Controllable turn-off converter valve for resisting commutation failure and converter

Abstract

The invention relates to a controllable turn-off converter valve for resisting commutation failure and a converter, and belongs to the technical field of power electronic commutation. The controllable turn-off converter valve is characterized in that a thyristor valve and a switching valve are connected in series and then are connected in parallel to two ends of an auxiliary branch which is connected in series with a first full-control device and is used for transferring fault current; the thyristor valve is conducted according to a commutation time sequence; the switching valve is cut off under the condition that the bridge arm current exceeds the preset safety current during commutation; the first full-control device is switched on when the switching valve is switched off and is switched off when the switching valve is switched off for a first preset time; the first preset duration is determined according to the recovery time of the thyristor valve. According to the invention, the difficulty of resisting commutation failure can be reduced, and the cost can be reduced.

Description

Technical Field

[0001] The invention relates to a controllable shut-off converter valve and a converter for resisting commutation failure, belonging to the technical field of power electronic commutation. Background Art

[0002] The traditional line commutated converter high voltage direct current (LCC-HVDC) transmission system has the advantages of long-distance large-capacity transmission and controllable active power, and is widely used around the world. As the core equipment of direct current transmission, the converter is the core functional unit for realizing AC and DC power conversion. Its operating reliability largely determines the operating reliability of the ultra-high voltage direct current grid.

[0003] Since traditional converters mostly use semi-controlled devices thyristors as core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multiple stages of thyristors and their buffer components in series. Since thyristors do not have self-shutoff capabilities, commutation failures are prone to occur in situations such as AC system failures, resulting in a surge in DC current and a rapid and large loss of DC transmission power, affecting the stable and safe operation of the power grid.

[0004] In order to solve the technical problem of unstable power grid operation caused by problems of thyristors themselves, capacitor-commutated converters or turn-off devices connected in series with thyristors are usually used to realize AC and DC power conversion. Among them, the capacitor-commutated converter increases the time area of ​​the commutation voltage of the converter valve by the capacitor voltage to ensure its reliable shutdown. However, a controllable capacitor module is formed by combining power electronic switches and capacitors to realize controllable capacitor input and voltage direction. In order to ensure reliable commutation, a large single-stage capacitor value is required, thereby increasing the voltage and current stress of the core component thyristor. The topological structure engineering is difficult to implement. The turn-off device is connected in series with the thyristor to form a hybrid converter, so that each bridge arm of the converter has the ability to be turned off, avoiding the occurrence of commutation failure. However, due to the large transmission capacity of conventional DC transmission, each bridge arm of the converter is subjected to high voltage and large current, and the cost and difficulty of implementation are relatively high. Summary of the invention

[0005] The purpose of the present invention is to provide a controllable shut-off converter valve and converter for resisting commutation failure, so as to solve the problem of high cost and great difficulty in resisting commutation failure in the prior art.

[0006] To achieve the above object, the solution of the present invention includes: A controllable shut-off commutation valve for resisting commutation failure of the present invention comprises: a thyristor valve and a switching valve connected in series and then connected in parallel to two ends of an auxiliary branch connected in series with a first fully-controlled device and used to transfer fault current; The thyristor valve is turned on according to the timing of phase change; The switching valve is cut off when the bridge arm current exceeds the preset safety current during phase change; The first fully-controlled device is turned on when the switching valve is turned off and is turned off after the switching valve is turned off for a first preset time period; The first preset time duration is determined according to the recovery time of the thyristor valve.

[0007] Furthermore, the switching valve includes: a second fully-controlled device and a diode-assisted valve connected in series.

[0008] Furthermore, the second fully controlled device includes: an insulated gate bipolar transistor with an emitter and a collector connected in series between the thyristor valve and the diode auxiliary valve, and a first capacitor discharge branch connected in parallel to the emitter and the collector for providing a reverse voltage to the thyristor valve when the insulated gate bipolar transistor is turned off.

