Space vector modulation for mutually commutated isolated three-phase converter systems

Converter systems consisting of a voltage source converter and a cycloconverter connected by a medium-frequency transformer have several attractive properties. They offer bidirectional AC/DC conversion as well as voltage transformation and isolation by the transformer. Furthermore, it is possible to achieve soft-switching conditions for all semiconductor devices by consistently commutating the two converters in alternation; hence the name ldquomutually commutated converter systemrdquo. Such a commutation scheme, however, imposes certain restrictions on the modulation of the converter system. A newly proposed space vector oriented modulation method promises superior performance compared to carrier-based modulation methods. This paper describes the implementation of the considered space vector modulation on the example of a 40 kVA prototype converter system. The experimental results show that the evaluated space vector modulation is particularly beneficial at low output voltages due to its inherent nature of maximizing the zero voltage vectors.