**2. Dual Active Bridge Based Energy Storage System for Photo Voltaic Applications**

As shown in Figure 3, in a dual active bridge-based energy storage system, the PV array is connected to the DC link directly and the battery is connected to the DC link through a DAB-based bidirectional DC-DC converter. The PV inverter is connected to the grid through an isolation transformer. The transformer secondary is the point of common coupling (PCC) i.e., the coupling point of the grid, PV inverter output and the local load. A sine filter is used at the output terminals of the PV-inverter to smoothen the inverter output voltage. In this paper, design, and control of the proposed system with a 100 kVA PV-inverter and energy storage of 25% capacity for 4 h minimum backup time are presented. An overview of the electrical requirements of the system is shown in Table 1. Since the local load is rated for a 415 V, 50 Hz, 3-phase, the PCC voltage is selected to be the same as the rated voltage of the local load to avoid an additional transformer across the load and the PCC. Design calculations for the system to meet the electrical specifications are presented in the next subsection.


**Table 1.** Electrical specifications/requirements of the system.
