3-Φ Bidirectional Buck-Boost Sinusoidal Input Current Three-Level SiC Y-Rectifier

Aiming for ever more compact and efficient Electric Vehicle (EV) battery chargers, in this paper a three-phase phase-modular buck-boost Three-Level Flying Capacitor Y-Rectifier (3L-FC-YR) is introduced. The unique circuit structure of the 3L-FC-YR requires time-varying flying capacitor voltages, making the safe and performant operation of such a converter system challenging. Accordingly, a special clamping modulation strategy is proposed which assures equal blocking voltage distribution among the power semiconductors. Further, control strategies and protection circuitry for system startup or failure-mode handling are discussed, such that all practical aspects of the 3L-FC-YR are covered. The concept is verified by means of closed-loop circuit simulations and the resulting waveforms are presented. Finally, a Pareto comparison considering the efficiency and power density limits of the 3L-FC-YR and the standard 2L-YR is conducted considering an extremely wide DC output voltage range of 200 V to 920 V according to the DC CCS HPC350 EV charging standard. The results indicate a significantly higher performance of the 3L approach and/or the feasibility of a CISPR 11 Class A compliant 3L-FC-YR prototype with a peak efficiency of 98.5 % and power density of 19 kW/dm3 (311 W/in3).