Analytical Method of Permanent Magnet Torque Machine with High Torque for Considering the Influence of Armature Magnetic Field

Abstract

Compared to the conventional permanent magnet synchronous machine (PMSM), the main characteristic of permanent magnet torque machine (PMTM) with high torque is that armature current is high, which has a great influence on magnetic circuit saturation, so this paper proposes a novel analytical method (AM) considering this problem. The key of this new AM is to consider armature reaction flux and armature leakage flux, which are closely related to output torque. Firstly, the expressions, including magnetomotive force (MMF) generated by permanent magnets (PMs) and armature windings are derived, and meanwhile slotting effect is considered by planning flux path. In addition, the expression of leakage flux density generated by armature windings are calculated, and flux density equivalence coefficient of tooth is calculated to be 2/3, which is used to solve the problem of uneven saturation of each tooth. Then, based on main flux factor and leakage flux factor proposed, an improved iteration process is proposed, and by this new process, the flux density of each yoke and tooth can be obtained, which is beneficial to obtain more accurate air-gap flux density and flux linkage. Finally, a prototype of 60-pole 54-slot is fabricated, and the performances of the electric machine, such as back electromotive force (EMF) and output torque, are calculated by this new AM and finite element method (FEM). The results of FEM and experimental test show that this new AM is good enough to calculate the performance of PMTM.