An Improved Pre-Filtered Three-Phase SRF-PLL for Rapid Detection of Grid Voltage Attributes

Phase-locked loops (PLLs) are often deployed in a specialized control unit of grid-connected converters (GCCs) for their control and protection purposes. Moreover, presence of DC-offset, fundamental negative sequence (FNS) component, and harmonics in the grid signal may hinder the dynamic performance of the PLLs. In this paper, a robust three-phase synchronous reference frame (SRF)-PLL algorithm has been presented. The proposed algorithm will be helpful for rapid tracking of fundamental grid voltage attributes with those including amplitude, phase, and frequency. This is achieved by employing a delayed signal cancellation (DSC) operator cascaded to a modified moving average filter based orthogonal signal generator (MAF-OSG) in the pre-filtering stage. This combination of filters improves the transient response time and demonstrate the potential performance of the scheme if fundamental positive sequence (FPS) component alone is present in the input signal. Also, an instantaneous symmetrical component method is applied to obtain FPS component which facilitates ease tuning of loop parameters. The proposed scheme is tested for nominal and off-nominal frequency conditions in MATLAB/Simulink environment.