Abstract: In order to ensure that the thyristor valve body can be accurately conducted during the solid state switch switching，a solid state switch trigger control unit was designed. Firstly，the structure and working principle of the solid state switch and the structure and function of the trigger control unit were introduced. Secondly，the function and working sequence of the core module logic loop of the trigger control unit were described in detail，the working principle of the important module voltage detection loop of the trigger control unit was introduced. A overvoltage protection circuit was proposed，which is more stable and simple than the traditional overvoltage protection circuit.Finally，the simulation model and experimental platform were built to verify the trigger function of the trigger control unit. The simulation and experimental results show the reliability and correctness of the trigger control unit.

      Key words: solid state transfer switch（SSTS）；trigger control unit（TCU）；logic loop；overvoltage protection；voltage detection