CN107346003B - Voltage source converter fault detection and positioning method and system - Google Patents
Voltage source converter fault detection and positioning method and system Download PDFInfo
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- CN107346003B CN107346003B CN201610296443.9A CN201610296443A CN107346003B CN 107346003 B CN107346003 B CN 107346003B CN 201610296443 A CN201610296443 A CN 201610296443A CN 107346003 B CN107346003 B CN 107346003B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/40—Testing power supplies
- G01R31/42—AC power supplies
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
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Abstract
The invention discloses a method and a system for detecting and positioning faults of a voltage source converter, and particularly provides a method for positioning a network side ground fault in a voltage source converter topology of a voltage source converter which is connected into a direct current power grid in a transformerless mode in a flexible direct current transmission system. Under the condition of locking the current converter for a short time, the zero sequence voltage of the current converter at two sides is detected, if the current converter is of a full-bridge structure, the zero sequence grounding current can be ensured not to be transmitted to an opposite side current converter station through a direct current side in a short-time full-closed locking or semi-closed locking mode, the half-bridge structure can detect the size of the zero sequence voltage output by the single-side current converter in a short-time locking mode, the zero sequence voltage is larger than a given value and exceeds a certain anti-jitter delay to judge that the current converter is a fault side.
Description
Technical Field
The invention belongs to the technical field of flexible alternating current and direct current transmission of a power system, and particularly relates to a method and a system for positioning a network side ground fault in a voltage source converter topology which is connected into a direct current power grid in a transformerless mode in a flexible direct current transmission system.
Background
In a modern alternating-current power distribution network, on one hand, the load density of a large city is continuously increased, the scale of a power transmission and distribution network is continuously enlarged, and the problems of short-circuit capacity, an electromagnetic ring network and the like are caused, the power distribution network generally adopts a high-voltage partition and medium-voltage open-loop operation mode, so that the utilization rate of system equipment is low, the reliability is reduced, on the other hand, the requirements of customers on power supply reliability and power quality are continuously improved, the sensitive load in the large city is gradually increased, and the short-time power supply interruption can bring large economic loss and even serious social. The flexible direct current transmission adopts a voltage source converter, active and reactive transmission can be independently adjusted, the flexible direct current technology is one of effective means for solving the problems of the existing power distribution network, the flexible direct current transmission can realize interconnection of an alternating current power grid under the condition of not increasing short-circuit capacity, the closed loop operation of the alternating current power grid is realized, the operation reliability of the power grid is improved, and the power quality and the operation efficiency of the power grid are improved.
The alternating current-direct current interconnected power grid based on flexible direct current transmission and distribution is one of the trends of power grid development, the voltage-sharing problem and the large loss problem which are puzzled on the basis of two-level flexible direct current transmission development are solved based on the development of a modular multi-level technology, and meanwhile, the harmonic waves of an alternating current system are reduced, so that the connection of the alternating current system without a transformer becomes possible. Thereby making it possible to reduce the total investment and volume of the converter station.
When the voltage source converter of the flexible direct current transmission system is connected into a power grid in a transformerless mode, when an alternating current system breaks down, the fault characteristics of the half-bridge MMC and the full-bridge MMC are similar, and the flexible ring network control device cannot isolate a zero sequence. For example, for an AG (single phase ground) fault, the non-fault phase voltage has a phase voltage boosted to a line voltage, and the ABC three-phase currents remain symmetrical. The converter station 2 can also show the fault characteristics of single-phase earth faults, the power frequency common mode alternating current component appears in direct current voltage, the control systems on two sides can not predict which side the fault occurs, thereby starting the fault control strategy to inhibit the zero sequence component, the common regulation and inhibition results on two sides can be caused to appear, because the zero sequence current components on two sides are actually the same in nature, the inhibition effects on two sides can be finally offset because the asynchronous relation of the current loops on two sides is regulated, therefore, the fault detection and positioning are needed, and on the basis of accurately positioning the fault side, the zero sequence component inhibiting mode by matching of two sides is determined.
Disclosure of Invention
The invention aims to provide a network side earth fault positioning method in a voltage source converter topology of a transformer-free mode access direct current power grid in a flexible direct current transmission system. If the fault side can not be judged by the differential current calculation method, and if the zero sequence voltage at the alternating current side is detected at the same time, the zero sequence voltage of the converters at the two sides is detected under the condition of short-time blocking of the converters. And judging the actual ground fault occurrence side by comparing the magnitude of the zero sequence voltage of each station.
