Temperature Estimation of Field-Oriented Control Induction-Motor Drives Based on DC-Signal Injection Suitable for Low Inertia

Thermal protection is an important aspect that should be considered in ac machines to prevent reduction of the lifetime. For economic reasons, temperature estimation is preferable than the installation of thermal sensors. Thus, several proposals based on dc-signal injection have been reported. Their main drawback is that a certain torque ripple is produced during the injection. On the other hand, the already published filtering techniques proposed to extract the dc components from the phase voltages and currents are based on transforming the per-phase variables to a synchronous reference frame, where the fundamental component is eliminated. For this transformation, the rotor position is needed. It is shown in this paper that, due to the disturbance caused in the position due to the torque ripple, the stator resistance estimation is deteriorated when the inertia is not high enough to make this perturbation negligible. In addition, a new technique is also presented to segregate the dc components from the phase currents and voltages, which is robust in terms of accuracy even when the speed/position is perturbed due to the injection. Experimental results validate the theory.