Speed Estimation Based on Rotor Slot Harmonics in Multiphase Induction Machines Under Open-Phase Fault

Multiphase (i.e., with more than three phases) induction machines (MIMs) are particularly attractive for safety-critical applications, because they are able to operate under open-phase fault. On the other hand, algorithms for sensorless speed estimation are of great interest, since, e.g., they improve reliability and decrease cost and maintenance. Among these methods, the approach based on rotor slot harmonics (RSHs) is especially popular, due to advantages such as its independence from time-varying parameters (e.g., resistances and inductances). In healthy machines, usually the fundamental or any given harmonic component has ideally equal magnitude in all stator phases. The previous RSH-based techniques rely on this characteristic. Conversely, under open-phase fault there is current imbalance. Moreover, due to the postfault strategies for optimum current reference generation, such imbalance varies with the load. Thus, the existing RSH-based methods are not suitable for open-phase fault, and alternative ones should be developed. This paper addresses the sensorless speed estimation based on RSHs for MIMs under open-phase fault. The main RSHs obtained in faulty situations are studied. Then, accordingly, a speed estimation technique for MIMs under open-phase fault is developed, able to work with good accuracy despite the variable current imbalance. Finite-element and experimental results are provided.