阅读说明：本技术 柔性直流换流阀的过压保护方法、装置及其存储介质 (Overvoltage protection method and device for flexible direct current converter valve and storage medium thereof ) 是由 邹常跃 赵晓斌 许树楷 李岩 杨双飞 冯俊杰 辛清明 卢毓欣 郭龙 于 2019-11-27 设计创作，主要内容包括：本发明实施例涉及一种柔性直流换流阀的过压保护方法、装置及其存储介质,应用于柔性直流输电系统上,包括以下步骤：S1.确定换流阀发生故障的相位；S2.导通相位对应上桥臂的开关元件；S3.释放换流阀中因故障产生的电流。通过确定换流阀发生故障的相位,根据确定换流阀发生故障的相位,导通与相位相对应上桥臂的开关元件,将发生故障的电流得到释放。与现有柔性直流输电过电压保护方法中采用避雷器防过压相比,该柔性直流换流阀的过压保护方法通过导通现有换流阀上的开关元件实现过压保护,避免了现有柔性直流输电中换流阀功率模块过压导致电子元器件损坏,也不会增加柔性直流输电系统的成本,也不会增大换流阀的体积。(The embodiment of the invention relates to an overvoltage protection method, an overvoltage protection device and a storage medium of a flexible direct current converter valve, which are applied to a flexible direct current transmission system and comprise the following steps: s1, determining a phase of a converter valve with a fault; s2, conducting a switching element of which the phase corresponds to the upper bridge arm; and S3, releasing the current generated by the fault in the converter valve. The failed phase of the converter valve is determined, and the switching element of the upper bridge arm corresponding to the phase is conducted according to the determined failed phase of the converter valve, so that the failed current is released. Compared with the prior flexible direct current transmission overvoltage protection method which adopts the lightning arrester to prevent overvoltage, the overvoltage protection method of the flexible direct current converter valve realizes overvoltage protection by switching on the switch element on the prior converter valve, avoids the damage of electronic components caused by overvoltage of a converter valve power module in the prior flexible direct current transmission, does not increase the cost of a flexible direct current transmission system, and does not increase the volume of the converter valve.)

1. An overvoltage protection method of a flexible direct current converter valve is applied to a flexible direct current transmission system and is characterized by comprising the following steps:

s1, determining a phase of a converter valve with a fault;

s2, switching on the switching element of the upper bridge arm corresponding to the phase;

and S3, releasing the current generated by the fault in the converter valve.

2. The method for overvoltage protection of a flexible direct current converter valve according to claim 1, wherein a converter valve in said flexible direct current transmission system comprises a double valve group consisting of two single valve groups, each of said single valve groups comprising a low-end valve group and a high-end valve group, and the step of overvoltage protection of each of said single valve groups comprises:

if the valve side of the high-end valve bank is in fault, only switching on the switching element of the upper bridge arm corresponding to the fault phase of the high-end valve bank;

and if the valve side of the low-end valve group is in fault with the ground, switching elements of an upper bridge arm corresponding to the fault phase of the low-end valve group are switched on, and switching elements corresponding to any phase are switched on the high-end valve group.

3. The method according to claim 1, wherein a plurality of power modules are arranged on the converter valve in the flexible direct current transmission system, each power module is provided with at least four switching elements, and the four switching elements are a first switching element, a second switching element, a third switching element and a fourth switching element.

4. The overvoltage protection method for the flexible direct current converter valve according to claim 3, wherein the switching element is a field effect transistor, a collector of the first switching element is connected to a collector of the third switching element, an emitter of the first switching element is connected to a collector of the second switching element, an emitter of the second switching element is connected to an emitter of the fourth switching element, and a collector of the fourth switching element is connected to an emitter of the third switching element;

the overvoltage protection method of the flexible direct current converter valve comprises the following steps:

s01, determining a phase of a converter valve which breaks down;

s02, conducting the second switch element or the third switch element of the upper bridge arm corresponding to the phase;

s03, releasing current generated by faults in the converter valve.

5. The utility model provides an overvoltage crowbar of flexible direct current change of current valve, is applied to on the flexible direct current transmission system, its characterized in that includes:

a fault determination unit for determining a phase of a fault occurring in the flexible direct current transmission system;

and the driving unit is used for conducting the switching element of the upper bridge arm corresponding to the failed phase according to the failed phase.

