Continuous Pulse-Density Modulation of Series-Resonant Converter for Wide-Range High-Resolution Output Voltage and High Efficiency

Pulse-density modulation (PDM) can achieve high efficiency in high-frequency dc–dc converters by implementing both zero-voltage-switching (ZVS) and zero-current-switching (ZCS). However, the discrete feature of pulse density, defined as the ratio of transferring energy switching cycles <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$P$</tex-math></inline-formula> to total switching cycles <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula>, limits the voltage regulation flexibility. This article proposes a continuous pulse-density modulation (CPDM) for bidirectional series-resonant converter (BSRC). Compared to conventional PDM methods, this approach integrates a hybrid modulation comprising pulsewidth modulation and phase-shift modulation into one of the energy transfer switching cycles. The duty cycle is regulated to achieve continuous voltage regulation. The phase shift is controlled to ensure that the resonant current reaches zero at the end of the switching cycle, thereby enabling both ZVS and ZCS to be achieved during the remaining switching cycles. In addition, the converter achieves perfect load-independent output voltage and high-efficiency features, making it well-suited for a wide range of dc–dc converter applications. Finally, a 500 W BSRC prototype is constructed to verify the proposed CPDM. A high efficiency of 95% is achieved across the entire load range, along with continuous voltage regulation capability and load-independent characteristics.