CN111273192B - Fault backup protection method and device for converter of flexible direct current transmission system - Google Patents
Fault backup protection method and device for converter of flexible direct current transmission system Download PDFInfo
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- CN111273192B CN111273192B CN202010194338.0A CN202010194338A CN111273192B CN 111273192 B CN111273192 B CN 111273192B CN 202010194338 A CN202010194338 A CN 202010194338A CN 111273192 B CN111273192 B CN 111273192B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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- H—ELECTRICITY
- 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
- H02H7/10—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 for converters; for rectifiers
- H02H7/12—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 for converters; for rectifiers for static converters or rectifiers
- H02H7/122—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 for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters
- H02H7/1225—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 for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters responsive to internal faults, e.g. shoot-through
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- H—ELECTRICITY
- 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
- H02H7/10—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 for converters; for rectifiers
- H02H7/12—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 for converters; for rectifiers for static converters or rectifiers
- H02H7/125—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 for converters; for rectifiers for static converters or rectifiers for rectifiers
- H02H7/1255—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 for converters; for rectifiers for static converters or rectifiers for rectifiers responsive to internal faults, e.g. by monitoring ripple in output voltage
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Abstract
The invention discloses a fault backup protection method for a converter of a flexible direct current transmission system, which comprises the following steps: step 1: collecting three-phase upper and lower bridge arm currents flowing through a voltage source type converter unit, and three-phase voltage source type converters and connecting variable lead currents; step 2: and (3) extracting and calculating the interphase short circuit characteristics of the converter region according to the analog quantities acquired in the step (1) and judging whether the converter region has an interphase short circuit fault. The invention also discloses a corresponding fault backup protection device for the converter of the flexible direct current transmission system. By adopting the technical scheme of the invention, the inter-phase short circuit fault in the voltage source type converter can be effectively detected.
Description
Technical Field
The invention belongs to the field of flexible direct current transmission, and particularly relates to a fault protection method and device for a converter of a flexible direct current transmission system.
Background
The Flexible direct current transmission system (Flexible-HVDC) can realize active power and reactive power decoupling control, can supply power to a passive network, has the advantages of compact structure, small occupied area, no problem of inversion side commutation failure and the like, and is more and more widely applied and more in Flexible direct current transmission engineering.
At present, there are two structures of a voltage source type converter in a flexible direct current transmission system: the first is that the bridge arm reactor is generally positioned between an alternating current connection point and a converter valve, the three-phase upper and lower bridge arm current transformers are positioned between the bridge arm reactor and the converter valve, and the three-phase voltage source type converter and the connection transformer lead current transformer can be positioned at any position of a lead, as shown in figure 1; the second is that the bridge arm reactor is positioned between the direct current positive pole common point or the negative pole common point and the converter valve, the three-phase upper and lower bridge arm current transformers are positioned between the bridge arm reactor and the converter valve, and the three-phase voltage source type converter and the connection variable lead wire current transformer can be positioned at any position of the lead wire, as shown in figure 2; no matter which bridge arm reactor and the bridge arm formed by the converter valve are arranged between the direct current positive pole common point and the negative pole common point.
When an interphase short-circuit fault occurs in the voltage source type converter shown in fig. 1 and 2, namely, between a dc positive common point and a negative common point, especially a slight interphase short-circuit fault occurs, the fault current is small, the currently configured main protection mainly adopts differential and overcurrent quick-break, and is likely not to act and does not have a fault phase identification function, and in addition, a continuous slight short-circuit fault may further deteriorate into a serious short-circuit fault, which may cause damage to equipment such as a converter valve and a bridge arm reactor. Therefore, the invention provides a fault backup protection method for a converter of a flexible direct current transmission system, which can effectively detect an inter-phase short circuit fault in a voltage source type converter and identify a fault phase of the voltage source type converter.
Disclosure of Invention
The purpose of the invention is: the method and the device for fault backup protection of the converter of the flexible direct-current transmission system can solve the problem that inter-phase short circuit faults, particularly slight inter-phase short circuit faults, in the voltage source type converter are difficult to identify. Further preferred solutions also solve the problem of difficulty in locating the fault.
In order to achieve the purpose, the invention adopts the following technical scheme:
a fault backup protection method for a converter of a flexible direct current transmission system is used for the direct current transmission system comprising at least one group of voltage source type converter units, wherein a bridge arm reactor and a converter valve of each bridge arm of each voltage source type converter unit are positioned between a direct current positive common point and a negative common point, and the method comprises the following steps:
step 1: collecting three-phase upper and lower bridge arm currents flowing through a voltage source type converter unit, and three-phase voltage source type converters and connecting variable lead currents;
step 2: and (3) extracting and calculating the interphase short circuit characteristics of the converter region according to the analog quantities acquired in the step (1) and judging whether the converter region has an interphase short circuit fault.
