Frequency Control in Microgrids in Grid-Connected and Islanding Conditions /

Abstract

Microgrids are becoming more important when trying to increase renewable penetration in current system due to increase in energy demand. In this sense, the interface between grid and electrical generation sources requires intelligent electronic devices such as dc/ac converters. Power electronic converters play an important role in systems such as PV, batteries and wind turbines where power is generated in an incompatible format with the distributed system. Voltage Source Converters (VSCs) improve the microgrid operation. To operate the microgrid in grid-connected and islanded mode of operation, a proper control is required. The control injects the active and reactive power from VSC of microgrid to main grid in a required manner. The unpredictable nature of renewable in islanded mode automatically demands for the master control to maintain the frequency of microgrid. The control system for grid connected/islanding microgrid is proposed that covers first two levels i.e. primary and secondary control. The controller requires no extra communication structure. In case of power shut down from main grid the proposed control meets the demand of load in islanding. The control gives flexibility to operate Microgrid in grid-connected and islanding modes by maintaining the frequency of system. BESS operates in both grid-connected and islanded modes by using PQ and primary frequency control respectively. In grid-connected mode, the system frequency is defined by grid and BESS injects the desired active and reactive power by using PQ control. The generator does not participate in this mode. In islanded mode of operation, the BESS stabilize the frequency of MG by using primary frequency control till the time the backup generator turns ON. Once the generator comes online, acting as secondary frequency control and supply active and reactive power, the BESS stops power injection/absorption and goes into standby mode. The PV system operates for both modes.