Design of a Flexible Control Platform for Soft-Switching Multi-Level Inverters

In modern high power medium voltage drives, multi-level converters are increasingly used. By employing topology modifications recently introduced, soft-switching technology can be applied to multi-level converters. Thereby, the switching losses are reduced significantly. As a result, the switching frequency can be increased thereby reducing the output filter size. However, common converter controls have to be modified. In this paper, a flexible control platform is presented that allows rapid prototyping of soft-switching topologies. An analysis of different ARCP topologies showed that all switching commands can be synthesized with synchronized signals of two-level ARCP converters. Therefore, a flexible state-machine for 2-level converters was developed first, which can also be used to build controls for multi-level topologies. It supports drivers with built-in intelligence as well as the control of additional switches that are required in some ARCP neutral-point-clamped (NPC) topologies. The switching commands for the state machines can be generated by standard multi-level modulation methods. Illegal switching states are filtered and multiple simultaneous commutations per phase are prevented for ARCP NPC converters. To verify the functionality, the control scheme was realized in an FPGA and a completely modular test-converter was developed. It can be used to quickly implement all common multi-level topologies and test different modulation strategies. Some experimental results are presented in this paper