operation gradually when the single-phase AC power supply voltage is positive during the start-up phase, and to charge the sub-modules in turn through a voltage sorting strategy until the voltage of all sub-modules reaches the rated value. When the single-phase AC power supply voltage is negative during the start-up phase, all sub-modules are in a locked state.

[0009] As a preferred embodiment, the flexible DC transmission converter valve section operation test circuit further includes an operation control device. The operation control device is used to control the first test valve section and the second test valve section in each test unit during the operation phase, such that the sum of the number of sub-modules put into the first test valve section and the number of sub-modules put into the second test valve section at any given time is equal to the total number n of sub-modules contained in the first test valve section or the second test valve section. Furthermore, the operation control device is also used to make each first test valve section or the second test valve section operate according to its own modulation wave, and to simulate actual engineering conditions by adjusting the amplitude and phase of the modulation wave.

[0010] As a preferred embodiment, the submodule is a half-bridge submodule, a full-bridge submodule, or a hybrid half-bridge / full-bridge submodule.

[0011] As a preferred embodiment, the rated peak voltage of the single-phase AC power supply is equal to the product of the total number n of sub-modules contained in the first test valve section or the second test valve section and the rated voltage of the sub-modules.

[0012] As a preferred embodiment, the number n of sub-modules connected in series in each first test valve section or second test valve section does not exceed 8.

[0013] Secondly, a control method for the test circuit of the valve section of the flexible DC transmission converter valve is provided, comprising the following steps: During the startup phase, when the single-phase AC power supply voltage is positive, the number of sub-modules put into operation is controlled, and the sub-modules are charged in turn through a voltage sorting strategy until the voltage of all sub-modules reaches the rated value; during the startup phase, when the single-phase AC power supply voltage is negative, all sub-modules are controlled to be in a locked state. During the operation phase, the first test valve section and the second test valve section in each test unit are controlled such that the sum of the number of sub-modules put into the first test valve section and the number of sub-modules put into the second test valve section at any time is equal to the total number n of sub-modules contained in the first test valve section or the second test valve section. Each first test valve section or the second test valve section is made to operate according to its own modulation wave, and the actual engineering working conditions are simulated by adjusting the amplitude and phase of the modulation wave.

[0014] As a preferred approach, for two test units, during the startup phase, when the single-phase AC power supply voltage is positive, the number of sub-modules controlled to be engaged is gradually reduced from 2n to n.

[0015] As a preferred embodiment, in the step of charging the sub-modules in turn using a voltage sorting strategy, the voltage sorting strategy includes: real-time detection of the voltage of all sub-modules, prioritizing charging the sub-module with the lowest voltage, and cutting off the sub-module with the highest voltage.

