Unified theory of torque production in AC, DC and reluctance motors

This paper uses the flux-MMF diagram to compare and contrast the torque production mechanism in seven common types of electric motor. The flux-MMF diagram is a generalized version of the flux-linkage versus current (ψ-i) diagram for switched-reluctance motors. It is illustrated for switched-reluctance, synchronous-reluctance, induction, brushless AC, brushless DC, interior PM and DC commutator motors. The calculated flux-MMF diagrams for motors with the same electromagnetic volume, airgap, slotfill and total copper loss are shown and are used to compare the low-speed torque and torque ripple performance. The motor designs used were reasonably optimized using a combination of commercially available motor CAD packages and finite-element analysis