A Novel Three-level Phase-Shift Modulation for Serial Half Bridge LLC Resonant Converter

In this paper, a novel three-level phase-shift modulation is proposed for serial half bridge (SHB) LLC resonant converter. The proposed modulation is capable of balancing current stress for all switches to realize balanced thermal stress and their longer lifetime. The operation principle of the proposed modulation strategy is presented and analyzed in detail. ZVS conditions are discussed in different operation modes to ensure high efficiency operation in the entire load range. In addition, the proposed three-level phase-shift modulation provides additional gain range to conventional two level modulations with variable switching frequency control so that very wide output/input voltage range can be achieved. The performance of the proposed modulation is experimentally verified on a 7.5 kW SHB LLC DC/DC converter prototype.