Multiple Delayed Signal Cancellation Filter-Based Enhanced Frequency-Locked Loop under Adverse Grid Conditions

An accurate and prompt estimation of phase angles, frequency, and magnitudes of the grid voltage is extremely important in paving a good platform for a fast and reliable operation of power grid monitoring, protection, and control. The phase-locked loop (PLL) served this purpose for decades, while the concept of the frequency-locked loop (FLL) has been proposed more recently. Even though the FLL and the PLL share some similarities, some differences still exist. Further research on FLLs can boost their capabilities and open up new windows in designing devices for grid synchronization. Multiple delayed signal cancellation (MDSC) filters are a peculiar system of filters. Their applications to FLLs can enrich FLL's performance. This article focuses on applying the stationary reference frame MDSC filters at in-loop and prefiltering stages of the FLL and compares its effectiveness with widely used cascaded delayed signal cancellation (CDSC) and complex bandpass filter (CBF) based filtering techniques. The application of the K-factor-methodology-based controller design to FLLs has also been explored for dynamic performance enhancements. A new cascaded multiple delayed signal cancellation (CMDSC) filter is proposed and is compared with its CDSC counterpart proposed in the literature to address the effects of dc offsets and imbalances under adverse grid conditions. The effectiveness of the proposed method is verified through OPAL-RT real-Time simulations and dSPACE ds1104 and TMS320F28335 microcontroller experimental test bench.