[0009] Furthermore, the second fully-controlled device also includes: a first voltage-equalizing resistor connected in parallel at both ends of the first capacitor discharge branch and a first lightning arrester for preventing overvoltage.

[0010] Furthermore, the diode-assisted valve comprises: a diode connected in series between the second fully-controlled device and the output end of the converter, the conduction direction of which is the same as the current direction of the converter valve.

[0011] Furthermore, the diode-assisted valve further includes: a first RC resistor-capacitor absorption network and a second voltage-equalizing resistor connected in parallel at both ends of the diode.

[0012] Furthermore, the first fully-controlled device includes: an integrated gate-commutated thyristor whose conduction direction is the same as the direction of the converter current.

[0013] Furthermore, the first fully-controlled device further includes: a first voltage stabilizing circuit and a third voltage balancing resistor connected in parallel at both ends of the integrated gate-commutated thyristor for stabilizing the voltage when the integrated gate-commutated thyristor is turned off.

[0014] Furthermore, the first fully-controlled device further comprises: a second lightning arrester connected in parallel at both ends of the integrated gate-commutated thyristor for preventing overvoltage.

[0015] Furthermore, the thyristor valve comprises: a thyristor whose conduction direction points to the switching valve.

[0016] Furthermore, the thyristor valve further includes: a second RC resistor-capacitor absorption network and a fourth voltage-equalizing resistor connected in parallel at both ends of the thyristor.

[0017] Furthermore, it also includes: a first saturated inductor connected in series with the first fully-controlled device.

[0018] Furthermore, it also includes: a second saturable reactor connected in series with the thyristor valve.

[0019] Furthermore, it also includes: a third lightning arrester connected in parallel at both ends of the auxiliary branch to prevent overvoltage.

[0020] Furthermore, it also includes: a bypass thyristor valve connected in parallel at both ends of the switching valve for bypassing the switching valve when the switching valve fails during normal operation.

[0021] Furthermore, the bypass thyristor valve comprises: a bypass thyristor having the same conduction direction as the converter current.

[0022] Furthermore, the bypass thyristor valve further includes: a third RC resistor-capacitor absorption network and a fifth voltage-equalizing resistor connected in parallel at both ends of the bypass thyristor.

[0023] A converter of the present invention comprises a plurality of bridge arms, each of which is provided with the above-mentioned controllable shut-off converter valve for resisting commutation failure.

[0024] The beneficial effects of the present invention are as follows: the present invention is a pioneering invention, and the controllable shut-off converter valve for resisting commutation failure of the present invention comprises: a thyristor valve and a switching valve are connected in series and then connected in parallel at both ends of an auxiliary branch connected in series with a first fully-controlled device and used to transfer fault current; the thyristor valve is turned on according to the timing of commutation; the switching valve is turned off when the bridge arm current exceeds the preset safety current during commutation; the control valve is turned on when the switching valve is turned off and is turned off after the switching valve cut-off time meets the first preset time; the first preset time is determined according to the recovery time of the thyristor valve. By first transferring the fault current and then shutting it off, the commutation failure can be resisted. The simple structure of the converter valve can reduce the production cost. At the same time, due to the simple operation, the difficulty can be reduced and the universality of the converter valve can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention; Figure 2 It is a flow chart of the working principle of a controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention; Figure 3 It is a structural schematic diagram of another controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention; Figure 4 is a schematic diagram of a waveform of a bridge arm current when a bypass thyristor valve is enabled, provided by an embodiment of the present invention; Figure 5 It is a waveform diagram of a bridge arm current during normal operation in a controllable shutdown mode for resisting commutation failure provided by an embodiment of the present invention; Figure 6It is a waveform diagram of a fault current when a bridge arm of a controllable shutdown mode for resisting commutation failure is shut down, provided by an embodiment of the present invention; Figure 7 It is a waveform diagram of a controllable shutdown mode for resisting commutation failure provided by an embodiment of the present invention, in which the fault current is transferred from the main branch 1 to the auxiliary branch 2 when the bridge arm is shut down. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0027] The idea of ​​the present invention is to provide a controllable shut-off converter valve and converter for resisting commutation failure, wherein the controllable shut-off converter valve includes: a thyristor valve and a switching valve connected in series and then connected in parallel at both ends of an auxiliary branch connected in series with a first fully controlled device and used to transfer fault current; the thyristor valve is turned on according to the timing of commutation; the switching valve is turned off when the bridge arm current exceeds the preset safety current during commutation; the control valve is turned on when the switching valve is turned off and is turned off after the switching valve cut-off time meets the first preset time; the first preset time is determined according to the recovery time of the thyristor valve. By first transferring the fault current and then shutting it off, the commutation failure can be resisted. The simple structure of the converter valve can reduce the production cost. At the same time, due to the simple operation, the difficulty can be reduced and the universality of the converter valve can be improved.

