Power management and state of charge restoration of direct current microgrid with improved voltage-shifting controller

Recently, direct current (DC) microgrid is gaining increased importance due to large-scale utilization of different DC sources, such as photovoltaic (PV), fuel cell, DC loads, and high-level integration of energy storage devices and renewable energy. Additionally, unlike conventional alternating current (AC) system, DC microgrid does not require reactive power and frequency control. Nevertheless, DC microgrid control is a complex task due to the connection of several distributed generators, loads, energy storages, and renewable energy sources, such as PV, and wind, to the common DC bus. The control of DC bus voltage, effective power split among the energy storage devices, and state of charge (SOC) restorations are important in a DC microgrid. This paper proposes a new average voltage shifting-based strategy to split power-sharing between battery and supercapacitor. In the proposed approach, an average voltage shifting term derived from the battery and supercapacitor is introduced to reduce the DC link voltage deviation. As compared to the droop control, the addition of the voltage shifting term acts like a high pass filter and blocks the DC component which helps the DC bus voltage restoration process. The DC microgrid is composed of a hybrid energy storage system formed by battery and supercapacitor, AC utility grid interfaced with three-phase voltage source converter (VSC), constant power load, constant resistive load, and distributed generator. The SOC of the supercapacitor is automatically restored after any disturbances whereas the battery SOC is maintained by energy exchange with the distributed generator or grid. The real-time digital simulator (RTDS) and dSPACE-based control hardware-in-loop results show that the proposed approach is reliable, leading to improved DC bus voltage control while maintaining proper power flow and SOC within the microgrid. The comparative study is also conducted to show the superiority of the proposed strategy with the existing method.