Power Balanced Electromagnetic Torque Computation in Electric Machines Based on Energy Conservation in Finite-Element Method

Time stepping finite-element method can be used to compute the electromagnetic torque on the rotor of electric machines. During calculation, the magnetic field equations are solved for finding the field distribution, and Maxwell stress tensor method is usually used for force distribution. However, the solutions from the two different sets of mathematical systems cannot guarantee the energy input and output of the system are balanced. In some cases unrealistic results may occur in that, for example, the calculated efficiency is higher than 100%. In particular, the accuracy of force computation is largely dependent on the mesh qualities and relative position changes along the integration path. In this paper, an algorithm of power balanced torque computation based on considerations of energy conservation is presented. The main salient merit of this method is that it guarantees the input energy and output energy are balanced as the rotor moves, and the computed torque is less sensitive to mesh quality and position changes.