传统交流配电网已难以满足新能源发电和直流用电负荷的高效接入，因此直流配电网应运而生。其中，高变压比的直流变压器是中低压直流配电网间互联的关键装置。但与交流变压器不同，半导体化的直流变压器在运行时存在开关动态过程和延时过程等非线性因素，不仅降低了直流变压器的运行性能，而且影响了直流配电网的安全与稳定。因此，本项目将对高变比直流变压器中的非线性因素进行深入研究，探讨直流变压器中非线性开关动态过程对变压器性能的影响，掌握两种开关动态过程在变压器系统中不同的作用机制；探讨变压器系统中非线性延时过程对变压器性能的影响，掌握三类延时过程在变压器系统中迥异的干涉机理；最终提出基于以上理论的非线性因素抑制技术及补偿策略。本项目的研究成果将有利于保障直流变压器的可靠运行，为未来直流配电网的规模化应用提供有力支撑，并进一步丰富电力系统电力电子化的理论内涵。

The traditional AC power distribution network has been difficult to meet the access of massive new energy resources and DC power load; thus, the DC power distribution network has emerged, where high voltage-ratio DC-DC transformer is the key device between middle and low voltage distribution networks. However, unlike traditional AC transformers, DC-DC transformers is constructed by semiconductor switches; thus, nonlinear factors are present in the DC-DC transformers, such as switching dynamic process and time-delay process, which decrease the performance of the DC-DC transformer and affect the safety and stability of DC power distribution at the same time. Therefore, this project will conduct an in-depth study on the nonlinear factors in high voltage-ratio DC-DC transformer. The effect of the nonlinear switching dynamic process on the transformer performance is first discussed, determining different mechanisms of two switching dynamic processes in the transformer system. The effect of nonlinear time-delay process is then discussed, determining different mechanisms of three types of time-delay process. The project finally proposes the nonlinear factor programming method, suppression technique and optimization strategy based on the above theory. The research results of this project are conducive to ensuring the operation reliability of DC-DC transformer, providing a strong support for the future DC distribution network, and enriching the theoretical connotation of electronization power system.