[0016] Compared with existing technologies, the flexible DC transmission converter valve section operation test circuit of the present invention has at least the following beneficial effects: To address the problems of low test capacity, poor test efficiency, complex power supply architecture, and high equipment cost and maintenance difficulty in existing flexible DC transmission converter valve section operation test circuits, this invention significantly improves the test efficiency of converter valve sections and shortens the engineering test cycle by optimizing the test unit topology and simplifying the power supply system architecture. The test circuit of this invention sets up at least two test units, each consisting of a first test valve section and a second test valve section connected in series. Multiple load inductors are also configured, with each of the first and second test valve sections of any one or more test units connected in series with a load inductor. The connection points of the load inductors are electrically connected to the intermediate nodes of other test units, providing a hardware foundation for synchronous testing of multiple valve sections. This overcomes the limitation of traditional test circuits that can only test two valve sections at a time, enabling simultaneous synchronous operation tests of four or more converter valve sections. Compared to the traditional single-test dual-valve-section testing mode, the topology of this application fully utilizes the structural advantages of parallel connection of multiple test units and interconnection of nodes, effectively doubling the test throughput under the premise of the same test duration and test power capacity. For large-scale flexible DC transmission projects containing hundreds of valve sections, this invention enables batch completion of valve section type tests, significantly reducing the overall testing cycle and solving the problems of low batch test quantity, high test iteration frequency, and low overall testing efficiency in existing technologies. It possesses strong engineering practical value. This invention employs a power supply structure consisting of a single-phase AC power supply with diodes and a loop inductor. The single-phase AC power supply can be uniformly connected to all test units through the loop inductor and diodes, achieving initial charging of all test valve sections and energy replenishment during the testing process. It eliminates the complex multi-DC voltage source power supply network built to adapt to multi-valve section testing and multi-loop power supply in existing technologies, replacing the complex power supply system with multiple power sources, multiple branches, and multiple control units with a simplified single-power-source, unidirectional power supply architecture. At the hardware level, the number of DC voltage sources, supporting control modules, sampling modules, and wiring accessories used is significantly reduced, greatly simplifying the overall hardware design and wiring structure of the test device. At the application level, the single power supply architecture eliminates the need to coordinate the synchronous operation of multiple power supplies and equal voltage and current control, avoiding problems such as synchronization errors, circulating current interference, and difficulty in parameter matching that exist in multi-power supply systems. This significantly reduces the debugging difficulty, operational failure rate, and subsequent maintenance costs of the test system, and significantly improves the operational stability and reliability of the test circuit. Through the structural design of interconnecting the load inductor with the intermediate nodes of multiple test units, this invention can flexibly adapt to various test conditions, such as simultaneous commissioning of multiple test units, independent testing of a single unit, and combined testing of multiple test units, meeting the operational test requirements of different numbers and specifications of converter valve sections. Simultaneously, the unified charging and replenishment mode of a single power supply ensures the charging consistency and test condition uniformity of all test valve sections, avoiding test parameter deviations caused by multi-power supply, effectively improving the test accuracy and comparability of test data in converter valve section type testing, and ensuring the accuracy of test results while improving test efficiency and reducing equipment costs.

[0017] Compared to existing technologies, the control method for the test circuit of the flexible DC transmission converter valve section of this invention has at least the following beneficial effects: During the startup phase, the test circuit controls the number of sub-modules engaged and employs a voltage sequencing strategy to charge each sub-module in turn until all sub-module voltages reach their rated values. This enables synchronous testing of four or more valve sections. In parallel charging conditions involving multiple valve sections and sub-modules, problems such as uneven charging voltage, overvoltage surges, and asynchronous charging due to individual sub-module capacitance deviations and line impedance differences are prone to occur, severely impacting the safety and effectiveness of the test startup. This invention's step-by-step engagement combined with voltage sequencing and sequential charging control strategy abandons the traditional coarse control mode of overall synchronous charging. It dynamically matches the charging sequence based on the real-time voltage status of each sub-module, orderly controlling the step-by-step engagement and charging of sub-modules, effectively offsetting the voltage imbalance problem caused by multiple parallel branches, and solving the charging imbalance problem in multi-valve section synchronous testing scenarios. Meanwhile, the stepped activation method avoids instantaneous high current surges, protects the converter valve submodule components, and ensures that the voltage of all submodules rises steadily to the rated value, achieving safe, orderly, and reliable startup of the test circuit and laying a solid foundation for subsequent steady-state testing. During operation, the first and second test valve sections in each test unit are controlled so that the sum of the number of submodules activated in the first and second test valve sections at any given time equals the total number of submodules (n) contained in either the first or second test valve section. This forms a stable and controllable test topology, locking the fixed flow path of the load current from a hardware operation logic perspective, avoiding problems such as sudden changes in the circuit path, current oscillations, and operational instability caused by dynamic fluctuations in the number of activated submodules. Compared to traditional test control methods, this constant constraint condition ensures that the circuit parameters remain constant during synchronous operation of multiple test units and multiple valve sections, significantly improving the operational stability of the test system. Meanwhile, based on the constraint that "the sum of the number of sub-modules engaged in the first and second test valve sections within each test unit at any given time is always equal to n," this invention can flexibly adjust the total output voltage of the test unit series by precisely adjusting the difference in the number of sub-modules engaged in the two test valve sections, accurately reproducing the dynamic voltage waveform of the converter valve bridge arm in actual engineering. This control method achieves continuous and precise regulation of the output voltage while ensuring the stability of the loop path, perfectly adapting to the operating conditions of actual flexible DC transmission projects. Through a coordinated modulation strategy with a constant total number of engaged sub-modules, combined with dynamic adjustment of the amplitude and phase of the preset modulation wave, this invention enables multiple test valve sections to synchronously generate voltage and current stresses completely equivalent to actual engineering conditions. This solves the defects of uneven stress distribution, distorted operating condition simulation, and inconsistent test conditions in single valve sections that are prone to occur in traditional multi-valve section synchronous tests, enabling four or more valve sections tested simultaneously to withstand electrical stresses at the level of real engineering projects.Type tests based on the control method of this invention can realistically reproduce the dynamic working state of the converter valve during actual operation, accurately assess the tolerance and operational performance of the converter valve sub-modules and the overall valve section, effectively verify the long-term operational reliability of the converter valve equipment under actual engineering conditions, and significantly improve the testing accuracy, effectiveness, and authority of the test data in converter valve type tests, providing reliable test basis for converter valve engineering applications. The control method of this invention ensures abnormal synchronous startup of multiple valve sections through start-up equalization control and ensures consistent steady-state operating conditions of multiple valve sections through constant parameter control, eliminating problems such as operating condition differences, invalid tests, and data failures that occur during multi-channel parallel tests. While significantly increasing the throughput of converter valve tests and shortening the engineering test cycle, it also ensures the consistency and reliability of multiple sets of parallel tests, achieving a dual improvement in test efficiency and test quality. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 Schematic diagram of the existing flexible DC transmission converter valve section operation test circuit topology; Figure 2 A schematic diagram of the topology of the test circuit for the operation of the flexible DC transmission converter valve section according to an embodiment of the present invention; Figure 3 A schematic diagram of the topology of the semi-full-bridge hybrid submodule in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, those skilled in the art can obtain other embodiments without creative effort.

