Discussion and correction of the equivalent circuit of induction motor and its torque generation

Abstract

To explore the actual electrical characteristics of the stator and rotor inside an induction motor, the magnetomotive force of each phase winding on both sides is expressed using a reasonable mathematical formula. According to Faraday's induction law, the counter electromotive force and induced voltage equations for both sides are derived. By substituting these mathematical equations into an Excel calculation worksheet, it is found that the electrical frequency cycles on both sides differ and their changing rules are identified. The voltages and currents of different frequency cycles on both sides are compared using the same unit average frequency periodic root mean square value. The comparison ratio provides the rotor equivalent impedance reference to the stator side, leading to the deduction of the correct induction motor equivalent circuit. The new equivalent circuit, verified through a series of circuit calculation analysis results, complies with energy conservation and Thevenin's theorem. From the overall energy distribution, it is observed that the active power on both sides’ accounts only for the copper loss and waste heat that cannot perform work. Conversely, the reactive power generates the magnetic field torque necessary to drive the load. Additionally, special periodic wave changes in the actual torque are discovered.