In order to achieve the purpose, the invention adopts the technical scheme that:
calculating the difference current between the current of the bridge arm reactor and the current of the network side, wherein the difference current is larger than a given value △ IsetExceeding a certain anti-jitter delay △ t1Judging as fault side, the difference flow is less than the given value △ IsetThe side is judged to be a non-fault side, and the positioning mode can be carried out under the condition of not locking the converter, wherein △ t1The value range is 0-5 s.
The lateral fault location method is suitable for the following neutral point grounding modes of an alternating current system: 1) the neutral point is not grounded; 2) the neutral point is grounded through a resistor; 3) the neutral point is grounded through an arc suppression coil, wherein the converter topology can be a half bridge, a full bridge or similar full bridge structure or a hybrid bridge arm structure of a half bridge and a full bridge or similar full bridge.
According to the network side ground fault positioning method, when a single-phase ground fault occurs at one end of the converter, the fault side can be positioned in a differential current detection mode under the conditions of two-phase ground faults and three-phase ground faults.
According to the network side ground fault positioning method, if the network side ground fault positioning method is a full-bridge structure, zero-sequence ground current can be guaranteed not to be transmitted to an opposite-side converter station through a direct current side in a short-time full-closed locking or semi-closed locking mode, and the half-bridge structure can detect the size of zero-sequence voltage output by an alternating current side in a short-time locking mode, wherein the size of the zero-sequence voltage is larger than a given value of △ UsetExceed a certain anti-jitter delay △ t2Side is judged as fault side, and the other sides are non-fault sides, wherein △ t2The value range is 0-5 s.
A network side earth fault positioning system comprises a current detection unit and a zero sequence voltage detection unitThe current detection unit detects the magnitude of the current at the network side and the current at the bridge arm, the zero sequence voltage detection unit detects the magnitude of the output zero sequence voltage, the logic comparison unit calculates the magnitude of the differential current between the two, and calculates the magnitude of the zero sequence voltage output by the current converter under the locking condition, the logic comparison unit calculates the magnitude of the differential current between the two, and the differential current is larger than a given value △ IsetExceeding a certain anti-jitter delay △ t1Judging as fault side, the difference flow is less than the given value △ IsetJudging the side as a non-fault side, and comparing the magnitude of the zero-sequence voltage of the alternating current side under the condition of locking the converter for a short time to be greater than a given value △ UsetAnd judging that the side exceeding a certain anti-jitter delay △ t2 is a fault side, and the other sides are non-fault sides, wherein the value range of △ t2 is 0-5 s.
After the scheme is adopted, the invention has the beneficial effects that:
(1) the multiple composite detection modes can conveniently detect one end of the converter with the grounding short circuit at the AC network side in the DC network, and facilitate the starting of a zero-sequence voltage or current suppression strategy at the converter side.
(2) After the method judges the fault side, all converters can be matched with each other in the control system to achieve the aim of jointly inhibiting zero-sequence current or voltage. The fault current component in the system is well inhibited, and the normal operation of each converter of the direct-current power grid is guaranteed.
Drawings
Fig. 1 is a schematic diagram of grid-side fault points k1 and k2 when two-terminal converters are connected in a transformerless dc mode.
Fig. 2 is a topology of the converter of the present invention, wherein the bridge arm modules can be Half Bridge (HBSM), Full Bridge (FBSM) or internal full bridge (SFBSM).
Detailed Description
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention aims to provide a method for positioning a network side earth fault in a voltage source converter topology of a voltage source converter which is connected into a direct current power network in a transformerless mode in a flexible direct current transmission system, which comprises the steps of detecting fault current, comparing the current magnitude of a bridge arm reactor with the measured current magnitude of a network side current transformer, calculating the magnitude of differential current between the bridge arm reactor and the network side current transformer according to the current direction of the bridge arm and the current direction of the network side, considering that the side is changed into the fault side when the differential current is larger than a given value, directly detecting the magnitude of output zero sequence voltage of a single-side converter in a short-time locked converter state, judging the fault side when the differential current is larger than the given value and exceeds a certain anti-jitter delay, detecting the zero sequence voltage of the two-side converters under the condition of short-time locked converter, and ensuring that the zero sequence earth current cannot be transmitted to an opposite, the half-bridge structure can detect the output zero sequence voltage of the single-side converter in a short-time locking mode, and the output zero sequence voltage is larger than a given value and exceeds a certain anti-jitter delay time to be judged as a fault side.
