Analysis of induction motors based on the numerical solution of the magnetic field and circuit equations

A method for the analysis of induction motors is presented. The analysis is based on the combined solution of the magnetic field equations and the circuit equations of the windings. The equations are discretized by the finite element method. The magnetic field is assumed to be two-dimensional. The three-dimensional features i.e. the skew of the rotor slots and the end-region fields are taken into account within the two-dimensional formulation. The general time-dependence of the field and the motion of the rotor are modelled correctly in a step-by-step solution. The amount of computation is reduced significantly if the time-dependence is assumed to be sinusoidal and phasor quantities are used in the solution. The method is applied to the calculation of a cage rotor motor and of a solid rotor motor. The sinusoidal approximation gives good results in the computation of steady-state locked-rotor quantities, but it does not model the motion of the rotor properly. The step-by-step method is used for computing machine quantities in steady and transient states. For instance the operation of the solid rotor motor supplied by a static frequency converter is simulated. The results obtained by the method agree well with the measured ones.reviewe