Because of the high voltage, high current and easy to be driven, IGBT become the optimal selection of the power convert system. As the improvement of power electronics, the voltage becomes higher and higher, such as high inverter, HVDC and Flexible HVDC system. The voltage should be dozens of kilo-volt. Single device cannot be used in these occasions. Thus, IGBTs for series connection is necessary.In the series connection of IGBTs, as the result of the different parameters and the delay of the drive signals, the main problem is unequal sharing of voltage respectively. The devices which withstand over voltage might be broken down and result in the fault of the whole circuit. Therefore， it is necessary to protect the over voltage of the IGBT.The method of active voltage clamping for the High-Voltage IGBTs for series connection is presented. The transient voltage suppressor(TVS) lied between the collector and gate of IGBT is adopted as active clamping circuit, and the clamping voltage value is decided by rated IGBT voltage and the working voltage. When turning of on the IGBT, TVS is broken down by over voltage, and the voltage between collector and emitter is clamped．
Stable operation of a high-voltage high-current dc photoemission gun for the bunched beam electron cooler in RHIC
