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CN-122000840-A - Voltage/frequency anti-islanding protection method and device based on negative sequence fault component acceleration

CN122000840ACN 122000840 ACN122000840 ACN 122000840ACN-122000840-A

Abstract

A voltage/frequency anti-islanding protection method based on acceleration of negative sequence fault components comprises the steps of monitoring voltage and frequency at a distributed power supply grid connection point in real time, detecting whether line protection acts and judging whether fault types are inter-phase faults when the voltage or frequency at the distributed power supply grid connection point exceeds a preset threshold value, calculating a grid connection point negative sequence voltage component U DG(2) in a fault transition period after the line protection acts and the inter-phase faults are confirmed, comparing the negative sequence voltage component U DG(2) with a preset setting value U DGset(2) , judging that the distributed power supply is located on a fault line if U DG(2) ＞U DGset(2) , executing acceleration grid disconnection action, and executing grid disconnection according to voltage/frequency anti-islanding protection criteria if U DG(2) ≤U DGset(2) . According to the invention, the negative sequence voltage amplitude difference of the fault line and the healthy line at the grid-connected point is used for combining the negative sequence voltage amplitude difference with the voltage/frequency anti-islanding protection criterion, so that the anti-islanding protection of the distributed power supply on the fault line can be accelerated during interphase fault.

Inventors

  • YANG FAN
  • HU WEI
  • CHEN HECHONG
  • LEI YANG
  • YANG ZHICHUN

Assignees

  • 国网湖北省电力有限公司电力科学研究院

Dates

Publication Date
20260508
Application Date
20260206

Claims (10)

  1. 1. The voltage/frequency anti-islanding protection method based on negative sequence fault component acceleration is characterized by comprising the following steps of: Monitoring voltage and frequency at the grid-connected point of the distributed power supply in real time; when the voltage or frequency at the grid-connected point of the distributed power supply exceeds a preset threshold value, detecting whether line protection acts or not and judging whether the fault type is interphase fault or not; after line protection action and phase-to-phase fault confirmation, calculating a parallel point negative sequence voltage component U DG(2) in a fault transition period T; Comparing the negative sequence voltage component U DG(2) with a preset setting value U DGset(2) , if U DG(2) ＞U DGset(2) , judging that the distributed power supply is positioned in a fault line, and executing an acceleration off-grid action; If U DG(2) ≤U DGset(2) , the disconnection is executed according to the voltage/frequency anti-islanding protection criterion.
  2. 2. The negative sequence fault component acceleration based voltage/frequency anti-islanding protection method of claim 1, characterized by: the preset threshold includes a voltage off-rating or a frequency off-rating.
  3. 3. The voltage/frequency anti-islanding protection method based on negative sequence fault component acceleration of claim 2, characterized in that said voltage deviation ratings are in particular: Or (b) (5); In the formula, The voltage at the grid-connected point of the distributed power supply is p.u. is the per unit value; The frequency deviation nominal value is specifically: Hz or Hz (6); In the formula, Is the frequency at the distributed power supply grid connection point.
  4. 4. The method for protecting voltage/frequency anti-islanding based on acceleration of negative sequence fault components as set forth in claim 1, wherein the determining of whether the fault type is an inter-phase fault is based on whether a negative sequence voltage component is present.
  5. 5. The method for protecting voltage/frequency anti-islanding based on negative sequence fault component acceleration of claim 1, wherein the fault transition period T= [ T trans ,t resp ], T trans is dynamic response delay time of the distributed power inverter, and T resp is control strategy complete response time.
  6. 6. The method for voltage/frequency anti-islanding protection based on negative sequence fault component acceleration of claim 1, wherein said method for calculating a parallel point negative sequence voltage component U DG(2) is as follows: according to a composite sequence network diagram of the power distribution network, a node voltage equation (4) and a mathematical model type (5) of a distributed power supply form a to-be-solved equation set, an iterative method is adopted for solving, and a final convergence criterion is shown as a formula (6); (4); (5); (6); The method comprises the steps of obtaining a node admittance matrix of a power distribution network, wherein Y is a node positive sequence voltage vector of the power distribution network, U (1) is composed of positive sequence voltages of all nodes, I s 、I PV.f is a system power supply injection current vector and a photovoltaic output current vector, U ̇ i(1) is a positive sequence voltage phasor of a node I, an upper mark k represents iteration times, I is a node number, epsilon is a set convergence threshold value, obtaining voltages and line currents of all nodes of the power distribution network, bringing inter-phase fault boundary conditions into the power distribution network on the basis of the node admittance matrix, and separating and calculating a grid-connected point negative sequence voltage component U DG(2) in a negative sequence network through a symmetrical component method.
  7. 7. The method for protecting voltage/frequency anti-islanding based on negative sequence fault component acceleration according to claim 1, wherein the preset setting value U DGset(2) is dynamically adjusted according to the fault point position, specifically: (8); Wherein U An outlet is the negative sequence voltage of the grid connection point when the outlet of the line fails, U Terminal end is the negative sequence voltage of the grid connection point when the tail end of the line fails, U Adjacent line outlet is the negative sequence voltage of the grid connection point when the outlet of the adjacent line fails, and K rel is a reliability coefficient.
  8. 8. The method for protecting voltage/frequency anti-islanding based on acceleration of negative sequence fault components of claim 1, wherein the acceleration off-grid action time is a sum of a line protection longest action time and a preset time margin.
  9. 9. The voltage/frequency anti-islanding protection method based on negative sequence fault component acceleration of claim 1, wherein said voltage/frequency anti-islanding protection criteria include a voltage abnormality criterion and a frequency abnormality criterion; The voltage abnormality criterion is as follows: When the distributed power supply is connected with the voltage at the point The off-line is performed at the corresponding time when the following condition is satisfied: (9); the frequency abnormality criterion is as follows: When the parallel distributed power supply is connected with the frequency at the point The off-line is performed at the corresponding time when the following condition is satisfied: (10)。
  10. 10. the voltage/frequency anti-islanding protection device based on negative sequence fault component acceleration is characterized by comprising: The voltage frequency monitoring module is used for monitoring the voltage and the frequency at the grid-connected point of the distributed power supply in real time; The circuit protection action and fault judging module is used for detecting whether the circuit protection action and judging whether the fault type is interphase fault or not when the voltage or the frequency at the grid-connected point of the distributed power supply exceeds a preset threshold value; The negative sequence voltage component calculation module is used for calculating a parallel point negative sequence voltage component U DG(2) in a fault transition period T after line protection action and phase-to-phase fault confirmation; The accelerating off-grid judging and executing module is used for comparing the negative sequence voltage component U DG(2) with a preset setting value U DGset(2) , if U DG(2) ＞U DGset(2) , judging that the distributed power supply is positioned in a fault line, and executing accelerating off-grid action; And the voltage/frequency anti-islanding protection execution module is used for executing off-grid according to the voltage/frequency anti-islanding protection criterion when the U DG(2) ≤U DGset(2) is in the process of U DG(2) ≤U DGset(2) .

