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Iron Loss Measurements under PWM Excitation for Ring Cores Made of Ultrathin Electrical Steel Sheets for a Stator Core

The iron loss of an induction motor powered by the sinusoidal wave of a commercial power source has been remarkably decreased by improving the electrical steel sheet used in a motor. However, in recent years, the permanent magnet motor and induction motor used in electric vehicles are often powered by a Pulse Width Modulation (PWM) inverter which shows good controllability. Iron loss in a stator core is increased by the carrier wave used in the PWM inverter. The iron loss of a ring core specimen made of electrical steel sheets of three kinds of thicknesses was evaluated under PWM inverter excitation. The thicknesses of the prepared electrical steel sheets were 0.08 mm, 0.1 mm, and 0.35 mm, respectively. In addition, in this paper, a number of problems that present when iron loss is evaluated under PWM excitation were investigated. For instance, the influence of switching-noise and dead-time of the PWM inverter on the iron loss were examined. Moreover, relationships between the carrier frequency, the modulation index and the iron loss were investigated. As a result, it was found that the iron loss of the ultrathin electrical steel sheet does not increase much even under PWM excitation.