Coordination Control Strategy for Multi-mode Photovoltaic and Energy Storage DC Micro-Grid

In the DC micro grid, the instability of micro power supply output and the fluctuation of the load lead to the fluctuation of the DC bus voltage. Therefore, a certain capacity of hybrid energy storage equipment containing batteries and super capacitors is required to configure. In this paper, a virtual impedance-based power allocation strategy for hybrid energy storage equipment is presented, which can realize real-time dynamic allocation of power to two kinds of energy storage equipment without real-time power detection. At the same time, in the off-grid operation mode of the DC micro grid, combined with the power difference between micro power supply and load and the state of charge (SOC) of the battery, based on the principle of photovoltaic (PV) output power priority, establish four working modes. When the sun light or load changes, the system can realize free and smooth switching between the four working modes, and ensure the power balance and the stability of the DC bus voltage. When the SOC of the battery reaches the upper and lower limit, each converter will automatically switch the control mode to prevent the battery from overcharging or over discharging, and can continue to maintain power balance and a constant DC voltage. The system simulation model was built on the PSCAD/EMTDC platform, and the simulation results under different working conditions verified the correctness and effectiveness of the proposed control strategy.