Coordinated Control of EV Charging Stations in Smart Transformer based Microgrid

This paper presents coordinated control scheme of electric vehicle charging stations (EVCSs) in smart transformer (ST) based microgrid. The microgrid is connected to the main grid through ST. Here, ST low voltage (LV) ac side converter is operating on the droop-control method. Battery energy storage system (BESS) and photovoltaic (PV) are connected to LVac line through droop-controlled converters. Two levels of hierarchical control structure have been implemented here: primary control and secondary control. EVCS connected at the load bus is used as the controllable unit in microgrid, which can regulate the voltage and frequency at load bus. Moreover, EVCS supports the microgrid with reactive power by varying their charging power. The secondary control at the microgrid centralised controller (MGCC) sends compensation signals to all the control units of droop-controlled converters and EVCS using the low bandwidth communication link. Simulation results show that the microgrid provides power at nominal voltage and frequency using secondary compensation signals. Along with controllable charging, EV supports reactive power as the voltage deviation at load bus goes beyond minimum threshold limit. The results are verified using the MATLAB/Simulink software.