Controllable commutation converter valve, v12 sub-valve thereof and control protection method

Abstract

The application belongs to the field of high-voltage direct current transmission and power electronics technology, and particularly relates to a controllable commutation converter valve, a V12 sub-valve thereof and a control protection method. The V12 sub-valve comprises n series H-bridge stage circuits, and each H-bridge stage circuit comprises two parallel large-current flow branches. One of the two parallel large-current flow branches is provided with a first diode and a second IGBT connected in series along the current direction, and the other of the two parallel large-current flow branches is provided with a first IGBT and a second diode connected in series along the current direction. A support capacitor is connected between the connecting point of the first diode and the second IGBT and the connecting point of the first IGBT and the second diode, and the positive terminal of the support capacitor is connected to the cathode of the first diode. The support capacitor is used for being cut off when the first and second IGBTs are turned on, and being put into operation when the first and second IGBTs are turned off. The application fundamentally solves the problems of uneven voltage distribution and insufficient current-carrying capacity of the series IGBTs, and is suitable for the controllable commutation converter valve in high-voltage and large-current direct current transmission projects.

Description

Technical Field

[0001] This invention belongs to the field of high voltage direct current transmission and power electronics technology, specifically relating to a controllable phase-commutation valve and its V12 sub-valve and control and protection method. Background Technology

[0002] In high-voltage direct current (HVDC) transmission projects, converter valves are the core equipment for converting AC to DC power. Traditional grid-commutated converter valves (LCCs) use semi-controlled thyristors, which carries the risk of commutation failure and has high requirements for the strength of the receiving-end power grid. While voltage source converters (VSCs) based on fully controlled devices can avoid commutation failure, they suffer from higher losses and costs in large-capacity, ultra-high-voltage scenarios.

[0003] Controllable commutation converter valves (CLCCs), as a novel topology, combine the economy of LCCs with the controllability of VSCs. Their typical structure usually includes a main flow branch (V11 and V12 sub-valves) and an auxiliary flow branch (V13 and V14 sub-valves). For example, the controllable commutation converter commutation control method and system disclosed in Chinese invention patent application CN119891341A, published on April 25, 2025, has a main branch thyristor valve V11, a main branch IGBT valve V12, and a parallel second thyristor valve V122 connected in series on the main branch. Among these, the V12 sub-valve is crucial for achieving controllable commutation. It needs to handle the large current connected in series with the V11 sub-valve (usually a thyristor valve) during system steady-state operation and rapidly establish voltage during commutation to assist in reliable current transfer between the main and auxiliary branches. However, in existing CLCC design schemes, power modules (such as H-bridges) used for V12 sub-valve face enormous challenges in bearing ultra-large steady-state currents (such as above 3kA), achieving rapid and controllable switching of capacitor energy, and long-term reliable operation and fault protection under high voltage stress. Specifically, these challenges lie in semiconductor device selection, excessive voltage stress on supporting capacitors, controllable switching strategies, and safe bypass and mode switching mechanisms under multiple faults.

[0004] The common circuit structure of V12 sub-valve in existing technology typically includes multiple cascaded IGBTs. However, this approach often faces several problems. For example, differences in the switching speed and parameters of each IGBT device can lead to voltage imbalances in the circuit. Solving this voltage imbalance requires additional complex voltage equalization circuits and corresponding control strategies, increasing hardware costs and system design complexity, and introducing more potential failure points. More importantly, the rated current capacity of the IGBT devices in existing V12 sub-valve technology is limited; 3000A devices are widely used in engineering. The long-term overload capacity of these IGBT devices is less than 1.1 times, which cannot meet the requirements of 5000A current capacity and overload capacity of more than 1.2 times required by current UHVDC thyristor converter valves. Summary of the Invention

[0005] The purpose of this invention is to provide a controllable commutation valve, its V12 sub-valve, and a control and protection method to solve the problems of voltage imbalance caused by using cascaded IGBTs in the V12 sub-valve in the prior art, as well as the hardware cost and system design complexity caused by solving voltage imbalance.