6. The over-voltage protection device for the flexible direct current converter valve according to claim 5, wherein if the converter valve in the flexible direct current transmission system comprises a double valve group consisting of two single valve groups, each single valve group comprises a low-end valve group and a high-end valve group; the driving unit includes:

the first driving unit is used for conducting the switching elements of the upper bridge arm of the high-end valve group;

and the second driving unit is used for conducting the switching elements of the upper bridge arm of the low-end valve group.

7. The overvoltage protection device of the flexible direct current converter valve according to claim 6, wherein if the fault determination unit determines that the valve side of the high-end valve group has a fault with the ground, the first driving unit turns on a switching element of an upper bridge arm corresponding to a fault phase of the high-end valve group.

8. The overvoltage protection device of the flexible direct current converter valve according to claim 6, wherein if the fault determination unit determines that the valve side of the low-side valve bank has a fault, the second driving unit drives a switching element of an upper bridge arm corresponding to a fault phase of the low-side valve bank to be turned on, and the first driving unit drives a switching element corresponding to any phase of the high-side valve bank to be turned on.

9. A storage medium comprising a memory and a processor,

the memory is used for storing program codes and transmitting the program codes to the processor;

the processor is configured to execute the method for overvoltage protection of a flexible direct current converter valve according to any one of claims 1 to 4 according to instructions in the program code.

Technical Field

The invention relates to the technical field of flexible direct current transmission, in particular to an overvoltage protection method and device for a flexible direct current converter valve and a storage medium of the overvoltage protection device.

Background

As a new generation of dc transmission technology, flexible dc transmission is still composed of a converter station and a dc transmission line (usually a dc cable), similar in structure to high voltage dc transmission. The existing converter stations in flexible direct current transmission are classified according to the number of poles and can be divided into a symmetrical unipolar system (or referred to as pseudo bipolar) and a symmetrical bipolar system. In the symmetrical bipolar system, because a direct grounding point exists at the direct current side of the symmetrical bipolar system, when a valve side of a converter valve of a converter station in the symmetrical bipolar system has a grounding fault, corresponding interval differential protection actions in the symmetrical bipolar system lock the converter in the converter station and send a tripping command, and a breaker of the symmetrical bipolar system is disconnected.

The circuit is generally broken by adopting a breaker in flexible direct current transmission, the breaker usually needs 30-50 ms to be broken, a power module in the converter can be continuously charged after the converter is locked and before the breaker is broken, and the voltage of the power module in the converter is possibly too high, so that a capacitor or a switching device on the power module is broken down due to overvoltage.

In order to solve the problems, lightning arresters are connected in parallel at two ends of a converter valve bridge arm in the existing flexible direct current transmission to limit the overvoltage level, for example, the patent of the invention of an overvoltage protection method of a modular multilevel voltage source converter valve with the publication number of CN103050955A is disclosed by the Chinese intellectual property office in 2013, 4 and 17. However, the lightning arrester in the flexible direct current transmission overvoltage protection method can increase the cost, and the added lightning arrester can occupy the space and increase the volume of the converter valve.

Therefore, how to avoid overvoltage of the power module of the converter valve without adding electronic components becomes an important technical problem to be solved urgently by those skilled in the art.

Disclosure of Invention

The embodiment of the invention provides an overvoltage protection method and device for a flexible direct current converter valve and a storage medium thereof, which are used for solving the technical problem that electronic components are damaged due to overvoltage of a converter valve power module in the existing flexible direct current transmission.

In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:

an overvoltage protection method of a flexible direct current converter valve is applied to a flexible direct current transmission system and comprises the following steps:

s1, determining a phase of a converter valve with a fault;

s2, switching on the switching element of the upper bridge arm corresponding to the phase;

and S3, releasing the current generated by the fault in the converter valve.

Preferably, the converter valve in the flexible dc power transmission system includes a double valve group consisting of two single valve groups, each single valve group includes a low-end valve group and a high-end valve group, and the step of overvoltage protection of each single valve group includes:

if the valve side of the high-end valve bank is in fault, only switching on the switching element of the upper bridge arm corresponding to the fault phase of the high-end valve bank;

and if the valve side of the low-end valve group is in fault with the ground, switching elements of an upper bridge arm corresponding to the fault phase of the low-end valve group are switched on, and switching elements corresponding to any phase are switched on the high-end valve group.

