基于充退磁理论的混合型变压器磁状态调制技术研究

According to the incomplete technical features of the traditional low frequency transformer and the existing power electronic transformer, in this paper, for the first time, a novel hybrid transformer structure was put forward based on the theory of magnetization and demagnetization. The modulation for transformer core unbalanced magnetic state caused by DC bias, inrush exciting current or voltage fluctuation can be realized by itself and the excitation current distortion and the phenomenon of unstable operation can be avoided. The mechanism analysis about that the core remanence could not fall off and disappear by itself through the timeliness principle of ferromagnetic materials. A new stepped AC/DC converter topology is established by designing auxiliary winding. When the transformer is in the condition of unbalanced magnetic state, DC magnetization, stepped AC de-magnetization and AC modulation current waveform are formed. The modulation of magnetic field is realized by injecting synchronous compensation flux into the core. The excitation current distortion caused by bias flux and remanent flux can be eliminated by the modulating flux. The shortcomings of traditional transformer function and uncontrollable power quality are solved, and the deficiency of cost and efficiency of power electronic transformer can also be filled. This method can balance the efficiency and function, and it is feasible in concrete engineering.

针对传统低频变压器和现有电力电子变压器发展不全面的技术特征，首次提出一种基于充、退磁理论的混合配电变压器新结构，实现对变压器铁心由于直流偏磁、励磁涌流或电压波动等带来的磁状态不平衡问题进行自适应调制，避免发生励磁电流畸变和运行不稳定现象。通过铁磁材料的时效性原理分析了铁心剩磁不会自行衰减消失的机理，设计辅助绕组建立一种新的阶梯式AC/DC变换器拓扑。在变压器磁状态失衡的条件下，形成DC充磁，阶梯型AC充、退磁和AC调制电流波形，对铁心注入同步补偿磁通进行磁场调制。通过调制磁通可以从根本上消除变压器铁心偏磁和剩磁引起的励磁电流畸变问题。解决传统变压器功能单一、电能质量不可控的缺点，填补了电力电子变压器产品成本、效率方面的不足。该方法可以实现二者在效率和功能上优势的互补，具备工程意义上的现实可行性。

传统工频变压器和电力电子变压器在功率变换和电能质量治理方面不协调发展趋势之下，有研究团队提出混合变压器（HDT）的概念。目前，国内学者对于HDT的研究主要集中在拓扑与功能上。主要包括单相混合变压器、基于传统AC/AC变换器的三相混合变压器和基于单级矩阵变换器的三相混合变压器。.本项目针对混合变压器开展研究，通过建立辅助绕组，连接电力电子变换器对混合变压器铁心磁状态进行调制。一方面，实现网中变压器在每次空载合闸和故障切除时铁心磁通平稳过渡，彻底消除励磁涌流的现象并通过退磁维持变压器铁心零剩磁的状态；另一方面，对于由于地磁干扰、直流输电和地铁牵引供电等非线性负载引起的变压器铁心偏磁现象，通过建立定向充磁磁场实现直流偏磁的反向补偿，并稳定励磁电流；最后，对于电力变压器变压波动和偏差，利用变换器输出调制波，进行电压补偿，从而维持负载电压的稳定状态。.目前，已经制作混合变压器样机4台，3kVA/1kVA各两台，针对变压器励磁涌流和变压器直流偏磁问题进行了模拟和补偿治理研究，基于非同步合闸和定向反向补偿策略可以有效的解决变压器在空载合闸时出现的励磁涌流和直流偏磁问题。可以实现变压器铁芯稳定的运行。通过搭建非同步合闸混合变压器样机平台验证本文方案的有效性，为当前电力系统躲“剩磁”、避“涌流”的现状，提供一定参考依据。