This paper proposes a coordinated control method for battery energy storage systems (BESSs) and load-ratio control transformer (LRT) to control the voltage of a middle-voltage 6.6-kV photovoltaic (PV)-supplied microgrid (MG). Each local BESS minimizes the active power flow through the feeder bus where it is installed. A central BESS minimizes the power flow from the utility to the MG through the interconnection point where it is installed, which in turn limits the load bus voltages in the MG, such as those supplied by PV systems and the utility. This paper proposes a central BESS structure which can act as a distribution static compensator when its batteries are fully charged or fully discharged. MGs with loop and radial structures are studied to evaluate the effectiveness of the proposed method. MATLAB/Simulink is used to simulate an MG model using actual PV data and residential loads from Ota City, Japan. Experiments are carried out on ANSWER (Active Network System with Energy Resources) to demonstrate the proposed control method.
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