Core loss estimation method for PWM inverter fed induction motors

Due to the harmonic content of the distorted supply voltage, the iron losses of PWM inverter fed induction motors are greater than the iron losses measured with sinusoidal supply. The prediction of this loss increase has been the subject of many studies, but it can be still considered as an open research field, in particular when fast and reliable estimation methods are requested. In the paper a previously developed method to predict the iron losses with PWM supply in magnetic laminations (using toroidal samples or the Epstein frame) and special induction prototypes (with a plastic squirrel cage) has been now used to predict the iron losses of five industrial induction motors with aluminum die cast rotor cages. The measured iron loss values have been collected by means of the conventional no-load test, both under sinusoidal and PWM supply conditions. The reported analyses and comments allow a critical discussion of the proposed estimation method and of the no-load test under PWM supply.