Thermal Modeling and Analysis of Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Abstract

Variable flux memory machine (VFMM) can be regarded as a promising candidate for electric vehicles (EVs) owing to its advantages of excellent flux adjustment capability and overall efficiency improvement over an extended operating range. However, the uncertain internal thermal behavior due to magnetization state (MS) change has an immense influence on electromagnetic performance of permanent magnet, which makes the precise MS estimation of low coercive force PM a challenging issue. To explore the benefits of MS manipulation on temperature rise reduction and provide an effective method to accurately evaluate temperature rise in VFMM, a magnetic-thermal coupling model of the newly developed hybrid-magnetic-circuit VFMM accounting for different MSs is established in this article. The lumped parameter thermal network (LPTN) model and computational fluid dynamics based finite-element (FE) method are employed to analyze the temperature characteristics, respectively. First, the losses of the investigated machine are calculated by adopting both the FE method and analytical equations. Afterward, the equivalent thermal resistances and heat transfer coefficients are determined by employing the LPTN model. Meanwhile, FE modeling is employed to analyze the three-dimensional thermal field distribution. Finally, a prototype machine is fabricated and experimentally measured, which can confirm the validity of the theoretical analyses.