An improved Q-PLL to overcome the speed reversal problems in sensorless PMSM drive

Many existing sensorless control methods are based on flux observers, where phase-locked loops (PLLs) were used to extract the position information from the estimated rotor flux. This paper proposes an improved quadrature-component-based phase locked loop (Q-PLL) scheme for sensorless control of permanent magnet synchronous motor (PMSM) drives. To show the superiority of the proposed method in solving the problem of speed reversal, other three kinds of PLLs are also presented for the aim of comparison. This improved PLL is integrated with SMO-based sensorless control of PMSM drives. Compared to conventional Q-PLL, the main advantage of the proposed PLL is that it can work well without a gain scheduling remedial strategy or a judgment of the sign of speed in terms of speed reversal. Furthermore, it has a better performance in the transient and steady state response. Both Simulation and experimental results are presented to demonstrate the good performances of the proposed Q-PLL.