Minimizing Reactive Current of a High Gain Dual Active Bridge Converter for Supercapacitor Based Energy Storage System Integration

In this paper, a control strategy is presented to operate a dual active bridge (DAB) converter at optimal operating point in terms of minimized reactive component of current. To interface a supercapacitor based energy storage system with the dc grid to absorb oscillating energy a DAB can be used. A DAB can provide galvanic isolation and can cater high voltage gain required to integrate a low voltage supercapacitor module with a higher voltage dc-link (voltage ratio more than 5). During operation, the voltage of the supercapacitor varies in wide range due to storage of oscillating energy. Also, during charging of the supercapacitor from zero voltage at the start of the operation and discharging to zero voltage at the end of the operation the voltage ratio varies from $\infty$ to 1.0. Due to large deviation of the voltage ratio from unity the reactive power in the DAB is increased. To minimize the reactive power flow an optimization method based on fundamental components is presented in this paper. By reducing the reactive component of the current overall current of the DAB for a fixed power flow is reduced. Experimental results showing implementation of the optimal solution are presented.