Influence of Critical Parameters in Lumped-Parameter Thermal Models for Electrical Machines

This paper investigates the influence of some critical parameters in lumped parameter thermal network (LPTN) models for electrical machines. Even though the conduction thermal resistances in LPTN models are well defined by analogy to electric circuit, some critical convection thermal resistances are still difficult to compute and usually determined by empirical rules based on the previous publications. Thus, these parameters, including the equivalent thermal resistance between the frame and the ambient, and the convection coefficients within the machine, e.g between the frame and the inner air, the end-winding and the inner air, the rotor and the inner air, as well as the equivalent airgap thermal resistance, etc., are discussed and evaluated. Moreover, the winding models and the estimation of the equivalent thermal conductivity are also discussed. Based on a totally enclosed natural cooled interior permanent magnet synchronous machine, a thermal analysis software package Motor-CAD is employed in this paper to provide a reference for comparison.