In a further preferred scheme, the step 2 further includes judging the phase with the fault according to the interphase short-circuit characteristics of the converter region.
In a further preferred scheme, the method further comprises the following step 3: if the interphase short circuit fault occurs in the converter region, the voltage source type converter is locked and the alternating current incoming line breaker connected with the voltage source type converter is tripped after the preset time delay.
In a further preferred embodiment, the inter-phase short-circuit fault feature of the converter region in step 2 includes: the peak value after the absolute value calculation is carried out on the three-phase upper bridge arm current, the peak value after the absolute value calculation is carried out on the three-phase lower bridge arm current, and the peak value after the absolute value calculation is carried out on the three-phase voltage source type current converter and the connection variable lead current.
In a further preferred embodiment, in step 2, the peak value after the absolute value calculation of the current of the upper three-phase bridge arm, the peak value after the absolute value calculation of the current of the lower three-phase bridge arm, or the peak value after the absolute value calculation of the current of the three-phase voltage source type converter and the connecting transformation lead is determined to be an interphase short-circuit fault in the converter region, where the peak values of any two phases are greater than a set current threshold.
In a further preferred embodiment, when any one of the following conditions is satisfied, it is determined that an inter-phase short-circuit fault occurs in the converter region:
1) after the absolute value of the current of the upper bridge arm of the three phases is calculated, the peak value of any two phases is larger than a first current fixed value, the widening time T is longer and the duration time exceeds a first detection time fixed value;
2) after the absolute value of the current of the three-phase lower bridge arm is calculated, the peak value of any two phases is larger than a second current fixed value, the widening time T is longer than a second detection time fixed value, and the duration time exceeds a second detection time fixed value;
3) after the absolute value of the current of the three-phase voltage source type current converter and the connecting variable lead is calculated, the peak value of any two phases is larger than the third current fixed value, the widening time T is prolonged, and the duration time exceeds the third detection time fixed value.
In a further preferred embodiment, the peak value after the absolute value calculation of the current of the three-phase upper bridge arm, or the peak value after the absolute value calculation of the current of the three-phase lower bridge arm, or the peak value after the absolute value calculation of the current of the three-phase voltage source type converter and the connecting variable lead wire, if a certain phase peak value is the minimum phase peak value in the three-phase peak values, it is determined that an inter-phase short circuit fault occurs in the other two phases.
In a further preferred scheme, the phase with the fault is judged by adopting any one of the following modes:
mode 1) after the absolute value of the current of the upper bridge arm of the three phases is calculated, if the M-phase peak value is the minimum peak value of the three phases, the other two phases are judged to have an interphase short circuit fault, and M refers to any one of the three phases;
mode 2) after the absolute value of the current of the three-phase lower bridge arm is calculated, if the M-phase peak value is the minimum phase peak value in the three-phase peak values, judging that the other two phases have an interphase short circuit fault, wherein M refers to any one of the three phases;
mode 3) after the three-phase voltage source type converter and the connecting variable lead wire current take absolute values to operate, if the M-phase peak value is the minimum phase peak value in the three-phase peak values, the other two phases are judged to have the interphase short circuit fault, and M refers to any one of the three phases.
In a further preferred embodiment, the stretch time T ranges from 0ms to a power frequency cycle of the ac system.
In a further preferred scheme, the first current fixed value, the second current fixed value and the third current fixed value are respectively larger than a peak value of three-phase upper bridge arm current, a peak value of three-phase lower bridge arm current and a peak value of three-phase voltage source type current converter and connection transformation lead current which are calculated according to a flexible direct current conversion formula according to a current running direct current instruction value of the converter station.
The invention also provides a fault backup protection device for the converter of the flexible direct current transmission system, which is used for the direct current transmission system comprising at least one group of voltage source type converter units, wherein a bridge arm reactor and a converter valve of each bridge arm of each voltage source type converter unit are positioned between a direct current positive common point and a direct current negative common point, and the device comprises:
a fault acquisition unit: collecting three-phase upper and lower bridge arm currents flowing through a voltage source type converter unit, and three-phase voltage source type converters and connecting variable lead currents;
a judging unit: and extracting and calculating the interphase short-circuit characteristics of the converter region according to the analog quantities acquired by the fault acquisition unit and judging whether the converter region has an interphase short-circuit fault.