[0006] To address the aforementioned technical problems, the first aspect of this invention provides a V12 sub-valve of a controllable commutation valve, comprising an n-stage H-bridge circuit connected in series. The H-bridge circuit includes two parallel high-current flow branches, one of which is equipped with a first diode and a second IGBT connected in series along the current direction, and the other high-current flow branch is equipped with a first IGBT and a second diode connected in series along the current direction. A supporting capacitor is connected between the series connection point of the first diode and the second IGBT and the series connection point of the first IGBT and the second diode, and the positive terminal of the supporting capacitor is connected to the cathode of the first diode. The supporting capacitor is used to disconnect when the first and second IGBTs are turned on and to connect when the first and second IGBTs are turned off.

[0007] In one possible implementation, a damping branch and / or a DC voltage equalization branch are connected in parallel at both ends of the two high current flow branches; the damping branch is equipped with a damping capacitor and a damping resistor in series to achieve voltage equalization of the H-bridge circuit under AC interruption conditions; the DC voltage equalization branch is equipped with a DC voltage equalization resistor in series to achieve voltage equalization of the H-bridge circuit under DC interruption conditions.

[0008] In one possible implementation, a discharge resistor is connected in parallel across the supporting capacitor to discharge the energy of the supporting capacitor.

[0009] In one possible implementation, the H-bridge circuit also includes a protection monitoring unit, which comprises a surge arrester unit and a bypass switch connected in parallel. The protection monitoring unit is connected in parallel with the support capacitor or in parallel with two high-current-carrying branches. The bypass switch is used to turn on when the voltage of the support capacitor continues to increase to a set voltage value after the surge arrester unit fails, or when the H-bridge circuit is in a short-circuit failure mode, where the short-circuit failure mode refers to the failure of two IGBTs or a short circuit in the support capacitor.

[0010] In one possible implementation, the H-bridge circuit also includes a first power extraction circuit for extracting power from a drain resistor.

[0011] In one possible implementation, the H-bridge stage circuit also includes a second power extraction circuit, which is used to extract power after being connected in series with the damping branch.

[0012] In one possible implementation, the central control unit of the V12 sub-valve includes two energy storage units, one of which is used to control the on and off of the first and second IGBTs, and the other is used to control the on and off of the bypass switch.

[0013] In one possible implementation, the discharge resistor comprises two sub-discharge resistors connected in series, with a first energy extraction circuit used to extract energy from one of the sub-discharge resistors.

[0014] To solve the above-mentioned technical problems, the second aspect of the present invention provides a controllable phase-commutation valve, wherein a V12 sub-valve is connected in series on the main flow branch, and the V12 sub-valve is any possible implementation of the first aspect of the present invention.

[0015] In one possible implementation, a V11 sub-valve is connected in series on the main current-carrying branch; the capacitance of the damping capacitor is half the capacitance of the single-stage thyristor damping capacitor of the V11 sub-valve, and the resistance of the DC voltage equalizing resistor is half the resistance of the DC voltage equalizing resistor of the single-stage thyristor of the V11 sub-valve.

[0016] In one possible implementation, the auxiliary current-passing branch of the controllable commutation valve is equipped with a series-connected V13 sub-valve and a V14 sub-valve; the number of IGBT stages in series in the V13 sub-valve is determined by the system's overcurrent turn-off capability; the V14 sub-valve and the V11 sub-valve use thyristor devices of the same voltage level, and the number of thyristor stages in series in the V14 sub-valve is not less than that in the V11 sub-valve.

[0017] In one possible implementation, the number of thyristors connected in series in the V11 sub-valve is determined by the insulation level.

[0018] To address the aforementioned technical problems, a third aspect of the present invention provides a control and protection method for a V12 sub-valve of a controllable commutation valve. The method includes: at the beginning of the arm current flow phase of the H-bridge circuit, controlling the first and second IGBTs to simultaneously conduct, causing the supporting capacitor to be short-circuited and discharged; upon entering the commutation phase, according to a control command, simultaneously turning off the first and second IGBTs to charge the supporting capacitor and establish a positive voltage; wherein the V12 sub-valve is any possible implementation of the first aspect of the present invention.

[0019] In one possible implementation, the method further includes: when it is detected that n2 H-bridge stage circuits in the V12 sub-valve of the same bridge arm are bypassed, then all H-bridge stage circuits of the V12 sub-valve are bypassed to switch the converter valve from the controllable commutation mode to the grid commutation mode.

