An IGCT converter valve

Abstract

The present invention relates to the technical field of high-voltage direct current transmission converter valves, and in particular to an IGCT converter valve. Each IGCT stage in the present solution includes an IGCT device and a buffer circuit and an IGCT lightning arrester respectively connected in parallel with the IGCT device, and a fuse is connected in series to the branch where the IGCT lightning arrester is located, and different voltage thresholds are set to turn on the IGCT according to the normal and abnormal working states of the IGCT energy acquisition and control unit. This solution can not only effectively avoid the risk of energy exceeding the limit or even explosion of the lightning arrester module by connecting a fuse in series to the branch where the lightning arrester module is located, but also the two-stage overvoltage protection logic plays a dual protection role for the circuit, which can greatly improve the stability of the IGCT converter valve, thereby improving the safety of the entire DC transmission line.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage direct current transmission converter valves, and in particular to an IGCT converter valve. Background Art

[0002] UHV DC transmission usually adopts grid-commutated commutation technology (LCC). While it is developing rapidly, some problems that are difficult to solve at this stage have emerged. In particular, LCC commutation technology uses half-controlled thyristor devices, which cannot shut off the current and have the inherent problem of commutation failure. When the AC grid voltage is disturbed, it is easy to cause commutation failure in the receiving-end converter, resulting in a series of problems such as interruption of DC power transmission and overvoltage at the sending end, which seriously affects the safety and stability of the power grid. Flexible DC transmission technology uses fully controlled IGBT devices, which have limited overvoltage and overcurrent tolerance and have the problem of difficulty in self-clearing DC short-circuit faults. When a short-circuit fault occurs in the DC system, the fault current develops rapidly and is difficult to cut off. It needs to be controlled by a DC circuit breaker or a full-bridge converter, which greatly increases the investment in the project and has poor technical and economic performance.

[0003] In contrast, the integrated gate-commutated thyristor (IGCT) has made great progress in manufacturing technology and operating losses. It is a fully controlled current-controlled switching device with reverse blocking capability, with the advantages of high withstand voltage, large through-current, low conduction voltage drop, high reliability and low manufacturing cost. Its low switching frequency operating characteristics are well matched with LCC commutation technology. The IGCT-based commutation valve can effectively resist commutation failure, actively shut down the current under fault conditions, shorten the fault time, reduce the disturbance of the DC system to the AC system, and improve the safe and stable operation capability of the DC system.

[0004] Since each bridge arm of the high-voltage and ultra-high-voltage direct current transmission converter valve is composed of up to dozens of IGCT stages in series, during operation, the various IGCT stages on a bridge arm are regarded as a whole and need to be opened and closed at the same time. However, the opening and closing times of the various IGCT stages on the same bridge arm are often inconsistent, and the IGCT stages that are opened first and closed later will be subject to voltage shock first, which is easy to cause the IGCT stages that are opened first and closed later to be damaged by overvoltage breakdown. The general solution is to connect a buffer circuit composed of a resistor and a capacitor in series in parallel at both ends of the IGCT device in the IGCT stage to buffer the overvoltage and balance the voltage at both ends of each IGCT stage. However, the loss of the buffer circuit is proportional to the capacitance of the damping capacitor. Often, due to the large capacitance of the damping capacitor, the loss of the buffer circuit occupying the converter valve is very large. Therefore, in order to protect the buffer circuit, the general solution is to connect a lightning arrester in parallel at both ends of the buffer circuit to reduce the capacitance of the buffer circuit, thereby greatly reducing the loss of the converter valve. However, this is easy to cause the risk of damage or even explosion of the lightning arrester due to energy exceeding the limit. Summary of the invention

[0005] The purpose of the present invention is to provide an IGCT converter valve to solve the problem in the prior art that when the opening or closing time of each IGCT stage on the same bridge arm of the IGCT converter valve is inconsistent, it is easy to cause the lightning arrester connected in parallel with each IGCT stage to exceed the energy limit and be damaged or even explode.

