Localization of the Losses in an Induction Machine Supplied by an Inverter

Abstract

In a previous paper, we have described a method of measurement and a simplified thermic model of the induction machine which allows to determine the heatings of the windings and of the magnetic circuit of the stator for different supplies. We carried on our investigations about the subject; with one more measurement (the rotor temperature), we deduce the value and the localization of the losses in the machine. The method consists in using a heating model and in determining the losses one knows badly in order to get heatings which are compatible with experiments. In this paper, after having briefly recalled the experimental device and the theoretic method, we propose measures allowing to identify the thermic model. There are many parameters indeed which are badly known and one must have recourse to tests led in simple conditions to adjust their values. Then, we test the method in the case of a sinus-wave supply. We put up the extra losses in the rotor, which are difficult to identify with another method. The model being well known, we can now study the losses when the machine is supplied by a square-wave voltage inverter. We give the distribution of the losses for different tests at synchronism (for different voltages or currents). We compare with the results we got with a sinus-wave supply. Finally, at nominal torque, we compare the heatings and the losses for different settings and we deduce, for the given configuration, which is the best supply. Then we discuss the precision of this method.