CN111585257A - Overvoltage stress control method and device for flexible direct current converter valve - Google Patents
Overvoltage stress control method and device for flexible direct current converter valve Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
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Abstract
The invention discloses an overvoltage stress control method and device for a flexible-straight converter valve, wherein the flexible-straight converter valve is electrically connected with a controllable lightning arrester, and the method comprises the following steps: acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct converter valve; judging whether the unbalanced voltage value exceeds a first preset voltage value or not and judging whether the unbalanced current value exceeds a preset current value or not; when the unbalanced voltage value exceeds a first preset voltage value and/or the unbalanced current value exceeds a preset current value, controlling a control switch of the controllable lightning arrester to be closed to execute a protection action; and when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value, controlling a control switch of the controllable lightning arrester to keep a disconnected state. Whether system faults occur or not is judged by detecting whether unbalanced voltage and/or unbalanced current on the valve side of the flexible direct current converter valve exceed preset values or not, and the controllable lightning arrester can rapidly act to reduce overvoltage stress of the flexible direct current converter valve.
Description
Technical Field
The invention relates to the technical field of electric power engineering, in particular to an overvoltage stress control method and device for a flexible direct current converter valve.
Background
The core equipment of the flexible direct current transmission technology is a flexible direct current converter valve, the structural schematic diagram of the flexible direct current transmission technology is shown in fig. 1, each bridge arm is formed by sub-modules with consistent manufacturing parameters in a cascading mode, and energy storage capacitors on the direct current side of a traditional two-level and three-level voltage source type converter are connected into the sub-modules in a dispersing mode, so that overvoltage stress of the sub-module capacitors determines overvoltage stress of the converter valve. When the converter valve has a fault, the converter valve serving as a receiving end in the flexible direct current transmission system is blocked from transmitting energy to the alternating current system, and the transmitting end converter valve still transmits rated active power to the receiving end, so that redundant energy exists in the receiving end converter valve, and the energy is stored in a sub-module capacitor in an electric field energy mode, so that the sub-module has an overvoltage phenomenon.
The most effective and economic means for suppressing the overvoltage of the system is to configure a lightning arrester, and the controllable lightning arrester is used as an improved lightning arrester, has low charge rate under the operating voltage, can deeply reduce residual voltage when put into use, enhances the overvoltage suppression capability of the controllable lightning arrester while improving the safety margin and reliability, and can be used as a technical scheme for suppressing the overvoltage stress of the flexible direct current converter valve. The structure of the controllable lightning arrester is schematically shown in fig. 2, and the controllable lightning arrester comprises a fixed part, a controllable part and a control switch part, wherein a switch device in the control switch part can be an electronic switch or a rapid mechanical switch. The control switch is in a switching-off state in a normal state, the whole controllable lightning arrester has low charge rate, the converter valve control protection system issues a switching-on command to the control switch after a fault, and the fixed part is independently accessed into the system after the control part is short-circuited to absorb redundant energy in the system and suppress system overvoltage.
Suppose that the rated DC active power of the system is PnomThe power transmitted to the alternating current system by the receiving end converter valve after the fault is PfltWhen the time required from the occurrence of a fault to the execution of the protection action is t, the number of the sub-modules which are put into one phase in normal operation is N, the capacitance parameter in a single sub-module is C, and the variable delta u of the capacitance voltage of the sub-modules before the controllable lightning arrester absorbs no energy after the occurrence of the faultsmThe following can be calculated:
as can be seen from the above formula, PnomN, C, etc. are system design parameters and basically do not change, so that overvoltage stress of the converter valve is mainly energy P transmitted to an alternating current system by the converter valve after failurefltAnd the time t needed for executing the protection action after the fault occurs. The controllable arrester action criterion is that the voltage average value of the bridge arm submodule of the converter valve exceeds a set protection fixed value generally, and the overvoltage protection flow chart of the converter valve is shown in figure 3. As can be seen from fig. 3, after a fault actually occurs, the controllable lightning arrester cannot perform a protection action to absorb system energy immediately, and when the average voltage of the sub-modules exceeds a certain threshold, the converter valve protection system determines that the fault occurs, and then the converter valve can perform the action, and at this time, the converter valve has already suffered a certain voltage stress. Considering that action delay also exists in controllable lightning protection action, if the converter valve has serious fault, P is causedfltWhen the sub-module overvoltage criterion is 0, the converter valve still absorbs power P during the period from the triggering of the sub-module overvoltage criterion to the real action of the controllable lightning arresternomFurther increasing the overvoltage stress of the converter valves, with the risk of damaging the converter valves.
