Torque ripple minimization for PMSM using online estimation of the stator resistances

The tolerances and limitations in design and manufacturing of both motors and inverters lead to parasitic resistances in the phases. Therefore, the phase resistances are asymmetric, which causes an asymmetry among the phase currents which in turn leads to torque ripples. This paper proposes a novel scheme for torque ripple minimization using online estimation of unbalanced stator resistances. The stator resistances of a permanent magnet synchronous motor are estimated by recursive least squares in rotational reference frame in real time. Torque ripple reduction is achieved by a compensation scheme in stationary reference frame. Because the proposed estimation method requires relatively little additional computing time in a field-oriented control, it could also be applied in online fault diagnosis. The effectiveness of the proposed scheme is proven in simulations and test-bench experiments.