A Hybrid Prefilter and In-loop Filter Based TOGI-L-SOGI-PLL Algorithm to Synchronize SPV-Wind Microgrid with Weak Distribution Grid

The phase-locked loops (PLL) are largely used to synchronize the microgrid. However, the practical aspects of a weak distribution grid, such as voltage distortion, unbalanced, and DC offset, severely affect the PLL performance. Consequently, the harmonics are generated at the microgrid’s point of common coupling (PPC), degrading its power quality (PQ) performance. Therefore, many pre/in-loop filter-based PLLs are designed to improve the PLL’s response in the aforementioned conditions. This work proposes a hybrid prefilter and in-loop filter-based method, where the third-order generalized integrator (TOGI) is used as a prefilter, and low pass second-order generalized integrator (L-SOGI) is used as an in-loop filter. This proposed algorithm offers improved harmonic rejection compared to the advanced higher-order generalized integrator methods such as fourth-order and fifth-order generalized integrator methods. Moreover, its response speed is comparable to these methods. In addition to improving the PLL’s response, this proposed algorithm is also used to filter the load currents in this work. These filter load currents are used to incorporate the multifunctional capabilities in the microgrid, such as active filtering and reactive power compensation. A comparison is made to demonstrate the designed algorithm’s performance. Further, it is implemented on the Simulink model of solar photovoltaic (SPV)-wind-based microgrid, working under distorted/unbalanced grid voltages and load currents conditions to further validate its performance.