构建以新能源为主体的新型电力系统是实现“双碳”目标的重要途径，其中电力电子变压器（Power Electronic Transformer, PET）在新型电力系统建设中扮演着关键角色，发挥能量路由器功能。隔离变压器作为 PET 的电磁耦合核心器件，直接影响电力电子变压器的整体性能。面向高密度、高效率及高可靠性的应用需求，变压器的发展趋势呈现为中高频化与大容量化，受到业界的广泛关注。本文基于中频、大容量特性以及电力电子拓扑的大漏感需求，对兆瓦级中频变压器的损耗展开深入分析，提出相应的设计方案和损耗优化措施，并成功研制出1.5MVA/600Hz 兆瓦级中频变压器。主要内容如下：首先针对变压器铁芯材料选型及损耗展开研究，提出了一种适用于中频和兆瓦级容量应用场景下的铁芯材料选型方法，并对中频、兆瓦级应用的铁芯材料进行比选。其次，针对大尺寸硅钢铁芯拐角处的磁密不均和损耗聚集问题，提出新型斜角交错接缝的结构设计方法，降低铁芯损耗。基于铁芯磁密分布特性，对 IGSE算法进行修正，提高了在大尺寸铁芯截面下的损耗计算精度，指导铁芯损耗优化。其次，对变压器绕组形式和损耗开展研究，依据涡流效应特性和百安级电流通流需求，提出一种中频阶梯式电流下的绕组损耗分析方法，成功确定适用于中频百安级变压器的低损大通流绕组形式—铜箔绕组。基于 Dowell 模型，提出一种铜箔绕组厚度优化方法，精确计算并选取最佳铜箔绕组厚度，减少绕组交流损耗。随后，对兆瓦级中频变压器漏感集成进行研究，分析了兆瓦级传输条件下双有源桥式 DC-DC 变换器（Dual Active Bridge, DAB）的的辅助电感需求及损耗分布。提出了一种基于附加铁芯的兆瓦级中频变压器磁集成技术，实现 mH 级大电感集成，降低电力电子变压器传输损耗，提高功率密度。同时，提出了详细的附加铁芯结构与分布式气隙设计方法，相比单一集中式气隙方案损耗降低超过 20%。最后，成功研制出一款基于超薄取向硅钢铁芯铜箔绕组的 1.5MVA/600Hz 兆瓦级中频变压器样机。对铁芯和绕组设计进行了深入分析，并采用斜角交错接缝与铜箔厚度最优化等方法减小变压器损耗。同时，对变压器进行了耐压、开路、短路及功率循环等性能测试。实验证明，变压器效率高达 99.57%，满足设计指标要求，并已成功应用于东莞松山湖中压配网柔性互联示范项目。
The construction of a new power system with new energy as the main body is animportant way to achieve the goal of "double carbon", in which the Power ElectronicTransformer (PET) plays a key role in the construction of the new power system, playing the function of energy router. The isolation transformer, as the core device ofelectromagnetic coupling of PET, directly affects the overall performance of the powerelectronic transformer. For high-density, high-efficiency and high-reliabilityapplications, the development trend of transformers is medium-high frequency andhigh-capacity, which are widely concerned by the industry. In this paper, based on themedium frequency and large capacity characteristics and the large leakage inductancerequirements of power electronics topology, we analyze the loss of megawatt-classmedium frequency transformers, propose corresponding design solutions and lossoptimization measures, and successfully develop 1.5MVA/600Hz megawatt-classmedium frequency transformers. The main contents are as follows:Firstly, a study is carried out for transformer core material selection and loss, and acore material selection method is proposed for medium frequency and megawattcapacity application scenarios, and core materials for medium frequency and megawattapplications are compared. Secondly, a new structural design method of diagonalstaggered joints is proposed to reduce core losses for the problem of uneven magneticdensity and loss aggregation at the corners of large-size silicon steel cores. Based on thecore magnetic density distribution characteristics, the IGSE algorithm is modified toimprove the accuracy of loss calculation under large-size core cross-section and guidethe core loss optimization. Next, the winding form and losses of transformers are studied. Based on the eddycurrent effect characteristics and the 100-amp current flow requirements, a winding lossanalysis method is proposed for medium-frequency stepped current, and a low-loss, high-throughput winding form - copper foil winding - is successfully determined formedium-frequency 100-amp transformers. Based on the Dowell model, a copper foilwinding thickness optimization method is proposed to accurately calculate and selectthe optimal copper foil winding thickness to reduce the winding AC losses.Subsequently, the megawatt-class medium frequency transformer leakageinductance integration is studied, and the auxiliary inductance requirements and lossdistribution of dual active bridge DC-DC converter (Dual Active Bridge, DAB) undermegawatt-level transmission conditions are analyzed. An additional core-basedmagnetic integration technique for megawatt-class medium frequency transformers isproposed to realize mH-level large inductor integration, reduce power electronictransformer transmission losses, and improve power density. Meanwhile, a detailedadditional core structure with distributed air gap design method is proposed, whichreduces the loss by more than 20% compared to a single centralized air gap scheme. Finally, a prototype 1.5MVA/600Hz megawatt-class medium frequencytransformer based on an ultra-thin oriented silicon steel core with copper foil windingwas successfully developed. The core and winding design was analyzed in depth andthe transformer losses were reduced using methods such as diagonal staggered jointsand copper foil thickness optimization. At the same time, the transformer was tested forperformance such as insulation withstand voltage, open circuit, short circuit and powercycle. The experiments proved that the transformer efficiency reached 99.57%, meetingthe design requirements, and has been successfully applied to the demonstration projectof Dongguan Songshan Lake medium voltage distribution network flexibleinterconnection.
