Improved transmission line model of the stator winding structure of an AC motor considering high-frequency conductor and dielectric effects

This paper proposes an equivalent circuit modeling method using the transmission line model to characterize the wideband behavior for the universal ac motors. Base on the measured network parameters of an ac motor, per-unit-length (PUL) transmission line parameters are extracted. Through analysis of the frequency-dependent PUL parameters, an equivalent circuit model is constructed with considering the high-frequency characteristics. The shunt admittance model is developed to capture the changing PUL capacitance by Lorentz model. Moreover, the resistance of the insulation sheet is modeled by analysis of the extracted PUL conductance. In addition, the series impedance model includes the skin effect of the winding conductors through investigation of the PUL inductance. The accuracy of the proposed equivalent circuit model is confirmed by comparing the PUL parameters with the previous transmission line motor model. The input impedance and the transfer impedance for the entire length of the phase line are compared with the measurement and the previous model results to verify the availability of the proposed equivalent circuit model. In addition, an electromagnetic (EM) field simulation including all of the conductors in the winding structure is implemented, and the simulation result is compared with the measurement. The proposed modeling method and EM field simulation method can be used to predict the wideband frequency characteristics of an ac motor for the initial motor design.