Torque ripple minimization in surface-mounted PM drives by means of PI + multi-resonant controller in synchronous reference frame

Non-sinusoidal back electromagnetic forces cause torque ripple in permanent magnet synchronous motors. These harmonics should be reduced by means of an appropriate current control to improve performance. Good results have been obtained with linear regulators such as repetitive controllers in synchronous reference frame (SRF) and resonant controllers in stationary frame. Repetitive controllers present drawbacks such as difficult frequency adaptation, due to its requirement for variable sampling frequency. On the other hand, previous approaches that employ resonant controllers in stationary frame pose several problems. These implementations are quite resource-consuming, since they need the online computation of trigonometric functions, and when the compensation is not limited to just low frequencies, instability occurs due to the system delay. In this paper, it is proposed to use resonant controllers in SRF for torque ripple minimization in surface-mounted permanent magnet machines, so that it is possible to reduce their number by four. Additionally, cosine terms calculation is optimized by Taylor series, and a frequency adaptive phase lead is included in each resonant controller to compensate the plant delay. In this manner, an effective torque ripple minimization is achieved with optimum resource-consumption and good stability margins, even if high and variable frequency components are compensated.