In a further preferred embodiment, the determining unit further determines the phase type of the fault according to an inter-phase short circuit characteristic of the converter region.
In a further preferred scheme, the system further comprises a processing unit, and if the judging unit confirms that an interphase short circuit fault occurs in the converter region, the voltage source type converter is locked and an alternating current incoming line breaker connected with the voltage source type converter is tripped after preset time delay.
In a further preferred embodiment, the determining unit determines an inter-phase short-circuit fault characteristic of the converter region, including: the peak value after the absolute value calculation is carried out on the three-phase upper bridge arm current, the peak value after the absolute value calculation is carried out on the three-phase lower bridge arm current, and the peak value after the absolute value calculation is carried out on the three-phase voltage source type current converter and the connection variable lead current.
In a further preferred embodiment, in the determining unit, the peak value after the absolute value calculation of the three-phase upper bridge arm current, the peak value after the absolute value calculation of the three-phase lower bridge arm current, or the peak value after the absolute value calculation of the three-phase voltage source type converter and the connecting transformation lead current is determined to be that an interphase short circuit fault occurs in the converter region, where the peak values of any two phases are greater than a set current threshold.
In a further preferred embodiment, in the determining unit, the peak value after the absolute value calculation of the three-phase upper bridge arm current, or the peak value after the absolute value calculation of the three-phase lower bridge arm current, or the peak value after the absolute value calculation of the three-phase voltage source type converter and the connecting transformation lead current is performed, if a certain phase peak value is the smallest phase peak value among the three-phase peak values, it is determined that an inter-phase short circuit fault occurs in the other two phases.
The invention has the beneficial effects that: by adopting the technical scheme of the invention, the inter-phase short circuit fault in the voltage source type converter can be effectively detected, and further, the preferred scheme can also effectively identify the fault phase of the voltage source type converter.
Drawings
Fig. 1 is a schematic diagram of a flexible dc voltage source type converter structure 1;
fig. 2 is a schematic diagram of a flexible dc voltage source type converter structure 2;
fig. 3 is a flowchart of an embodiment of a method for fault backup protection of a converter of a flexible dc power transmission system according to the present application;
fig. 4 is a flowchart of another embodiment of a method for fault backup protection of a converter of a flexible dc power transmission system according to the present application;
fig. 5 is a schematic diagram of an embodiment of a converter fault backup protection device of a flexible direct current transmission system according to the present application;
fig. 6 is a schematic diagram of another embodiment of the converter fault backup protection device of the flexible direct current transmission system according to the present application.
Detailed Description
The present invention will be better understood and implemented by those skilled in the art by the following detailed description of the technical solution of the present invention with reference to the accompanying drawings and specific examples, which are not intended to limit the present invention.
Fig. 3 is a flowchart of an embodiment of a method for fault backup protection of a converter of a flexible direct current transmission system according to the present invention, including the following steps:
step 1: the three-phase upper and lower bridge arm currents flowing through the voltage source type current converter unit, the three-phase voltage source type current converter and the connection variable lead current are collected.
Step 2: and (3) extracting and calculating the interphase short circuit characteristics of the converter region according to the analog quantities acquired in the step (1) and judging whether the converter region has an interphase short circuit fault.
Wherein, interphase short-circuit fault characteristics include: the peak value after the absolute value calculation is carried out on the three-phase upper bridge arm current, the peak value after the absolute value calculation is carried out on the three-phase lower bridge arm current, and the peak value after the absolute value calculation is carried out on the three-phase voltage source type current converter and the connection variable lead current.
The method for judging the interphase short-circuit fault comprises the following steps: and judging that the interphase short-circuit fault occurs in the converter region when the peak value obtained by the absolute value calculation of the three-phase upper bridge arm current, the peak value obtained by the absolute value calculation of the three-phase lower bridge arm current, or the peak value obtained by the absolute value calculation of the three-phase voltage source type converter and the connecting variable lead current is larger than a set current threshold value.
In a preferred embodiment, it is determined that an inter-phase short-circuit fault occurs in the converter region when any one of the following conditions is satisfied:
1) after the absolute value of the current of the upper bridge arm of the three phases is calculated, the peak value of any two phases is larger than a first current fixed value, the widening time T is longer and the duration time exceeds a first detection time fixed value;
2) after the absolute value of the current of the three-phase lower bridge arm is calculated, the peak value of any two phases is larger than a second current fixed value, the widening time T is longer than a second detection time fixed value, and the duration time exceeds a second detection time fixed value;
3) after the absolute value of the current of the three-phase voltage source type current converter and the connecting variable lead is calculated, the peak value of any two phases is larger than the third current fixed value, the widening time T is prolonged, and the duration time exceeds the third detection time fixed value.