Description

Voltage/frequency anti-islanding protection method and device based on negative sequence fault component acceleration Technical Field The invention belongs to the field of anti-islanding protection of power distribution networks. Background The construction of a novel power system taking new energy as a main body provides a brand new challenge for protection control of a power distribution network, wherein the research on anti-islanding protection of a distributed power supply is particularly critical. When a distribution line fails, the distributed power sources (Distributed Generation, DG) on the failed line should achieve fast fault disconnection, while DG on non-failed line should have low voltage ride through (Low Voltage Ride Through, LVRT) capability without off-grid. Aiming at the voltage/frequency anti-islanding protection method, part of the method meets the requirement of the current national standard GB/T33593-2017 on the distributed power grid-connected technology requirement, the voltage/frequency anti-islanding protection device needs to complete action within 2 seconds when the voltage is lower than a set value, when the method is easy to cause the line to fail, DG on adjacent lines is disconnected sequentially, the power unbalance of a system is aggravated, the stability of a power grid is threatened, part of the method meets the requirement of the international standard IEEE 1547 on the voltage/frequency anti-islanding protection device, namely, the maximum time under part of the scene can reach hundreds of seconds, the method is easy to cause slow subsequent fault treatment such as reclosing, and the existing method mostly has the problems of long time of the distributed power grid-disconnected on a fault line, insufficient frequency sensitivity, mistaken grid-disconnected of the distributed power of a non-fault line and the like, and the requirement of the power distribution network on fault response speed and selectivity can not be met. Disclosure of Invention The invention aims to provide a voltage/frequency anti-islanding protection method based on negative sequence fault component acceleration, which realizes rapid detection of islanding after line faults and can meet the requirements of DG on rapid off-grid and maintenance of traversing operation when voltage/frequency is abnormal when faults occur. According to the invention, the negative sequence voltage amplitude difference of the fault line and the healthy line at the grid-connected point is used for combining the negative sequence voltage amplitude difference with the voltage/frequency anti-islanding protection criterion, so that the anti-islanding protection of the distributed power supply on the fault line can be accelerated during interphase fault. The technical scheme adopted by the invention is that the voltage/frequency anti-islanding protection method based on negative sequence fault component acceleration comprises the following steps: Monitoring voltage and frequency at the grid-connected point of the distributed power supply in real time; when the voltage or frequency at the grid-connected point of the distributed power supply exceeds a preset threshold value, detecting whether line protection acts or not and judging whether the fault type is interphase fault or not; after line protection action and phase-to-phase fault confirmation, calculating a parallel point negative sequence voltage component U DG(2) in a fault transition period T; Comparing the negative sequence voltage component U DG(2) with a preset setting value U DGset(2), if U DG(2)＞UDGset(2), judging that the distributed power supply is positioned in a fault line, and executing an acceleration off-grid action; If U DG(2)≤UDGset(2), the disconnection is executed according to the voltage/frequency anti-islanding protection criterion. The preset threshold is set based on the IEEE 1547-2018 standard, including voltage off-rating or frequency off-rating. The voltage deviation rating is specifically: Or (b) (5) In the formula,The voltage at the grid-connected point of the distributed power supply is p.u. is the per unit value; The frequency deviation nominal value is specifically: Hz or Hz (6) In the formula,Is the frequency at the distributed power supply grid connection point. The basis for judging whether the fault type is interphase fault is that whether a negative sequence voltage component exists or not. The fault transition period T= [ T trans,tresp ], wherein T trans is dynamic response delay time of the distributed power inverter, and T resp is control strategy complete response time. The method for calculating the parallel point negative sequence voltage component U DG(2) is as follows: according to a composite sequence network diagram of the power distribution network, a node voltage equation (4) and a mathematical model type (5) of a distributed power supply form a to-be-solved equation set, an iterative method is adopted for solving, and a final co