[0020] The beneficial effects of this invention are as follows: This invention improves the structure of the V12 sub-valve by introducing an H-bridge circuit architecture. The two arms of this V12 sub-valve (i.e., two parallel high-current flow branches) respectively include a first diode and a second IGBT connected in series along the current direction, and a first IGBT and a second diode connected in series along the current direction, with a supporting capacitor connected to the intermediate busbar. This H-bridge topology can actively provide voltage equalization capability for the series-connected IGBT devices, fundamentally alleviating the inherent problem of uneven voltage distribution in series-connected IGBTs, making the operating state of each device more balanced, and significantly reducing the risk of damage due to overvoltage. At the same time, this H-bridge topology can effectively solve the problem of insufficient current-carrying capacity of a single branch IGBT, reducing the current stress and operating heat loss of the IGBT, greatly improving the overall reliability of the V12 sub-valve, and meeting the requirements of converter valves for DC engineering projects above 5000A. Attached Figure Description

[0021] Figure 1 This is a topology diagram of a single-stage H-bridge circuit of the V12 sub-valve in Embodiment 1 of a controllable phase-switching and reverse-flow valve of the present invention. Figure 2 This is a topology diagram of the controllable commutator valve (CLCC) of the present invention; Figure 3 This is a topology diagram of a single-stage H-bridge circuit of the V12 sub-valve in Embodiment 2 of a controllable phase-switching and reverse-flow valve of the present invention. Figure 4 This is a schematic diagram of the power extraction and control circuit of the central control unit of the H-bridge stage circuit of the present invention; Figure 5 This is the timing diagram of the CLCC mode natural commutation control of the present invention; Figure 6 This is the natural commutation current path diagram of the CLCC mode of the present invention; Figure 7 This is the LCC mode commutation control timing diagram of the present invention; Figure 8 This is the LCC mode commutation current path diagram of the present invention. Detailed Implementation

[0022] This invention introduces an H-bridge circuit architecture into a V12 sub-valve, specifically comprising an n-stage H-bridge circuit connected in series. The H-bridge circuit includes two parallel high-current flow branches. One high-current flow branch contains a first diode and a second IGBT connected in series along the current direction. The other high-current flow branch also contains a first IGBT and a second diode connected in series along the current direction. A supporting capacitor is connected between the series connection point of the first diode and the second IGBT and between the series connection points of the first IGBT and the second diode, with the positive terminal of the supporting capacitor connected to the cathode of the first diode. The supporting capacitor is switched off when the first and second IGBTs are turned on and switched on when the first and second IGBTs are turned off. This V12 sub-valve can actively provide voltage equalization capability for the series-connected IGBT devices, fundamentally alleviating the inherent problem of uneven voltage distribution in series-connected IGBTs. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings.

[0023] Implementation method 1 of the V12 sub-valve of a controllable commutation valve: The present invention provides a V12 sub-valve, which is a large-capacity V12 sub-valve and is an important component of a controllable commutation valve.

[0024] This embodiment uses a V12 sub-valve applied to, for example... Figure 2 The controllable commutation valve shown is used as an example for explanation. Figure 2 As shown, the controllable commutator valve includes a main current-carrying branch and an auxiliary current-carrying branch, which are connected in parallel. The V12 sub-valve and the V11 sub-valve are connected in series to form the main current-carrying branch, while the V13 and V14 sub-valve are connected in series to form the auxiliary current-carrying branch. Furthermore, the number of thyristors connected in series in the V11 sub-valve is determined by the insulation level, the number of IGBTs connected in series in the V13 sub-valve is determined by the system's overcurrent turn-off capability, and the V14 sub-valve uses thyristor devices of the same voltage rating as the V11 sub-valve, with the number of thyristor stages connected in series in the V14 sub-valve being no less than that in the V11 sub-valve.

[0025] The V12 sub-valve is composed of n-stage H-bridge circuits connected in series. If an 800kV DC project adopts a dual twelve-pulse controllable commutator valve structure, the typical value of n for the V12 sub-valve is 8. If a 500kV DC transmission project adopts a twelve-pulse controllable commutator valve structure, the typical value of n for the V12 sub-valve is 10.

