Modeling of induction machines including stator and rotor slot effects

Three-phase as well as single-phase induction machines form the backbone of a substantial portion of the adjustable-speed drives' applications. Among the current estimation techniques available for speed-sensorless induction motor drives, speed measurement based on rotor or principal slot harmonics (RSH or PSH) detection in machine line current happens to be a prominent one. In practice, two predominant RSH can be seen. The present paper attempts to investigate the effect of slot permeance on the production of RSH. Simulation studies on a small motor but with a popular stator, rotor slot, and pole combination suggest that their effect is less significant compared to rotor space harmonics effect. Also, out of the two aforementioned RSH, the cause of the less significant slot harmonic is shown to be the negative-sequence-current-induced reverse rotating field. Voltage unbalances and constructional imperfections can cause negative-sequence current even in a healthy machine. Thus, although the less significant RSH is absent in the simulated line current of an idealized machine running from a balanced supply, it can be detected in an actual machine.