Analysis of magnetic field and torque for all-harmonic-torque motor with surface-mounted permanent magnets

With the development of the advanced industrial products and technologies, the requirements for permanent magnet synchronous motors (PMSM) with high torque density are increasing. This paper proposed a new type of PMSM, named All-Harmonic-Torque PMSM (AHT-PMSM), which could use all harmonics of the magneto motive force (MMF) generated by permanent magnets and armature currents to enhance the electromagnetic torque. The stator windings structure, drive converter configurations and control model of the AHT-PMSM are illustrated firstly. And then the harmonic characteristics of the MMF generated by permanent magnets and armature currents are analyzed. It is found that the MMFs of permanent magnets and armature currents include the same order harmonics and each order harmonic is orthonormal for each other. Finally the calculation process of the average electromagnetic torque for AHT-PMSM based on harmonic MMFs is deduced. It is demonstrated that the theoretical average electromagnetic torque of AHT-PMSM is improved by 23% comparing to that of the normal sinusoidal PMSM when they are with the same structure sizes and armature MMFs. A 24-slot/4-pole AHT-PMSM and sinusoidal PMSM prototypes with the same sizes are modeled and manufactured, the comparison conclusion is validated by the finite element analyses (FEA) and experimental results.