An Input Inductor Flying Capacitor Multilevel Converter Utilizing a Combined Power Factor Correcting and Active Voltage Balancing Control Technique for Buck-Type AC/DC Grid-Tied Applications

This paper presents a novel circuit topology and control strategy for use in single-phase buck-type power factor correction (PFC) ac-dc rectifiers. We propose a topological change to the flying capacitor multilevel (FCML) converter to place inductors at the input rather than the conventional output along with a novel control strategy for ac-dc operation. The proposed topology retains the high efficiency and power density advantages of the FCML topology while enabling improved control of the input current for PFC operation, and better EMI performance for the same magnetic energy storage. An active flying capacitor voltage balancing control technique is presented, which enables high bandwidth (e.g., 120 Hz) control of the flying capacitor voltages. The new circuit topology and enabling control technique are demonstrated in a six-level, 240V(rms)/48V(dc), 817W hardware prototype.