Online stator resistance tracking for reluctance and interior permanent magnet synchronous motors

In the frame of the green economy, anisotropic synchronous motors are gaining considerable shares of market. There are already several interesting proposals about the accurate magnetic modelling of their complex magnetic structure, that generally require the a priori knowledge of the stator resistance. It is true that there are many papers even about the resistance estimation, but quite surprisingly most of them either require the knowledge of other parameters or do not meet the specifications on accuracy and online tracking. Above all, existing injection-based techniques are oriented to isotropic motors and the injection is given as reference to the current component that is not involved in the torque production. The simple transfer to anisotropic motors would cause non-negligible torque ripple. This paper focuses a new method for the online estimation and tracking of the stator resistance, specially suited for anisotropic motors. The usual injection procedure is reversed, i.e. there is a current injection followed by a voltage measurement. It will be demonstrated that the method features a resistance measurement with the best signal-to-noise ratio, for a given torque ripple. The technique does not require the knowledge of any other parameter. The paper includes both the mathematical foundations and experimental results on a laboratory prototype.