Three-level LC resonant converter based on first-harmonic-synchronized PWM

Three-level LC resonant converters employ a series-connected full-bridge structure to match voltage levels and reduce voltage stress of the power switch devices. However, in applications with large voltage fluctuations, traditional control methods require a wide frequency regulation range, complicating transformer and controller design. To offer a solution, a three-level LC resonant converter is proposed, which utilizes first-harmonic-synchronized pulse-width-modulation (PWM) to achieve wide-range voltage regulation with a fixed switching frequency. The converter voltage gain depends solely on the internal phase-shift ratio of the primary and secondary bridge arms, allowing for automatic and smooth adjustment of both the amplitude and direction of power transmission. Moreover, the midpoint voltage and switching loss are dynamically balanced through PWM phase compensation and timed driving signal transformation, respectively. Additionally, a 25 kW prototype was built and tested to evaluate the feasibility of the proposed converter.