Generalized Switching Sequence for Voltage Balancing in a Flying Capacitor DC-DC Converter with Quasi-2-Level Modulation

Abstract:
A generalized voltage balancing algorithm is proposed for a multilevel flying capacitor (FC) bridge used in a dual active bridge (DAB) medium voltage DC-DC converter with quasi-2-level modulation. The operation of the flying capacitor converter (FCC) in a DAB is explained and the voltage imbalance problem is illustrated. The results of the proposed algorithm are presented in the form of a switching sequence that allows to balance the voltage of the flying capacitors in open loop during steady-state operation. The algorithm is generalized to be used with an n-level FCC in a half bridge or a full bridge configuration. The proposed method produces a balanced switching sequence based on fixed criteria such as symmetric use of converter and minimization of losses. Simulation results are presented for a 13-level FCC in a half bridge and full bridge configuration.