A novel sensorless control method of IPMSM using dual PLL structure

Harmonics in back electromotive force (EMF) would greatly affect the accuracy of traditional sensorless control methods, and some of them may even fail. Phase locked loop (PLL) is a useful tool for phase detection in multiple-harmonic system, and is suitable for the control system of Interior Permanent Magnet Synchronous Motor (IPMSM) as it is often filled with harmonics when the motor is not carefully designed. In this paper, Dual-PLL structure is proposed to obtain the fundamental harmonic of the quantities of the motor, which are used in the speed and position estimation. The first PLL is the main path of the estimation and the phase of αβ-axes voltage is determined, while the second PLL focuses on speed estimation with low ripples. Extra measurement of the terminal voltage of the motor is not necessary and only the q-axis inductance is needed when the motor is run at i_d=0. The delay caused by the digital control and the IGBT-composed inverter is also considered. Experiments are finished on an inverter fed IPMSM control system, which demonstrates the correctness of both proposed strategies with good steady performance.