[0028] An embodiment of a controllable shut-off converter valve for resisting commutation failure: Embodiment 1: Figure 1 is a schematic diagram of a controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention, such as Figure 1 As shown, the controllable shut-off converter valve includes: a main branch 1 with one end connected to the bridge arm bus and the other end connected to the output end of the converter; an auxiliary branch 2 connected in parallel at both ends of the main branch 1; and a protection branch 3 connected in parallel at both ends of the auxiliary branch 2.

[0029] Among them, the main branch 1 includes a thyristor valve 101 and a switching valve 102 connected in series and a bypass thyristor valve 103 connected in parallel at both ends of the switching valve 102; the auxiliary branch 2 includes a first fully controlled device 201; and the protection branch 3 includes a third lightning arrester MOV3. A current transformer Ct for real-time acquisition of the bridge arm current Iv1 is connected in series to the bridge arm bus. The thyristor valve 101 is used to conduct according to the timing of phase switching; the switching valve 102 is used to be cut off when the bridge arm current Iv1 exceeds the preset safety current I0 during phase switching; the first fully controlled device 201 is turned on when the switching valve 102 is turned off and is cut off after the switching valve 102 is turned off for a first preset time.

[0030] The first preset time is determined according to the recovery time of the thyristor valve. The following explanation is given by taking the first preset time of 600 microseconds (μs) as an example.

[0031] The switching valve 102 includes a second fully-controlled device 102A and a diode-assisted valve 102B connected in series.

[0032] The thyristor valve 101, the second fully-controlled device 102A, the bypass thyristor valve 103 and the first fully-controlled device 201 are all controlled by a controller in the control system. They may be controlled by the same controller or different controllers, which is not particularly limited in the present invention. In order to reduce the size of the device, the following description will be given by taking the control of the same controller as an example.

[0033] The thyristor valve 101 includes: a thyristor Th1 whose conduction direction points to the switching valve 102 , and a gate of the thyristor Th1 is used to connect to a controller.

[0034] In order to limit the circuit voltage rise rate to be too large and ensure the safe operation of the thyristor Th1, as an optional implementation, the thyristor valve 101 also includes a second RC resistor-capacitor absorption network connected in parallel at both ends of the thyristor Th1. The second RC resistor-capacitor absorption network includes: a twelfth resistor R12 and a twelfth capacitor C12 connected in series.

[0035] In order to realize DC voltage balancing for the thyristor Th1 , as an optional implementation, the thyristor valve 101 further includes a fourth voltage balancing resistor connected in parallel at both ends of the thyristor Th1 .

[0036] The second fully controlled device 102A includes an insulated gate bipolar transistor (IGBT) with an emitter and a collector connected in series between the thyristor valve 101 and the diode-assisted valve 102, and the gate of the IGBT is used to connect to the controller. The IGBT in the embodiment of the present invention is an IGBT including a body diode.

