Piecewise variable parameter loss model of laminated steel and its application in fine analysis of iron loss of inverter-fed induction motors

Due to the coaction of supply harmonics and harmonic fields inside the motors, the mechanism and distribution characteristics of iron losses become more complicated in inverter-fed induction motors. Therefore, accurate prediction and fine analysis of iron loss are very important at the design stage of high-efficiency inverter-fed induction motor. In order to predict the iron losses accurately, this paper proposes a piecewise iron loss model whose parameters vary with the amplitude and frequency of flux density, and two additional flux density terms are introduced to the classical iron loss model considering the nonlinearity of magnetic material and harmonic fields. With this model, the iron losses are calculated for an inverter-fed 5.5kW induction motor. The results reveal the distribution characteristics of hysteresis and eddy current losses in stator and rotor cores, and acquire the characteristics of additional iron loss caused by harmonic fields. By the comparison of predicted and measured no-load iron loss under different supply voltages and switching frequencies, the proposed model and analysis results are validated.