Disclosure of Invention
The invention aims to provide a method and a device for controlling overvoltage stress of a flexible-straight converter valve.
In order to solve the above technical problem, a first aspect of an embodiment of the present invention provides an overvoltage stress control method for a flexible-direct converter valve, where the flexible-direct converter valve is electrically connected to a controllable lightning arrester, and the method includes the following steps:
acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct current converter valve;
judging whether the unbalanced voltage value exceeds a first preset voltage value or not, and judging whether the unbalanced current value exceeds a preset current value or not;
when the unbalanced voltage value exceeds the first preset voltage value and/or the unbalanced current value exceeds the preset current value, controlling a control switch of the controllable lightning arrester to be closed to execute a protection action;
and when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value, controlling a control switch of the controllable lightning arrester to keep a disconnected state.
Further, the unbalanced voltage UunbalanceThe calculation formula of (2) is as follows:
Uunbalance＝|uva+uvb+uvc|，
wherein u isva、uvb、uvcIs three-phase alternating current voltage at the valve side of the converter valve;
the calculation formula of the unbalanced current is as follows:
Iunbalance＝|∑(iiu-iid)|，
wherein iiuIs a one-phase upper bridge arm current iidThe upper arm current direction is defined to be positive from the direct current side to the alternating current side, the lower arm current direction is defined to be positive from the alternating current side to the direct current side, and subscripts i are a, b, and c, for the lower arm current of the corresponding phase.
Further, before obtaining the unbalanced voltage and the unbalanced current on the valve side of the flexible direct current converter valve, the method further includes:
obtaining the maximum value of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valve;
judging whether the maximum value of the average value of the bridge arm submodule voltage is greater than or equal to a second preset voltage value or not;
when the maximum value of the average voltage value of the bridge arm sub-modules is greater than or equal to the second preset voltage value, controlling a control switch of the controllable lightning arrester to be closed to execute the protection action;
and when the maximum value of the average value of the bridge arm submodule voltages is smaller than the second preset voltage value, acquiring the unbalanced voltage and the unbalanced current on the valve side of the flexible-straight converter valve.
Further, the maximum value U of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valveave_maxThe calculation formula of (2) is as follows:
Uave_max＝max{Uiu_ave、Uid_ave}，
wherein, Uiu_aveIs the average value of the voltage of the bridge arm submodule on one phase, Uid_aveAnd subscript i is a, b and c corresponding to the voltage average value of the lower bridge arm submodule of the corresponding phase.
Further, the controllable arrester comprises: the control switch comprises a fixed component, a controllable component and a control switch, wherein the fixed component and the controllable component are connected in series;
the control switch of controllable arrester of control closes and carries out the protection action, includes:
controlling the control switch to be closed to enable the controllable component to be in short circuit;
wherein, the control component is an electronic switch or a rapid mechanical switch.
Accordingly, a second aspect of an embodiment of the present invention provides an overvoltage stress control device for a flexible direct current converter valve, including:
the first detection module is used for acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct current converter valve;
the first judgment module is used for judging whether the unbalanced voltage value exceeds a first preset voltage value or not and judging whether the unbalanced current value exceeds a preset current value or not;
the control module is used for controlling a control switch of the controllable lightning arrester to be closed to execute a protection action when the unbalanced voltage value exceeds the first preset voltage value and/or the unbalanced current value exceeds the preset current value;
the control module is further used for controlling a control switch of the controllable lightning arrester to keep an off state when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value.
Further, the unbalanced voltage UunbalanceThe calculation formula of (2) is as follows:
Uunbalance＝|uva+uvb+uvc|，
wherein u isva、uvb、uvcIs three-phase alternating current voltage at the valve side of the converter valve;
the calculation formula of the unbalanced current is as follows:
Iunbalance＝|∑(iiu-iid)|，
wherein iiuIs a one-phase upper bridge arm current iidThe upper arm current direction is defined to be positive from the direct current side to the alternating current side, the lower arm current direction is defined to be positive from the alternating current side to the direct current side, and subscripts i are a, b, and c, for the lower arm current of the corresponding phase.
Further, the overvoltage stress control device for the flexible direct current converter valve further comprises:
the second detection module is used for obtaining the maximum value of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valve;
the second judgment module is used for judging whether the maximum value of the average value of the voltages of the bridge arm sub-modules is greater than or equal to a second preset voltage value or not;
the control module is further configured to control a control switch of the controllable arrester to be closed to execute the protection action when the maximum value of the average voltage value of the bridge arm sub-modules is greater than or equal to the second preset voltage value, and obtain the unbalanced voltage and the unbalanced current on the valve side of the flexible direct current converter when the maximum value of the average voltage value of the bridge arm sub-modules is less than the second preset voltage value.