[0026] like Figure 1As shown, the H-bridge circuit includes two parallel high-current branches (also called two bridge arms), composed of four semiconductor devices: a first insulated-gate bipolar transistor (IGBT, IGBT1), a second insulated-gate bipolar transistor (IGBT2), and two diodes (D1 and D2), connected in parallel and in series. Each IGBT device contains an anti-parallel diode. One high-current branch connects IGBT1 and IGBT2 in series along the current direction, forming one bridge arm. The other high-current branch connects IGBT1 and IGBT2 in series along the current direction, forming the other bridge arm. The same type of devices are used diagonally; that is, IGBT1 and IGBT2 are of the same type, and IGBT1 and IGBT2 are of the same type. The steady-state current carrying capacity of the IGBT should be greater than 3kA, the steady-state current carrying capacity of the diode should be greater than 5kA, and the blocking voltage withstand capability of both the IGBT and the diode should be greater than 4.5kV, so that the H-bridge circuit has a steady-state high current carrying capacity of not less than 6kA.

[0027] The H-bridge stage circuit also includes a controllable support capacitor module, which includes a support capacitor C3. The two ends of support capacitor C3 are connected to the busbar between the first diode D1 and IGBT2, and between IGBT1 and the second diode D2, respectively. The positive terminal of support capacitor C3 is connected to the cathode of diode D1, and the negative terminal is connected to the anode of diode D2. That is, the positive terminal of support capacitor C3 is connected to the busbar between the cathode of the first diode D1 and the collector of IGBT2, and the negative terminal is connected to the busbar between the emitter of IGBT1 and the anode of the second diode D2. The support capacitor has a withstand voltage of 4.5kV or higher, with a typical value of 6kV. The IGBT multiplexing of the V12 sub-valve serves as the switching switch for the controllable support capacitor module. When IGBT1 and IGBT2 are on, support capacitor C3 is off; when IGBT1 and IGBT2 are off, support capacitor C3 is on.

[0028] To ensure the H-bridge circuit voltage remains at a safe level, two additional branches are added: a damping branch and a DC voltage equalization branch. Both branches are connected in parallel with the high-current-carrying branch. These branches ensure that both DC and AC voltages in the H-bridge circuit remain at safe levels. A damping capacitor C2 and a damping resistor R3 are connected in series on the damping branch to achieve voltage equalization in the H-bridge circuit under AC off-state conditions. Furthermore, the capacitance of damping capacitor C2 is half the capacitance of the single-stage thyristor in the V11 sub-valve, ensuring that in the off-state, the AC voltage of the V12 sub-valve H-bridge is half that of the V11 sub-valve single-stage thyristor, protecting IGBTs and other devices from overvoltage damage. A DC voltage equalization resistor R4 is connected in series on the DC voltage equalization branch to achieve voltage equalization of the H-bridge stage circuit under DC current interruption conditions. This ensures that the DC voltage of the V12 sub-valve H-bridge stage is half that of the V11 sub-valve single-stage thyristor when the circuit is interrupted, thus protecting IGBTs and other devices from overvoltage damage.

[0029] To ensure circuit safety and prevent overvoltage damage to components, this H-bridge stage circuit further includes a discharge branch, which is connected in parallel with the supporting capacitor C3. A high-impedance discharge resistor R5 is connected in series in the discharge branch. As one embodiment of the discharge resistor R5, it specifically comprises two sub-discharge resistors R1 connected in series. 5-1 and R 5-2 It is used for energy extraction from the central control unit, capacitor voltage monitoring circuit, and discharge of capacitor energy when the equipment is shut down.

[0030] To prevent overvoltage damage to the circuit, the H-bridge stage circuit further incorporates a protection and monitoring unit connected in parallel with the supporting capacitor C3. This unit includes a parallel overvoltage protection unit (also known as the surge arrester unit MOV2) and a bypass switch K1. The surge arrester unit MOV2 consists of a zinc oxide surge arrester valve and a fuse connected in series. During long-term operation, the MOV's charge rate is below 50%. When the H-bridge interrupts the fault current, the capacitor voltage begins to rise, reaching the surge arrester's DC reference voltage, at which point the surge arrester begins to absorb energy. If the surge arrester valve malfunctions, a large current flows, causing the MOV's fuse to blow. The fuse's air gap generates a high withstand voltage, and the MOV exits protection mode. When the H-bridge interrupts the short-circuit fault current again, the capacitor voltage increases to the set voltage value U1, and the H-bridge's central control unit controls the bypass switch K1 to conduct. Alternatively, the bypass switch K1 is activated when the H-bridge stage circuit is in a short-circuit failure mode, which refers to two IGBT failures or a short circuit in the supporting capacitor C3. The effective current carrying capacity of bypass switch K1 is not less than 3000A. To increase the reliability and current carrying capacity of the bypass switch, two sets of bypass switches can be used in parallel. That is, bypass switch K1 specifically includes two bypass switches K1 connected in parallel. 1-1 and K 1-2 Once the bypass switch is engaged, it does not have a remote disconnection function; it must be disconnected locally after the equipment is shut down.

