Wide-Area Robust H2/H∞ Control with Pole Placement for Damping Inter-Area Oscillation of Power System

The damping of inter-area oscillations is an important problem in electric power systems (Klein et al., 1991; Kundur, 1994; Rogers, 2000). Especially in China, the practices of nationwide interconnection and ultra high voltage (UHV) transmission are carrying on and under broad researches (Zhou et al., 2010), bulk power will be transferred through very long distance in near future from the viewpoints of economical transmission and requirement of allocation of insufficient resources. The potential threat of inter-area oscillations will increase with these developments. If inter-area oscillations happened, restrictions would have to be placed on the transferred power. So procedures and equipments of providing adequate damping to inter-area oscillations become mandatory. Conventional method coping with oscillations is by using power system stabilizer (PSS) that provides supplementary control through the excitation system (Kundur, 1994; Rogers, 2000; Larsen et al., 1981), or utilizing supplementary control of flexible AC transmission systems (FACTS) devices (Farsangi et al., 2003; Pal et al., 2001; Chaudhuri et al., 2003, 2004). Decentralized construction is often adopted by these controllers. But for inter-area oscillations, conventional decentralized control may not work so well since they have not observability of system level. Maximum observability for particular modes can be obtained from the remote signals or from the combination of remote and local signals (Chaudhuri et al., 2004; Snyder, et al., 1998; Kamwa et al., 2001). Phasor measurement units (PMUs)-based wide-area measurement system (WAMS) (Phadke, 1993) can provide system level observability and controllability and make so-called wide-area damping control practical. On the other hand, power system exists in a dynamic balance, its operating condition always changes with the variations of generations or load patterns, as well as changes of system topology, etc. From control theory point of view, these changes can be called uncertainty. Conventional control methods can not systemically consider these uncertainties, and often need tuning or coordination. Therefore, so-called robust models are derived to take these uncertainties into account at the controller design stage (Doyle et al., 1989; Zhou et al., 1998). Then the robust control is applied on these models to realize both disturbance attenuation and stability enhancement.