Fast Steady-State Analysis in Time-Stepping Finite-Element Simulation of Induction Motors Based on Virtual Blocked Rotor Techniques

Induction motor time-stepping finite-element analysis requires a lengthy transient response time to build up the complete steady-state magnetic field distribution in both stator and rotor. Various methods to speed up the convergence of the time-stepping finite-element (TS-FE modeling are investigated in this article. A so-called "virtual blocked rotor" technique is developed by using an eddy-current solver in the frequency domain to approximate the initial conditions, including the frozen permeabilities, potentials/energies, the stator winding and rotor bar currents, etc. Then, these well-prepared initial conditions are imported into the transient TS-FE time-domain solver (model). Significant reduction of the length of the transient response to reach convergence is accomplished. In addition, the promise of this method lies in its use in future large-scale design optimization studies. In order to further reduce the computational burden, a "virtual blocked rotor" concept/method in the TS-FE time-domain solution is also developed, which effectively reduces the required number of ac cycles and central processing unit real time to reach steady state.