Experimental comparison of methods of employing IGBTs connected in series

The direct series connection of high-voltage, high-current IGBTs is attractive. However, it is necessary to consider the problem of voltage sharing between devices in a string. Close matching high-current devices in every detail is impractical. Various voltage-balancing methods have been proposed. Here, the hard switched performance of a series string of three press-pack IGBTs is compared to that for two key voltage-balancing strategies: active voltage control and active clamping. The results are compared on the basis of total losses, distribution of losses between the devices and peak voltages reached. It is concluded that the method of active voltage control has clear advantages over the other two approaches.