A General Phase-Locked Loop to Enhance Sensorless Control of PMSM Based on Back Electromotive Force

To overcome the two shortcomings of the traditional phase-locked loop (PLL): incapability in realizing speed reversal and an unsatisfactory position tracking performance between dynamic and steady-state states, a new general PLL (GPLL) is proposed for permanent magnet synchronous motors sensorless control based on back electromotive force (BEMF) in both the stationary αβ-axis and the rotary
dq
-axis. Through constructing a new input error signal, the sign of the speed variable in position error signal can be eliminated. Nevertheless, this constructed error signal contains double-fundamental frequency position information, resulting in two sets of convergence points, i.e., 0ΰ or 180ΰ from the actual position. To avoid incorrect convergence, a polarity correction function, based on the relationship between estimated BEMF and estimated speed, is designed to cooperate with the GPLL. Then, the sensorless drive can converge into correct position both in positive and negative rotation conditions. Furthermore, an estimated speed feedforward compensation is integrated into the GPLL, then the position tracking error can be reduced in linear acceleration and deceleration conditions, which enhances the dynamic tracking ability of the sensorless drive. Finally, the GPLL are realized both in a sliding mode observer on αβ-axis and a Luenberger observer on
dq
-axis, and their effectiveness is verified in comparison with conventional PLL-based method and an active flux observer in terms of speed reversal ability, dynamic and steady-state performance, etc.