[0031] Moreover, the central control unit (i.e., central control unit) of the V12 sub-valve is as follows: Figure 4 As shown, the central control unit includes an energy storage unit E1 for controlling the IGBT switch and an energy storage unit E2 for controlling the bypass switch. E1 and E2 are completely independent. E1 is connected to the drive circuits of IGBT1 and IGBT2 to control the IGBT's on / off state. E2 is connected to the drive circuit of bypass switch K1 to control its on / off state. Both E1 and E2 are powered by two energy extraction circuits, EH1 and EH2, to ensure the reliability of the control power supply. After the second energy extraction circuit E1 completes its energy extraction, it can achieve 20 (example) cycles of IGBT switch control. The first energy extraction circuit E2 remains energized after its energy extraction, used to control the bypass switch K1 to engage. The two energy extraction circuits EH1 and EH2 are as follows: Figure 4 As shown, the first energy extraction circuit EH2 extracts energy by voltage division through the high-impedance energy discharge resistor R5, and the second energy extraction circuit EH1 extracts energy by series connection with the damping resistor R3 and the damping capacitor C2.

[0032] The V12 sub-valve has the following three commutation operating modes depending on the different commutation conditions: Mode 1: H-bridge current-carrying mode - controllable capacitor module bypass. At the start of the bridge arm current-carrying phase, the two IGBTs in the H-bridge are turned on simultaneously, the high-voltage capacitor (i.e., the supporting capacitor C3) completes discharge, and the capacitor voltage of the supporting capacitor C3 drops to close to 0V.

[0033] Mode 2: H-bridge shutdown mode - controllable capacitor module engaged. Upon entering the commutation phase, the current in this bridge arm begins to decrease. According to the control timing, the two IGBTs in the H-bridge simultaneously turn off. The bridge arm current flows through diodes (first diode D1 and second diode D2) and then through the high-voltage capacitor (i.e., the supporting capacitor C3). After charging the high-voltage capacitor, the capacitor establishes a positive voltage. This positive voltage assists in the commutation of the main and auxiliary bridge arm currents of the controllable commutation valve. The energy stored in the capacitor is used for the next triggering phase of this bridge arm, returning to Mode 1 for discharge.

[0034] Mode 3: H-bridge bypass mode - controllable capacitor module exits, including high-voltage bypass mode and low-voltage bypass mode. After the H-bridge enters bypass mode, the voltage across the H-bridge is approximately 0V. During the current-carrying phase, the current flows through the first diode D1, the bypass switch K1, and the second diode D2.

[0035] High-voltage bypass mode: When the capacitor voltage in the H-bridge increases and exceeds the surge arrester protection level, and the surge arrester has failed, the capacitor voltage continues to increase to the set voltage value U1. When the bypass K1 switch is turned on, U1 is less than 70% of the high-voltage capacitor withstand voltage level U2.

[0036] Low-voltage bypass mode: After the IGBT devices and capacitors in the H-bridge fail, it is a short-circuit failure mode. At this time, there is no positive voltage across the capacitor, and the central control unit of the H-bridge controls the bypass switch K1 to turn on.

[0037] Furthermore, damage to electrical components in the H-bridge stage circuit will manifest as overvoltage or undervoltage, initiating the bypass switch activation strategy. Once the bypass switches of the V12 sub-valve in each arm of the controllable commutation valve reach the set value n2, the valve control system will activate all bypass switches in the H-bridge stage circuits of the twelve-pulse controllable commutation valve within a valve hall. The twelve-pulse commutation valve will switch from controllable commutation mode to grid commutation mode until planned shutdown for maintenance. The natural commutation control timing diagram and current path diagram in CLCC mode are shown below. Figure 5 , 6 As shown, the commutation control timing diagram and commutation current path diagram in LCC mode are respectively as follows: Figure 7 , 8 As shown.

