Control and experiment of a modular push-pull PWM converter for a battery energy storage system

This paper presents a modular push-pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium- or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms based on a cascade connection of multiple bidirectional PWM chopper cells with floating dc capacitors. This paper proposes a new control method for a three-phase MPC, which makes it possible to regulate six average voltages of the floating dc capacitors in each arm independently without any interference. This attractive feature eliminates a need of arm-balancing control, leading to a simpler and more reliable system. The validity of the operating performance and control method developed in this paper is confirmed by experiment using a three-phase, 200-V, 5-kW downscaled system.