Application of automatic choice of step size for time stepping finite element method to induction motors

Although the time stepping finite element method (FEM) is a powerful tool to simulate the operation of electrical machines, it has not been applied to practical problems widely because it requires a large amount of CPU time. This paper proposes to control the time step size automatically within the program to save the computing time substantially. It will be shown that only simple formulae for estimating the local truncation errors at each time step using Backward Euler's method or Crank-Nicolson's method are all that required to be derived. These formulae require no extra complicated computation. Hence the reported algorithm can be extended easily to many finite element investigations to make FEM a practical tool to industrial problems. The strategy in choosing the optimal step size is described. The proposed algorithm is used to study the transient behaviour of an induction motor.