Smart control of BESS in PV integrated EV charging station for reducing transformer overloading and providing battery-to-grid service

Uncontrolled charging demand in an electric vehicle charging station (EVCS) can potentially result in the overloading of the grid coupling transformer that will affect the transformer's lifetime. This paper proposes a smart coordinated control of photovoltaic (PV) and battery energy storage system (BESS) integrated in an EVCS in order to avoid transformer overloading. BESS is designed to provide the additional EV power demand which is greater than the transformer's rated capacity and thus reduce transformer overloading. In addition, the smoothing control of PV power output when PV output is lower than a threshold value is incorporated in the control method. Also, BESS which is used to provide grid services i.e battery to grid (B2G) is also incorporated in the designed smart control when the energy selling price is attractive to the BESS operator. Considering a single point connection type, B2G can only be implemented when there is no EV demand. Furthermore, B2G and battery recharging power is maintained within the transformer's rated capacity to avoid overloading during their particular services. Two different sizes of BESS and transformer capacity are considered to demonstrate the overloading of transformer for a particular time of the day. A small EVCS with integrated PV-BESS in a residential area and food center is simulated to validate the efficacy of the proposed coordinated control technique. Simulation results demonstrate that the integrated BESS with the proposed control method effectively minimizes transformer overloading during all the studied network operating conditions. Moreover, BESS successfully smooths out PV power output, provide grid service and recharge the battery within the defined rated transformer capacity and thus avoids transformer overloading while satisfying design constraints.