The widening time T value taking principle when the interphase short circuit fault occurs in the converter region is confirmed to be as follows: the broadening time T range is between 0ms and the power frequency cycle of the alternating current system, and the power frequency cycle of the 50Hz alternating current system is 20 ms; the power frequency cycle of a 60Hz AC system is 16.67 ms. The first current fixed value, the second current fixed value and the third current fixed value are respectively larger than a peak value of three-phase upper bridge arm current, a peak value of three-phase lower bridge arm current and a peak value of three-phase voltage source type current converter and connection variable lead current which are calculated according to a flexible direct current conversion formula according to a current running direct current instruction value of the converter station.
In a preferred embodiment, on the basis of the above embodiment, the step 2 further includes determining the phase with the fault according to the inter-phase short circuit characteristics of the converter region. The specific phase identification method comprises the following steps: and if a certain phase peak value is the minimum phase peak value in the three-phase peak values, judging that the other two phases have the interphase short circuit fault.
In a preferred embodiment, the phase of the fault is determined by any one of the following methods:
mode 1) after the absolute value of the current of the upper bridge arm of the three phases is calculated, if the M-phase peak value is the minimum peak value of the three phases, the other two phases are judged to have an interphase short circuit fault, and M refers to any one of the three phases;
mode 2) after the absolute value of the current of the three-phase lower bridge arm is calculated, if the M-phase peak value is the minimum phase peak value in the three-phase peak values, judging that the other two phases have an interphase short circuit fault, wherein M refers to any one of the three phases;
mode 3) after the three-phase voltage source type converter and the connecting variable lead wire current take absolute values to operate, if the M-phase peak value is the minimum phase peak value in the three-phase peak values, the other two phases are judged to have the interphase short circuit fault, and M refers to any one of the three phases.
In a preferred embodiment, as shown in fig. 4, on the basis of the above embodiment, the method further includes step 3: if the interphase short circuit fault occurs in the converter region, the voltage source type converter is locked and the alternating current incoming line breaker connected with the voltage source type converter is tripped after the preset time delay.
The following describes a second embodiment with reference to fig. 1:
for example, as shown in fig. 1, assuming that the operation is performed by a dc current command 1000A, the dc voltage is 500KV, and the voltage of the secondary side of the coupling transformer is 300KV, the calculation is performed according to a flexible dc current conversion formula:
the peak value of the three-phase upper bridge arm current is equal to:
the peak value of the three-phase lower bridge arm current is equal to:
when no fault exists, the peak value of the current of the three-phase voltage source type converter and the connecting transformer lead is equal to:
when an F3AB fault occurs, the phase A current of the upper bridge arm, the phase B current of the upper bridge arm, the phase A current of the lower bridge arm, the phase A current of the voltage source type converter and the connecting variable lead wire and the phase B current of the voltage source type converter and the connecting variable lead wire are increased, the peak value of the phase A current of the upper bridge arm is larger than a first current fixed value, and the peak value of the phase B current of the upper bridge arm is larger than the first current fixed value; the peak value of the phase current of the lower bridge arm A is larger than the second current fixed value, and the peak value of the phase current of the lower bridge arm B is larger than the second current fixed value; the peak value of the phase current of the voltage source type converter and the connecting variable lead wire A is larger than a third current fixed value, the peak value of the phase current of the voltage source type converter and the connecting variable lead wire B is larger than a third current fixed value, wherein the first current fixed value is larger than the peak value of the three-phase upper bridge arm current when no fault exists, the second current fixed value is larger than the peak value of the three-phase lower bridge arm current when no fault exists, and the third current fixed value is larger than the peak value of the three-phase voltage source type converter and the connecting variable lead wire current when no fault exists.
Then, calculating the minimum values of the phase current A of the upper bridge arm, the phase current B of the upper bridge arm and the phase current C of the upper bridge arm, and if the phase current C of the upper bridge arm is minimum, judging that the phase A and the phase B have an interphase short circuit fault;
calculating the minimum values of the phase current A of the lower bridge arm, the phase current B of the lower bridge arm and the phase current C of the lower bridge arm, and if the phase current C of the lower bridge arm is minimum, judging that the phase A and the phase B have an interphase short circuit fault;
the minimum values of the phase current of the voltage source type converter and the connecting variable lead wire A, the phase current of the voltage source type converter and the connecting variable lead wire B and the phase current of the voltage source type converter and the connecting variable lead wire C are calculated, and if the phase current of the voltage source type converter and the phase current of the connecting variable lead wire C is minimum, the phase short circuit fault between the phase A and the phase B can be judged.
