A Survey of Phase-Locked Loop Technologies in Sensorless Position Estimation of Permanent Magnet Synchronous Motor Drives

The phase-locked loop (PLL) algorithm uses the external input reference signal to control the frequency and phase of the internal oscillation signal of the loop; thus, the control signal and the internal signal can be synchronized to achieve the purpose of phase locking. This algorithm has been widely used in the sensorless position estimation technology of permanent magnet synchronous motor (PMSM) drives. The PLL can eliminate the steady-state error effectively and achieve better phase tracking accuracy. Furthermore, its low-pass filtering characteristics can effectively filter the high-frequency harmonics and chattering signals of the estimated back emotional force (BEMF) and flux linkages. Thus, by utilizing the PLL algorithm, the position estimation accuracy in PMSM can be highly improved. In this article, the existing PLL algorithms for sensorless PMSM control are reviewed systematically. Furthermore, the key challenges and opportunities for future research are identified.