A Simple but Reliable Loss Model for Inverter-Supplied Induction Motors

A semiempirical induction motor loss model is developed as a function of motor power rating. The aim is the estimation of losses caused by harmonic-distorted (e.g., PWM) current and voltage supplies. The model may consider harmonics between about 100 and 20 000 Hz and is constructed for power ratings between 1 and 1000 kW. Losses in rotor, stator, and iron (including most important stray losses) are separately estimated and suitably combined. This leads to a simple penalization factor for the time-harmonic currents, which is a function of motor size and which is quasi-linearly depending on harmonic frequency. Total losses are then calculated by the superposition of separate harmonic current or voltage effects. The penalization factor is experimentally verified. The importance of iron (plus stray) losses has been clearly shown. The model predictions are in close agreement with loss measurements on inverter-fed induction motors.