In order to achieve the above purpose, the solution of the invention is:
the method comprises the steps of detecting fault current, comparing the current of a bridge arm reactor with the current of a network side, calculating the magnitude of differential current between the bridge arm reactor and the network side according to the current direction of the bridge arm and the current direction of the network side, and judging the actual ground fault occurrence side by comparing the magnitude of the differential current of each stationsetExceeding a certain anti-jitter delay △ t1Judging as fault side, the difference flow is less than the given value △ IsetThe side is judged to be a non-fault side, and the positioning mode can be carried out under the condition of not locking the converter, wherein △ t1The value range is 0-5 s.
If the fault side can not be judged by the differential flow calculation method, if the zero sequence voltage on the alternating current side is detected at the same time,the method comprises the specific implementation mode that if the converter is in a full-bridge structure, the zero-sequence grounding current can be ensured not to be transmitted to the opposite converter station through the direct current side in a short-time full-closed locking or semi-closed locking mode, and the half-bridge structure can detect the output zero-sequence voltage of the alternating current side in a short-time locking mode, wherein the output zero-sequence voltage of the alternating current side is greater than a given value of △ UsetExceed a certain anti-jitter delay △ t2Side is judged as fault side, and the other sides are non-fault sides, wherein △ t2The value range is 0-5 s.
The lateral fault location method is applied to the following neutral point grounding methods of an alternating current system: 1) the neutral point is not grounded; 2) the neutral point is grounded through a resistor; 3) the neutral point is grounded through an arc suppression coil, wherein the converter topology can be a half bridge, a full bridge or similar full bridge structure or a hybrid bridge arm structure of a half bridge and a full bridge or similar full bridge.
The specific implementation scheme of the network side earth fault positioning system is as follows: the system comprises a current detection unit, a zero sequence voltage detection unit, a logic comparison unit and a fault detection positioning unit.
The current detection unit detects the magnitude of the current at the network side and the current of the bridge arm, the zero sequence voltage detection unit detects the magnitude of the output zero sequence voltage, the logic comparison unit calculates the magnitude of the difference current between the current detection unit and the bridge arm, and calculates the magnitude of the output zero sequence voltage of the current converter under the locking condition, the logic comparison unit calculates the magnitude of the difference current between the current detection unit and the bridge arm, and the difference current is larger than a given value △ IsetExceeding a certain anti-jitter delay △ t1Judging as fault side, the difference flow is less than the given value △ IsetJudging the side as non-fault side, and detecting the output zero sequence voltage of the single-side converter to be greater than a given value △ U under the condition of short-time blocking of the convertersetExceed a certain anti-jitter delay △ t2Side is judged as fault side, and the other sides are non-fault sides, wherein △ t2The value range is 0-5 s. The fault detection positioning unit combines the two comparison results, firstly detects the magnitude of the differential flow to judge the fault side, and if the fault side can not pass through the differential flowThe differential current calculation method judges the fault side, if the zero sequence voltage of the alternating current side is detected at the same time, the short-time locked converter is started immediately, and the size of the zero sequence voltage of the converters at two sides is detected. And judging the actual ground fault occurrence side by comparing the magnitude of the zero sequence voltage of each station.
Claims (6)
1. A fault detection and positioning method for a voltage source converter is characterized in that fault current is detected, bridge arm current and network side current are compared, difference current between the bridge arm current and the network side current is calculated according to the bridge arm current direction and the network side current direction, the actual ground fault occurrence side is judged by comparing the difference current of each station, specifically, the difference current is compared with a preset current threshold, and the difference current is larger than a set threshold △ IsetAnd exceeds a predetermined anti-shake delay △ t1Judging the side as fault side, and the difference flow is less than set threshold △ IsetJudging the side as a non-fault side;
when the differential flow is less than the set threshold value △ IsetWhen the side is judged to be a non-fault side, namely a fault side can not be judged by a differential current calculation method, if zero sequence voltage is detected at the AC side at the same time, the zero sequence voltage of the converter is detected under the condition of short-time converter locking, and the actual ground fault occurrence side is judged by comparing the zero sequence voltage of each station; the step of comparing the zero sequence voltage of each station specifically refers to comparing the zero sequence voltage with a preset voltage threshold value.
