Performance Improvement of Quasi-Type-1 PLL by using a Complex Notch Filter

The synchronous reference frame phase-locked loop (SRF-PLL) is widely used for synchronization applications. However, it suffers from a poor performance under unbalanced and distorted grid conditions. To improve the filtering capability of SRF-PLL, moving average filter (MAF) is incorporated into its control loop at the cost of a slow transient response of PLL in recently published literature. To further improve their dynamic performance without compromising the disturbance rejection capability and stability, a novel PLL based on quasi-type-1 PLL structure is proposed in this paper. A complex notch filter is incorporated into the QT1-PLL to eliminate the fundamental frequency negative sequence voltage component. The window length of MAF in QT1-PLL is reduced. And MAF is responsible for rejecting the rest of harmonics. Parameter design guidelines are suggested to obtain the minimum settling time for both phase jump and frequency jump. The proposed PLL provides a faster transient response with higher stability margins. The effectiveness of the proposed PLL is confirmed through simulation and experimental results and comparison with advanced PLLs.