交直流耦合作用弱化稳定性机理及应对措施

Mechanisms and Countermeasures for Stability Deterioration Caused by Interactions Between AC and HVDC Systems

继"十一五"末复龙—奉贤特高压直流投运后,2014年四川复龙地区还将投运溪洛渡—浙江±800kV/8 000MW特高压直流输电工程。由于配套溪洛渡电站部分机组先于直流投运,为充分利用水电,2013年溪洛渡电站将通过长链型交流通道,经复龙换流站接入四川主网。研究表明,复龙换流站交流出线故障,由于网架结构薄弱和交直流耦合作用等不利因素影响,送端机组存在第2摆暂态失稳和功角增幅振荡等稳定问题,并成为制约水电充分利用的关键因素。文中通过送端混联电网受扰后特征量动态轨迹分析,揭示了直流功率快速恢复导致送端机组回摆过制动继而引发第2摆暂态失稳,以及直流送电功率随振荡中心电压起伏而"助增促降"交流线路功率波动,弱化系统振荡阻尼的物理机理。提出了相应的控制措施,为过渡期水电大容量外送提供了重要技术支撑。

Following the Fulong-Fengxian ultra-high voltage direct current （UHVDC） transmission project put into operation at the end of the llth five-year plan, Xiluodu-Zhejiang ±800 kV/8 000 MW UVHDC will be put into operation in 2014. Because the supporting generators are commissioned ahead of the UHVDC project, Xiluodu hydropower station will have to be connected to Sichuan power grid by long-chain alternating current （AC） channel in 2013 in order to make full use of hydropower. Studies show that AC fault occurred at the outlet of Fulong converter station will cause the second swing transient instability and oscillations of increasing power angle amplitude due to AC and direct current （DC） coupling interactions. Based on the disturbed dynamic trajectory, the mechanisms that the second swing transient instability caused by DC power fast recovery and weakening of oscillation damping caused by DC power fluctuation are revealed. Based on the stability influence factors analyzed for the transition of the UHVDC construction, the corresponding control measures are proposed. The conclusion provides important technical support to enhance hydropower output capacity.