Characterizing medium-voltage high-power devices under conventional and soft-switching conditions

Research has intensified to increase the switching frequency or to reduce the power losses in high-power converters. Two different methods were investigated: on the one hand, new devices were developed with an improved hard-switching behavior, on the other hand, soft-switching converter topologies have been proposed. In practice, it becomes very difficult to compare all the published experimental results due to the different current and voltage levels in each experiment. To accommodate medium-voltage device characterization, a new high-power test bench is developed that enables a direct comparison between hard-switching, snubbered and soft-switching (ZCS and ZVS) devices in continuous mode up to 6 kV peak voltage. The test bench consists of two inverter phase legs, which are coupled by an inductor and linked to a common DC-bus. One phase leg is built with a conventional snubber circuit, the second one is realized according to the ARCP-topology enabling ZVS and ZCS characterization. Both legs are cooled by a water cooling system which allows a calorimetric determination of the power losses. Experimental results with standard GTO devices are provided.