Topology and Control Strategy Improvement of Middle Stage of Power Electronic Transformer Based on Modular Multilevel Converter

The typical topology of power electronic transformers based on modular multilevel converters have problems such as excessive switching loss at high frequencies and power unbalance of multi-module DC/DC converters. This paper proposes a phase-shifted full-bridge zero voltage and zero current switching DC/DC converter, which improves the structure of DC/DC converter of typical topology. This improved structure can effectively reduce switching loss. Thus, it is more suitable for high frequency and high power applications. Moreover, an output current equalization control strategy is given for multi-module DC/DC converters with input in series and output in parallel structure, which can keep power balanced by balancing output current of each module. Finally, a simulation model is established and the effectiveness of improved topology and control strategy of power electronic transformer are verified.