Abstract: Parallel capacitor banks can effectively improve the efficiency and quality of power transmission in

the application process of power distribution network. However，due to some unreasonable factors in the switching

mode of power capacitors，it will also generate overvoltage，thus affecting the power grid. stability. The transient

state of power capacitor switching was researched and analyzed. For the closing transient，by establishing a singlephase equivalent circuit when the power capacitor combination switches were connected in parallel，the power capacitor switching transient process was simplified. For the opening transient，the recovery voltage generated was calulated by the circuit breaker contact during the power capacitor switching state. The synchronous switch controller was composed of hardware such as energy storage capacitor，switching power supply，power drive output interface and current/voltage sensor interface to realize overvoltage protection of power capacitors. In order to verify the application performance of this method，experimental analysis was carried out. When the synchronous controller was used to perform switching tests on power capacitors in two states of closing and opening，the threephase voltage fluctuations were symmetrical and regular，and the amplitude changes were relatively stable，the overvoltage peak of the power capacitor was effectively suppressed. The experimental test results show that the proposed method has high switching stability and good overvoltage suppression effect.

      Key words: power capacitor；phase-controlled switching；transient analysis；synchronous controller；overvoltage suppress