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On the mechanism and control for the ultra-low frequency oscillation in NY Power Grid with large-scale hydropower
(North China Electric Power University, China)
基金项目:This work was supported by the National Natural Science Foundation of China (Nos. 51477050, 50707035) and 111 plan (No. B08013).
On the mechanism and control for the ultra-low frequency oscillation in NY Power Grid with large-scale hydropower
Ancheng XUE,Jiawei WANG,Chao ZHENG,Joe H. CHOW,Tianshu BI
(State Key Laboratory of Alternate Electrical Power System with Renewable Energy Source (North China Electric Power University), Changping District, Beijing 102206, China;China Electric Power Research Institute, Haidian District, Beijing 100192, China;Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, Troy 12180, New York State, U.S.A.)
The power grid with large proportion of hydropower may engage the ultra-low frequency oscillation (ULFO), which threatening the operation of system. To the NY Power Grid system, whose dimension is over thousands, this paper reveals the cause of ULFO with the phase portrait method, i.e., lies in the saturation of the different limits of the governor system of the generators, in other words, the occurrence of limit cycle is due to the non-smooth bifurcation. And furthermore, it proposes two methods to suppress ULFO with the philosophy of destroying the condition of non-smooth bifurcation. In detail, first, the phenomenon of ULFO in NY Power Grid, the damping characteristics and the limits in the governor system of the hydropower units are presented. Second, based on the non-smooth bifurcation theory, the mathematical basis of the oscillation in the non-smooth system caused by the saturation of limits is introduced. And then, the non-oscillation and oscillation dynamic of the system corresponding to without/with limits in the governor system are analyzed. Furthermore, it discusses the influence of the saturation of single limit on the characteristics of ULFO with the phase portraits. Moreover, the phase portraits of the ULFO under different faults is analyzed, and it shows that the limiting saturation occurs with a large enough disturbance. Thus, the ULFO is resulting from the negative damping of generation and the saturation of multiple limits under a large enough disturbance. In addition, according to the above mechanism, two strategies to suppress the ULFO, i.e., the governor parameters tuning and the fault strength relief are designed. The simulation shows the effectiveness of proposed strategies.
Key words:  Ultra-low frequency oscillation, governor system, limit, non-smooth bifurcation, limit cycle