Further, the maximum value U of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valveave_maxThe calculation formula of (2) is as follows:
Uave_max＝max{Uiu_ave、Uid_ave}，
wherein, Uiu_aveIs the average value of the voltage of the bridge arm submodule on one phase, Uid_aveSubscript i is a, b and c, and is the average value of the voltage of the corresponding lower bridge arm submodule.
Further, the controllable arrester comprises: the control switch comprises a fixed component, a controllable component and a control switch, wherein the fixed component and the controllable component are connected in series;
the control module controls the control switch of the controllable lightning arrester to close and execute the protection action, and comprises:
controlling the control switch to be closed to enable the controllable component to be in short circuit;
wherein, the control component is an electronic switch or a rapid mechanical switch.
The technical scheme of the embodiment of the invention has the following beneficial technical effects:
whether a fault occurs or not is judged by detecting whether unbalanced voltage and/or unbalanced current on the valve side of the flexible-direct converter valve exceeds a preset value or not, so that a controllable lightning arrester can quickly execute protection action to reduce overvoltage stress of the flexible-direct converter valve when a serious fault occurs, waiting time for triggering voltage average value overvoltage protection fixed value of a submodule is not needed for a system submodule capacitor to absorb energy, the controllable lightning arrester can quickly execute protection action, time from the real occurrence of the fault to the effective input of the controllable lightning arrester is shortened, the controllable lightning arrester can absorb surplus power of the system in advance, and the flexible-direct converter valve is prevented from being damaged; in addition, the maximum value of the average value of the voltages of the bridge arm submodules is compared with a preset value, so that the basis of system fault judgment is increased, and the system reliability is improved.
Drawings
Fig. 1 is a schematic structural diagram of a flexible straight converter valve provided in an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a controllable lightning arrester provided by an embodiment of the invention;
FIG. 3 is a flow chart of a conventional over-voltage protection logic for a converter valve provided by an embodiment of the present invention;
fig. 4 is a flowchart of an overvoltage stress control method for a flexible direct current converter valve according to an embodiment of the present invention;
FIG. 5 is a logic flow diagram for controlling over-voltage stress of a compliant converter valve according to an embodiment of the present invention;
fig. 6 is a block diagram of an overvoltage stress control device for a flexible direct current converter valve according to an embodiment of the present invention.
Reference numerals:
1. the device comprises a first detection module 2, a first judgment module 3, a control module 4, a second detection module 5 and a second judgment module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
Fig. 4 is a flowchart of a method for controlling overvoltage stress of a flexible direct current converter valve according to an embodiment of the present invention.
Fig. 5 is a logic flow diagram of an embodiment of an overvoltage stress control logic for a soft-dc converter valve.
Referring to fig. 4 and 5, a first aspect of an embodiment of the present invention provides a method for controlling an overvoltage stress of a flexible direct current converter valve, including: the flexible direct current converter valve is electrically connected with the controllable lightning arrester, and the method comprises the following steps:
and S200, acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct converter valve.
S400, judging whether the unbalanced voltage value exceeds a first preset voltage value or not, and judging whether the unbalanced current value exceeds a preset current value or not.
S600, when the unbalanced voltage value exceeds a first preset voltage value and/or the unbalanced current value exceeds a preset current value, controlling a control switch of the controllable lightning arrester to be closed to execute protection action.
And S800, when the unbalanced voltage value does not exceed a first preset voltage value and the unbalanced current value does not exceed a preset current value, controlling a control switch of the controllable lightning arrester to keep a disconnected state.
When the unbalanced voltage value exceeds a first preset voltage value and the unbalanced current value exceeds a preset current value, the unbalanced criterion is jointly determined by the voltage and current unbalance degree of the converter valve, and misoperation of the controllable lightning arrester caused by damage of measuring equipment, measurement errors or communication errors is prevented.
In particular, the unbalanced voltage UunbalanceThe calculation formula of (2) is as follows:
Uunbalance＝|uva+uvb+uvc|，
wherein u isva、uvb、uvcIs the three-phase alternating voltage on the valve side of the converter valve.
