A Novel Light Load Performance Enhanced Variable-switching-frequency and Hybrid Single-dual-phase-shift Control for Single-stage Dual-active-bridge Based AC/DC Converter

Full-bridge power-factor-correction (PFC) front-end + dual-active-bridge (DAB) AC/DC topology is widely used in industry, e.g., electrical vehicle on-board charger. Such two-stage topology limits the system efficiency, and the bulky DC link bus capacitor makes the system power density relatively low. Compared to the two-stage design, the single-stage design, unfolding bridge + DAB, eliminates the bulky DC link bus capacitor and operates the front-end with only 60Hz switching frequency, thereby has the potential to increase the system power density and efficiency. A novel variable-switching-frequency and hybrid single-dual-phase-shift (VSF-SDPS) control strategy is proposed and analyzed for the DAB based single-stage topology. The proposed VSF-SDPF control consists of two phase shifts to guarantee Zero-Voltage-Switching (ZVS) over the full range of the AC line voltage, and frequency modulation to achieve boost PFC. The conventional front-end PFC is simplified to an unfolding bridge by changing DAB control strategy to achieve PFC and ZVS at the same time. Besides, a special ZVS boundary is utilized to solve the grid current distortion problem when the switching frequency saturated, which is especially severe at light load condition. Simulation results and experimental validation are presented under 50Vrms AC line voltage and 200V DC battery voltage test condition.