[0021] Please see Figure 1 The existing test circuit for the operation of the flexible DC transmission converter valve can only test two valve sections at a time, resulting in extremely low test efficiency and excessive time consumption, which cannot meet the requirement that all valve sections in the project need to be tested. Figure 1 SM1, SM2, SM3, SM4, SM5 and SMn are all sub-modules (SM) of the MMC modular multilevel converter. L loadIt is a load reactor connected in series between the test valve section and the valve section under test. It is used to limit the circuit fault current, simulate the actual load reactance of the project, and form the energy storage and current limiting element of the main circuit of the test. U A This indicates the voltage across the test valve section; U B This indicates the voltage across the tested valve section.

[0022] This invention analyzes the principles and requirements of valve section operation tests and designs an improved valve section operation test circuit that can simultaneously conduct operation tests on four or more valve sections, greatly improving test efficiency and reducing test time.

[0023] Please see Figure 2 The flexible DC transmission converter valve section operation test circuit proposed in this embodiment includes: At least two test units, each test unit is composed of a first test valve section and a second test valve section connected in series, and both the first test valve section and the second test valve section are composed of n sub-modules (SM1, SM2...SMn) connected in series; A single-phase AC power supply S containing a diode D, a loop inductor L, and multiple load inductors are provided. The first and second test valve sections of any one or more test units are connected in series with one of the load inductors, and the connection points of the load inductors are electrically connected to the intermediate nodes of other test units. The single-phase AC power supply S is connected to all test units through the loop inductor L and the diode D, respectively, for initial charging of all first and second test valve sections and replenishment of energy during the test.

[0024] In one possible implementation, Figure 2 The test unit shown has two sections (left test phase and right test phase), and a total of four test valve sections. The first test valve section and the second test section of the first test unit are each connected in series with one of the load inductors (the load inductor L of the first test valve section). up Second test valve section load inductance L down The load inductance connection point of the first test unit is electrically connected to the intermediate node of the second test unit.

