Recent advances in modular permanent magnet machines: electromagnetic and thermal perspectives

This paper reviews recent advances in modular permanent magnet (PM) machines and their associated thermal management strategies. It begins by examining developments in conventional PM machines and highlighting their limitations, particularly in fault tolerance and manufacturability. To overcome these challenges, modular stator configurations have been extensively investigated over the past decade. The review discusses the key advantages of modular PM machines, including improved torque density, efficiency, operational reliability, and enhanced fault-tolerant capability, supported by findings from recent studies. The paper then presents a comprehensive review of state-of-the-art thermal management techniques for PM machines, emphasizing their importance in maintaining performance, reliability, and durability under increasingly high-power densities and thermal stresses. Both passive and active cooling approaches are considered, including air cooling, liquid cooling, heat pipes, oil-spray cooling, shaft cooling, and emerging ferrofluid-based cooling technologies. Advances in thermal modelling and coupled electromagnetic–thermal optimization are also highlighted as important enablers for improving machine performance and efficiency. Furthermore, the review explores the interaction between stator modularity and thermal management, with particular attention to how modular machine architectures affect heat generation, thermal paths, cooling integration, and overall thermal performance. Finally, the paper identifies key research challenges and outlines future opportunities for the development of high-performance, thermally robust PM machines for next-generation energy and transportation applications.