Abstract This paper aims to establish the impedance calculation model of nonlinear copper-coated solid rotor induction motors. This model takes into account the magnetic field distortion caused by the non-linearity of the rotor core material. A method of impedance calculation based on an effective magnetization curve is proposed, which can calculate the permeability of the nonlinear rotor core at different slips and reduce the impedance calculation error caused by the non-linearity of the rotor material. Based on the effective magnetization curve, a simplified calculation method of rotor impedance considering temperature change is proposed to estimate the performance of the motor quickly. First, assuming that the magnetic permeability of the rotor core is a fixed value, the vector magnetic potential in the rotor surface domain is solved using the two-dimensional subdomain method of electromagnetic field on the copper-coated solid rotor model. Then, the analytical expression of the rotor core and the total impedance of the rotor is obtained. A method considering the nonlinearity of the rotor core material is proposed to calculate the magnetic permeability of the rotor core by equivalent magnetic field energy conservation from the original magnetization curve of nonlinear materials. The effective magnetization curve is obtained, and the permeability is calculated under different slips. The rotor core, rotor total impedance, electromagnetic torque, and power factor are calculated using the two-dimensional time-harmonic finite element method, effective magnetization curve analysis method, and original magnetization curve analysis method. The results show that the effective magnetization curve analysis method is more accurate than the original magnetization curve analysis method, especially at the stable operating point with a small slip. The resistivity and effective magnetization curve of the rotor copper layer and core at 200℃ are applied to the analytical method. A simplified calculation method is presented, which only changes the resistivity of the rotor copper layer and core. Therefore, the performance of the rotor can be calculated quickly when the temperature changes. However, because the change of the rotor core permeability is ignored, errors still exist in the calculated torque and power factor. The following conclusions can be drawn. (1) The analytical method calculates the permeability of the rotor core under saturation conditions, and the relative permeability of the rotor core surface decreases first and then increases with the slip increase. (2) The equivalent B-H curve analytical method is more accurate in calculating rotor impedance, electromagnetic torque, and power factor than the original B-H curve analytical method. (3) A simplified calculation method that only changes the material resistivity is presented, which can quickly calculate the steady-state performance of the motor when temperature changes. However, when the rotor temperature varies widely, it is necessary to evaluate the performance error at the maximum temperature to determine the applicability of this method.
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2024, Vol. 39 
