Elimination of reactive power in dual active bridge by hybrid of phase shift and PWM control

In applications of distributed power generation and uninterruptable power supply for green and smart buildings, energy storage systems (ESS) with high voltage DC bus have been widely considered. Advanced energy storage device (ESD) such as lithium-ion batteries and super-capacitors however have low terminal voltages. Connecting many ESD cells in series is an acceptable solution but requires complex cell equalization circuitry to keep the state-of-charge of each cell balanced. The alternative is to develop a bidirectional DC-DC converter to interface the low terminal voltage ESDs to the high voltage DC bus. The dual-active-bridge (DAB) topology is suited for bidirectional DC-DC conversion due to its simple structure and soft switching nature. However reactive power is a major drawback when using traditional phase shift (TPS) control. In this paper, a hybrid of phase shift and PWM (HPSP) control strategy is proposed to eliminate the reactive power. Comparing with the TPS control, smaller rms current is required for the same power rating, which will improve the system efficiency. Mathematical model of transmission power is established for the TPS and the HPSP control. Simulation results verifying the excellent performance of the proposed control method are presented in this paper.