Multilevel Energy Management of a DC Microgrid Based on Virtual-Battery Model Considering Voltage Regulation and Economic Optimization

This paper presents a multi-level energy management framework for DC microgrids with multiple energy storage systems (ESSs) to ensure reliable power dispatch, stable voltage regulation and economic daily operation. In the primary layer, an advanced Virtual-battery drooped control is constructed for the ESSs, which can realize adaptive load sharing and state of charge (SOC) balancing. A decentralized Bus-Signaling control is proposed to prevent single-point-of-failure, where the mode-switching voltages of the utility grid and photovoltaic are adjustable based on the VirtualOCV curve of the Virtual-battery model. A current feedforward control strategy is scheduled as the secondary control to reduce bus voltage deviation, which is verified through simulation. A small signal model is developed to investigate the effects of the Virtual-battery parameters, SOC value and constant power load on system stability through root locus analysis. In the energy management level, an improved particle swarm optimization algorithm is applied to obtain the optimal setting of the Virtual-battery model parameters for minimum daily operating cost. A discrete model is derived to calculate the capacity loss of the batteries. Finally, the proposed control hierarchy is verified in the MATLAB/Simulink environment and the simulation results prove the feasibility and priority of the proposed multi-level energy management.