SOGI -αβCDSC Quasi Type-l PLL Control for Seamless Transition Between Grid Connected and Autonomous Operating Modes of Microgrid

Abstract

The microgrid is generally designed to switch its operating mode from grid connected mode to autonomous mode during the disruption in grid supply so that the power supply remains undisturbed at the load terminal. The effectiveness of shifting microgrid operation from one mode to another is governed by the parameters of the local grid and point of common coupling (PPC) voltages such as amplitude, frequency, and phase. However, their estimation is defected by the DC offset, harmonics, and unbalance in the voltages. Therefore, this work proposes a second-order generalized integrator (SOGI) and αβ-cascaded delay signal cancellation (αβCDSC) (m = 4, 8)- quasi-type-l phase-locked loop (PLL) method, which effectively estimates the voltage parameters in the above-specified issues in the sensed voltages. The presented SOGI-αβCDSC method demonstrates similar filtering capability and dynamics response as the full-length αβCDSC CDSC (m= 2, 4, 8, 16) method, with reduced execution time. In addition, the introduced SOGI-αβCDSC is used as a filter to the local load currents, connected at the PCC of the microgrid. These filtered load currents are administered by the designed control to provide ancillary services, such as compensation to the load harmonics current and its reactive power, utilizing the microgrid's power converter. The Simulation validation is presented to showcase the performance of the designed control.