基于主导惯量中心的紧急功率支援综合策略研究

Study of emergency DC power support strategy based on dominant center of inertia

当交直流系统遭受大扰动,导致有功失衡而使系统稳定受到威胁时,利用直流系统的快速可控性进行紧急功率支援可缓解功率不平衡状况,提高系统暂态稳定性,但如何选择紧急功率支援信号使调制效果达到最优仍需探索。直流线路连接的互联区域电网,暂态下区域电网主导惯量中心间的转速偏差能够保留系统重要的动态信息,集成紧急功率支援的控制信号,相比于传统的由本地信息构成的调制信号效果更优。以暂态过程中发电机组的动能增加为准来度量主要参与机组,形成'主导惯量中心'(the Dominant Center Of Inertia,DCOI),在主导惯量中心转速偏差为调制信号的基础上,结合功率提升/回降,形成一种紧急功率支援综合策略。在四川电网的仿真中表明:基于主导惯量中心的紧急功率支援方案可有效地提高大扰动下暂态系统的稳定性,结合功率提升/回降的紧急功率支援综合策略可进一步发挥直流调制维护系统暂态稳定的潜能。

A fault in a complex power grid with DC and AC transmission in parallel can cause remnant power not be sent out, which will accelerate the rotation of sending-grid generators and decelerate the rotation of receiving-grid. Emergency DC power support relied on over-load ability of HVDC will improve the imbalance of active power and advance the transient stability of AC/DC system. How to select the signal to control emergency power support which can achieve optimal modulation effect still needs to be further explored. This paper identifies and selects the ＂dangerous generators＂ to make the dominant center of inertia while discarding all ＂harmless＂ ones by appraising the kinetic energy in the during-fault period respectively. The inter-area speed differences equivalent by dominant center of inertia is able to represent the abnormal information of the nonlinear dynamic behavior of the power system based on a model in which two AC systems are connected by a HVDC link. Sichuan Power Grid connected with Southwest Power Grid is used to testify the method. Test results show that the signal deriving from the dominant center of inertia is more efficient than the traditional signal made of the frequencies at both sides. The DC modulation based on the inter-area speed differences equivalent by dominant center of inertia combined with DC power rise/drop will achieve optimal modulation effect.