[0006] In order to solve the above technical problems, the present invention provides an IGCT converter valve, comprising an IGCT valve section, each IGCT valve section comprises at least two IGCT stages connected in series, each IGCT stage comprises an IGCT device and a buffer circuit and an IGCT lightning arrester respectively connected in parallel with the IGCT device, each IGCT stage is also provided with an IGCT energy taking and control unit, and a fuse is connected in series on the branch where the IGCT lightning arrester is located;

[0007] When the IGCT energy acquisition and control unit itself works normally and detects that the voltage across the corresponding IGCT exceeds the set first voltage threshold, a trigger signal is immediately sent to turn on the corresponding IGCT; when the IGCT energy acquisition and control unit fails and the voltage across the IGCT exceeds the set second voltage threshold, the IGCT is forced to turn on itself, and the first voltage threshold is less than the second voltage threshold.

[0008] Beneficial effects: On the one hand, the present invention can effectively avoid the risk of energy exceeding the limit or even explosion of the lightning arrester module by connecting a fuse in series on the branch where the lightning arrester module is located; on the other hand, the first voltage threshold can play a first-level protection role for the IGCT, and the second voltage threshold can play a second-level protection role for the IGCT, and can avoid the situation where the voltage at both ends of the IGCT exceeds the second voltage threshold, thereby playing a dual protection role for the circuit. The combination of the two aspects can greatly improve the stability of the IGCT converter valve, thereby improving the safety of the entire DC transmission line.

[0009] Furthermore, the IGCT valve section also includes a valve section arrester connected in parallel therewith.

[0010] Beneficial effect: By connecting lightning arresters in parallel at both ends of the entire IGCT valve section, the entire IGCT valve section and saturated reactor can be effectively prevented from being damaged by overvoltage impact, which has the effect of improving the robustness of the entire IGCT valve section and extending the life of the IGCT converter valve.

[0011] Furthermore, the IGCT valve section also includes a saturated reactor connected in series therewith.

[0012] Beneficial effect: By connecting a saturated reactor in series on the entire IGCT valve section, it is possible to suppress a large voltage deviation and alleviate voltage flicker when the IGCT valve section is in action, thereby stabilizing the IGCT valve section voltage, improving the robustness of the entire IGCT valve section, and extending the life of the IGCT converter valve.

[0013] Furthermore, a lightning arrester is connected in parallel at both ends of the saturated reactor.

[0014] Beneficial effect: By connecting a lightning arrester in parallel at both ends of each IGCT device, the overvoltage generated during the IGCT shutdown process is limited. As a supplement to the buffer circuit to suppress the overvoltage generated during the shutdown process, it can not only play a role in overvoltage protection, but also reduce the capacitance of the damping capacitor, thereby reducing the loss of the converter valve.

[0015] Furthermore, the IGCT energy taking and control unit is connected to the gate of the IGCT device.

[0016] Beneficial effect: The IGCT stage is controlled to be turned on or off according to the control signal sent by the control system, and the voltage across the IGCT stage is monitored in real time. When it is detected that the IGCT stage that should be in the off state is in the on state, a shutdown command is sent to the IGCT stage to avoid commutation failure.

[0017] Furthermore, the buffer circuit is composed of a resistor and a capacitor connected in series.

[0018] Beneficial effect: The buffer circuit composed of R1 and CI in series can equalize the voltage of the IGCT stages in series when the converter valve is actuated, and at the same time suppress the overvoltage generated when each IGCT stage is actuated. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the principle of the DC power transmission IGCT converter of the present invention;

[0020] Figure 2 It is a schematic diagram of the topological structure of the IGCT converter valve of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0022] IGCT converter valve embodiment:

[0023] The inverter side of the IGCT converter valve of this embodiment adopts a single 6-pulse converter in series, each bridge arm includes two IGCT valve sections A connected in series, each IGCT valve section A includes at least three IGCT stages connected in series, and each IGCT stage includes an IGCT device and a buffer circuit connected in parallel with the IGCT device, such as Figure 1 As shown in the figure, U a , U b , U c They represent three-phase AC power supply, L represents commutation inductance, the two endpoints on the right side of the figure represent the two poles of the input DC voltage, and the 6 A represent 6 bridge arms. Each bridge arm is connected in series with multiple grid-commutation valves composed of multiple identical IGCT stages connected in series.

