On PQ Control of BESS in Grid-Connected Mode and Frequency Control in Islanded-Mode for Micro-Grid Application

This paper presents the control algorithm for Battery Energy Storage System (BESS) connected in Micro-Grid (MG), operating in grid-connected and islanded-mode. The MG consists of configurable units such as BESS, PV, diesel generator and load. The BESS is connected with Voltage Source Converter (VSC) for active and reactive power sharing in grid-connected mode. Two control scheme algorithms are presented. Firstly, inner current control loop and secondly outer active/reactive power (PQ) control loop is presented. Also the charging and discharging control of BESS is designed to maintain the SOC. In islanded-mode, Power-frequency (P-f) control of BESS is proposed to maintain the frequency of MG and supply power to the load. P-f control provides reference power for PQ control. BESS provide primary frequency control to MG; however, the low power capacity of BESS demands for a backup. Diesel generator provides a backup frequency control in islanded-mode, supply active/reactive power to loads and charge the BESS. The control is designed in dq reference frame. The simulation results show the effectiveness of control system.