Snubberless balancement of series connected insulated gate devices by a novel gate control strategy

The series connection of insulated gate devices, such as MOSFETs or IGBTs, is increasingly used in high-voltage power converters where the demand for fast power switches is growing. The main problem in such an application is to guarantee the voltage balance across the devices both at steady-state and during switching transients, in order to avoid damaging overvoltages. In this paper, a novel approach is used to balance the voltage during switching transients by controlling the charge profile of the input gate capacitance. The main advantages of the proposed method consist in avoiding the common use of balancing capacitors in the output power side, and in working on the gate drive signals only. The application of the proposed gate drive technique is discussed first and then validated by experimental tests applied to the control of two series connected devices (MOSFETs or IGBTs). The proposed approach is also applicable for more than two devices. In particular, the validity has been proven by computer simulations for three components. Finally, a comparison is performed between the switching behaviors of two different configurations: a high-voltage application having for a high-voltage single switch device; or a series of two lower voltage rated devices. The advantage of the latter configuration, having the proposed active voltage balancing, over the former has been experimentally demonstrated with regard to the turn-off power losses