Isolated 3-Level DC-DC Converter with Complete ZVS Using Magnetizing Inductors

An isolated dc–dc converter with dedicated 3-level modulation is proposed to achieve a 4:1 output voltage range, and complete zero-voltage-switching (ZVS) of all active switches using the magnetizing inductors. The single input 3-level modulation scheme coordinates the phase-shift, duty cycle, and switching frequency to ensure 1) the magnetizing currents are independent of load voltage and current; 2) the output voltage is proportional to the modulation input. As a result, the dual half- and full-bridge modes of the switching network are unified and modeled as a voltage-controlled voltage source, with the same control parameters for both modes of operation. In addition, the magnetizing-to-series inductance ratios of the leading and lagging transformers are increased to 100 and 25 times, respectively. Therefore, the circulating current is low, and the series inductors can be integrated into the transformers. The proposed topology is intended for high-power applications with a wide output voltage range but less input voltage variation. A $\text{30}\,\text{kW}$ prototype with a power density of $\text{7.2}\,\text{kW}/\text{L}$ and an output voltage of $\text{165}\,\text{V}$ - $\text{680}\,\text{V}$ was built and tested to verify the characteristics and feasibility of the proposed H8 topology plus modulation scheme.