[0037] In order to accelerate the turn-off of the thyristor Th1, as an optional implementation, the second fully-controlled device 102A further includes: a first capacitor discharge branch connected in parallel to the emitter and collector of the IGBT. The first capacitor discharge branch includes: a first capacitor C1, a first diode D1, and a fourteenth resistor R14. The first capacitor C1 is connected in series with the fourteenth resistor R14 and then connected in parallel to the emitter and collector of the IGBT, and the first diode D1 is connected in parallel to the fourteenth resistor R14. The turn-off voltage generated by the first capacitor C1 is opposite to the voltage of the thyristor Th1, so as to accelerate the turn-off of the thyristor Th1.

[0038] In order to realize DC voltage balancing for the IGBT, as an optional implementation, the second fully-controlled device 102A further includes: a first voltage balancing resistor R1 connected in parallel across the emitter and collector of the IGBT.

[0039] In order to prevent overvoltage, as an optional implementation, the second fully-controlled device 102A further includes: a first lightning arrester MOV1 connected in parallel across the emitter and collector of the IGBT.

[0040] The diode-assisted valve 102B includes: a diode D2 which is connected in series between the emitter of the IGBT and the output end of the converter transformer and has a conduction direction which is the same as the current direction of the converter valve.

[0041] The reverse withstand voltage of the diode-assisted valve 102B is greater than or equal to the reverse withstand voltage of the bypass thyristor valve 103 .

[0042] In order to limit the circuit voltage rise rate to be too large and ensure the safe operation of the diode D2, as an optional implementation, the diode auxiliary valve 102B also includes: a first RC resistor-capacitor absorption network connected in parallel at both ends of the diode D2. The first RC resistor-capacitor absorption network includes: an eleventh resistor R11 and an eleventh capacitor C11 connected in series.

[0043] In order to realize DC voltage balancing for the diode D2, as an optional implementation, the diode-assisted valve 102B further includes: a second voltage balancing resistor R2 connected in parallel at both ends of the diode D2.

[0044] To prevent a large voltage deviation on the main branch 1, as an optional implementation, the main branch 1 further includes: a second saturated reactor L2 connected in series with the thyristor valve 101. Specifically, one end of the second saturated reactor L2 is connected to the bridge arm bus, and the other end is connected to the anode of the thyristor Th1.

[0045] The first fully controlled device 201 includes an integrated gate commutated thyristor (IGCT) having the same conduction direction as the current direction of the commutator valve, the gate of the IGCT being used to connect to the controller; the current shutoff capability of the IGCT is higher than that of the IGBT.

[0046] In order to reduce the voltage instability caused by the asynchronous shutdown of the IGCT, as an optional implementation, the first fully controlled device 201 also includes: a first voltage stabilizing circuit connected in parallel at both ends of the IGCT. The first voltage stabilizing circuit includes: a fifteenth resistor R15, a second capacitor C2 and a third diode D3; the fifteenth resistor R15 is connected in series with the second capacitor C2 and then connected in parallel at both ends of the IGCT, and the third diode D3 is connected in parallel at both ends of the fifteenth resistor R15, and the conduction direction points to the second capacitor C2.

[0047] In order to realize DC voltage balancing for the IGCT, as an optional implementation, the first fully-controlled device 201 further includes: a third averaging resistor R3 connected in parallel at both ends of the IGCT.

[0048] In order to ensure that the voltage sharing of each stage of IGCTs connected in series is consistent, as an optional implementation, the first fully-controlled device 201 further includes: a second lightning arrester MOV2 connected in parallel at both ends of the IGCT.

[0049] In order to prevent a large amount of voltage deviation on the auxiliary branch 2, as an optional implementation, the auxiliary branch 2 further includes: a first saturated reactor L1 connected in series with the first fully-controlled device 201. Specifically, one end of the first saturated reactor L1 is connected to the bridge arm bus, and the other end is connected to the anode of the integrated gate-commutated thyristor IGCT.

[0050] The bypass thyristor valve 103 is used to bypass the switching valve 102 when the switching valve 102 fails during normal operation. The bypass thyristor valve 103 includes: a thyristor Th2 having the same conduction direction as the current direction of the converter valve.

