Thermal Modelling and Characteristics of Permanent Magnet Synchronous Machines with Single and Dual Rotors Accounting for Different Cooling Methods

This paper evaluates the thermal characteristics of surface-mounted permanent magnet (PM) synchronous machines (SPMSMs) with single inner or outer rotor, and dual rotors by using high-fidelity lumped-parameter thermal models (LPTMs). These high-fidelity LPTMs can accurately predict both the average and midpoint temperatures by introducing compensation thermal resistances, thereby both distributed loss generation and multi-dimensional heat flows can be considered. The developed LPTMs are further applied to evaluate the thermal performance of inner-rotor, outer-rotor, and dual-rotor PMSMs under natural and liquid cooling conditions. It is shown that the thermal limit of the winding insulation severely restricts torque production, and thus, frame liquid cooling is most suitable for inner-rotor PMSMs, while hollow shaft liquid cooling is more effective for outer- and dual-rotor PMSMs. Meanwhile, with the same space envelope and thermal constraints, the inner-rotor PMSM can produce comparable or even higher torque compared to the outer-rotor counterpart. However, the dual-rotor PMSM exhibits inferior torque output capacity, which is not only limited by its electromagnetic characteristics but also further deteriorated due to the limited heat dissipation capability of the internal stator.