Common-Mode Voltage Analysis and Suppression Strategy for Three-Level Dual-Active-Bridge Converter

The three-level dual-active-bridge (DAB) converter has the advantages of low-voltage stress, voltage matching, and electrical isolation, and is a topology-level solution for medium-voltage power systems. However, due to the operation of power devices in high-frequency switching states, the nodes with high-frequency potential jumps in the circuit will generate leakage current through the parasitic capacitance to the ground and the distributed capacitance between the primary and secondary windings of the transformer, resulting in common mode (CM) conducted electromagnetic interference and significantly reducing the reliability of the converter system. In order to solve this issue, this article establishes an equivalent CM noise model for three-level DAB converter and conducts in-depth theoretical analysis of the equivalent CM voltage. On this basis, the solution strategies of suppressing CM voltage are proposed and discussed in detail. By combining the symmetrical coupled phase-shifted inductor and the CM voltage cancellation scheme, various factors that cause time-varying equivalent CM voltage can be eliminated, greatly suppressing CM components in the system. Simulation and experimental results are provided to validate that the proposed strategy can achieve good performance in suppressing time-domain CM voltage/current and frequency-domain CM EMI.