Supervisory control of bipolar DC microgrids equipped with three-port multidirectional DC–DC converter for efficiency and system damping optimization

Abstract Up to date, voltage balancing converters tend to balance the voltage of BPDCMG buses with active sources or transferring the power from one bus to another one. Furthermore, batteries available in the BPDCMG were charged equally by positive and negative buses. This power sharing strategy does not guarantee an optimum performance of the entire system. To achieve higher efficiency and reduce energy costs, this paper proposes a tertiary control level including an optimization method for achieving efficient operation and system damping improvement in a bipolar DC microgrid (BPDCMG). The proposed control scheme is applied to a three-port multidirectional DC–DC converter (TMC). This converter provides a voltage-balancing function for the BPDCMG and adjusts the states of charge (SoC) of battery. It is assumed that, the renewable energy sources (RESs) are connected to the BPDCMG by converters. Since the power losses of each converter depend on its output power, the virtual resistors (VR) of the droop primary control are applied as decision variables to adjust the current sharing ratio among the RESs. Moreover, a secondary control level is used to regulate the output voltage decreased by primary droop control and to adjust the system damping when VRs change. Comprehensive simulation studies are carried out and a BPDCMG laboratory setup is implemented in order to validate the effectiveness of the proposed hierarchical control strategy. The simulation and experimental results show that the system efficiency is improved and the desired transient response is ensured with the proposed tertiary control.