Converter valve and protection method for reverse recovery period of thyristor of converter valve

Abstract

The invention relates to a converter valve and a protection method for a reverse recovery period of a thyristor thereof, and the method comprises the steps: monitoring whether a thyristor level returns a reverse voltage or not in response to the turn-off of the thyristor level in the converter valve; when the thyristor level returns a reverse voltage, the voltage change rate of the two ends of the thyristor level is monitored within a preset time threshold value, and when the voltage change rate reaches a preset change rate threshold value, the valve control system generates a pulse signal to trigger the thyristor level to be conducted, so that logic judgment conditions are increased, and accurate control over protection in the reverse recovery period of the thyristor is achieved; therefore, the protection of the reverse recovery period of the thyristor under the influence of different working conditions and environments is achieved. And meanwhile, the valve control system is used for driving the thyristor to trigger the pulse, so that the phenomenon of inaccurate triggering or triggering delay caused by triggering the thyristor by equipment in the converter valve is avoided.

Description

Technical Field

[0001] The present invention relates to a commutation valve and a protection method for the reverse recovery period of thyristors, belonging to the field of high-voltage direct current power transmission in a power system. Background Art

[0002] In high-voltage direct current power transmission, the protection trigger during the reverse recovery period plays a very important role in the safe and stable operation of the commutation valve and even the entire converter station system.

[0003] Equipment failures or some operations in the converter station may cause a very steep positive transient voltage across the thyristors within a very short time after the commutation valve is turned off. This transient positive high voltage may cause the thyristors to be forced to break down and be damaged. This is because when the thyristors are reliably turned off, they can withstand the forward blocking voltage, and their withstand ability is very high; while during the reverse recovery period, due to the existence of reverse recovery period charges, the reverse recovery period withstand ability of the thyristors is greatly reduced. Therefore, a reverse recovery period protection function needs to be configured for the thyristors of the commutation valve.

[0004] At present, although the implementation methods of the reverse recovery period protection functions of commutation valves with different technical routes vary greatly, the thyristor trigger pulses for finally performing the protection action are all issued by the trigger control unit at the thyristor level of the commutation valve or a separately configured reverse recovery period protection unit, rather than directly issued by an independent valve control system. Therefore, under extreme specific working conditions, the trigger control unit at the thyristor level of the commutation valve or the separately configured reverse recovery period protection unit will be out of control or insensitive, resulting in phenomena such as incorrect triggering of thyristors. Summary of the Invention

[0005] The purpose of the present invention is to provide a commutation valve and a protection method for the reverse recovery period of thyristors thereof, so as to solve the problem of incorrect triggering of thyristors during the reverse recovery period.

[0006] To achieve the above purpose, on the one hand, the present invention proposes a protection method for the reverse recovery period of thyristors of a commutation valve, including: Responding to the turn-off of the thyristor level in the commutation valve, monitoring whether the thyristor level returns to the reverse voltage; When the thyristor level returns to the reverse voltage, monitoring the voltage change rate across the thyristor level within a preset time threshold, and when the voltage change rate reaches a preset change rate threshold, the valve control system generates a pulse signal to trigger the thyristor level to conduct.

[0007] Further, the voltage change rate across the thyristor level is monitored by a monitoring unit connected in parallel with the thyristor level.

[0008] Further, a voltage-sharing capacitor is also connected between the monitoring unit and the thyristor level; the monitoring unit includes a sampling module; wherein, The current flowing through the voltage-sharing capacitor is collected by the sampling module, and the rate of change of the voltage across the thyristor stage is calculated.

[0009] Further, the comparator in the monitoring unit compares the rate of change of the voltage across the thyristor stage with a preset rate-of-change threshold; when the rate of change of the voltage reaches the preset rate-of-change threshold, the optical emission module in the monitoring unit generates a feedback pulse and sends the feedback pulse to the valve control system, so that the valve control system generates a pulse signal based on the feedback pulse.

[0010] Further, the preset time threshold is determined according to the parameters of the thyristors in the thyristor stage.

[0011] On the other hand, the present invention also proposes a converter valve, including a thyristor stage, a monitoring unit and a valve control system, wherein the thyristor stage, the monitoring unit and the valve control system are used to execute the following instructions: In response to the turn-off of the thyristor stage in the converter valve, monitor whether the thyristor stage returns a reverse voltage; When the thyristor stage returns a reverse voltage, monitor the rate of change of the voltage across the thyristor stage within a preset time threshold, and when the rate of change of the voltage reaches the preset rate-of-change threshold, the valve control system generates a pulse signal to trigger the conduction of the thyristor stage.

[0012] Further, the rate of change of the voltage across the thyristor stage is monitored by a monitoring unit connected in parallel with the thyristor stage.

