Superposed control strategies of a BESS for power exchange and microgrid power quality improvement

A grid-connected battery energy storage system (BESS) has multiple applications as a grid supporting unit. Most common applications consider the ability of a BESS to decouple electric power generation and consumption in different contexts which is usually desirable from the grid operator point of view. A microgrid consisting of renewable energy sources connected with power electronic converters can experience difficulties with harmonic voltages and reactive inrush currents. Reactive currents may cause a voltage drop in the line impedances. Voltage fluctuations and harmonics can cause issues such as equipment tripping, overheating and malfunctioning. The stability of the microgrid is dependent upon the microgrid units' abilities to mitigate and compensate for these phenomena. A BESS can be used to simultaneously exchange active power between the battery and the grid and improve the power quality of a microgrid. With independent cascaded control of currents and active and reactive power, a BESS can control the reactive power balance in a microgrid and therefore ensure voltage stability. In addition, a BESS can serve as an active harmonic filter. Due to the transient nature of the described phenomena, these control schemes require control in real time. All the applications mentioned above can be realized simultaneously with suitable control design where the different controlled quantities are superposed. This paper reviews the technology of a BESS and the required control systems to realize the power quality features and presents simulation results as proof of their feasibility. The simulations demonstrate how a BESS can greatly contribute to microgrid stability while also performing active power exchange.