A Hybrid Field Analytical Method of Hybrid-Magnetic-Circuit Variable Flux Memory Machine Considering Magnet Hysteresis Nonlinearity

Abstract

Variable flux memory machine (VFMM) is considered a promising solution for traction drives due to their distinctive merits of globally high efficiency over an extended operating range. However, the variable flux property of the low-coercive-force (LCF) permanent magnet (PM) together with an interior hybrid magnet rotor structure brings great challenges for the magnetic field modeling of VFMM. To address the above issues, this article proposes a new hybrid field analytical method for a recently developed hybrid-magnetic-circuit VFMM (HMC-VFMM), which combines the magnetic equivalent circuit (MEC) solution, the Schwarz–Christoffel (SC) transformation, and the subdomain model. First, the remanences of LCF PMs subject to different <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> -axis magnetizing currents are determined by the MEC model, in which the nonlinear magnetic reluctances are calculated by the finite element (FE) model. Subsequently, the air-gap flux density distributions of the slotless stator model under different magnetization states (MSs) are predicted by adopting the open-circuit MEC model. Afterward, the relative permeance function is obtained by using SC transformation considering the stator slotting effect. Then, the no-load flux density distributions of the machine under different MSs are predicted by the proposed method. Besides, a subdomain model taking into account the armature reaction is employed to further obtain the torque characteristic of the machine. Finally, the effectiveness of the proposed method is verified by both FE simulations and test results.