直流孤岛送电系统的功率输送能力分析

Power transmission capability analysis of DC island transmission system

传统高压直流输电系统存在送端孤岛运行的可能性,而直流孤岛送电系统的功率输送能力是其运行特性的重要方面,因此对直流孤岛送电系统的功率输送能力进行了针对性的研究。在PSCAD/EMTDC仿真程序中搭建了直流孤岛送电系统模型;通过理论计算和时域仿真2种方法分别绘制系统最大功率曲线,根据直流电流指令值变化速率的不同,分类讨论了慢速电流变化时的励磁模型和励磁参数对系统功率输送能力的影响、快速电流变化时励磁参数对系统过渡过程的影响;将所提方法应用于分析送端交流系统故障,阐述失稳机理并提出改善措施。仿真结果表明:基于功率输送能力分析的直流电流限幅和发电机强励措施能显著改善直流孤岛送电系统发生故障后的暂态响应特性。

The sending-end system of the traditional HVDC transmission system may operate in islanding mode and the power transmission capability of DC island transmission system is important in its operation,so that the power transmission capability is deeply studied. The model of DC island transmission system is built with PSCAD/EMTDC simulation program and the MPCs（Maximum Power Curves） of the system are drawn by theoretical calculation and time-domain simulation. According to the different change rates of DC current reference,the influences of excitation models and parameters on the power transmission capability in low current change rate,and the influences of excitation parameters on the system transient process in high current change rate are discussed respectively. The proposed method is applied to analyze the faults in the sending-end system,then the mechanism of instability is expounded and some improvement measures are put forward. Simulative results show that DC current amplitude limiting and generator excitation forcing based on power transmission capability analysis can significantly improve the transient response characteristics of DC island transmission system with faults.