[0013] Further, a voltage-sharing capacitor is also connected between the monitoring unit and the thyristor stage; the monitoring unit includes a sampling module; wherein, The current flowing through the voltage-sharing capacitor is collected by the sampling module, and the rate of change of the voltage across the thyristor stage is calculated.

[0014] Further, the comparator in the monitoring unit compares the rate of change of the voltage across the thyristor stage with a preset rate-of-change threshold; when the rate of change of the voltage reaches the preset rate-of-change threshold, the optical emission module in the monitoring unit generates a feedback pulse and sends the feedback pulse to the valve control system, so that the valve control system generates a pulse signal based on the feedback pulse.

[0015] Further, the preset time threshold is determined according to the parameters of the thyristors in the thyristor stage.

[0016] The beneficial effects of the present invention are as follows: In response to the turn-off of the thyristor stage in the converter valve, it is monitored whether the thyristor stage returns to a reverse voltage; when the thyristor stage returns to a reverse voltage, the rate of change of the voltage across the thyristor stage is monitored within a preset time threshold, and when the rate of change of the voltage reaches a preset rate-of-change threshold, the valve control system generates a pulse signal to trigger the conduction of the thyristor stage, so as to achieve precise control of the protection of the thyristor reverse recovery period by adding logical judgment conditions, thereby achieving the protection of the thyristor reverse recovery period under the influence of different working conditions; at the same time, the valve control system is used to drive the thyristor trigger pulse to avoid the phenomenon of inaccurate triggering or triggering delay caused by the equipment in the converter valve triggering the thyristor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic flowchart of a method for protecting the reverse recovery period of a converter valve thyristor provided by the present invention; Figure 2 is a schematic diagram of the signal control timing in an actual application scenario of a method for protecting the reverse recovery period of a converter valve thyristor provided by the present invention; Figure 3 is a schematic diagram of a partial structure of a converter valve in an actual application scenario provided by the present invention; Figure 4 is a schematic diagram of the structure of a monitoring unit of a converter valve in an actual application scenario provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] The inventive concept of the present invention lies in: changing the reverse recovery period protection control pulse from being issued by the equipment in the converter valve to being issued by the valve control system, and at the same time cooperating with directly monitoring the rate of change of the voltage across the thyristor, so as to achieve precise and error-free protection of the thyristor reverse recovery period, ensuring that the reverse recovery period protection function is not affected under the condition that the original trigger control architecture of the valve control system remains unchanged, and also avoiding the situation of mis-triggering of the converter valve caused by the reverse recovery period protection action of the thyristor during the reverse recovery period under certain special working conditions, thereby achieving the purpose of controlling and optimizing the reverse recovery period protection function of the valve control system for the thyristor.

[0020] Method Embodiment 1: The present invention proposes a method for protecting the reverse recovery period of a converter valve thyristor, as Figure 1 shown, is a schematic flowchart of a method for protecting the reverse recovery period of a converter valve thyristor provided by the present invention. Among them, the method includes step S11 and step S12. Specifically: The DC control and protection system is used to send control commands to the valve control system to control the operating state of the valve control system. After the DC control and protection system issues an unlocking signal to the valve control system, the valve control system is in the unlocked operating mode and receives the pulse signal issued by the DC control and protection system for controlling the converter valve. Among them, the pulse signal for controlling the converter valve includes but is not limited to the CP signal, etc. In the actual application scenario, when the converter valve control pulse for controlling the converter valve received by the valve control system changes from invalid to valid, a pulse signal for normally triggering the thyristor to conduct will be generated. When the converter valve control pulse for controlling the converter valve received by the valve control system changes from valid to invalid, the thyristor will be turned off.

[0021] Execute step S11. In response to the turn-off of the thyristor stage in the converter valve, monitor whether the thyristor stage returns a reverse voltage; it should be noted that the thyristor stage refers to a component composed of several thyristors. In the actual application scenario, monitor whether the thyristor stage returns a negative voltage establishment signal.

[0022] Step S12. When the thyristor stage returns a reverse voltage, monitor the voltage change rate across the thyristor stage within a preset time threshold. When the voltage change rate reaches the preset change rate threshold, the valve control system generates a pulse signal to trigger the conduction of the thyristor stage; it should be noted that the preset time threshold is determined according to the parameters of the thyristors in the thyristor stage; the voltage change rate across the thyristor stage is monitored through a monitoring unit connected in parallel with the thyristor stage. Specifically, a voltage-sharing capacitor is also connected between the monitoring unit and the thyristor stage; the monitoring unit includes a sampling module; among them, the current flowing through the voltage-sharing capacitor is collected by the sampling module, and the voltage change rate across the thyristor stage is calculated.

