Decomposition of Electric Motor Torque According to Electromagnetic Field Sources

This paper proposes a systematic approach to isolate and quantify electromagnetic forces and torques between any two distinct parts of an electric motor. The approach is based on a decomposition of the magnetic field into components that are generated by different magnetized or current-carrying motor parts. Forces and torques exerted by the field components can be computed using the conventional force and torque formulas. The proposed decomposition is applied to a squirrel-cage induction motor and to a permanent magnet synchronous motor. In these examples, the magnetic fields are decomposed according to current-carrying conductors, magnetized iron, and permanent magnets. Thereafter, the torques exerted by these fields are specified. The results predict which part-pairs of the motor produce the desired and undesired behavior, for example, torque and torque ripple, respectively.