Phase-Shifted PWM with Dynamic Phase Shift Control and Zero Sequence Injection to Minimize Inductor Current Ripple in Three-Phase Flying Capacitor Multilevel Converters

摘要

Space-Vector Pulse Width Modulation (SVPWM) is a common modulation method to reduce the inductor current ripple in three-phase 6-switch dc-ac converters. Because of the reduced voltage rating of power devices and inductor current ripple, multilevel converters have become popular for high power density and efficiency applications. Among many multilevel topologies, the flying capacitor multilevel (FCML) topology has been demonstrated with high efficiency and power density due to the use of high energy density capacitors. However, if the FCML topology is used in three-phase converters, the complexity of SVPWM will dramatically increase with the number of levels. In this paper, a new modulation technique for three-phase FCML converters is proposed. The control technique greatly reduces the inductor current ripple, and maintains the characteristics of Phase-Shifted PWM (PSWPM), which can achieve natural balancing of flying capacitor voltages in the FCML. The proposed modulation technique is implemented in a digital control system and tested with a three-phase FCML inverter built with three six-level FCML converters. The detail operation of the proposed modulation, the implementation in the digital controller, and the hardware experimental results are discussed.