Preferably, a plurality of power modules are arranged on a converter valve in the flexible direct current transmission system, each power module is provided with at least four switching elements, and the four switching elements are a first switching element, a second switching element, a third switching element and a fourth switching element respectively.

Preferably, the switching element is a field effect transistor, a collector of the first switching element is connected to a collector of the third switching element, an emitter of the first switching element is connected to a collector of the second switching element, an emitter of the second switching element is connected to an emitter of the fourth switching element, and a collector of the fourth switching element is connected to an emitter of the third switching element;

the overvoltage protection method of the flexible direct current converter valve comprises the following steps:

s01, determining a phase of a converter valve which breaks down;

s02, conducting the second switch element or the third switch element of the upper bridge arm corresponding to the phase;

s03, releasing current generated by faults in the converter valve.

The invention also provides an overvoltage protection device of the flexible direct current converter valve, which is applied to a flexible direct current transmission system and comprises the following components:

a fault determination unit for determining a phase of a fault occurring in the flexible direct current transmission system;

and the driving unit is used for conducting the switching element of the upper bridge arm corresponding to the failed phase according to the failed phase.

Preferably, if the converter valves in the flexible dc power transmission system comprise a double valve group consisting of two single valve groups, each single valve group comprises a low-end valve group and a high-end valve group; the driving unit includes:

the first driving unit is used for conducting the switching elements of the upper bridge arm of the high-end valve group;

and the second driving unit is used for conducting the switching elements of the upper bridge arm of the low-end valve group.

Preferably, if the fault determination unit determines that the valve side of the high-end valve group has a fault in the ground, the first driving unit turns on the switching element of the upper bridge arm corresponding to the phase of the high-end valve group having the fault.

Preferably, if the fault determination unit determines that the valve side of the low-end valve group has a fault in the ground, the second driving unit drives the switching element of the upper bridge arm corresponding to the phase of the low-end valve group having the fault to be turned on, and the first driving unit drives the switching element corresponding to any phase of the high-end valve group to be turned on.

The present invention also provides a storage medium comprising a memory and a processor,

the memory is used for storing program codes and transmitting the program codes to the processor;

the processor is used for executing the overvoltage protection method of the flexible direct current converter valve according to the instructions in the program codes.

According to the technical scheme, the embodiment of the invention has the following advantages:

1. according to the overvoltage protection method of the flexible direct current converter valve, the phase position of the converter valve with the fault is determined, the switch element of the upper bridge arm corresponding to the phase position is conducted according to the determined phase position of the converter valve with the fault, and the current with the fault flows to three-phase alternating current through the conducted switch element to form a current release loop, so that the current with the fault is released. Compared with the existing overvoltage protection method for the flexible direct current power transmission by adopting the lightning arrester to prevent overvoltage, the overvoltage protection method for the flexible direct current converter valve realizes overvoltage protection by conducting a switch element on the existing converter valve, avoids the damage of electronic components caused by overvoltage of a converter valve power module in the existing flexible direct current power transmission, does not increase the system cost, and does not increase the volume of the converter valve;

2. the overvoltage protection device of the flexible direct current converter valve determines a failed phase through the fault determination unit, and controls the switching elements of the upper bridge arm of the converter valve on the corresponding phase to be switched on by the driving unit according to the failed phase, so that the failed current is released, electronic elements on a power module in the converter valve are prevented from being damaged, and overvoltage protection of the flexible direct current converter valve is realized.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

Fig. 1 is a schematic diagram of a converter valve of a single valve group of a conventional bipolar flexible direct current transmission system.

Fig. 2 is a schematic diagram of a converter valve of a double valve group of a conventional bipolar flexible direct current transmission system.

Fig. 3 is a current loop diagram after a fault occurs on the a-phase valve side ground of a converter valve in a conventional bipolar flexible direct current transmission system.

Fig. 4 is a simulation diagram of a voltage change process in a charging process when the existing bipolar flexible direct-current power transmission system is directly locked after a fault occurs.

Fig. 5 is a flowchart illustrating steps of an overvoltage protection method for a flexible dc converter valve according to an embodiment of the present invention.

Fig. 6 is a block diagram of a converter valve power module in the overvoltage protection method for the flexible dc converter valve according to the embodiment of the present invention.

Fig. 7 is a simulation diagram of the overvoltage protection method for the flexible dc converter valve according to the embodiment of the present invention during the fault voltage variation.