[0038] In summary, the V12 sub-valve of this invention is composed of multiple H-bridge stage circuits connected in series. Each H-bridge stage circuit includes a two-parallel, two-series current-carrying main circuit composed of high-power IGBTs and diodes, a parallel damping and voltage equalization circuit, and a controllable support capacitor module. This module uses the IGBTs in the H-bridge as switching switches to achieve intelligent connection and disconnection of the support capacitor. Simultaneously, this invention proposes three core operating modes: current-carrying mode (capacitor bypass), shutdown mode (capacitor connection to assist commutation), and bypass mode (fault protection). Furthermore, by incorporating surge arresters with fuses, remotely triggerable bypass switches, and an independent redundant central control unit power supply system, a comprehensive protection system from devices and modules to the valve level is constructed. When the number of faulty H-bridges reaches a certain value, the system can automatically switch the entire converter valve from controllable commutation mode to grid commutation mode, greatly improving the system's reliability and fault ride-through capability under high-capacity operating conditions. This invention is applicable to controllable commutation converter valves in high-voltage, high-current DC transmission projects.

[0039] Embodiment 2 of the V12 sub-valve of a controllable commutation valve: The circuit topology of the V12 sub-valve in this embodiment is as follows: Figure 3As shown in the figure, while maintaining the H-bridge main circuit structure, the difference from the V12 sub-valve implementation method 1 includes: the protection monitoring unit (including the parallel-connected surge arrester unit MOV2 and bypass switch K1) is no longer connected in parallel across the supporting capacitor C3, but rather in parallel across the damping branch, meaning it is also connected in parallel with two high-current-carrying branches. In this case, due to changes in some fault current paths, the rated current-carrying capacity of the first diode D1 and the second diode D2 can be appropriately reduced, for example, to half of the engineering DC current. This modification still achieves overvoltage protection and safety bypass functions, but differs in the fault current path and device stress distribution.

[0040] An implementation method for a controllable commutation valve: This invention discloses a controllable commutator valve, which primarily consists of a V12 sub-valve connected in series on its main current-carrying branch. The V12 sub-valve specifically comprises n-stage H-bridge circuits connected in series. The value of n is determined based on the engineering voltage level. For example, for an 800kV DC project using a dual twelve-pulse structure, a typical value of n is 8. For a 500kV DC project using a twelve-pulse structure, a typical value of n is 10. The circuit diagram of each H-bridge circuit is shown below. Figure 1 As shown.

[0041] The main current-carrying branch is also connected in series with a V11 sub-valve, and the V13 and V14 sub-valve are connected in series to form an auxiliary current-carrying branch, which is connected in parallel with the main current-carrying branch. The number of thyristors connected in series in the V11 sub-valve is determined by the insulation level, and the number of IGBTs connected in series in the V13 sub-valve is determined by the system's overcurrent turning-off capability. The V14 sub-valve uses the same voltage-level thyristor devices as the V11 sub-valve, and the number of thyristor stages connected in series in the V14 sub-valve is no less than that in the V11 sub-valve.

[0042] The following example uses a twelve-pulse controllable commutator valve applied in a 500kV DC transmission project. Its V12 sub-valve is composed of 10 (n=10) H-bridge stage circuits connected in series. The specific implementation of each H-bridge stage circuit is as follows: Semiconductor device selection and connection: An IGBT module with a steady-state current capacity of 3kA / 4.5kV was selected, which integrates an anti-parallel diode. A fast recovery diode module with a steady-state current capacity of 5kA / 4.5kV was also selected. Figure 2 In this method, the first diode D1 is connected in series with IGBT2, IGBT1 is connected in series with the second diode D2, and then connected in parallel to form the main current-carrying circuit of the H-bridge.

[0043] Support capacitor module: A 6kV metallized film capacitor with a capacitance value calculated based on commutation energy requirements is selected. Its positive and negative terminals are connected to the designated busbars. A high-resistance discharge resistor network R5, consisting of two 50kΩ resistors connected in series, is connected in parallel across the capacitor for monitoring and discharge.

[0044] Auxiliary and protection circuit: The damping circuit connected in parallel across the H-bridge consists of a 4μF damping capacitor C2 and a 30Ω damping resistor R3 connected in series. The DC equalizing resistor R4 consists of two 22kΩ resistors connected in series. A 1mA zinc oxide surge arrester MOV2 with a DC reference voltage of 2.5kV and a protection level of 3.5kV is connected in parallel across the supporting capacitor C3. MOV2 is connected in series with a high breaking capacity fuse. The bypass switch K1 is a mechanical switch with a rated current of 5000A and is connected in parallel with MOV2.

