Large fluctuations of power output of Photovoltaic(PV) system will cause the corresponding voltage fluctuations at Point of Common Coupling(PCC), which leads to frequent switching of reactive power compensation devices. Normally reactor with circuit breaker, Thyrister Controlled Reactor(TCR) or Static Var Generator(SVG) are used for regulating over voltage caused by high PV power output, but with problems of high cost, high loss, complex control and poor reliability. The paper proposes a novel one-control-three type of Thyrister Switched Capacitor (TSC) for compensating the grid connected distributed PV system, which coordinated with distribution transformer to improve voltage quality on PCC. The proposed type only use single thyrister to control three phase capacitors, the switching process is both simple and reliable. A simulation is conducted to show the effectiveness of proposed TSC by comparing it with conventional TSC and circuit breaker switched capacitor. Simulation results show that proposed TSC can effectively handle surge current, and the control method is simple and reliable. The total device cost is further lowered down comparing with existing devices without sacrificing switching performance, which shows high practicability in the circumstances of Var compensation of distributed PV systems.

distributed PV system, Thyrister Swithed Capacitor; one-control-three type; typology design; surge current