Voltage Balancing Methodology Using Singular Energy Storage System in Bipolar DC Microgrid

The development of power electronics technology and the growth of distributed energy resources have brought attract to bipolar DC microgrid. However, voltage unbalances between positive and negative poles occur in bipolar DC microgrid due to irregular load. To resolve this problem, voltage balancers are being used. Voltage balancers are classified into two types: centralized and distributed. The centralized voltage balancers have the drawback of not resolving voltage unbalances over long-distance lines or to the end-load. The distributed voltage balancers increase the cost due to the construction of additional facilities. To resolve for these disadvantages, the energy storage system is installed in a bipolar DC microgrid. However, energy storage system has the disadvantage of having to be installed individually at each voltage pole. This paper proposes a voltage balancing method that applies the functions of bidirectional converters and voltage balancers to a single energy storage system. By using the proposed method, power is stored and supplied through battery charging/discharging control while simultaneously reducing voltage unbalances between positive and negative poles. Additionally, the proposed method reduces the number of power conversion stages and enhances the reliability of bipolar DC microgrid. The proposed method was validated through simulation analysis and experimental validation using a 2.5 kW capacity prototype.