[0045] Central control unit: Installed near each H-bridge stage circuit. The second energy harvesting circuit EH1 draws energy from the midpoint of the leakage resistor R5; the first energy harvesting circuit EH2 draws energy from the connection point of the damping resistor R3 and the damping capacitor C2. The two energy sources charge independent energy storage units E1 and E2 respectively. E1 stores energy to drive the gates of IGBT1 and IGBT2, while E2 stores energy to drive the closing coil of the bypass switch K1. The central control unit receives optical signal commands from the valve control system, executes control over the IGBTs and bypass switch, and can also transmit local status information such as capacitor voltage.

[0046] An implementation method for controlling and protecting the V12 sub-valve of a controllable phase-commutation valve: The present invention provides a control and protection method for the V12 sub-valve of a controllable commutator valve, which is based on Figure 1 The V12 sub-valve shown is used for implementation. The corresponding control and protection process is implemented as follows: During normal operation, each cycle executes mode 1 and mode 2 sequentially: during the current conduction period, the IGBT is turned on and the capacitor voltage is close to zero; during the bridge arm commutation overlap period, when the main and auxiliary currents commutate, the IGBT is turned off and the current charges the capacitor to establish voltage.

[0047] If MOV2 of a certain H-bridge overheats due to continuous overvoltage operation, its series-connected fuse will blow, and MOV2 will be deactivated. If the H-bridge subsequently shuts off the fault current again, the capacitor voltage will rise to U1 (e.g., set to 4kV). Based on the monitored voltage signal, the central control unit will trigger the E2 energy storage release and close the bypass switch K1, and the H-bridge will enter the high-voltage bypass mode (mode 3).

[0048] If a short circuit occurs in one of the IGBTs of an H-bridge, the capacitor will never charge, and the voltage will be zero. The central control unit detects the abnormally low voltage, and after a delay confirmation, controls the bypass switch K1 to close, entering the low-voltage bypass mode (mode 3).

[0049] The valve control system monitors the status of the H-bridge stage circuits of all V12 sub-valves in real time. Assuming a setpoint n2=3, when it detects that three H-bridge stage circuits in the same V12 sub-valve arm are bypassed, the valve control system immediately issues a command to activate all bypass switches for the H-bridge stage circuits of all V12 sub-valves in the entire twelve-pulse valve within that valve hall. At this time, all H-bridge stage circuits of the V12 sub-valves are short-circuited, the controllable commutation function fails, and the entire twelve-pulse valve exits CLCC operation, becoming a pure thyristor LCC valve, continuing to operate in grid commutation mode until planned shutdown for maintenance.

[0050] In summary, to address the shortcomings of existing controllable commutator valve V12 sub-valve in terms of high current flow, controllable voltage establishment, and fault protection, this paper proposes a high-capacity controllable commutator valve V12 sub-valve topology and its control and protection method that is structurally reliable, flexible in control, and fully protected.

[0051] This invention optimizes the H-bridge circuit topology, employs parallel high-current devices, reuses IGBT control capacitor switching, and sets up multiple energy extraction and protection mechanisms. This enables the V12 sub-valve to reliably carry current under ultra-large steady-state current, quickly and controllably establish auxiliary voltage at the moment of commutation, and possesses the ability to perform step-by-step fault protection and seamless mode switching from the component level, bridge arm level to the valve hall level. This greatly improves the practicality and reliability of the controllable commutation converter valve in large-capacity high-voltage DC projects.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A V12 sub-valve of a controllable commutation valve, characterized in that, The circuit includes an n-stage H-bridge circuit connected in series. The H-bridge circuit includes two parallel high-current flow branches. One high-current flow branch has a first diode and a second IGBT connected in series along the current direction. The other high-current flow branch has a first IGBT and a second diode connected in series along the current direction. A supporting capacitor is connected between the series connection point of the first diode and the second IGBT and the series connection point of the first IGBT and the second diode. The positive terminal of the supporting capacitor is connected to the cathode of the first diode. The supporting capacitor is used to disconnect when the first and second IGBTs are turned on and to connect when the first and second IGBTs are turned off.

