Cascaded Delayed Signal Cancellation-Based Three-Phase Phase-Locked Loop for Enhanced Per-Phase Detection under Unbalanced Grid Conditions

This paper proposes an enhanced three-phase Phase-Locked Loop (PLL) algorithm based on Cascaded Delayed Signal Cancellation (CDSC) for accurate per-phase detection under unbalanced grid conditions. PLL is essential for extracting grid frequency and phase in grid-connected power converter applications. However, conventional three-phase PLLs are mainly used for inverter control and have limitations in accurately estimating independent per-phase quantities under voltage unbalance and grid distortion. To address this limitation, an enhanced CDSC-PLL is proposed, in which each phase is independently processed and an average-based compensation method is applied. Through this approach, the effects of the harmonic components in the estimated angular frequency are reduced. The performance of the proposed algorithm was verified under unbalanced grid conditions. The results show that the proposed method achieves improved harmonic suppression and effective per-phase phase estimation compared with a Moving Average Filter (MAF)-based PLL and a conventional CDSC-PLL.