[0024] In actual engineering, each bridge arm of an IGCT-based grid phase-changing valve is often composed of several to dozens of IGCT devices connected in series, and the opening and closing times of multiple IGCT devices are inconsistent, which can easily cause the IGCT devices that are opened later and closed earlier to be damaged by overvoltage breakdown.

[0025] In the case of overvoltage caused by inconsistent opening or closing, this embodiment connects a buffer circuit and a lightning arrester module in parallel at both ends of the IGCT as a measure to dynamically equalize the voltage and suppress overvoltage. Adding a lightning arrester module connected in parallel can reduce the capacitance value of the buffer circuit, thereby significantly reducing the loss of the converter valve.

[0026] However, when lightning arrester modules are connected in parallel at both ends of each IGCT as overvoltage protection, if a primary IGCT fails and cannot be shut down, when the bridge arm is shut down, the lightning arrester module connected in parallel with the faulty IGCT will withstand the overvoltage and operate, thereby establishing a current path. The lightning arrester module will then periodically absorb energy, which may easily cause the lightning arrester module to exceed the energy limit and be damaged or even explode, thereby affecting the normal operation of the entire converter valve. Therefore, in this embodiment, a fuse is connected in series on the branch where the lightning arrester module is located. When a certain IGCT fails and cannot be shut down, the faulty IGCT is shut down by disconnecting the fuse, thereby protecting the lightning arrester module while avoiding affecting other normal IGCTs.

[0027] Based on the above considerations, the structural diagram of each IGCT level constructed in this embodiment is as follows: Figure 2As shown, it includes an IGCT device and a buffer circuit connected in parallel with the IGCT, and a branch composed of a lightning arrester module and a fuse connected in series, and an IGCT energy acquisition and control unit is connected in series to the buffer circuit, and the IGCT energy acquisition and control unit is also connected to the gate of the IGCT device. Among them, the buffer circuit is composed of a resistor and a capacitor in series, and its function is to make the series IGCT stage voltage equalized in dynamic state, and at the same time suppress the overvoltage when the IGCT stage is turned off; the function of the lightning arrester module is to limit the overvoltage generated when the IGCT stage is turned on or off, as a supplement to the buffer circuit suppressing the overvoltage generated when it is turned off, to reduce the capacitance value of the buffer circuit and reduce the loss of the converter valve; the IGCT energy taking and control unit takes energy from the IGCT device, and its function is to control the opening or closing of the IGCT stage according to the control signal sent by the control system, and monitor the voltage at both ends of the IGCT stage in real time. When it is detected that the IGCT stage that should be in the off state is in the on state, a shutdown command is sent to the IGCT stage to avoid commutation failure; the function of the lightning arrester module is to reduce the capacitance value of the buffer circuit, thereby greatly reducing the loss of the converter valve; the function of the fuse is to disconnect the IGCT device when the IGCT device connected in parallel with it fails, so as to avoid the lightning arrester module from exceeding the energy limit and being damaged or even exploding.

[0028] For the IGCT valve section composed of the above-mentioned multiple IGCT stages connected in series, the number of IGCT stages required to be connected in series for each IGCT valve section can be adjusted according to the insulation level of the converter valve. This embodiment also takes multiple protection measures for the IGCT valve section by optimizing the circuit structure, specifically, Figure 2 As shown in the figure, each IGCT valve section is connected in series with a saturated reactor, a lightning arrester is connected in parallel at both ends of the series circuit of the IGCT valve section and the saturated reactor, and a sub-lightning arrester is connected in parallel at both ends of the saturated reactor. Among them, the function of the saturated reactor is to control the large voltage deviation and alleviate the voltage flicker during the opening or closing process of the IGCT valve section, so as to stabilize the voltage of the IGCT valve section; the function of the lightning arrester is to prevent the entire IGCT valve section and the saturated reactor from being damaged by the impact of overvoltage; the function of the sub-lightning arrester is to further protect the saturated reactor from the impact of overvoltage.

