A Method to Improve the Dynamic Performance of Moving Average Filter-Based PLL

Abstract

Phase-locked loop (PLL) technique is widely used for synchronization applications. A variety of moving average filter (MAF)-based PLLs have been presented in recently published literatures. MAF-based PLL can completely eliminate the effect of unbalanced voltage, characteristic harmonics, and dc offset. Unfortunately, the open-loop bandwidth is drastically reduced after incorporating MAF into the PLL structure. The problem is analyzed in detail in this paper, and it is proved to be caused by the large MAF window width which is determined by the lowest order harmonic. Then, an improved method named differential MAF-PLL (DMAF-PLL) is proposed. This method can rapidly eliminate the lowest order harmonic to narrow the MAF window width. DMAF-PLL is realized by incorporating a special proportional component into the MAF-based PLL. The special proportional component can online change its value according to the frequency of input signal, and it will not introduce phase lag, so as not to deteriorate the stability of PLL. DMAF-PLL increases the open-loop bandwidth and greatly improves the dynamic performance of MAF-based PLL, and it is easy to be implemented with low computational burden. DMAF-PLL can be used in both three-phase and single-phase voltage systems. Simulation and experimental results are included to validate the effectiveness and robustness of the proposed method.