Application and Verification of Spiral Water Cooling for Rotor in High-Power Density Motors

Effective thermal management of the rotor is crucial for high-speed permanent magnet (PM) motors seeking to enhance power density. This article proposes spiral water cooling (SWC) to effectively mitigate the rise in rotor temperature resulting from significant rotor eddy current losses in fractional-slot concentrated-winding motors. This advanced cooling structure consists of a hollow shaft with multiple spiral ducts on its surface and a rotor hub constructed from a high thermal conductivity material, joined together through the interference fit. By employing the spoke-type rotor in the prototype, the rotor hub comes into direct contact with the heat sources from other rotor components, thereby achieving exceptional heat dissipation capabilities. The 3-D computational fluid dynamics (CFDs) model is utilized to investigate the fluid flow characteristics of the SWC and elucidates the impact of parameters such as rotational speed, coolant flow rate, and duct size on the convective heat transfer coefficient (CHTC) of the cooling structure. In addition, the advantages of SWC are illustrated by comparing the cooling performance of SWC and hollow shaft cooling (HSC) with different cooling media. On this basis, the temperature distribution of each component of the prototype is forecasted. Experiments and simulations definitively proved the effectiveness of the proposed rotor cooling structure and the accuracy of the calculation results.

I. Introduction

High-speed permanent magnet synchronous motors (PMSMs) have outstanding advantages such as high power density, high efficiency, and good control characteristics, and have been widely used in electric drive systems [1]. In recent years, there has been an increasing focus within the research community on PMSMs with fractional-slot concentrated-winding (FSCW) stators because of their easy manufacturability, wide constant power speed range, and low torque ripple [2]. Furthermore, the configuration of FSCW with tooth-wound coils is more conducive to improving volumetric power density because of shorter end winding [3].