[0051] In order to limit the circuit voltage rising rate from being too large and ensure the safe operation of the thyristor Th2, as an optional implementation, the first fully-controlled device 201 also includes: a third RC resistor-capacitor absorption network connected in parallel at both ends of the thyristor Th2. The third RC resistor-capacitor absorption network includes: a thirteenth resistor R13 and a thirteenth capacitor C13 connected in series.

[0052] In order to realize DC voltage balancing for the thyristor Th2, as an optional implementation, the first fully-controlled device 201 further includes: a fifth voltage balancing resistor R5 connected in parallel at both ends of the thyristor Th2.

[0053] The third lightning arrester MOV3 in the protection branch 3 is used to limit the forward and reverse overvoltages at both ends of the bridge arm.

[0054] Combine the following Figure 2 The working principle of a controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention is described.

[0055] Figure 2 FIG. 1 is a flow chart showing the working principle of a controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention. Figure 2 As shown, the current transformer Ct collects the current Iv1 on the bridge arm in real time, and uploads the current Iv1 on the bridge arm to the control system, sets the safety current I0 in advance, and uploads the safety current I0 to the control system.

[0056] The controller in the control system triggers the thyristor valve 101 to turn on according to the commutation timing. After a second preset time, it determines whether Iv1 is greater than I0. If Iv1>I0, it means that the commutation cannot be normal. At this time, the controller controls the second fully-controlled device 102A to be turned off and controls the first fully-controlled device 201 to be turned on.

[0057] At this time, the fault current of the main branch 1 will be transferred to the auxiliary branch 2, reducing the fault current in the main branch 1, and the thyristor valve 101 can be turned off.

[0058] After the cut-off time of the switching cut-off valve 102 meets 600 μs, the controller controls the first fully-controlled device 201 to be cut off, and the phase change is completed forcibly.

[0059] If Iv1≤I0, it means that phase switching can be normal temporarily.

[0060] In order to ensure that the phase switching is foolproof, when Iv1≤I0, after the third preset time, it will be determined again whether Iv1 is greater than I0. If Iv1 is still less than or equal to I0, it means that the phase switching is successful; if Iv1>I0, it means that the phase switching cannot be performed normally. At this time, the controller controls the second fully-controlled device 102A to be cut off and controls the first fully-controlled device 201 to be turned on.

[0061] Among them, the safety current I0 is generally 200A.

[0062] Embodiment 2: The difference between Example 2 and Example 1 is that the main branch 1 includes multiple thyristor valves 101, multiple second fully-controlled devices 102A, multiple diode auxiliary valves 102B and multiple bypass thyristor valves 103, and the auxiliary branch 2 includes multiple first fully-controlled devices 201, in order to ensure the reliable shutdown of the bridge arm current and improve the success rate of commutation.

[0063] In order to facilitate the description of the connection relationship, the embodiment 2 of the present application is illustrated by taking two thyristor valves 101, three second fully-controlled devices 102A, three diode-assisted valves 102B, four bypass thyristor valves 103, and three first fully-controlled devices 201 as examples. Figure 3 .

[0064] Figure 3 is a schematic diagram of the structure of another controllable shut-off converter valve for resisting commutation failure provided by an embodiment of the present invention, such as Figure 3 As shown, the controllable shut-off converter valve includes: a main branch 1 with one end connected to the bridge arm bus and the other end connected to the output end of the converter; an auxiliary branch 2 connected in parallel at both ends of the main branch 1; and a protection branch 3 connected in parallel at both ends of the auxiliary branch 2.

[0065] The main branch 1 is provided with a second saturated reactor L2, a first thyristor valve 101, a second thyristor valve 101, a first second fully-controlled device 102A, a second second fully-controlled device 102A, a third second fully-controlled device 102A, a first diode-assisted valve 102B, a second diode-assisted valve 102B, and a third diode-assisted valve 102B, which are connected in series in sequence. The first bypass thyristor valve 103, the second bypass thyristor valve 103, the third bypass thyristor valve 103, and the fourth bypass thyristor valve 103 are connected in series in sequence and then connected in parallel at both ends of the switching valve 102.

