Design and Analysis of a High-frequency CLLC Resonant Converter with Medium Voltage insulation for Solid-State-Transformer

The isolated DC/DC converter is the key component in high-frequency medium-voltage solid-state transformer. This paper presents a comprehensive design of a CLLC converter, including the design of transformer and resonant tank. The transformer insulation is designed to pass the partial discharge and applied voltage test. And its impact on transformer leakage inductance, as well as the resonant converter characteristic is discussed. Also, the transformer is optimized based on loss and volume trade-off. Then the relation of zero voltage switching (ZVS) condition and circuit parameters and load condition is derived from equivalent circuit. The impact of magnetizing inductance, leakage inductance, MOSFETs junction cap, and characteristic factor Q on ZVS condition is revealed. Finally, this paper provides a guidance to select dead-time appropriately and demonstrates the design on a 200kHz converter with 1.6kV input and 1.1kV output, and achieves a peak efficiency of 98.9%.