[0025] In one possible implementation, the test circuit for the operation of the flexible DC transmission converter valve section in this embodiment further includes a start-up control device. During the start-up phase, when the single-phase AC power supply voltage is positive, the start-up control device controls the gradual change in the number of sub-modules activated and charges the sub-modules in turn using a voltage sequencing strategy until all sub-module voltages reach their rated values. During the start-up phase, when the single-phase AC power supply voltage is negative, all sub-modules are in a locked state.

[0026] In one possible implementation, the flexible DC transmission converter valve section operation test circuit of this embodiment further includes an operation control device. The operation control device is used to control the first test valve section and the second test valve section in each test unit during the operation phase, such that the sum of the number of sub-modules put into the first test valve section and the number of sub-modules put into the second test valve section at any time is equal to the total number n of sub-modules contained in the first test valve section or the second test valve section. Furthermore, the operation control device is also used to make each first test valve section or the second test valve section operate according to its own modulation wave, and to simulate the actual engineering working conditions by adjusting the amplitude and phase of the modulation wave.

[0027] This embodiment maintains a constant sum of the number of sub-modules in the first and second test valve sections of each test unit (equal to n), thereby providing a fixed path for the load current. Simultaneously, by controlling the difference in the number of modules in the first and second test valve sections, the total output voltage after series connection is precisely adjusted to simulate the voltage waveform of the actual converter valve bridge arm. The reasons for this arrangement are: (1) ensuring current continuity: a total of n modules are in the circuit, ensuring continuous current flow; (2) achieving bipolar modulation: positive, negative, and zero voltages can be easily simulated through the difference; (3) energy balance: near the zero-crossing point, half of the sub-modules are in operation in both the first and second test valve sections, facilitating energy exchange and balance between the first and second test valve sections.

[0028] Please see Figure 3 In the topology of MMC, the converter consists of three phase units. Each phase includes upper and lower arms. Each arm is composed of several sub-modules connected in series. The sub-module type can be half-bridge, full-bridge, or a hybrid of half-bridge and full-bridge.

[0029] Figure 3 In U a , U b , U c These are the three-phase AC phase voltages of the power grid, and also the voltages connected to the AC side of the converter. a, b, c Three-phase power frequency voltage; U d This refers to the DC bus voltage, which is the total voltage at the positive and negative DC ports of the converter. u o Output voltage for the submodule port; C Provide a supporting capacitor for the submodule to maintain the stability of the submodule's rated voltage; i ap , i bp , i cp They are respectively a, b, c Three-phase upper bridge arm current; i an , i bn , i cn They are respectively a, b, c Three-phase lower bridge arm current; i o This refers to the output port current of the submodule. L s These are bridge arm reactors, connected in series in the upper and lower bridge arm circuits of each phase. S1~S4 represent IGBTs (Insulated Gate Bipolar Transistors), and D1~D4 represent freewheeling diodes.

[0030] Half-bridge submodule Bridge Sub Module (HBSM) generally has three working states: 1) Blocked state: S1 and S2 are not conducting.

[0031] 2) Engagement status: S1 is on, S2 is off.

[0032] 3) Resection state: S1 is not conductive, S2 is conductive.

[0033] Full-bridge submodule Bridge Sub A module (FBSM) typically has four operating states: 1) Blocked state: S1, S2, S3 and S4 are not conducting.

[0034] 2) Positive input state: S1 and S4 are both on.

[0035] 3) Resection status: S1 and S2 are both conducting or S3 and S4 are both conducting.

[0036] 4) Negative input state: Both S2 and S3 are on.

[0037] In one possible implementation, the rated peak voltage of the single-phase AC power supply is equal to the product of the total number n of submodules contained in the first or second test valve section and the rated voltage of the submodules.

[0038] In one possible implementation, the number of sub-modules n connected in series in each test valve section does not exceed 8. Specifically, the number of n can be determined according to the engineering test requirements.