Specifically, the calculation formula of the unbalanced current is as follows:
Iunbalance＝|∑(iiu-iid)|，
wherein iiuIs a one-phase upper bridge arm current iidThe upper arm current direction is defined to be positive from the direct current side to the alternating current side, the lower arm current direction is defined to be positive from the alternating current side to the direct current side, and subscripts i are a, b, and c, for the lower arm current of the corresponding phase.
In an implementation manner of the embodiment of the present invention, before acquiring the unbalanced voltage and the unbalanced current on the valve side of the flexible direct current converter valve in step S200, the method further includes:
and S110, obtaining the maximum value of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valve.
And S120, judging whether the maximum value of the average value of the voltages of the bridge arm submodules is greater than or equal to a second preset voltage value or not.
And S130, controlling a control switch of the controllable lightning arrester to be closed to execute a protection action when the maximum value of the average voltage value of the bridge arm sub-modules is greater than or equal to a second preset voltage value.
And S140, when the maximum value of the average value of the voltages of the bridge arm sub-modules is smaller than a second preset voltage value, executing the step S200 to obtain the unbalanced voltage and the unbalanced current on the valve side of the flexible-straight converter valve.
Before judging the unbalanced voltage and the unbalanced current on the valve side of the flexible direct current converter valve, the maximum value of the average value of the voltages of the bridge arm sub-modules can be judged, and if the maximum value of the average value of the voltages of the bridge arm sub-modules exceeds a second preset voltage value, the controllable lightning arrester also needs to be started. The maximum value of the average value of the voltages of the bridge arm sub-modules is judged, so that the basis for judging the system fault is increased, and the safety of the system is improved.
Specifically, the maximum value U of the average value of the voltages of the bridge arm submodules of the flexible-straight converter valveave_maxThe calculation formula of (2) is as follows:
Uave_max＝max{Uiu_ave、Uid_ave}，
wherein, Uiu_aveIs the average value of the voltage of the bridge arm submodule on one phase, Uid_aveSubscript i is a, b and c, and is the average value of the voltage of the corresponding lower bridge arm submodule.
Specifically, the controllable arrester includes: the controllable component is connected with the fixed component in series; the control switch of the controllable arrester of control closes and carries out the protection action, includes: and controlling the control switch to be closed to enable the controllable component to be in short circuit. Wherein, the control component is an electronic switch or a rapid mechanical switch. The protection action executed by the controllable lightning arrester is used for short-circuiting the controllable component by controlling the closing of an electronic switch or a quick mechanical switch which is connected with the controllable component in parallel, and the fixed component is independently connected into the system to absorb redundant energy in the system so as to inhibit the overvoltage of the system.
Fig. 6 is a block diagram of an overvoltage stress control device for a flexible direct current converter valve according to an embodiment of the present invention.
Referring to fig. 5, a second aspect of the embodiments of the present invention provides an overvoltage stress control device for a flexible direct current converter valve, the flexible direct current converter valve being electrically connected to a controllable lightning arrester, the control device comprising: the device comprises a first detection module 1, a first judgment module 2 and a control module 3. The first detection module 1 is used for acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct current converter valve. The first judging module 2 is configured to judge whether the unbalanced voltage value exceeds a first preset voltage value, and judge whether the unbalanced current value exceeds a preset current value. The control module 3 is used for controlling a control switch of the controllable lightning arrester to be closed to execute a protection action when the unbalanced voltage value exceeds a first preset voltage value and/or the unbalanced current value exceeds a preset current value; the control module 3 is further configured to control the control switch of the controllable lightning arrester to maintain an off state when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value.
In particular, the unbalanced voltage UunbalanceThe calculation formula of (2) is as follows:
Uunbalance＝|uva+uvb+uvc|，
wherein u isva、uvb、uvcIs the three-phase alternating voltage on the valve side of the converter valve.
Specifically, the calculation formula of the unbalanced current is as follows:
Iunbalance＝|∑(iiu-iid)|，
wherein iiuIs a one-phase upper bridge arm current iidThe upper arm current direction is defined to be positive from the direct current side to the alternating current side, the lower arm current direction is defined to be positive from the alternating current side to the direct current side, and subscripts i are a, b, and c, for the lower arm current of the corresponding phase.
