FEM calculation of rotor losses in a medium speed direct torque controlled PM synchronous motor at different load conditions

A numerical analysis of rotor losses in a medium speed direct torque controlled permanent-magnet synchronous motor (PMSM) is presented. The calculation of stator currents at no-load and at rated torque was performed by using a DSP-based emulator, which simulates the performance of a real direct torque controlled PMSM. The emulated stator currents were used in the two-dimensional finite-element method analysis where the rotor losses were calculated. It is shown that in the medium speed direct torque controlled PMSM, the rotor losses are considerably higher when operating at no-load compared to rated torque operation at the same rotation speed. Calculated rotor losses are compared to the measured no-load losses of the direct torque controlled PMSM at 7500 rpm.