Back-EMF based Sensorless Control of PMSM with an Improved PLL for Eliminating the Position Estimation Fluctuation

Conventional back-EMF based sensorless control methods suffer the harmonic fluctuation of position estimation owing to the 5th and 7th current harmonics brought by the inverter nonlinearities. In this paper, a linear extended state observer (LESO)-based position estimation method with an improved phase-locked loop (PLL) is proposed to eliminate the harmonic fluctuation. Two LESOs provide the chattering-free estimation of back-electromotive force (EMF) for both α-and β-axis. A second-order generalized integrator (SOGI) is incorporated into the conventional PLL, thus eliminating the 6th harmonic component of the position estimation error in the feedforward path of the PLL. Compared with the state-of-art proposals, which normally utilize at least four SOGIs or other kinds adaptive filters to eliminate the 5th and 7th harmonics of the estimated back-EMF for both α- and β-axis, the proposed method only employs one SOGI while still holds a good position error harmonics elimination performance. In this way, the system complexity and computational burden can be significantly reduced. Simulation results confirm the effectiveness of the proposed method.