Losses in three-phase induction machines fed by PWM converter

The paper deals with the analysis and evaluation of test results of PWM converter-fed induction motors. The test results presented point out the dependency of the harmonic losses on the pulse frequency. The measured values were obtained by means of a novel high precision power-analyzer capable of measuring the harmonics of voltage, current and power. Following a detailed investigation regarding the sources of the harmonic losses the paper describes new methods for determining the harmonic losses by both calculation and measurement. The calculation is based on a new equivalent circuit comprising specific impedances for imaging the eddy-current circuits within the iron core derived from the fundamental equations of the three-phase asynchronous machine. These impedances permit the calculation of the harmonic iron losses under the influence of the eddy-currents in all sections of the magnetic circuit caused by the harmonics. Measured and calculated losses were found to correspond satisfactorily for the various voltage harmonics.