The Research Of Unidirectional Fault Current Limiter Based On TCSC

In recent years, the continuous development of our country power system and the increasing use of distributed generation makes the short circuit problem highlight year by year. So the research of the fault current limiter which can limit the power system short circuit capacity and improve the running stability effectively has received the attention of people. But the traditional fault current limiter which is applied to connect the power grid and micro grid, generally limit the short circuit current in both directions. When micro power grid has fault, limiting current may reduce the quality of micro grid power, and the protection coordination of relay between power grid and micro power grid will lose.This paper proposes a unidirectional fault current limiter, when used in point of common coupling during the power grid has short-circuit fault,can limit the output of the micro power grid, and ensure the short circuit current from micro power grid to power grid will not result in the breaker in large power grid misoperation, and not affect the power grid relay protection coordination. When the micro power grid has fault or has big load startup, the unidirectional fault current limiter doesn’t act. This strategy can improve the power quality and reliability of the micro grid, and keep the protection coordination between power grid and the micro power grid.The topology of the unidirectional fault current limiter use the improved structure based on TCSC series current-limiting inductance. The inductance connecting in the circuit or not is controlled by the opening or closing of quick switch KGS. This construction can adjust power flow during the system normal operation, and realize the effect of limiting short circuit current, alleviating voltage drop when there is a short circuit fault. It can increase the flexibility of the operation.Control system adopts hierarchical control strategy. Upper control is in accordance with the operation of the whole system in the different patterns, when the system operate normaly, the device is equivalent to a series compensation device; When through fault detection module judgment power grid short circuit fault occurs, the device is working on fault current limiter model. The middle control uses the mode of closed-loop constantimpedance control. The bottom control is the thyristor trigger control. In addition forced current synchronization method of capacitive trigger interval is used to solve the problem of the mode switch of TCSC.This article uses the combination of voltage and power in rapid detection algorithm to detect whether the short-circuit fault happens. And the recognition of the fault direction uses the method of detecting the change of phase Angle of the fault current in positive sequence component before the fault and after it. Enter the determination results of the two algorithms to control module of unidirectional fault current limiter to control the operation mode of the unidirectional fault current limiter. Finally in the MATLAB simulation model is set up to verify the working characteristic of the unidirectional fault current limiter.