Numerical computation of torques in permanent magnet motors by Maxwell stresses and energy method

A numerical computation of torques for three different permanent magnet excited motors is presented. In all cases the no-load torques have been derived from the vector potential, which is computed by the finite-element method, both by directly applying the Maxwell stress formula and as the derivative of the magnetostatic energy with respect to the rotation angles. In one of the cases the on-load torques have also been computed. Instead of the energy function, a total work function at constant current is used. The agreement between the torque values obtained by the two methods is very good