Periodic torque ripples minimization in PMSM using learning variable structure control based on a torque observer

PM synchronous motor drives are widely used for high-performance industrial servo applications where torque smoothness is an essential requirement. However, parasitic torque pulsations do exist in PMSM drive due to non-perfect sinusoidal flux distribution, cogging torque and current measurement errors. A consequence of these torque ripples is speed oscillation that deteriorates the drive performance particularly at low speeds. In this paper, we propose a simple plug-in learning variable structure control (LVSC) scheme for generating a compensation reference current to improve the steady-state torque and hence the speed responses. A torque observer is designed to estimate the instantaneous motor torque, which can be used as the feedback of the proposed LVSC scheme. Extensive experimental investigations have been carried out in order to evaluate the performance of the scheme. Test results obtained demonstrate the effectiveness of the proposed control scheme in reducing torque ripples significantly.