[0066] The auxiliary branch 2 is provided with a first saturable reactor L1 , a first first fully-controlled device 201 , a second first fully-controlled device 201 and a third first fully-controlled device 201 which are connected in series in sequence.

[0067] The protection branch 3 is provided with a third lightning arrester MOV3 connected in series.

[0068] A current transformer Ct for real-time acquisition of the bridge arm current Iv1 is connected in series on the bridge arm busbar. For detailed descriptions of the second saturated reactor L2, the thyristor valve 101, the diode auxiliary valve 102B, the bypass thyristor valve 103, the first saturated reactor L1, the first fully controlled device 201 and the third lightning arrester MOV3, reference can be made to the relevant descriptions in the aforementioned embodiment 1, which will not be repeated here.

[0069] It is understandable that, for those skilled in the art, after knowing the working principle of the controllable shut-off valve when the main branch 1 includes a single thyristor valve 101, a single second fully-controlled device 102A, and a single bypass thyristor valve 103, and the auxiliary branch 2 includes a single first fully-controlled device 201, the working principle of the controllable shut-off valve when the main branch 1 includes multiple thyristor valves 101, multiple second fully-controlled devices 102A, and multiple bypass thyristor valves 103, and the auxiliary branch 2 includes multiple first fully-controlled devices 201 can be clearly imagined, and will not be repeated here.

[0070] Figure 4 is a waveform diagram of a bridge arm current when a bypass thyristor valve is enabled, provided by an embodiment of the present invention. Figure 4 As shown, Figure 4 (a) in the figure shows the current waveform of the current Iv1 at both ends of the bridge arm. The horizontal axis represents the time Time in seconds (s), and the vertical axis represents the amplitude in kiloamperes (KA). Figure 4 (b) in the figure shows the voltage waveform of the voltage Uv1 at both ends of the bridge arm, where the horizontal axis represents time Time in seconds, and the vertical axis represents amplitude in kilovolts (KV).

[0071] When the switching valve fails, in order to ensure the normal operation of the power grid, the bypass thyristor valve is enabled. If the commutation is normal, the bridge arm current Iv1 and the bridge arm voltage Uv1 will show a periodic waveform.

[0072] exist Figure 4 In the example, the cycle of 20 milliseconds (ms) is used for illustrative purposes. Taking the bridge arm current Iv1 as an example, the current rises and falls, showing an "m" shape, which accounts for about one-third of the entire cycle, about 6.6ms. Under normal circumstances, after 6.3ms, you can start to judge the size of Iv1 and I0. If Iv1 is less than I0 at 6.3ms, it means that the commutation is normal. Therefore, the second preset time is equal to 6.3ms, which is related to the rise and fall time of the current. When setting, it is generally set at the falling edge.

[0073] In order to ensure the commutation is foolproof, when Iv1≤I0, after the third preset time, it will be determined again whether Iv1 is greater than I0, and the sum of the third preset time and the second preset time must be less than 6.6ms to ensure that it is still a falling edge. The embodiment of the present invention takes 200μs as an example for exemplary description.

[0074] Figure 5 is a waveform diagram of a bridge arm current during normal operation in a controllable shutdown mode for resisting commutation failure provided by an embodiment of the present invention, such as Figure 5 As shown, Figure 5 (a) in the figure shows the current waveform of the current Iv1 at both ends of the bridge arm. Figure 5 (b) in the figure shows the voltage waveform of the voltage Uv1 at both ends of the bridge arm. Considering the use of a small current to turn off the thyristor valve, a controllable turn-off commutation valve provided by an embodiment of the present invention to resist commutation failure is used. Figure 5 It can be seen that the bridge arm voltage Uv1 and the bridge arm current Iv1 both change periodically, indicating that the controllable shut-off converter valve has high reliability in resisting commutation failure.