The method is used for a direct current transmission system comprising at least one group of voltage source type converter units, wherein bridge arm reactors and converter valves of each bridge arm of each voltage source type converter unit are located between a direct current positive pole common point and a negative pole common point. By adopting the method, the internal interphase short-circuit fault of the voltage source type converter can be effectively detected.
Fig. 5 shows an embodiment of the converter fault backup protection device for a flexible direct current transmission system according to the present application, which includes: the device comprises a fault acquisition unit and a judgment unit.
A fault acquisition unit: the three-phase upper and lower bridge arm currents flowing through the voltage source type current converter unit, the three-phase voltage source type current converter and the connection variable lead current are collected.
A judging unit: and extracting and calculating the interphase short-circuit characteristics of the converter region according to the analog quantities acquired by the fault acquisition unit and judging whether the converter region has an interphase short-circuit fault. The interphase short-circuit fault characteristics of the converter region include: the peak value after the absolute value calculation is carried out on the three-phase upper bridge arm current, the peak value after the absolute value calculation is carried out on the three-phase lower bridge arm current, and the peak value after the absolute value calculation is carried out on the three-phase voltage source type current converter and the connection variable lead current. And judging that the interphase short-circuit fault occurs in the converter region when the peak value obtained by the absolute value calculation of the three-phase upper bridge arm current, the peak value obtained by the absolute value calculation of the three-phase lower bridge arm current, or the peak value obtained by the absolute value calculation of the three-phase voltage source type converter and the connecting variable lead current is larger than a set current threshold value.
In a preferred embodiment, the determining unit further determines the phase with the fault according to the interphase short-circuit characteristics of the converter region. And if a certain phase peak value is the minimum phase peak value in the three-phase peak values, judging that the other two phases have the interphase short circuit fault.
In another embodiment shown in fig. 6, the protection device further includes a processing unit, and if it is determined that an inter-phase short circuit fault occurs in the converter region in the determining unit, the processing unit locks the voltage source converter and trips an ac incoming line breaker connected to the voltage source converter after a preset delay.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (12)
1. A method for fault backup protection of a converter of a flexible dc power transmission system, the method being used in a dc power transmission system comprising at least one set of voltage source converter cells, the bridge arm reactors and converter valves of each bridge arm of the voltage source converter cells being located between a dc positive common point and a dc negative common point, the method comprising the steps of:
step 1: collecting three-phase upper and lower bridge arm currents flowing through a voltage source type converter unit, and three-phase voltage source type converters and connecting variable lead currents;
step 2: extracting and calculating the interphase short-circuit characteristics of the converter region according to the analog quantities acquired in the step 1, judging whether the converter region has an interphase short-circuit fault or not, and judging the phase with the fault according to the interphase short-circuit characteristics of the converter region;
the phase judging the fault according to the interphase short circuit characteristics of the converter region specifically comprises: and if a certain phase peak value is the minimum phase peak value in the three-phase peak values, judging that the other two phases have the interphase short circuit fault.
2. The method for fault backup protection of a converter of a flexible direct current transmission system according to claim 1, further comprising the step 3: if the interphase short circuit fault occurs in the converter region, the voltage source type converter is locked and the alternating current incoming line breaker connected with the voltage source type converter is tripped after the preset time delay.
3. The method according to claim 1, wherein the interphase short-circuit fault signature of the converter region in step 2 comprises: the peak value after the absolute value calculation is carried out on the three-phase upper bridge arm current, the peak value after the absolute value calculation is carried out on the three-phase lower bridge arm current, and the peak value after the absolute value calculation is carried out on the three-phase voltage source type current converter and the connection variable lead current.
4. The method for fault backup protection of the converter of the flexible direct current transmission system according to claim 3, wherein in the step 2, the peak value after the absolute value calculation of the current of the upper three-phase bridge arm, the peak value after the absolute value calculation of the current of the lower three-phase bridge arm, or the peak value after the absolute value calculation of the current of the three-phase voltage source type converter and the connecting variable lead is determined, and the peak value of any two phases is greater than a set current threshold, and it is determined that the interphase short circuit fault occurs in the converter region.
