幅频周期时变调制的内电势激励下交流网络不对称故障分析

电力系统电源正由同步电机向电力电子化换流器快速转变，交流网络发生不对称故障时，换流器输出正序和负序内电势呈现幅值/频率周期时变调制特征，传统基于相量和阻抗概念的不对称故障分析方法适应性不足，无法提取故障电气量特征，系统控制保护设计依据面临严峻挑战。本项目围绕幅频周期时变调制内电势激励下网络不对称故障，提出适用的不对称故障分析方法，揭示不对称故障电气量特征和物理内涵。首先，研究幅频周期时变调制内电势数学描述方法，建立空间矢量、三相瞬时值和“类相量”数学模型，刻画换流器内电势特征，并分析电气量对称分解的可行性和分解方法；其次，考虑网络的原始数学关系，建立网络的“类阻抗”计算模型，掌握对称分解方法下网络耦合特性和等效电路；最后，分别在不对称电气量下和对称分解电气量下进行不对称故障分析计算，提取故障电气量特征和变化规律。本项目研究成果将为系统控制保护提供理论参考，支撑电力电子化电力系统可靠运行。

The power source of the power system is rapidly changing from synchronous generators to power electronic converters. When there is an asymmetric fault in the AC network, the positive and negative sequence voltages controlled by the converter present the characteristics of amplitude/frequency periodic time-varying modulation. The traditional asymmetric fault analysis method based on phasor and impedance models is not adaptive enough to extract the fault electrical characteristics, which causes the basis of system control and protection facing severe challenges. This project focuses on the asymmetric fault of the AC network excited by amplitude/frequency periodic time-varying modulation internal voltage, and proposes an applicable asymmetric fault analysis method to reveal the electrical characteristics and physical connotation of asymmetric fault. Firstly, the mathematical description method of amplitude/frequency periodic time-varying modulation internal voltage is studied, and the mathematical models of space vector, three-phase instantaneous value, and "quasi-phasor" are established to characterize the internal voltage of converters. Meanwhile, the feasibility and decomposition method of symmetrical decomposition of electrical quantities are analyzed. Secondly, considering the original mathematical relationship of the AC network elements, a "quasi-impedance" calculation model of the AC network is established, and the coupling characteristics and equivalent circuit of the AC network under the symmetrical decomposition method are mastered. Finally, the asymmetric fault analysis is carried out under asymmetric electric quantities and symmetric decomposed electric quantities, respectively. Besides, the fault electric quantities are calculated to extract the characteristics and variation of fault electrical quantities. The research results of this project will provide a theoretical basis for system control and protection, and support the reliable operation of power electronics-dominated power systems.