Energy Management Strategy for Grid-Tied Microgrids Considering the Energy Storage Efficiency

A grid-tied microgrid (MG) with a battery energy storage system (BESS) is studied in this paper. The energy storage efficiencies of the BESS are considered to optimize the operational cost of the MG. Two quadratic functions are verified and utilized to formulate the efficiencies of BESS in both charge and discharge process. Afterward, constraints of MG power scheme are investigated based on aforementioned equations. Furthermore, the 24-h ahead forecasting data of photovoltaic (PV) generation and loads demand are also utilized during MG modeling. To minimize the operational electricity cost of the MG in the next 24 h, a nonlinear programming with discontinuous derivatives solver is applied based on the proposed constraints. Additionally, to balance the power flow of MG and reduce the effects of the forecasting error of PV generation, a two steps MG management strategy is therefore developed based on the scheduled power. Experiments are conducted to verify the relationship between battery energy storage efficiency and charging/discharging current of the lithium-ion battery. Moreover, the proposed energy management strategy is validated by the hardware-in-the-loop experiments for real-time MG operation.