Referring to fig. 6, in an embodiment of the present invention, the apparatus for controlling overvoltage stress of a flexible direct current converter valve further includes: a second detection module 4 and a second judgment module 5. The second detection module 4 is used for obtaining the maximum value of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valve. The second judging module 5 is used for judging whether the maximum value of the average value of the voltages of the bridge arm sub-modules is larger than or equal to a second preset voltage value. The control module 3 is also used for controlling a control switch of the controllable lightning arrester to be closed to execute a protection action when the maximum value of the average voltage value of the bridge arm sub-modules is greater than or equal to a second preset voltage value; and when the maximum value of the average value of the voltages of the bridge arm sub-modules is smaller than a second preset voltage value, the control module 3 acquires unbalanced voltage and unbalanced current on the valve side of the flexible-straight converter valve.
Specifically, the maximum value U of the average value of the voltages of the bridge arm submodules of the flexible-straight converter valveave_maxThe calculation formula of (2) is as follows:
Uave_max＝max{Uiu_ave、Uid_ave}，
wherein, Uiu_aveIs the average value of the voltage of the bridge arm submodule on one phase, Uid_aveSubscript i is a, b and c, and is the average value of the voltage of the corresponding lower bridge arm submodule.
Specifically, in this embodiment, the controllable arrester includes: the controllable component is connected with the fixed component in series; the control module controls the closing of a control switch of the controllable lightning arrester to execute protection actions, and the control module comprises: and controlling the control switch to be closed to enable the controllable component to be in short circuit. Wherein, the control component is an electronic switch or a rapid mechanical switch.
The embodiment of the invention aims to protect an overvoltage stress control method of a flexible-straight converter valve, wherein the flexible-straight converter valve is electrically connected with a controllable lightning arrester, and the method comprises the following steps: acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct converter valve; judging whether the unbalanced voltage value exceeds a first preset voltage value or not and judging whether the unbalanced current value exceeds a preset current value or not; when the unbalanced voltage value exceeds a first preset voltage value and/or the unbalanced current value exceeds a preset current value, controlling a control switch of the controllable lightning arrester to be closed to execute a protection action; and when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value, controlling a control switch of the controllable lightning arrester to keep a disconnected state. The overvoltage stress control device of the flexible direct current converter valve is also protected. The technical scheme has the following effects:
whether a fault occurs or not is judged by detecting whether unbalanced voltage and/or unbalanced current on the valve side of the flexible-direct converter valve exceeds a preset value or not, so that a controllable lightning arrester can quickly execute protection action to reduce overvoltage stress of the flexible-direct converter valve when a serious fault occurs, waiting time for triggering voltage average value overvoltage protection fixed value of a submodule is not needed for a system submodule capacitor to absorb energy, the controllable lightning arrester can quickly execute protection action, time from the real occurrence of the fault to the effective input of the controllable lightning arrester is shortened, the controllable lightning arrester can absorb surplus power of the system in advance, and the flexible-direct converter valve is prevented from being damaged; in addition, the maximum value of the average value of the voltages of the bridge arm submodules is compared with a preset value, so that the basis of system fault judgment is increased, and the system reliability is improved.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.
Claims (10)
1. The overvoltage stress control method of the flexible direct current converter valve is characterized in that the flexible direct current converter valve is electrically connected with a controllable lightning arrester, and the method comprises the following steps:
acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct current converter valve;
judging whether the unbalanced voltage value exceeds a first preset voltage value or not, and judging whether the unbalanced current value exceeds a preset current value or not;
when the unbalanced voltage value exceeds the first preset voltage value and/or the unbalanced current value exceeds the preset current value, controlling a control switch of the controllable lightning arrester to be closed to execute a protection action;
and when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value, controlling a control switch of the controllable lightning arrester to keep a disconnected state.
2. The Flex direct current converter valve overvoltage stress control method according to claim 1,
the unbalanced voltage UunbalanceThe calculation formula of (2) is as follows:
Uunbalance＝|uva+uvb+uvc|，
wherein u isva、uvb、uvcIs three-phase alternating current voltage at the valve side of the converter valve;
the calculation formula of the unbalanced current is as follows:
Iunbalance＝|∑(iiu-iid)|，
wherein iiuIs a one-phase upper bridge arm current iidThe upper arm current direction is defined to be positive from the direct current side to the alternating current side, the lower arm current direction is defined to be positive from the alternating current side to the direct current side, and subscripts i are a, b, and c, for the lower arm current of the corresponding phase.
3. The limp-straight converter valve overvoltage stress control method according to claim 1, wherein before obtaining the valve side unbalanced voltage and the unbalanced current of the limp-straight converter valve, the method further comprises:
obtaining the maximum value of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valve;
judging whether the maximum value of the average value of the bridge arm submodule voltage is greater than or equal to a second preset voltage value or not;
when the maximum value of the average voltage value of the bridge arm sub-modules is greater than or equal to the second preset voltage value, controlling a control switch of the controllable lightning arrester to be closed to execute the protection action;
and when the maximum value of the average value of the bridge arm submodule voltages is smaller than the second preset voltage value, acquiring the unbalanced voltage and the unbalanced current on the valve side of the flexible-straight converter valve.