[0023] At the same time, the comparator in the monitoring unit compares the voltage change rate across the thyristor stage with the preset change rate threshold; when the voltage change rate reaches the preset change rate threshold, the optical emission module in the monitoring unit generates a back-check pulse and sends the back-check pulse to the valve control system, so that the valve control system generates a pulse signal based on the back-check pulse.

[0024] Through steps S11 - S12, the monitoring unit is used to monitor the voltage change rate across the thyristor stage, and combined with the external monitoring system to generate pulse signals, realizing sensitive induction of the signal changes of the thyristor stage during the reverse recovery period and timely generating trigger pulses, which not only reduces the failure rate but also reduces the equipment cost.

[0025] In a preferred embodiment of the present invention, when the unlocking signal (preferably the DEBLOCK signal) sent by the DC control and protection system to the valve control system is valid, the valve control system is in the unlocked operation mode; when the valve control system responds to receiving the converter valve control pulse signal (preferably the CP signal) sent by the DC control and protection system, if the CP signal changes from an invalid signal to a valid signal, the valve control system generates a pulse signal (preferably the FP signal) for normally triggering the thyristor to conduct.

[0026] If the CP signal changes from a valid signal to an invalid signal, monitor the negative voltage establishment signal (preferably the NP signal) returned by the thyristor stage, and after monitoring the NF signal, open the reverse recovery period protection window for a fixed time t1, where the value of t1 is determined by the parameter characteristics of the thyristor. At the same time, the sampling module of the monitoring unit collects the current flowing through the voltage-sharing capacitor and calculates the voltage change rate across the thyristor stage, and compares the voltage change rate across the thyristor stage with a preset change rate threshold through a comparator in the monitoring unit; when the voltage change rate reaches the preset change rate threshold, the optical emission module in the monitoring unit generates a back-check pulse (preferably the du / dt_IP signal) and sends the du / dt_IP signal to the valve control system so that the valve control system immediately generates the FP signal to conduct the thyristor again, thereby realizing the reverse recovery period protection function of the thyristor.

[0027] Method Embodiment 2: As Figure 2 shown, it is a signal control timing schematic diagram of a protection method for the reverse recovery period of a converter valve thyristor provided by the present invention in an actual application scenario. Among them, in the first timing: in response to the CP signal changing from a valid signal to an invalid signal and monitoring the NF signal returned by the thyristor, open the reverse recovery period protection window for a fixed time t1. When the monitoring unit generates the du / dt_IP signal within t1, since the valve control system does not receive the DEBLOCK signal sent by the DC control and protection system, the FP signal is not generated. In the second timing: in response to the CP signal changing from a valid signal to an invalid signal and monitoring the NF signal returned by the thyristor, open the reverse recovery period protection window for a fixed time t1. When the monitoring unit generates the du / dt_IP signal within t1, since the valve control system is in the unlocked operation mode based on the DEBLOCK signal, the FP signal is generated to trigger the thyristor stage to conduct. It can be seen that the generation of the final FP signal requires the valve control system to be in the unlocked operation mode, and the CP signal changes from a valid signal to an invalid signal, and the du / dt_IP signal is generated before it can be generated.

[0028] Converter Valve Embodiment 1: The present invention also provides a commutation valve, which includes thyristor levels, a monitoring unit, and a valve control system. The thyristor levels, the monitoring unit, and the valve control system are configured to execute the following instructions: In response to the turn-off of the thyristor levels in the commutation valve, monitor whether the thyristor levels return a reverse voltage.

[0029] When the thyristor levels return a reverse voltage, monitor the rate of change of the voltage across the thyristor levels within a preset time threshold. When the rate of change of the voltage reaches a preset rate-of-change threshold, the valve control system generates a pulse signal to trigger the conduction of the thyristor levels. Among them, the monitoring of the rate of change of the voltage across the thyristor levels is performed by a monitoring unit connected in parallel with the thyristor levels; a voltage-sharing capacitor is also connected between the monitoring unit and the thyristor levels; the monitoring unit includes a sampling module; among them, the current flowing through the voltage-sharing capacitor is collected by the sampling module, and the rate of change of the voltage across the thyristor levels is calculated. The comparison of the rate of change of the voltage across the thyristor levels with the preset rate-of-change threshold is performed by a comparator within the monitoring unit; when the rate of change of the voltage reaches the preset rate-of-change threshold, an optical emission module within the monitoring unit generates a back-check pulse and sends the back-check pulse to the valve control system, so that the valve control system generates a pulse signal based on the back-check pulse.

[0030] As Figure 3 shown, it is a partial structural schematic diagram of a commutation valve provided by the present invention in an actual application scenario. Among them, n thyristors form the thyristor levels, and a voltage-sharing capacitor C1 (for valve section voltage sharing) and a du / dt monitoring unit are connected in parallel at both ends of the thyristor levels. The du / dt monitoring unit uploads a du / dt over-limit action signal to the valve control system, so that the valve control system sends a pulse signal to each thyristor.