5. The method for fault backup protection of the converter of the flexible direct current transmission system according to claim 4, characterized by specifically determining that an interphase short circuit fault occurs in the converter region when any one of the following conditions is satisfied:
1) after the absolute value of the current of the upper bridge arm of the three phases is calculated, the peak value of any two phases is larger than a first current fixed value, the widening time T is longer and the duration time exceeds a first detection time fixed value;
2) after the absolute value of the current of the three-phase lower bridge arm is calculated, the peak value of any two phases is larger than a second current fixed value, the widening time T is longer than a second detection time fixed value, and the duration time exceeds a second detection time fixed value;
3) after the absolute value of the current of the three-phase voltage source type current converter and the connecting variable lead is calculated, the peak value of any two phases is larger than the third current fixed value, the widening time T is prolonged, and the duration time exceeds the third detection time fixed value.
6. The method for fault backup protection of the converter of the flexible direct current transmission system according to claim 1, wherein the phase with the fault is determined by any one of the following methods:
mode 1) after the absolute value of the current of the upper bridge arm of the three phases is calculated, if the M-phase peak value is the minimum peak value of the three phases, the other two phases are judged to have an interphase short circuit fault, and M refers to any one of the three phases;
mode 2) after the absolute value of the current of the three-phase lower bridge arm is calculated, if the M-phase peak value is the minimum phase peak value in the three-phase peak values, judging that the other two phases have an interphase short circuit fault, wherein M refers to any one of the three phases;
mode 3) after the three-phase voltage source type converter and the connecting variable lead wire current take absolute values to operate, if the M-phase peak value is the minimum phase peak value in the three-phase peak values, the other two phases are judged to have the interphase short circuit fault, and M refers to any one of the three phases.
7. The method of claim 5, wherein the dwell time T ranges from 0ms to a power frequency period of the AC system.
8. The method according to claim 5, wherein the first current fixed value, the second current fixed value and the third current fixed value are respectively larger than a peak value of three-phase upper bridge arm current, a peak value of three-phase lower bridge arm current and a peak value of three-phase voltage source type converter and connecting transformer lead current which are calculated according to a flexible direct current conversion formula according to a current running direct current command value of the converter station.
9. A flexible dc power transmission system converter fault backup protection arrangement for a dc power transmission system comprising at least one set of voltage source converter cells, the bridge arm reactors and converter valves of each bridge arm of said voltage source converter cells being located between a dc positive common and a negative common, the arrangement comprising:
a fault acquisition unit: collecting three-phase upper and lower bridge arm currents flowing through a voltage source type converter unit, and three-phase voltage source type converters and connecting variable lead currents;
a judging unit: extracting and calculating interphase short-circuit characteristics of the converter region according to the analog quantities acquired by the fault acquisition unit, judging whether the converter region has an interphase short-circuit fault or not, and judging the phase with the fault according to the interphase short-circuit characteristics of the converter region;
the phase judging unit judges the phase with the fault according to the interphase short-circuit characteristics of the converter area specifically comprises the peak value obtained after the absolute value calculation of the current of the upper bridge arm of the three phases is carried out, or the peak value obtained after the absolute value calculation of the current of the lower bridge arm of the three phases is carried out, or the peak value obtained after the absolute value calculation of the current of the three-phase voltage source type converter and the connecting variable lead is carried out, and if a certain phase peak value is the minimum phase peak value in the three-phase peak values, the other two phases are judged to have the interphase short-circuit fault.
10. The device according to claim 9, further comprising a processing unit, wherein if the determining unit determines that the converter region has an inter-phase short circuit fault, the processing unit locks the voltage source converter and trips an ac incoming line breaker connected to the voltage source converter after a predetermined delay.
11. The converter fault backup protection device of claim 9, wherein the determining of the interphase short-circuit fault characteristics of the converter region in the unit comprises: the peak value after the absolute value calculation is carried out on the three-phase upper bridge arm current, the peak value after the absolute value calculation is carried out on the three-phase lower bridge arm current, and the peak value after the absolute value calculation is carried out on the three-phase voltage source type current converter and the connection variable lead current.
12. The converter fault backup protection device according to claim 11, wherein the determination unit determines that an inter-phase short circuit fault occurs in the converter region, when a peak value obtained by calculating an absolute value of a current of an upper three-phase arm, a peak value obtained by calculating an absolute value of a current of a lower three-phase arm, or a peak value obtained by calculating an absolute value of a current of a three-phase voltage source converter and a connecting variable lead is larger than a predetermined current threshold.
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