4. The Flex direct current converter valve overvoltage stress control method according to claim 3,
maximum value U of voltage average value of bridge arm submodule of flexible-straight converter valveave_maxThe calculation formula of (2) is as follows:
Uave_max＝max{Uiu_ave、Uid_ave}，
wherein, Uiu_aveIs the average value of the voltage of the bridge arm submodule on one phase, Uid_aveSubscript i is a, b and c, and is the average value of the voltage of the corresponding lower bridge arm submodule.
5. The flexible direct current converter valve overvoltage stress control method according to any one of claims 1 to 4, wherein the controllable lightning arrester comprises: the control switch comprises a fixed component, a controllable component and a control switch, wherein the fixed component and the controllable component are connected in series;
the control switch of controllable arrester of control closes and carries out the protection action, includes:
controlling the control switch to be closed to enable the controllable component to be in short circuit;
wherein, the control component is an electronic switch or a rapid mechanical switch.
6. An overvoltage stress control device for a flexible direct current converter valve, wherein the flexible direct current converter valve is electrically connected with a controllable lightning arrester, the control device comprising:
the first detection module is used for acquiring unbalanced voltage and unbalanced current on the valve side of the flexible direct current converter valve;
the first judgment module is used for judging whether the unbalanced voltage value exceeds a first preset voltage value or not and judging whether the unbalanced current value exceeds a preset current value or not;
the control module is used for controlling a control switch of the controllable lightning arrester to be closed to execute a protection action when the unbalanced voltage value exceeds the first preset voltage value and/or the unbalanced current value exceeds the preset current value;
the control module is further used for controlling a control switch of the controllable lightning arrester to keep an off state when the unbalanced voltage value does not exceed the first preset voltage value and the unbalanced current value does not exceed the preset current value.
7. The FLIP OVER-VOLTAGE STRESS CONTROL DEVICE OF claim 6,
the unbalanced voltage UunbalanceThe calculation formula of (2) is as follows:
Uunbalance＝|uva+uvb+uvc|，
wherein u isva、uvb、uvcIs three-phase alternating current voltage at the valve side of the converter valve;
the calculation formula of the unbalanced current is as follows:
Iunbalance＝|∑(iiu-iid)|，
wherein iiuIs a one-phase upper bridge arm current iidThe upper arm current direction is defined to be positive from the direct current side to the alternating current side, the lower arm current direction is defined to be positive from the alternating current side to the direct current side, and subscripts i are a, b, and c, for the lower arm current of the corresponding phase.
8. The limp direct converter valve overvoltage stress control device according to claim 6, further comprising:
the second detection module is used for obtaining the maximum value of the average value of the voltages of the bridge arm sub-modules of the flexible-straight converter valve;
the second judgment module is used for judging whether the maximum value of the average value of the voltages of the bridge arm sub-modules is greater than or equal to a second preset voltage value or not;
the control module is further configured to control a control switch of the controllable arrester to be closed to execute the protection action when the maximum value of the average voltage value of the bridge arm sub-modules is greater than or equal to the second preset voltage value, and obtain the unbalanced voltage and the unbalanced current on the valve side of the flexible direct current converter when the maximum value of the average voltage value of the bridge arm sub-modules is less than the second preset voltage value.
9. The limp direct converter valve overvoltage stress control device according to claim 8,
maximum value U of voltage average value of bridge arm submodule of flexible-straight converter valveave_maxThe calculation formula of (2) is as follows:
Uave_max＝max{Uiu_ave、Uid_ave}，
wherein, Uiu_aveIs the average value of the voltage of the bridge arm submodule on one phase, Uid_aveSubscript i is a, b and c, and is the average value of the voltage of the corresponding lower bridge arm submodule.
10. The soft DC converter valve overvoltage stress control device according to any one of claims 6 to 9,
the controllable arrester comprises: the control switch comprises a fixed component, a controllable component and a control switch, wherein the fixed component and the controllable component are connected in series;
the control module controls the control switch of the controllable lightning arrester to close and execute the protection action, and comprises:
controlling the control switch to be closed to enable the controllable component to be in short circuit;
wherein, the control component is an electronic switch or a rapid mechanical switch.
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