Forced air-cooling of modular flux switching PM machines using flux gaps as cooling channels

This paper investigates the thermal performance of modular flux-switching permanent magnet (FSPM) machines under forced air cooling. Unlike conventional designs with continuous stator iron core, the modular configuration with segmented stator core introduces flux gaps between stator segments that can be used as extra cooling channels to increase the internal heat exchange surface area. To assess the impact of this innovative cooling design, models with varying flux gap widths (0–8 mm) were analysed using 3D computational fluid dynamics (CFD) modelling. Results indicate that at constant inlet air speed, the lowest machine temperature is achieved at 1 mm flux gap. Under constant pressure loss, the optimal cooling is achieved at a 4 mm flux gap. Although extreme flux gap widths hinder the cooling efficiency, the modular FSPM machines still outperform their nonmodular counterparts thermally. The study also examines the effect of rotor speed, revealing that higher speeds induce greater turbulence and reduce machine temperature, particularly beyond 2800 rpm, albeit with increased system pressure loss. The CFD simulation results were validated through a series of thermal experiments, confirming the accuracy of the CFD models and demonstrating the feasibility of using flux gaps as cooling channels in modular FSPM machines.