Reduction of numerical errors of time-stepping finite element analysis for dynamic simulation of electric machines

The time-stepping finite element method (TS-FEM) can couple the magnetic field, electric circuit and mechanical torque balance equations together and has been widely used to simulate the dynamic characteristics of electric machines. Despite its heavy computational burden, the accuracy of TS-FEM is still limited by a host of practical constraints. Also, it is difficult to accurately model the sliding surface of the stator mesh and the rotor mesh in rotating electric machines. In this paper, a curvilinear element to approximate the curved geometry of sliding surface is presented to increase the computational accuracy. To reduce the numerical error of the derivative quantities, a modified nonlinear iterative formulation is adopted. To reduce the computing time, an adaptive time step size algorithm is also proposed. The proposed strategy and algorithm are verified by the FEM examples as reported in this paper.