高频磁谐振超导空心变压器的理论与实验研究

The high-frequency transformer (HFT), as a key component of DC-DC converters in power electronic transformer (PET), plays a role of voltage conversion, power transmission and electrical isolation, and its size, weight and loss determine the performance of PET. Being restricted by losses and magnetic saturation of iron core, HFT with iron-core is difficult to achieve a large capacity, but the efficiency of air-core HFT is a little lower. Applying superconducting technology and magnetic resonance technology into air-core HFT can avoid the loss and the saturation of the iron core, improve the efficiency and the capacity of the HFT, reduce the volume and the weight, and overcome the problem that conventional HFT is difficult to achieve a large capacity. Up to now, the study of high-frequency magnetic resonant superconducting air-core transformer has not been carried out internationally. Hence, this project will carry out research on a new-type transformer of high frequency magnetic-resonance type air-core superconducting transformer: studying the characteristics of high-frequency ac-losses, current-carrying capacity, and the maximum frequency of superconducting tapes and coils; studying the method to reduce ac losses of superconducting coils; optimizing the design of superconducting coils; fabricating the model prototype of the transformer, testing and analyzing its operating characteristics and electromagnetic compatibility characteristics, so as to obtain optimization method of high-frequency magnetic resonant air-core superconducting transformer with both high efficiency and large capacity. This work can provide technical support for the development of both large-scale renewable energy grid and DC power transmission technology.

作为电力电子变压器中DC-DC变换器的关键部件，高频变压器不仅承担电压变换、能量传输与电气隔离的功能，其体积、重量、损耗更决定了电力电子变压器的性能。受磁芯损耗与磁饱和的限制，高频铁芯型变压器难以实现大容量，而空心型变压器的效率又偏低。将超导技术与磁耦合谐振技术用于高频空心变压器，既可避免磁芯损耗与磁饱和问题，又能提高效率与容量，降低体积与重量，从而克服常规铁芯变压器高频下难以实现大容量的难题。目前，国际上对高频磁谐振超导空心变压器的研究尚未开展。为此，本项目将对高频磁谐振超导空心变压器这一新型变压器开展研究：研究高温超导带材的高频损耗、载流能力及极限频率特性，以及超导绕组高频损耗的减小方法；在此基础上，优化设计并研制模型样机，并对其运行特性与电磁兼容特性进行测试分析，从而获得高效、大容量高频磁谐振超导空心变压器的优化设计方法，为大规模可再生能源并网与直流输电技术的发展提供技术保障。

高频变压器是电力电子变压器中DC-DC变换器的关键部件。磁芯型高频变压器难以实现大容量，而常规绕组空芯型变压器虽可提高容量，但效率偏低，其效率与线圈电阻有关。鉴于高频谐振式变压器可以提高效率，及超导体独有的低损耗特性，将超导体用于谐振式高频空芯变压器具有较大效率与容量优势。为此，本文项目系统开展了高频谐振式超导空芯变压器的理论与实验研究，主要成果如下：对典型高温超导带材临界电流的各向异性特性进行了测量与分析，并对临界电流的各向异性实验数据进行了解释，确定了钇系二代带材做超导变压器线圈绕组材料更合适。实验和仿真研究了高温超导带材及线圈的高频交流损耗特性，给出了高温超导带材和线圈的交流传输损耗随频率的变化规律，阐明了二代高温超导带材基底磁性的强弱对不同损耗分量的影响机理，结果表明，无磁性基底高温超导带材更适合绕制高频超导变压器。为定量评估超导带材及线圈的适用频率范围，提出了“极限频率”参数。为提高变压器的效率，研究了磁通分流器减小高温超导绕组交流传输损耗的方法，对单饼/双饼线圈用磁通分流器的几何尺寸和位置进行了优化设计，阐明了磁通分流器减小超导线圈交流传输损耗的机理。仿真研究了磁通分流器对线圈高频传输损耗的影响，定量评估了磁通分流器可有效减少超导线圈总交流损耗的频率和电流范围。理论分析了不同磁谐振拓扑的能量传输特性，综合考虑电压增益和补偿电容标幺值，选定了适合作为变压器的谐振拓扑类型。基于所选拓扑，设计了一台100 kVA高频谐振式超导空芯变压器。为验证设计方案的正确性，制作了容量为2kVA、额定频率为2.2kHz的高频谐振式高温超导空芯变压器样机，并测试了不同输入参数时样机的运行特性。结果显示高频谐振式超导空芯变压器样机的一些运行特性与常规变压的存在显著不同，在100V方波输入时所设计样机的运行效率为94.5%。