Abstract In flexible AC transmission systems, the “Sen” transformer (ST) is an economical and effective method for voltage regulation and power flow control, which can achieve independent control of active and reactive power. The ST is a three-phase multi-winding transformer based on the on-load tap-changing technology. In order to reveal the internal characteristics of the ST, this paper proposes an analytical electromagnetic model considering the multi-winding coupling in the ST with the three-phase three-limb structure. Firstly, according to the electromagnetic coupling relationship in the ST, a magnetic equivalent circuit model consisting of self-inductance coefficients and mutual inductance is derived via the unified magnetic equivalent circuit (UMEC). Secondly, an electric circuit model for the internal voltage and current of the ST is established based on the electrical connection between the ST and the external system. Finally, an analytical electromagnetic model considering multi-winding coupling for the ST is obtained by combining the magnetic equivalent circuit model and the electric circuit model. Two case studies have been carried out on a three-phase three-limb model of the ST with the help of MATLAB. The effectiveness of the proposed model is verified by comparing the obtained analytic results with the existing results from time-domain simulation about the series compensating voltage of the ST. In addition, the voltages and currents of windings in the ST in the conditions of different transformer core structures and ferromagnetic materials are investigated for evaluating the influence of magnetic coupling on the results.

中文翻译：

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多绕组耦合“森”变压器的电磁分析模型

摘要 在柔性交流输电系统中，“森”变压器（ST）是一种经济有效的电压调节和潮流控制方法，可以实现有功和无功功率的独立控制。ST 是一种基于有载分接变换技术的三相多绕组变压器。为了揭示ST的内部特性，本文提出了一种考虑ST中多绕组耦合的三相三肢结构的解析电磁模型。首先，根据ST中的电磁耦合关系，通过统一磁等效电路（UMEC）推导出由自感系数和互感组成的磁等效电路模型。第二，基于ST与外部系统的电气连接，建立ST内部电压和电流的电路模型。最后，结合磁等效电路模型和电路模型，得到了考虑多绕组耦合的ST的解析电磁模型。在 MATLAB 的帮助下，对 ST 的三相三肢模型进行了两个案例研究。通过将得到的解析结果与现有的 ST 串联补偿电压时域仿真结果进行比较，验证了该模型的有效性。此外，