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Iron losses in current-controlled PWM inverter fed induction machines

Modern PWM inverters utilise high switching frequency and are frequently operated as current controlled (CCPWM). Due to existence of the higher order voltage harmonics in inverter output voltage, an increase in induction motor iron loss inevitably takes place. This paper investigates experimentally iron core losses in two PWM inverter fed induction motors, with closed loop current control of ramp comparison type. The machines are operated under no-load conditions and particular emphasis is placed on influence of inverter switching frequency on the iron loss increase. Tests were performed for switching frequencies in the range between 3.35 kHz and 7.5 kHz. It is shown that increase of switching frequency above approximately 4 kHz has insignificant effect on the total iron loss.