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In order to reduce the chattering and phase shift, this article proposes an enhanced sliding mode observer (SMO) for the sensorless control of permanent magnet synchronous motor (PMSM). In the conventional SMO, a low-pass filter (LPF) is commonly employed to extract the back electromotive forces (EMFs) from the sliding mode switching function, which brings the phase shift and degrades the precision of position and speed estimations. In this article, a frequency-adaptive complex-coefficient filter (FACCF) is adopted to replace the LPF. Since the FACCF has no phase shift and amplitude attenuation at the central frequency, it can be used to extract the EMFs without distortion while the chattering can also be suppressed. For an easy parameter design, the normalized phase-locked loop is used to obtain accurately the position and speed estimations. The experiments are carried out on a 3-kW PMSM drive, and the results verify the effectiveness of the proposed method.

This paper proposes an improved sliding-mode observer (SMO) for the sensorless control of permanent-magnet synchronous motor (PMSM). In the conventional SMO, a lowpass filter (LPF) is used to reduce the chattering caused by the signum function. That will bring the phase lag and affect the precision of the observer. The improved SMO adopts the self-adapting complex-coefficient filter (SACCF) to replace the LPF. The SACCF has no phase lag and amplitude attenuation at the mid-frequency. Thus, it can extract the back electromotive force (EMF) without distortions while suppressing the chattering. Then the improved SMO use the normalized phase-locked loop (PLL) to track the rotor position and speed accurately. Finally, the simulations and experiments are carried out with a 3kW PMSM, and the results verify the effectiveness of the proposed method.

In permanent magnet synchronous motor (PMSM) drive systems, there are 5th, 7th, 11th, 13th and other low order current harmonics due to the non-ideal factors such as the distortion of the air-gap field and the nonlinear characteristics of the inverter. In order to suppress the current harmonics and improve the system performance, repetitive controller is employed in parallel with proportional integral (PI) controller of current loop in the synchronous rotating dq coordinate system in this paper. Repetitive control originates from the internal model principle of control theory, which has inhibitory effect on periodic disturbances. It can suppress integer harmonic of a given frequency and get high-accuracy output waveforms. This method does not need to increase any hardware, and is easy to implement. Simulations and experiments are carried out to verify the effectiveness of the proposed method for current harmonic suppression.