Physical Understanding of Multiple Saliencies in Induction Motors and their Impact on Sensorless Control

In the first part of the paper a detailed investigation of the physical reasons for the behaviour of an induction machine excited with high-frequency test signals is presented. The measured impedance curves are heavily influenced by the saturation level of the rotor slot bridges. The saturation phenomena of the closed rotor slots can be divided into mechanical angle-dependent and independent groups. The saturated and the opened rotor slots lead to non-sinusoidal hf-field distribution. The measured curves and the assumptions made are verified by FE calculations and an equivalent magnetic circuit. In the paper's second part a new method for sensorless control is presented. Because of the inimitability of the measured impedance curves, the method is based on the minimum error between the measured curves during the machine's operation and precommissioned reference curves. Operation at standstill, and even at zero-frequency, is possible without any problems.