[0039] Another embodiment of the present invention provides a control method for the test circuit of the valve section of the flexible DC transmission converter valve, comprising the following steps: During the startup phase, when the single-phase AC power supply voltage is positive, the number of sub-modules put into operation is controlled, and the sub-modules are charged in turn through a voltage sorting strategy until the voltage of all sub-modules reaches the rated value; during the startup phase, when the single-phase AC power supply voltage is negative, all sub-modules are controlled to be in a locked state. During the operation phase, the first test valve section and the second test valve section in each test unit are controlled such that the sum of the number of sub-modules put into the first test valve section and the number of sub-modules put into the second test valve section at any time is equal to the total number n of sub-modules contained in the first test valve section or the second test valve section. Each first test valve section or the second test valve section is made to operate according to its own modulation wave, and the actual engineering working conditions are simulated by adjusting the amplitude and phase of the modulation wave.

[0040] for Figure 2 The test unit shown has two configurations. At the beginning of the module bypass test, a single-phase AC power supply charges the module capacitors of the four connected valve sections. Once the module capacitor voltage of a valve section reaches the control threshold, the control device gradually reduces the number of engaged sub-modules from 2n to n. During this process, a voltage sorting strategy is used to switch and charge the sub-modules in turn until all sub-module voltages reach their rated values. Subsequently, in the operation phase, the control device ensures that the sum of the number of engaged sub-modules in the upper and lower test valve sections of the left and right test phases at any given time is always equal to the total number of sub-modules n contained in a single test valve section. The control device makes the valve sections operate according to their respective modulation waves. Adjusting the amplitude and phase of the modulation waves ensures that the module voltage and valve section current are essentially consistent with actual engineering conditions, thereby verifying the module's stress resistance capability.

[0041] In one possible implementation, when charging sub-modules in turn using a voltage sorting strategy, the voltage sorting strategy includes: real-time detection of the voltage of all sub-modules, prioritizing charging the sub-module with the lowest voltage, and cutting off the sub-module with the highest voltage.

[0042] Compared with existing technologies, the flexible DC transmission converter valve section operation test circuit and its control method proposed in this invention, relying on the overall innovation of multi-test unit parallel topology architecture and adaptive collaborative control strategy, breaks through the technical limitations of traditional test devices and forms significant technical advantages in terms of test efficiency, system architecture, and engineering economy. Existing traditional converter valve section operation test circuits are limited by topology structure and can only realize the operation test of two valve sections at a time. The test throughput is low and the batch test cycle is long. For large-scale flexible DC transmission projects with hundreds of valve sections, the overall type test is time-consuming and the ability to ensure project progress is weak. Moreover, they generally adopt complex multi-DC voltage source power supply networks with a large number of devices and complex architecture, resulting in many problems such as high system debugging difficulty, high operating cost, and cumbersome later maintenance. This invention breaks the limitation of the number of tests per batch in traditional test circuits by setting up at least two test units consisting of dual valve sections connected in series, combined with a multi-load inductor node interconnection topology. It can stably realize the simultaneous operation test of four or more valve sections. Under the same test conditions and test duration, it significantly increases the throughput of converter valve tests and shortens the type test cycle of batch valve sections by several times. It effectively solves the technical pain points of low test efficiency and slow progress of large-scale engineering tests in existing technologies, and significantly improves the overall efficiency of converter valve factory tests and type tests.

[0043] Meanwhile, this invention abandons the complex multi-DC voltage source power supply architecture of existing technologies and adopts an integrated power supply scheme of single-phase AC power supply with diodes and loop inductors. It can realize unified initial charging and test energy replenishment for all test valve sections, greatly simplifying the hardware topology and power supply control logic of the test device, significantly reducing the configuration of redundant power supply equipment, control modules and supporting lines, effectively reducing the equipment investment cost, debugging cost and operation and maintenance cost of the test system, streamlining the overall architecture of the test system and improving the operational stability of the device.

