Abstract

Due to marked axial and tangential magnetic leakage and low torque density of APMG, an external magnetic regulating ring is developed in this study based on APMG to form a DEM-APMG structure of bidirectional excitation and bidirectional modulation. The low-speed permanent magnet rotor of the DEM-APMG is sandwiched between the inner and outer flux regulating rings, which can convert the axial and tangential flux leakage of the APMG into useful harmonics to increase the output torque and torque density of the DEM-APMG. In this study, mathematical analysis is used to describe the air gap magnetic density and electromagnetic torque model of a DEM-APMG, which essentially describes the root cause of the increase in torque density. Using 3-D finite element static and dynamic simulations, the transmission characteristics of the APMG and DEM-APMG are compared and analyzed. Results show that the maximum static torque of the DEM-APMG high-speed and low-speed permanent magnet rotor with the same outer diameter increase by 22.7% and 23.8%, respectively, compared with APMG, 26% and 29%, respectively, in steady-state operation, and the torque density increases by 24%. The influence of the primary structural parameters on the transmission characteristics is also investigated using the control variable method. Results show that the duty cycle of the magnet adjusting block, the axial length of the high-speed permanent magnet and the low-speed permanent magnet have the strongest effect on the torque density of the DEM-APMG. When the axial length of the high-speed permanent magnet and low-speed permanent magnet is 8mm, and the duty cycle is 0.4, the torque density can reach the optimal value of 156kNm/m³.