电力电子变压器具有电气隔离、电压等级变换、电能质量调节等优点，在交直流输配电网、微电网、新能源并网等领域具有广泛的应用前景。高频变压器是电力电子变压器及隔离型DC/DC变换器的核心组成部分，其功率密度高，结构紧凑，散热问题是高频变压器的研究热点，而高频变压器中的高频振荡还会产生额外的高频损耗，使发热问题更为严重。本文对高频变压器的电磁-损耗-热进行综合分析，重点考虑了高频振荡导致的额外高频损耗对变压器温升的影响，以一台3 kW/40 kHz 纳米晶磁芯高频变压器样机为研究对象开展仿真和实验研究。首先，建立了考虑变压器分布电容的三维电磁模型，采用有限元分析法对高频变压器进行瞬态磁场及静电场分析；利用电场能量法求解高频变压器的分布电容，并对分布电容进行实验提取；将仿真分析结果与实验测试结果进行对照，验证了仿真分析方法的合理性。其次，综合考虑高频变压器的工作频率损耗及高频振荡导致的额外高频损耗，对纳米晶磁芯高频变压器的损耗特性进行了分析。对纳米晶磁芯的宽频域范围损耗特性进行了实验测量及研究，并基于广义斯坦梅兹公式和叠加定理分别建立了高频变压器磁芯损耗及铜损的数值模型；基于损耗计算模型，根据3 kW双主动全桥变换器样机的实验电压和电流波形，定量计算了高频变压器的损耗，并重点研究了高频振荡导致的额外高频损耗。最后，对高频变压器的温升特性进行研究，并对其散热结构进行了设计。建立电-磁-热多物理场模型，利用有限元仿真分析了高频变压器的稳态温度场分布，重点研究了高频损耗对高频变压器带来的温升影响；同时，通过实验测试了高频变压器样机在有无高频振荡时的温升数据，并将其与仿真分析结果对照，验证了仿真分析方法的合理性；针对高频变压器样机，设计了灌封导热硅胶的散热结构，并通过仿真和实验验证了散热结构的有效性。
Power electronic transformer has the advantages of electrical isolation, voltage level transformation, and power quality regulation. It has a wide application prospect in the fields of AC/DC transmission and distribution grid, microgrid, and new energy grid connection. High-frequency transformer is the core component of power electronic transformer and isolated DC/DC converter. Its power density is high, the structure is compact, and the heat dissipation problem is the research hotspot of high-frequency transformer. The high-frequency oscillation in high-frequency transformer will also produce additional high-frequency loss, which makes the heating problem more serious. In this paper, the electromagnetic, loss, and heat characteristics of high-frequency transformer are comprehensively analyzed, and the impact of additional high-frequency loss caused by high-frequency oscillation on the temperature rise of transformer is mainly considered. The simulation and experimental research are carried out on a 3 kW/40 kHz nanocrystalline core high-frequency transformer prototype.Firstly, a three-dimensional electromagnetic model considering the parasitic capacitance of transformer is established, and the transient magnetic field and electrostatic field of high-frequency transformer are analyzed by finite element analysis method; The electric field energy method is used to solve the equivalent parasitic capacitance of high-frequency transformer, and the equivalent parasitic capacitance is extracted experimentally; The simulation analysis results are compared with the experimental test results to verify the rationality of the simulation analysis method.Secondly, considering the working frequency loss of high-frequency transformer and the additional high-frequency loss caused by high-frequency oscillation, the loss characteristics of nanocrystalline core high-frequency transformer are analyzed. The loss characteristics of nanocrystalline core in wide frequency domain are experimentally measured and studied, and the numerical models of core loss and copper loss of high frequency transformer are established respectively based on the generalized Steinmetz formula and superposition theorem; Based on the loss calculation model, according to the experimental voltage and current waveforms of 3 kW dual active bridge (DAB) converter prototype, the loss of high-frequency transformer is calculated quantitatively, and the additional high-frequency loss caused by high-frequency oscillation is mainly studied.Finally, the temperature rise characteristics of high-frequency transformer are studied, and its heat dissipation structure is designed. The electric magnetic thermal multi physical field model is established, and the steady-state temperature field distribution of high-frequency transformer is analyzed by finite element simulation, with emphasis on the impact of high-frequency loss on the temperature rise of high-frequency transformer; At the same time, the temperature rise data of high-frequency transformer prototype with or without high-frequency oscillation are tested by experiment, and compared with the simulation analysis results to verify the rationality of the simulation analysis method; Aiming at the prototype of high-frequency transformer, the heat dissipation structure of potted thermal conductive silica gel is designed, and the effectiveness of the heat dissipation structure is verified by simulation and experiment.
