Capacitor voltage balancing of a three-level bi-directional buck-boost converter for battery energy storage system

Three-level bi-directional buck-boost converter has the advantages of low voltage stress of the switches and low current ripples. This paper presents a capacitor voltage balancing method of a three-level bi-directional buck-boost converter for battery energy storage system. Classic phase-shifted PWM method is used to control this converter and all the switches are operated at the same constant switching frequency. The voltages of upper and lower DC-link capacitors are regulated by adjusting the width of two PWM signals, which varies the charging time of the upper and lower DC-link capacitors in each switching period essentially. Simulation and experimental results are presented to verify the validity of this method.