Smoothing Output Power Fluctuations of DGs in Microgrids Using Battery Energy Storage System

In distributed generations (DG) such as wind turbines (WT) and photovoltaic systems (PV), since power production is directly dependent on weather conditions and wind speed, their powers have an intermittent nature. This intermittent characteristic can lead to power fluctuation, frequency deviation, reduction of power quality and reliability indexes at the Point of Common Coupling (PCC). In this paper, a grid-tied microgrid including WT and PV is studied and the effect of weather conditions and wind speed changes on power fluctuation and frequency deviatiom is investigated. In order to smooth the power fluctuations, a battery energy storage system (BESS) is used. Control system of this BESS consists of three control levels. Through the first two control levels, the DGs reference power is calculated aiming to smooth the network power. Effective life and protection of the BESS is considered in reference power calculation process. Afterward, the generated reference power is injected to the grid proper control system of voltage source converter connecting battery storage to PCC. In order to validate the effectiveness of BESS control system for smoothing power fluctuations of DGs, simulations studies have been done in MATLAB/ Simulink software. The results confirm that the proposed BESS control system is capable to reduce the output power fluctuations of DGs, Such a way that the average frequency of the fluctuations harmonic content reduce from 15.5 to 5.4 percent.