统一潮流控制器接入对距离保护的影响及对策

统一潮流控制器(Unified Power Flow Controller, UPFC)接入交流系统将改变传输线的潮流，进而对距离保护产生重要的影响。为了研究UPFC的接入对线路距离保护的影响，文章建立了UPFC直流侧电压的暂态数学模型，进而推导出在UPFC存在时阻抗元件的测量阻抗表达式。通过定量分析测量阻抗在阻抗复平面上的轨迹变化，发现UPFC的串联侧注入电压改变阻抗元件的动作边界。为了减小UPFC对距离保护性能的影响，提出了距离保护的偏移圆特性，并配合功率方向元件构成完整的距离保护方案。在MATLAB/Simulink中建立UPFC系统模型，仿真结果表明，与基于广义回归神经网络的自适应保护方案相比，所提出的距离保护方案具有更高的可靠性、选择性和灵敏度。

Analysis of the influence of UPFC on distance protection and the corresponding improved distance protection scheme

Unified power flow controller connected to AC system will change the power flow of transmission line, and then have an important influence on distance protection. In order to analyse the influence of UPFC on the performance of distance protection, the transient mathematical model of DC voltage of UPFC is established, and then the expression of apparent impedance in the presence of UPFC is derived. By analyzing the change of impedance trajectory on the impedance complex plane, it is found that the injected series voltage of UPFC changes the trip boundary of impedance element. In order to eliminate the influence of UPFC on the performance of distance protection, the offset circle characteristic of distance protection is proposed in this paper. The distance protection zone and the directional power relay comprise the distance protection scheme. Finally, the UPFC model is established in Matlab/Simulink. Various simulations show that the distance protection scheme proposed in this paper has higher reliability, selectivity and sensitivity compared with the adaptive protection scheme based on generalized regression neural network.