Online Estimation of Per-Phase Stator Resistance Based on DC-Signal Injection for Condition Monitoring in Multiphase Drives

Multiphase drives with high reliability are receiving increasing attention by the research community in safety-critical applications. Condition monitoring is an effective way to improve drive reliability, because it can detect the development of faults and offer the possibility of predictive maintenance. Among the different condition monitoring methods, online estimation of stator resistance is a promising technique for its ability to detect high-resistance connections, overheating of stator windings and other defects. In this article, an online estimation method of stator resistance based on dc-signal injection is proposed for multiphase drives. The dc currents are injected in the subspace with the smallest main inductance to minimize the induced torque ripple. Phase voltages are measured and the dc components are extracted to calculate the resistance in all the phases. Compared with existing methods, the proposed method can estimate the per-phase stator resistance with higher accuracy and higher robustness, which provides additional benefits in condition monitoring applications. In addition, the proposed method is derived in a general way, which makes it applicable to most kinds multiphase drive systems. Experimental results on a nine-phase induction machine and a five-phase induction machine validate the high accuracy, high robustness, and high generality of the proposed technique.