Fig. 8 is a frame diagram of overvoltage protection after the overvoltage protection method for the flexible dc converter valve according to the embodiment of the present invention fails.

Fig. 9 is a block diagram of an overvoltage protection device for a flexible dc converter valve according to an embodiment of the present invention.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the application provides an overvoltage protection method and device for a flexible direct current converter valve and a storage medium thereof, which are used for solving the technical problem that electronic components are damaged due to overvoltage of a converter valve power module in the existing flexible direct current transmission.

The converter valve in the existing bipolar flexible direct current transmission system can be a single valve group or a double valve group. Fig. 1 is a schematic diagram of a converter valve of a single valve group of a conventional bipolar flexible direct current transmission system, and fig. 2 is a schematic diagram of a converter valve of a double valve group of a conventional bipolar flexible direct current transmission system.

As shown in fig. 1 and 2, the input end of a converter valve in a conventional bipolar flexible direct current transmission system is connected with three-phase alternating current, and the output end of the converter valve outputs direct current. A plurality of power modules are arranged on the converter valve, and the converter valve connected with each phase of the three-phase alternating current is provided with the power modules. The converter valve of the existing bipolar flexible direct current transmission system is not provided with a parallel arrester.

It should be noted that each power module is provided with at least four switching elements, and the four switching elements are respectively a first switching element, a second switching element, a third switching element and a fourth switching element.

As shown in fig. 3 and 4, fig. 3 is a current loop diagram after a fault occurs to a phase a valve side ground of a converter valve in a conventional bipolar flexible direct current transmission system, and fig. 4 is a simulation diagram of a voltage change process in a charging process when a direct lock is performed after the fault occurs in the conventional bipolar flexible direct current transmission system.

After the A phase valve side of a converter valve in the bipolar flexible direct current transmission system is grounded and has a fault, direct current in the bipolar flexible direct current transmission system still exists, the direct current in the bipolar flexible direct current transmission system flows through a power module of an upper bridge arm of a converter valve of a B phase or a C phase which does not have the fault, the power module connected with the upper bridge arm of the B phase or the C phase is charged, until an alternating current breaker in the bipolar flexible direct current transmission system is disconnected, a current loop is cut off, and the bipolar flexible direct current transmission system can not completely cut off the current loop. Between the fault and the complete cut-off of the current loop of the alternating current circuit breaker, after 1.5ms, the alternating current bus differential protection action on the valve side of the converter valve generally locks the converter valve, then a power module of an A, B, C three-phase upper bridge arm connected with three-phase alternating current presents a half-wave uncontrolled rectification characteristic, and one phase with a smaller instantaneous value of voltage on the valve side of the A, B, C three-phase converter valve is conducted, as shown in fig. 3, when a power module of a bridge arm on a phase B connected with the three-phase alternating current is conducted, the phase B between the three-phase alternating current and the converter valve is a conducting loop, the direct current charges the conducting loop until the alternating current circuit breaker is disconnected, and the conducting loop of the phase B is not disconnected, so that the charging of the conducting loop of the phase. As shown in fig. 4, it can be known from fig. 4 that the voltage rise occurs after 7s when the bipolar flexible dc power transmission system is directly locked after a fault occurs, and the voltage of the conductive loop of the B phase can rise from 2.1kV to 4.3kV during the charging process, and the rising voltage may damage the power module.

Therefore, an embodiment of the present invention provides an overvoltage protection method for a flexible dc converter valve, which is applied to a flexible dc power transmission system, as shown in fig. 5, fig. 5 is a flowchart illustrating steps of the overvoltage protection method for the flexible dc converter valve according to the embodiment of the present invention.

The embodiment of the invention provides an overvoltage protection method of a flexible direct current converter valve, which comprises the following steps:

s1, determining a phase of a converter valve with a fault;

s2, conducting a switching element of which the phase corresponds to the upper bridge arm;

and S3, releasing the current generated by the fault in the converter valve.

In step S1 of an embodiment of the invention, it is determined which phase of the three phases connected to the converter valves in the flexible direct current power transmission system is faulty.

It should be noted that determining the phase of a converter valve that is malfunctioning can be quickly located by the valve side ac bus differential protection of the converter valve to determine which phase is malfunctioning.

