Phase-Shift-Controlled Isolated Buck-Boost Converter With Active-Clamped Three-Level Rectifier (AC-TLR) Featuring Soft-Switching Within Wide Operation Range

An active-clamped three-level rectifier (AC-TLR) is derived from the diode-clamped three-level inverter, by replacing the active switches and the diodes in the three-level inverter with the diodes and active switches, respectively. Novel isolated buck-boost converters, featuring single-stage conversion and soft-switching within wide operation range, are developed based on the proposed AC-TLR. By utilizing the AC-TLR, the voltage stress on the power devices and passive components, including the rectifying diodes, the active-clamping switches, the flying capacitor, and output filter capacitors, is reduced to the half of the output voltage. Low-voltage rating switching devices with better switching and conduction performances and a transformer with reduced turns ratio and parasitic parameters are used to enhance the efficiency. The full-bridge isolated buck-boost converter with the proposed AC-TLR is analyzed in detail as an example. An optimized phase-shift control strategy is employed to realize isolated buck and boost conversion. Soft switching of all of the switching devices in both the primary- and secondary-side circuits is achieved within the whole operation range by using the proposed AC-TLR and the phase-shift control strategy. Experimental results on a prototype with 380-V output verify the effectiveness of the proposed AC-TLR and its derived isolated buck-boost converters.