Full-Bridge Diode-Clamped Four-Level Symmetric Switching Converter.

In this paper, we propose a novel full-bridge (FB) diode-clamped four-level symmetric switching converter. Multi-neighboring reference vector discontinuous PWM (MNRV DPWM) for FB topology was implemented using a symmetric half-bridge (HB)-based control approach that incorporates an offset voltage addition method. A diode-clamped four-level symmetrical switching circuit with pulse-amplitude-modulation (PAM) was proposed and its working principle was explained in detail. Voltage gain, duty loss factor, and zero-voltage-switching (ZVS) condition were derived by analyzing the steady-state operating characteristics of the proposed converter. The required input and output capacitance values were also calculated explicitly. The voltages across the series-connected input DC-link capacitors were well balanced and the output voltage was controlled in a simple linear manner by PAM. The proposed method offers the advantage of reducing circulating current when compared to the existing phase-shift method, thanks to the inclusion of an additional power delivery period. The effectiveness of the proposed converter was verified through simulation and prototype experiments. The power conversion efficiency exceeded 91.44% at an output power ( $P_{O})$ of 250W or higher, with a peak efficiency of 95.23% achieved at $P_{O}=750\text{W}$ .