A Compact Single-Phase Cascaded Three-Level AC/DC Converter With Variable DC Bus Voltage and Low CM Noise

This article proposes a new topology technology of a two-stage ac/dc converter with variable dc bus voltage control. The technology is a cascaded combination of a new type of single-inductor-based cascaded three-level totem-pole power-factor-correction (PFC) circuit and a three-level LLC half-bridge converter. Although the existing variable dc bus voltage control strategy based on a two-level ac/dc converter exhibits better overall efficiency than fixed dc bus control, it faces problems such as high withstand voltage stress of the power semiconductor device and large inductance volt-second product and filter volume. In order to address these issues, a novel cascaded three-level ac/dc converter with 600 V withstand voltage devices and phase-shift modulation technology is proposed. The new single-inductor-based mirror-symmetric cascaded three-level totem-pole PFC can achieve low common-mode electromagnetic interference without relying on impedance balance. As verification of the proof-of-concept, a hardware prototype of a scale-down 1 kW ac/dc converter is developed. The experimental results show that the converter can operate in an ultrawide battery terminal voltage range of 220–420 V, with a peak efficiency of 96.35%, and a power density of 28% higher than the traditional two-level converter.