Zero-Tracking SOGI Enabled Synchronization and Control of DFIG-BES based AC Microgrid

This paper presents a seamless transition between grid-tied and islanded mode of operation of a wind turbine fed microgrid. A doubly-fed induction generator based wind turbine is selected for variable speed operation. Battery energy storage (BES) is utilized as the DC-link between stator side converter and rotor side converter. The BES maintains the DC-link voltage level and preserves continuity of supply to the local loads connected to the microgrid. For grid-tied mode of operation, a zero tracking second order generalized integrator (ZTSOGI) based algorithm is employed for fundamental components extraction. A frequency locked loop (FLL) is enabled with the ZTSOGI structure for frequency and phase angle estimation. The ZTSOGI structure is a modified version of SOGI structure, where frequency deviations are estimated by the tracking zeros. The linearized model of ZTSOGI-FLL is employed here, which shows the system having a large damping factor compared to SOGI-FLL, using the same gains. The employed integral based fundamental extraction method shows satisfactory power quality current waveforms fed to the utility in compliance to the IEEE-519 standard (total harmonic distortion<5%).