送端系统对交直流系统输送功率极限的影响

Effect of Sending-end System on Maximum Transmission Power of AC/DC System

分析了直流输电系统整流侧连接于不同强度交流系统的运行特性,研究了定电流控制下整流侧的功率输送极限。通过分析功率曲线和换相角曲线,指出了送端系统在额定电流控制下能够保证稳定运行,并且发现受换流器换相角的限制,整流侧系统强度越小,直流输电系统整流侧的输送能力越弱;提出了电流调制裕度和短路比之间的关系,指出了能够保证一定功率提升裕度的送端系统最小短路比。通过进一步分析参数变化对电流调制裕度和短路比之间关系的影响,指出在相同的短路比下,换流变压器参数的选取(额定容量和等效电抗等)对送端系统输送功率极限有较大的影响。

The operation characteristics of the high-voltage direct current（HVDC）rectifier connected to AC system with different strengths are analyzed,and the maximum transmission power of the rectifier under current control is pointed out.Through the analysis of the power curve and overlap angle curve,it is indicated that the rectifier side is always stable when the HVDC system is under the rated operating condition.However,the maximum transmission power of the rectifier is limited by the strength of the connecting AC system,under the restriction of overlap angle in the converter.The relationship between the current modulation margin and short circuit ratio（SCR）of the sending-end system is proposed.Also,the minimum SCR of the sending-end AC system is proposed which is necessary for the connecting rectifier to increase the maximum active power.Furthermore,the effect of parameters of the rectifier on the direct current modulation margin and the SCR of the sending-end AC system are discussed.The choice of the parameters of converter transformer（nominal capacity and equivalent reactance,etc）can largely affect the maximum transmission power under the same SCR.