[0029] The present invention can make full use of the full control characteristics of the IGCT device, can control its opening and closing, and can effectively solve the problem of commutation failure on the inverter side of the DC power transmission project. At the same time, since the long-term failure mode of the IGCT level is short circuit, and includes a fuse connected in series with the lightning arrester module in the IGCT level, the fuse can play a good protective role on the lightning arrester module, and has the advantage of preventing the lightning arrester module from being damaged or even exploding due to energy exceeding the limit.

[0030] In this embodiment, during the normal operation of the converter valve, the IGCT energy acquisition and control unit in the converter valve controls the opening and closing of the IGCT according to the control signal sent by the control system. The specific control strategy is as follows:

[0031] The superior control system sends a trigger signal to control the corresponding IGCT to turn on.

[0032] The superior control system sends a shutdown signal to control the corresponding IGCT to shut down.

[0033] The IGCT energy acquisition and control unit monitors the voltage across the corresponding IGCT stage in real time. When it detects that the IGCT that should be in the off state is in the on state, it sends a shutdown command to the IGCT to avoid commutation failure.

[0034] Two-level overvoltage protection is set for IGCT. When the IGCT energy acquisition and control unit itself works normally and detects that the voltage across the corresponding IGCT exceeds the set first voltage threshold, a trigger signal is immediately sent to turn on the corresponding IGCT; when the IGCT energy acquisition and control unit fails and the voltage across the IGCT exceeds the set second voltage threshold, the IGCT is forced to turn on itself, and the first voltage threshold is less than the second voltage threshold.

[0035] For example: if the IGCT withstand voltage is 6.5KV, the first voltage threshold is set to 6.3KV, and the corresponding IGCT is turned on when it reaches 6.3KV; the first voltage threshold may exceed 6.5KV, that is, the corresponding IGCT will be turned on only after overvoltage occurs. In this way, the first voltage threshold can play the first level protection role for the IGCT, and the second voltage threshold can play the second level protection role for the IGCT, and it can also avoid the situation where the voltage at both ends of the IGCT exceeds the second voltage threshold, thereby playing a double protection role for the circuit and effectively avoiding the occurrence of explosion.

Claims

1. An IGCT converter valve, comprising an IGCT valve section, each IGCT valve section comprising at least two IGCT stages connected in series, each IGCT stage comprising an IGCT device and a buffer circuit and an IGCT lightning arrester respectively connected in parallel with the IGCT device, and each IGCT stage is also provided with an IGCT energy taking and control unit, characterized in that: A fuse is connected in series on the branch where the IGCT arrester is located; When the IGCT energy acquisition and control unit itself works normally and detects that the voltage across the corresponding IGCT exceeds the set first voltage threshold, a trigger signal is immediately sent to turn on the corresponding IGCT; when the IGCT energy acquisition and control unit fails and the voltage across the IGCT exceeds the set second voltage threshold, the IGCT is forced to turn on itself, and the first voltage threshold is less than the second voltage threshold.

2. The IGCT converter valve according to claim 1, characterized in that: The IGCT valve section also includes a valve section arrester connected in parallel therewith.

3. The IGCT converter valve according to claim 1, characterized in that: The IGCT valve section also includes a saturated reactor connected in series therewith.

4. The IGCT converter valve according to claim 3, characterized in that: Sub-lightning arresters are connected in parallel at both ends of the saturated reactor.

5. The IGCT converter valve according to any one of claims 1 to 4, characterized in that: The IGCT energy taking and control unit is connected to the gate of the IGCT device.

6. The IGCT converter valve according to claim 5, characterized in that: The buffer circuit is composed of a resistor and a capacitor connected in series.

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