[0075] Figure 6 is a waveform diagram of the fault current when the bridge arm is turned off in a controllable off mode for resisting commutation failure provided by an embodiment of the present invention, such as Figure 6 As shown, Figure 6 (a) in the figure shows the current waveform of the current Iv1 at both ends of the bridge arm. Figure 6 (b) in the figure shows the voltage waveform of the voltage Uv1 at both ends of the bridge arm, as shown in Figure 6 As shown in (a), between 0.27s and 0.28s, the bridge arm current Iv1 suddenly changes at 0.276.3s. It should have dropped, but it suddenly rose, indicating a commutation failure. The controllable shut-off converter valve provided in the embodiment of the present invention can be used to resist and realize forced commutation.

[0076] Figure 7 1 is a waveform diagram of a controllable shutdown mode for resisting commutation failure provided by an embodiment of the present invention, in which the fault current is transferred from the main branch 1 to the auxiliary branch 2 when the bridge arm is shut down, as shown in FIG. Figure 7 As shown, Figure 7 (a) in the figure shows the waveform of the main branch current, where the horizontal axis represents time (in seconds) and the vertical axis represents amplitude (in KA). Figure 7 (b) in the figure shows the current waveform of the transfer branch, where the horizontal axis represents time (in seconds) and the vertical axis represents amplitude (in KA). Figure 7 (c) in FIG. 1 shows the total current waveform of the bridge arm current Iv1.

[0077] from Figure 7 As can be seen from (a) in the figure, between 0.27s and 0.28s, the main branch current suddenly changes, lasting for t1, and then the main branch is turned off. Figure 7 As can be seen from (b) in the figure, the sudden current is transferred to the auxiliary branch for a duration of t2, and then the auxiliary branch is shut down. When the current in the main branch suddenly increases, it indicates that there is a risk of commutation failure, which can be prevented by applying the controllable shut-off commutation valve provided in the embodiment of the present invention, so that the current in the main branch is transferred to the auxiliary branch, and then the switching valve is shut down. Figure 7 As can be seen from (c) in the figure, the total current waveform of Iv1 is the superposition of the main branch current waveform and the auxiliary branch current waveform at the same time, which proves that the main branch current has been transferred to the auxiliary branch and can be reliably switched.

[0078] A controllable shut-off commutation valve for resisting commutation failure provided by an embodiment of the present invention comprises: a thyristor valve and a switching valve are connected in series and then connected in parallel at both ends of an auxiliary branch connected in series with a first fully-controlled device and used to transfer fault current; the thyristor valve is turned on according to the timing of commutation; the switching valve is turned off when the bridge arm current exceeds the preset safety current during commutation; the control valve is turned on when the switching valve is turned off and is turned off after the switching valve cut-off time meets the first preset time; the first preset time is determined according to the recovery time of the thyristor valve. By first transferring the fault current and then shutting it off, the commutation failure can be resisted. The simple structure of the commutation valve can reduce the production cost. At the same time, due to the simple operation, the difficulty can be reduced and the universality of the commutation valve can be improved.

[0079] An implementation method of a converter: A converter provided in an embodiment of the present invention includes a plurality of bridge arms, each of which is provided with the above-mentioned controllable shut-off converter valve for resisting commutation failure.

[0080] A converter provided in an embodiment of the present invention can achieve the same beneficial effects as the aforementioned controllable shut-off converter valve for resisting commutation failure, which will not be described in detail here.

Claims

1. A controllable shut-off converter valve for resisting commutation failure, characterized in that: include: The thyristor valve and the switching valve are connected in series and then connected in parallel to the two ends of the auxiliary branch which is connected in series with the first fully-controlled device and is used to transfer the fault current; The thyristor valve is turned on according to the timing of phase switching; The switching valve is cut off when the bridge arm current exceeds the preset safety current during phase switching; The first fully-controlled device is turned on when the switching valve is turned off and is turned off after the switching valve is turned off for a first preset time; The first preset time duration is determined according to the recovery time of the thyristor valve.

