Inductive decoupling of parallel connected commutation cells for dynamic current balancing

For high power applications both the series and the parallel connection of semiconductors are commonly used for increasing the output power of converters. This parallel connection of devices demands a balanced current sharing. A method for current balancing in parallel commutation cells is detailed analysed in this paper. For the parallel connection of devices the realization of a dynamic and static load current sharing is essential. With respect to this the influences of both the delay times of the semiconductors and the commutation cell inductances get more important with increasing switching frequency. Differences in these parameters might cause overcurrents in some devices, especially at the turn-off commutation. These overcurrents can result in critical voltage spikes. Utilizing small inductances symmetrically installed between the commutation cells and the load causes a balanced dynamic current sharing. These inductances act as current sources and achieve a voltage decoupling between the different commutation cells during the commutation. In the case of different delay times of the switches a step-by-step commutation will be achieved. The fundamental basics and a theoretical analysis are presented. Furthermore experimental results are shown and the benefits and disadvantages of this technique are discussed.