For the high-speed permanent magnet synchronous motors (HSPMSMs), their magnetic fields are more complicated with the rotating magnetization and harmonics considered. Furthermore, there are interaction effects on motor iron loss from high frequency, temperature and compressive stress. In order to obtain the accurate HSPMSM iron loss calculation model, different iron loss models are proposed considering these physical factors, and the iron loss model considering the interaction effect of the multi-physics factors is given. The magnetic field, temperature field and stress field are analyzed for HSPMSM by FEM. Then the proposed models are employed to calculate the iron loss of the silicon steel sheet and the prototype. The accuracy of the proposed iron loss model, which can consider the interaction effect of the multi-physics factors, is verified by the experimental test measurements on the prototype.

Aiming at the shortcomings of complex mechanical transmission structure and low efficiency of the existing belt conveyor driven by asynchronous motor, this paper focuses on the investigation of a new type of low-speed high-torque-density direct-drive permanent magnet synchronous motor (LHDPMSM) for driving the belt conveyor. The proposed LHDPMSM utilizes external rotor structure to achieve the goal of fully direct drive of the belt conveyor. First, the topology and advantages of the straight-shape external-rotor LHDPMSM is introduced. Then the selection rules of the pole-slot combination are studied. Furthermore, an improved subdomain model is established based on the idea of segmentation for fast calculation of the no-load magnetic field of the proposed straight-shape external-rotor LHDPMSM. Moreover, the operating performance of the proposed LHDPMSM with load fluctuations was verified by FEA. In addition, an efficient cooling system based on Z-shape water channels and hollow shaft was designed, and a LPTN model was established for temperature fast calculation. Since the cooling system has a negative impact on the shaft mechanical strength, the mechanical strength of the shaft and other fragile components of the LHDPMSM was analyzed to ensure the safe operation of the motor. Finally, a prototype is manufactured and tested to validate the design concept introduced in this paper.

In order to accurately estimate the temperature rise for high‐power high‐speed permanent magnet machines (HSPMMs), a novel temperature calculation method considering the non‐linear variation of material properties with temperature is proposed based on multi‐physics co‐simulation analysis. According to the theory of computational fluid dynamics and heat transfer, the computation model of fluid–solid–heat coupling heat transfer is established, and the coupled field is calculated using finite volume method with fundamental assumptions and corresponding boundary conditions. With the influences from temperature gradient and water flow rate considered, the heat transfer coefficients of water pipe surfaces are obtained by the application of the inverse iteration method. Thus, HSPMM temperature and fluid field can be simulated numerically by the finite volume methods, while the spatial temperature distributions for the machine main components are analysed in this study. The 1.12 MW, 18,000 rpm HSPMM is prototyped with experiments conducted on it, while the test data are then compared with the calculated results, which validate the correctness of the solution method of the coupled field.

In order to address the challenges of high loss density, difficult heat dissipation, and irreversible demagnetization in high temperature of high-speed permanent magnet machine, an innovative cooling structure with axial ventilation and self-cooling rotor is proposed to enhance temperature distribution. The cooling efficiency of the cooling structure is defined, and the influence of the rotor vent on the electromagnetic and air friction loss is analyzed. The governing equation for the fluid flow in a rotating pipe is derived from a fluid model analysis of a ventilation hole rotating at any angle to the axis of rotation. The calculated results are validated against the results obtained from computational fluid dynamics. The sensitivity of rotor cooling performance to various control factors using the variance index method. Subsequently, the cooling structure was enhanced based on the findings of the analysis. The calculation results indicate that the heat dissipation effect of the axial ventilation self-cooled rotor has decreased by 4.17 °C compared to before the improvement. The temperature rise experiment verified the accuracy of temperature calculation and the effectiveness of the cooling structure, providing strong support for the design of axial self-ventilation cooling system for high-speed machines.