[0031] Commutation valve Embodiment 2: As Figure 4 shown, it is a structural schematic diagram of the monitoring unit of a commutation valve provided by the present invention in an actual application scenario. Among them, the du / dt monitoring unit is composed of a sampling module, a comparator, and an optical emission module. Among them, the sampling module calculates the du / dt value borne by the valve section by collecting the current flowing through the voltage-sharing capacitor C1; the comparator compares the collected du / dt value with a preset threshold. If the du / dt value is greater than the preset value, it controls the optical emission module to generate a back-check pulse du / dt_IP and sends it to the valve control through an optical fiber; the valve control device generates a thyristor trigger pulse according to the control command issued by the DC control and protection system.

[0032] Meanwhile, in actual application scenarios, the valve control device is used for the normal triggering, reverse recovery period protection triggering and status monitoring of the converter valve. It adopts a dual-system redundant configuration. Under normal circumstances, one system is the primary system and the other is the standby system. Only the primary system sends the trigger pulses for triggering the thyristors. The valve control system can also record the waveforms of the reverse recovery period protection action pulses sent, which is convenient for system analysis.

[0033] In summary, the beneficial effects of the present invention are as follows: The reverse recovery period protection trigger pulses are sent by the valve control system, avoiding the commutation failure caused by the thyristor control unit or the reverse recovery period protection unit in the converter valve misoperating and triggering the thyristors by itself under extreme working conditions; not only is the judgment logic of the du / dt monitoring unit simple, but the electronic components that make up the monitoring unit can be realized at low cost; the failure rate is reduced.

Claims

1. A protection method for a thyristor of a converter valve during a reverse recovery period, characterized in that: include: In response to the thyristor stage in the converter valve being turned off, monitoring whether the thyristor stage returns a reverse voltage; When the thyristor stage returns to reverse voltage, the voltage change rate across the thyristor stage is monitored within a preset time threshold, and when the voltage change rate reaches a preset change rate threshold, the valve control system generates a pulse signal to trigger the thyristor stage to conduct.

2. The protection method for the reverse recovery period of the thyristor of the converter valve according to claim 1 is characterized in that: The rate of change of the voltage across the thyristor stage is monitored by a monitoring unit connected in parallel with the thyristor stage.

3. The protection method for the reverse recovery period of the thyristor of the converter valve according to claim 2 is characterized in that: A voltage-equalizing capacitor is also connected between the monitoring unit and the thyristor stage; The current flowing through the voltage-equalizing capacitor is collected by a sampling module in the monitoring unit, and the voltage change rate across the thyristor stage is calculated.

4. The protection method for the reverse recovery period of the thyristor of the converter valve according to claim 3 is characterized in that: The comparator in the monitoring unit compares the voltage change rate at both ends of the thyristor stage with a preset change rate threshold; when the voltage change rate reaches the preset change rate threshold, the optical transmission module in the monitoring unit generates a backcheck pulse and sends the backcheck pulse to the valve control system, so that the valve control system generates a pulse signal based on the backcheck pulse.

5. The protection method for the reverse recovery period of the thyristor of the converter valve according to any one of claims 1 to 4, characterized in that: The preset time threshold is determined according to the parameters of the thyristors in the thyristor stage.

6. A flow control valve, characterized in that: The invention comprises a thyristor stage, a monitoring unit and a valve control system, wherein the thyristor stage, the monitoring unit and the valve control system are used to execute the following instructions: In response to the thyristor stage in the converter valve being turned off, monitoring whether the thyristor stage returns a reverse voltage; When the thyristor stage returns to reverse voltage, the voltage change rate across the thyristor stage is monitored within a preset time threshold, and when the voltage change rate reaches a preset change rate threshold, the valve control system generates a pulse signal to trigger the thyristor stage to conduct.

7. The flow control valve according to claim 6, characterized in that: The rate of change of the voltage across the thyristor stage is monitored by a monitoring unit connected in parallel with the thyristor stage.

8. The flow control valve according to claim 7, characterized in that: A voltage-equalizing capacitor is also connected between the monitoring unit and the thyristor stage; The current flowing through the voltage-equalizing capacitor is collected by a sampling module in the monitoring unit, and the voltage change rate across the thyristor stage is calculated.

9. The flow control valve according to claim 8, characterized in that: The comparator in the monitoring unit compares the voltage change rate at both ends of the thyristor stage with a preset change rate threshold; when the voltage change rate reaches the preset change rate threshold, the optical transmission module in the monitoring unit generates a backcheck pulse and sends the backcheck pulse to the valve control system, so that the valve control system generates a pulse signal based on the backcheck pulse.

10. The converter valve according to any one of claims 6 to 9, characterized in that: The preset time threshold is determined according to the parameters of the thyristors in the thyristor stage.

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