Modeling of Iron Losses of Electrical Machines and Transformers Fed by PWM Inverters

With the development of power electronic techniques, pulse-width modulated (PWM) inverters are widely used to control electrical machines, to feed transformers and to interface renewable energy systems. There are abundant high frequency harmonics in the output voltage of a PWM inverter, which increase the iron loss and result in a de-rating of the machine or transformer. Predicting the iron losses caused by the PWM voltage is very important for the design of electrical machines and transformers fed by PWM inverters. Eddy current loss is the main part of the iron loss caused by PWM. In this paper, after analyzing the harmonic components of PWM voltage, the effects of different parameters of PWM on the eddy current loss are derived. The relationship of eddy current losses with switching frequency and amplitude modulation ratio is considered. The iron losses modeled with the proposed analytical methods of a single phase transformer are compared with results of time-stepping finite element analysis to gain confidence. The relationship of duty cycle and eddy current loss of PWM supplied DC motors is also studied in this paper.