Abstract：Temperature rise calculation is a complex problem in modeling high-power high-frequency transformers (HFT). An accurate and fast thermal model is significant for the optimal design and stable operation of HFT. At present, lumped parameter thermal network model is usually built through dimensionality reduction, and its calculation precision is easily affected by structural parameters. It is difficult to achieve accurate hot spot prediction in optimizing a wide parameter range. A three-dimensional thermal model of HFT considering anisotropic thermal conductivity is constructed based on the finite difference method (FDM). The discretization error of the three-dimensional thermal model is quantitatively analyzed, which is mainly affected by the loss density, thermal conductivity, and size of the finite difference element. In order to minimize the number of finite differential elements while ensuring the calculation accuracy of the thermal model, three-dimensional sizes of the differential element are adjusted actively according to the discretization error expression. For HTF with nanocrystalline core and litz wire winding, the element sizes in the direction along the width, height of winding and the thickness of core are the key parameters affecting the accuracy of temperature rise calculation. The parameter adaptability of the proposed thermal model is verified in detail with finite element simulation, including structural parameters, loss density, and heat dissipation conditions. The results show that the maximum error of the model is less than 10% in a wide range of parameters. However, the error of the traditional lumped parameter thermal network model is significantly affected by the structural parameters, and the error varies in the range of 10%~80% within the same parameter variation range. Based on the proposed thermal model, the efficiency-power density optimal design of a 10 kHz 150 kW transformer was carried out with the parameter scanning method. The upper limit of temperature rise was set to 100 K, and the differential element sizes were adjusted according to the error of less than 5 K. The optimization design program calculated 500 000 design points within 371 s with parallel computing, and the average time of three-dimensional thermal model calculation for a single design point was 2.8 ms. The temperature rise calculation results of the design points on the optimal design boundary were verified, and the error was less than 5.5%. Compared with finite element simulation and the lumped parameter thermal network model, the proposed three-dimensional thermal model based on FDM balances calculation accuracy and calculation speed. On the optimal design boundary, with the increase of power density, the transformer efficiency gradually decreases, and the temperature rise gradually increases. The maximum power density to meet the 100 K temperature rise requirement was about 9 kW/L, and the transformer efficiency was about 99.82%. A 150 kW transformer prototype was processed according to the optimized design point with maximum power density, and the maximum temperature rise was 103 K under rated working conditions.
骆仁松, 汪涛, 文继峰, 王子龙, 虞晓阳. 大功率高频变压器三维温升计算及优化设计方法[J]. 电工技术学报, 2023, 38(18): 4994-5005.
Luo Rensong, Wang Tao, Wen Jifeng, Wang Zilong, Yu Xiaoyang. Three-Dimensional Temperature Calculation and Optimization Design Method for High Power High-Frequency Transformer. Transactions of China Electrotechnical Society, 2023, 38(18): 4994-5005.
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2023, Vol. 38 
