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| Equivalent Model of Temperature Field and Temperature Field Analysis of Interior Permanent Magnet Synchronous Motor Based on Electromagnetic-Thermal Bidirectional Coupling |
| Wang Yubin, Lin Yang |
| College of New Energy China University of Petroleum (East China) Qingdao 266580 China |
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Abstract Accurately determining the temperature distribution during motor operation is crucial for safe operation. As a boundary condition in thermal field analysis, the heat transfer coefficient at the motor surface significantly impacts the accuracy of temperature distribution calculations. The main factors include motor size and the temperature difference between the motor surface and the surrounding environment. The coefficient becomes a nonlinear variable that changes with the environmental temperature difference, resulting in significant discrepancies between finite element calculations and experimental values. This paper proposes a correction method for the heat transfer coefficient based on iterative electromagnetic-thermal bidirectional coupling.
Using an 18-slot, 8-pole interior permanent magnet synchronous motor (IPMSM) as a case study, the heat sources are first analyzed, including copper losses in the windings, core losses, eddy current losses in the magnets, windage losses, and mechanical losses. The impact of temperature on the material properties of motor components is also considered to recalibrate motor losses during the electromagnetic-thermal coupling process. The temperature field analysis considers the three modes of heat transfer: conduction, convection, and radiation. An equivalent temperature field model is constructed. Heat conduction within the motor, between components such as windings and the stator-rotor, is determined by equivalent thermal conductivity factors based on slot fill and stacking coefficients. For internal convection of IPMSM, the motor is divided into blocks based on flow velocity, and the equivalent thermal conductivities are determined using empirical methods. Heat transfer between the motor surface and the environment is analyzed using appropriate heat transfer coefficient formulas based on the motor’s actual structure and the principle of similarity. By considering motor size and the temperature difference between the motor surface and the surrounding environment, the heat transfer coefficient is corrected using the results from electromagnetic-thermal bidirectional coupling calculations, thus improving the accuracy of the temperature field distribution. Finite element temperature field calculations for various operating speeds (800 r/min, 900 r/min, and 1 000 r/min) are performed using the empirical formula and the proposed correction method. Experimental results indicate that the proposed correction method reduces the error between the housing temperature field calculated by finite elements and the experimental data to within 4%. The base temperature error is reduced to within 3%. Compared to the empirical formula, this method effectively reduces the discrepancy between the finite element calculation and experimental results.
The following conclusions can be drawn. (1) The proposed heat transfer coefficient correction method, which accounts for motor size and the actual operating temperatures of the housing and frame, significantly reduces the error between finite element calculations and experimental results. (2) During motor operation, the material properties of the permanent magnets and armature windings change with temperature, resulting in variations in heat loss sources. The electromagnetic-thermal bidirectional coupling analysis method is more accurate than one-way coupling in reflecting the motor's actual operating conditions. (3) The frame structure has an impact on the motor's temperature field. The winding ends closer to the frame have lower temperatures than those farther from the frame. This structural effect should be considered in thermal field analysis.
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Received: 30 October 2024
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2025, Vol. 40 