[0044] Based on this, the invention includes a dedicated control method that addresses the challenge of voltage balancing in parallel charging of multiple valve sections through a voltage sequencing and alternating charging strategy during the startup phase, ensuring synchronous and stable startup of the multiple valve sections. During the operation phase, the method constrains the total number of dual-valve section submodules in each test unit to be constant at n, and, in conjunction with modulation amplitude and phase adjustment, accurately simulates actual engineering operating conditions while ensuring stable test circuit conditions. This guarantees equivalent electrical stress and accurate and reliable test data during synchronous testing of multiple valve sections. This invention achieves an organic combination of efficient parallel testing of multiple valve sections and high-precision operating condition simulation, significantly improving test efficiency, simplifying system architecture, reducing engineering costs, while ensuring the accuracy and authority of the tests.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A test circuit for the operation of a flexible DC transmission converter valve section, characterized in that, include: At least two test units, each test unit consisting of a first test valve section and a second test valve section connected in series, and both the first test valve section and the second test valve section consisting of n sub-modules connected in series; A single-phase AC power supply containing diodes, a loop inductor, and multiple load inductors are provided. The first and second test valve sections of any one or more test units are connected in series with one of the load inductors, and the connection points of the load inductors are electrically connected to the intermediate nodes of other test units. The single-phase AC power supply is connected to all test units through the loop inductor and the diodes, respectively, for initial charging of all first and second test valve sections and replenishment of energy during the test. It also includes a start-up control device, which is used to control the number of sub-modules put into operation to change gradually when the single-phase AC power supply voltage is positive during the start-up phase, and to charge the sub-modules in turn through a voltage sorting strategy until the voltage of all sub-modules reaches the rated value; when the single-phase AC power supply voltage is negative during the start-up phase, all sub-modules are in a locked state. It also includes an operation control device, which is used to control the first test valve section and the second test valve section in each test unit during the operation phase, such that the sum of the number of sub-modules put into the first test valve section and the number of sub-modules put into the second test valve section at any time is equal to the total number n of sub-modules contained in the first test valve section or the second test valve section; and the operation control device is also used to make each first test valve section or the second test valve section operate according to its own modulation wave, and to simulate the actual engineering working conditions by adjusting the amplitude and phase of the modulation wave.

2. The test circuit for the operation of the flexible DC transmission converter valve section according to claim 1, characterized in that, The test unit is provided in two parts, namely the first test unit and the second test unit. The first test valve section and the second test valve section of the first test unit are each connected in series with the load inductor. The connection point of the load inductor of the first test unit is electrically connected to the intermediate node of the second test unit.

3. The test circuit for the operation of the flexible DC transmission converter valve section according to claim 1, characterized in that, The submodule can be a half-bridge submodule, a full-bridge submodule, or a hybrid half-bridge / full-bridge submodule.

4. The test circuit for the operation of the flexible DC transmission converter valve section according to claim 1, characterized in that, The rated peak voltage of the single-phase AC power supply is equal to the product of the total number n of sub-modules contained in the first test valve section or the second test valve section and the rated voltage of the sub-modules.

5. The test circuit for the operation of the flexible DC transmission converter valve section according to claim 1, characterized in that, The number of sub-modules n connected in series in each first test valve section or second test valve section shall not exceed 8.

6. A control method for the test circuit of the valve section of the flexible DC transmission converter valve as described in claim 1, characterized in that, Includes the following steps: During the startup phase, when the single-phase AC power supply voltage is positive, the number of sub-modules put into operation is controlled, and the sub-modules are charged in turn through a voltage sorting strategy until the voltage of all sub-modules reaches the rated value; during the startup phase, when the single-phase AC power supply voltage is negative, all sub-modules are controlled to be in a locked state. During the operation phase, the first test valve section and the second test valve section in each test unit are controlled such that the sum of the number of sub-modules put into the first test valve section and the number of sub-modules put into the second test valve section at any time is equal to the total number n of sub-modules contained in the first test valve section or the second test valve section. Each first test valve section or the second test valve section is made to operate according to its own modulation wave, and the actual engineering working conditions are simulated by adjusting the amplitude and phase of the modulation wave.

7. The control method according to claim 6, characterized in that, For the two test units, during the startup phase, when the single-phase AC power supply voltage is positive, the number of sub-modules controlled to be engaged gradually decreases from 2n to n.

8. The control method according to claim 6, characterized in that, In the step of charging the sub-modules in turn using a voltage sorting strategy, the voltage sorting strategy includes: real-time detection of the voltage of all sub-modules, prioritizing charging the sub-module with the lowest voltage, and cutting off the sub-module with the highest voltage.

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