Control strategy of HESS with dual active bridge bidirectional DC/DC converter in DC microgrid

A novel hybrid energy storage system (HESS) is proposed to eliminate the voltage fluctuations in DC microgrid. The HESS is composed of a dual active bridge bidirectional DC/DC converter (DAB-BDC) and a bidirectional buck/boost converter in cascade. In this way, a super capacitor is used to compensate the high frequency voltage fluctuations in the DC bus through the DAB-BDC. The Li-ion battery is used to compensate the low frequency voltage fluctuations through the bidirectional buck/boost converter which works until the super capacitor terminal voltage out of its threshold. The structure of DAB-BDC can provide electrical isolation, and reduce the rated voltage of energy storage devices. Moreover, in the cascaded structure, the HESS can stabilize the DC bus voltage smoothly, and prolong the battery life effectively. The simulation results verified the effectiveness and feasibility of the proposed structure and control strategy.