Per-Phase Stator-Resistance Estimation by DC-Signal Injection in Open-Phase Fault-Tolerant Six-Phase Induction Motor Drives

Multiphase machine drives are advantageous over three-phase ones in features such as tolerance to open-phase faults (OPFs). Six-phase (6P) ones offer an excellent compromise between complexity and fault tolerance. In particular, those with a symmetrical arrangement of the stator phase windings and a single neutral point provide superior postfault capability. To ensure high reliability and performance, the stator resistance should be monitored. This can be attained with good robustness to uncertainties by dc-signal injection. This article proposes a dc-based resistance estimation method for symmetrical 6P induction machines that achieves the following main characteristics simultaneously for the first time: estimation of individual stator phase resistances and suitability for either healthy or OPF conditions. The dc injection is performed so that no torque ripple is produced and so that the increase in loss, peak current, and braking torque is relatively small. The method is designed so that it is robust to the deviation in the stator neutral-point voltage due to resistance asymmetry. Experimental results are provided.