2. The voltage source converter fault detection and location method of claim 1, wherein comparing the magnitude of the differential current of each station is performed under the condition of not locking the converter, wherein △ t is used as reference1The value range is 0-5 s.
3. A voltage source converter fault detection and location method according to claim 1, characterized by: the fault detection and positioning method is suitable for the following neutral point grounding modes of an alternating current system:
1) the neutral point is not grounded;
2) the neutral point is grounded through a resistor;
3) three modes of grounding the neutral point through an arc suppression coil;
the current converter topology is a half-bridge structure, a full-bridge structure, or a similar full-bridge structure, or a mixed bridge arm structure of a half-bridge and a similar full-bridge, or a mixed bridge arm structure of a full-bridge and a similar full-bridge.
4. A voltage source converter fault detection and location method according to claim 1, characterized by: the fault detection and positioning method is used for processing single-phase earth faults, two-phase earth faults and three-phase earth faults at one end of the current converter.
5. The method as claimed in claim 1, wherein the short-term full-locking or half-locking mode is used to ensure that zero-sequence ground current is not transmitted to the opposite converter station through the DC side when the converter topology is full-bridge, and the short-term locking mode is used to detect the zero-sequence voltage output by the single-side converter when the converter topology is half-bridge, and when the voltage is greater than a predetermined threshold value of △ UsetAnd exceeds a certain anti-jitter delay △ t2If so, the side is judged to be a fault side, and otherwise, the side is judged to be a non-fault side.
6. A voltage source converter fault detection positioning system is characterized in that: the system comprises a current detection unit, a zero sequence voltage detection unit, a logic comparison unit and a fault detection positioning unit;
the current detection unit detects the magnitude of the current of the network side and the current of the bridge arm;
the zero sequence voltage detection unit detects the magnitude of zero sequence voltage at the alternating current side;
the logic comparison unit calculates the magnitude of the difference current between the grid side current and the bridge arm current, and when the difference current is larger than a set threshold △ IsetAnd exceeds a certain anti-jitter delay △ t1Judging that the side is a fault side, and the differential flow is less than a given value △ IsetJudging that the side is a non-fault side;
when the differential flow is less than the set threshold value △ IsetWhen the side is judged to be a non-fault side, namely the logic comparison unit cannot judge the fault side through a differential current calculation method, the logic comparison unit receives the zero sequence voltage obtained by the zero sequence voltage detection unit under the condition of locking the converter and judges according to the zero sequence voltage that the zero sequence voltage is greater than a set threshold value △ UsetAnd exceeds a certain anti-jitter delay △ t2If so, judging the side is a fault side, and the other sides are non-fault sides;
the fault detection positioning unit firstly detects the size of the differential flow to judge the fault side by combining the comparison result, and when the differential flow is smaller than a set threshold value △ IsetWhen the logic comparison unit cannot judge the fault side through a differential current calculation method, the short-time blocking current converter is started immediately, the magnitude of the zero sequence voltage of the alternating current side is detected, and the actual ground fault occurrence side is judged through comparing the magnitudes of the zero sequence voltages of all the stations.
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| CN108490369B (en) * | 2018-03-07 | 2019-03-15 | 西南交通大学 | HVDC transmission system inverter fast fault locating method |
| CN109142974B (en) * | 2018-08-31 | 2020-08-28 | 天津大学 | Alternating current line single-end fault location method suitable for flexible direct current feed-in |
| CN109617026B (en) * | 2018-10-12 | 2020-03-27 | 天津大学 | Ultrahigh-speed protection method for earth fault of direct-current power grid converter station |
| CN114217171B (en) * | 2021-12-15 | 2023-08-01 | 广东电网有限责任公司 | Single-phase grounding fault detection method for converter valve side of flexible direct current transmission system |
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| JP2013121223A (en) * | 2011-12-07 | 2013-06-17 | Hitachi Ltd | Power converter |
| CN103701145A (en) * | 2014-01-02 | 2014-04-02 | 浙江大学 | Mixed MMC-based mixed direct current power transmission system |
| CN103887772A (en) * | 2013-09-11 | 2014-06-25 | 南京南瑞继保电气有限公司 | Flexible DC power transmission grounding measurement device and protection method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101540501A (en) * | 2009-04-17 | 2009-09-23 | 中国南方电网有限责任公司超高压输电公司 | Ground electrode circuit protective system and device of high-voltage DC transmission system |
| JP2013121223A (en) * | 2011-12-07 | 2013-06-17 | Hitachi Ltd | Power converter |
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