2. The controllable shut-off converter valve for resisting commutation failure according to claim 1, characterized in that: The switching valve comprises: a second fully-controlled device and a diode-assisted valve connected in series.

3. The controllable shut-off converter valve for resisting commutation failure according to claim 2 is characterized in that: The second fully-controlled device includes: an insulated gate bipolar transistor with an emitter and a collector connected in series between the thyristor valve and the diode-assisted valve, and a first capacitor discharge branch connected in parallel to the emitter and the collector for providing a reverse voltage for the thyristor valve when the insulated gate bipolar transistor is turned off.

4. The controllable shut-off converter valve for resisting commutation failure according to claim 3 is characterized in that: The second fully-controlled device further includes: a first voltage-equalizing resistor connected in parallel at both ends of the first capacitor discharge branch and a first lightning arrester for preventing overvoltage.

5. The controllable shut-off converter valve for resisting commutation failure according to claim 2, characterized in that: The diode-assisted valve comprises: a diode connected in series between the second fully-controlled device and the output end of the converter, and having a conduction direction the same as the current direction of the converter valve.

6. The controllable shut-off converter valve for resisting commutation failure according to claim 5, characterized in that: The diode-assisted valve further includes: a first RC resistor-capacitor absorption network and a second voltage-equalizing resistor connected in parallel at both ends of the diode.

7. The controllable shut-off converter valve for resisting commutation failure according to claim 1, characterized in that: The first fully-controlled device includes: an integrated gate-commutated thyristor whose conduction direction is the same as the converter current direction.

8. The controllable shut-off converter valve for resisting commutation failure according to claim 7, characterized in that: The first fully-controlled device further includes: a first voltage stabilizing circuit and a third voltage balancing resistor connected in parallel at both ends of the integrated gate-commutated thyristor for stabilizing the voltage when the integrated gate-commutated thyristor is turned off.

9. The controllable shut-off converter valve for resisting commutation failure according to claim 8, characterized in that: The first fully-controlled device further includes: a second lightning arrester connected in parallel at both ends of the integrated gate-commutated thyristor for preventing overvoltage.

10. The controllable shut-off converter valve for resisting commutation failure according to claim 1, characterized in that: The thyristor valve comprises a thyristor whose conduction direction points to the switching valve.

11. The controllable shut-off converter valve for resisting commutation failure according to claim 10, characterized in that: The thyristor valve further includes: a second RC resistor-capacitor absorption network and a fourth voltage-equalizing resistor connected in parallel at both ends of the thyristor.

12. The controllable shut-off converter valve for resisting commutation failure according to claim 1, characterized in that: Also includes: A first saturable reactor connected in series with the first fully-controlled device.

13. The controllable shut-off converter valve for resisting commutation failure according to claim 12, characterized in that: Also includes: A second saturable reactor is connected in series with the thyristor valve.

14. The controllable shut-off converter valve for resisting commutation failure according to any one of claims 1 to 13, characterized in that: Also includes: A third lightning arrester is connected in parallel at both ends of the auxiliary branch circuit to prevent overvoltage.

15. The controllable shut-off converter valve for resisting commutation failure according to any one of claims 1 to 13, characterized in that: Also includes: A bypass thyristor valve is connected in parallel at both ends of the switching valve and is used to bypass the switching valve when the switching valve fails during normal operation.

16. The controllable shut-off converter valve for resisting commutation failure according to claim 15, characterized in that: The bypass thyristor valve comprises: a bypass thyristor having the same conduction direction as the converter current.

17. The controllable shut-off converter valve for resisting commutation failure according to claim 16, characterized in that: The bypass thyristor valve further includes: a third RC resistor-capacitor absorption network and a fifth voltage-equalizing resistor connected in parallel at two ends of the bypass thyristor.

18. A converter, comprising a plurality of bridge arms, characterized in that: Each bridge arm is provided with a controllable shut-off converter valve for resisting commutation failure as described in any one of claims 1 to 17.

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