In step S2 of the embodiment of the present invention, in the flexible direct current power transmission system, the converter valve is provided with an upper arm and a lower arm, each of the upper arm and the lower arm is provided with a power module connected to each of the upper arm and the lower arm, and the power modules are provided with a plurality of switching elements.

It should be noted that, according to the phase determined that the converter valve has a fault, the switching element on the power module of the upper bridge arm corresponding to the phase is turned on, so that the current having the fault flows to the three-phase alternating current through the turned-on switching element to form a current release circuit. The switching element may be a field effect transistor of a triode or a field effect transistor of an MOS transistor.

In step S3 of the embodiment of the present invention, according to the turned-on switching element of step S2, a current having a fault is caused to flow to the three-phase ac power through the turned-on switching element to form a current release loop, so that the current having the fault is discharged.

According to the overvoltage protection method for the flexible direct current converter valve, the failed phase of the converter valve is determined, the switching element of the upper bridge arm corresponding to the phase is conducted according to the determined failed phase of the converter valve, and the failed current flows to the three-phase alternating current through the conducted switching element to form a current release loop, so that the failed current is released. Compared with the prior flexible direct current transmission overvoltage protection method which adopts the lightning arrester to prevent overvoltage, the overvoltage protection method of the flexible direct current converter valve realizes overvoltage protection by conducting the switch element on the prior converter valve, avoids the damage of electronic components caused by overvoltage of a converter valve power module in the prior flexible direct current transmission, does not increase the system cost, and does not increase the volume of the converter valve.

Fig. 6 is a block diagram of a converter valve power module in the overvoltage protection method for the flexible dc converter valve according to the embodiment of the present invention.

In one embodiment of the present invention, as shown in fig. 6, a plurality of power modules are disposed on the converter valve, and each of the power modules is disposed with at least four switching elements, which are a first switching element T1, a second switching element T2, a third switching element T3 and a fourth switching element T4. In this embodiment, the switching element is preferably a triode, the collector of the first switching element T1 is connected to the collector of the third switching element T3, the emitter of the first switching element T1 is connected to the collector of the second switching element T2, the emitter of the second switching element T2 is connected to the emitter of the fourth switching element T4, and the collector of the fourth switching element T4 is connected to the emitter of the third switching element T3. Wherein the side where the emitter of the first switching element T1 is connected to the collector of the second switching element T2 is the dc side of the converter valve and the side where the collector of the fourth switching element T4 is connected to the emitter of the third switching element T3 is the ac side of the converter valve. The overvoltage protection method of the flexible direct current converter valve comprises the following steps:

s01, determining a phase of a converter valve which breaks down;

s02, conducting a second switching element T2 or a third switching element T3 of which the phases correspond to the upper bridge arm;

and S03, releasing the current generated by the fault in the converter valve.

As shown in fig. 7, after a fault occurs in the a-phase valve side ground of the converter valve in the flexible direct current transmission system, the direct current in the flexible direct current transmission system still exists, and the direct current in the flexible direct current transmission system flows through the second switching element T2 or the third switching element T3 of the upper arm of the converter valve in the a-phase, so that the current in the a-phase is released. As shown in fig. 8, it can be seen from fig. 8 that the voltage after 7s does not rise when the flexible dc power transmission system is directly locked after a fault occurs, and the power module in the converter valve is prevented from being damaged due to the voltage rise after the fault occurs in the flexible dc power transmission system. Compared with the existing flexible direct current transmission system, the logic of the differential protection action outlet corresponding to the converter valve side ground fault of the existing flexible direct current transmission system is changed into the second switch element T2 or the third switch element T3 for conducting the power module of the upper bridge arm of the converter valve, so that the overvoltage phenomenon of the power module in the converter valve is avoided.

In one embodiment of the present invention, as shown in fig. 2, the converter valve in the flexible dc power transmission system comprises a double valve group consisting of two single valve groups, each single valve group comprising a low-end valve group and a high-end valve group, and the step of overvoltage protection of each single valve group comprises:

if the valve side of the high-end valve bank is in fault, only conducting the second switching element T2 or the third switching element T3 of the upper bridge arm corresponding to the fault phase of the high-end valve bank;

if the valve side of the low-end valve bank is in fault, the second switch element T2 or the third switch element T3 of the upper bridge arm corresponding to the fault phase of the low-end valve bank is conducted, and the second switch element T2 or the third switch element T3 corresponding to any phase is conducted on the high-end valve bank.