2. The V12 sub-valve of the controllable commutation valve according to claim 1, characterized in that, Two high-current-carrying branches are connected in parallel at both ends with damping branches and / or DC voltage equalization branches; the damping branches are equipped with series-connected damping capacitors and damping resistors to achieve voltage equalization of the H-bridge circuit under AC interruption conditions; the DC voltage equalization branches are equipped with series-connected DC voltage equalization resistors to achieve voltage equalization of the H-bridge circuit under DC interruption conditions.

3. The V12 sub-valve of the controllable commutation valve according to claim 1, characterized in that, A discharge resistor is connected in parallel across the two ends of the supporting capacitor to discharge the energy of the supporting capacitor.

4. The V12 sub-valve of the controllable commutation valve according to claim 1, characterized in that, The H-bridge circuit also includes a protection and monitoring unit, which includes a surge arrester unit and a bypass switch connected in parallel. The protection and monitoring unit is connected in parallel with the support capacitor or in parallel with two high-current-flow branches. The bypass switch is used to turn on when the voltage of the support capacitor continues to increase to a set voltage value after the surge arrester unit fails, or when the H-bridge circuit is in a short-circuit failure mode. The short-circuit failure mode refers to the failure of two IGBTs or the short circuit of the support capacitor.

5. The V12 sub-valve of the controllable commutation valve according to claim 3, characterized in that, The H-bridge stage circuit also includes a first power extraction circuit, which is used to extract power from the leakage resistor.

6. The V12 sub-valve of the controllable commutation valve according to claim 2, characterized in that, The H-bridge stage circuit also includes a second power extraction circuit, which is used to extract power after being connected in series with the damping branch.

7. The V12 sub-valve of the controllable commutation valve according to claim 4, characterized in that, The central control unit of the V12 sub-valve includes two energy storage units. One energy storage unit is used to control the on and off of the first and second IGBTs, and the other energy storage unit is used to control the on and off of the bypass switch.

8. The V12 sub-valve of the controllable commutation valve according to claim 5, characterized in that, The energy discharge resistor includes two sub-energy discharge resistors connected in series, and the first energy extraction circuit is used to extract energy from one of the sub-energy discharge resistors.

9. A controllable commutation valve, comprising a main flow branch, wherein a V12 sub-valve is connected in series on the main flow branch, characterized in that, The V12 sub-valve is the V12 sub-valve of the controllable commutation valve as described in any one of claims 1 to 8.

10. The controllable commutation valve according to claim 9, characterized in that, A V11 sub-valve is also connected in series on the main current-carrying branch; the capacitance of the damping capacitor is half the capacitance of the single-stage thyristor damping capacitor of the V11 sub-valve, and the resistance of the DC voltage equalizing resistor is half the resistance of the DC voltage equalizing resistor of the single-stage thyristor of the V11 sub-valve.

11. The controllable commutation valve according to claim 10, characterized in that, The auxiliary current-passing branch of the controllable commutation valve is equipped with V13 sub-valve and V14 sub-valve connected in series; the number of IGBT stages connected in series in the V13 sub-valve is determined by the system's overcurrent shut-off capability; the V14 sub-valve and the V11 sub-valve use the same voltage level thyristor devices, and the number of thyristor stages connected in series in the V14 sub-valve is not less than that in the V11 sub-valve.

12. The controllable commutation valve according to claim 10, characterized in that, The number of thyristors connected in series in the V11 sub-valve is determined by the insulation level.

13. A control and protection method for the V12 sub-valve of a controllable commutation valve, characterized in that, The method includes: At the beginning of the bridge arm current flow stage of the H-bridge circuit, the first and second IGBTs are turned on simultaneously, so that the supporting capacitor is short-circuited and discharged. When entering the commutation stage, the first and second IGBTs are turned off simultaneously according to the control command in order to charge the support capacitor and establish a positive voltage. Wherein, the V12 sub-valve is the V12 sub-valve of the controllable commutation valve as described in any one of claims 1 to 8.

14. The control and protection method for the V12 sub-valve of the controllable commutation valve according to claim 13, characterized in that, The method further includes: when it is detected that n2 H-bridge stage circuits in the V12 sub-valve of the same bridge arm are bypassed, the H-bridge stage circuits of all V12 sub-valves are bypassed to switch the converter valve from the controllable commutation mode to the grid commutation mode.

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