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

This paper 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: 1) high withstand voltage stress of the power semiconductor device and 2) large inductance volt-second product and filter volume. In order to address these issues, a novel cascaded three-level AC/DC converter with 600V 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 (CM) electromagnetic interference without relying on impedance balance. As verification to the proof-of-concept, a hardware prototype of a scale-down 1kW AC/DC converter is developed. The experimental results show that the converter can operate in an ultra-wide battery terminal voltage range of 220∼420V, with a peak efficiency of 96.35%, and a power density of 28% higher than the traditional two-level converter.