Study On Small Signal Stability Of Power System With Time-delay

With the rapid adva ncement of China’s power construction and fast enhancement of interconnection between different areas, the power grid’s security and stability are facing greater attention a nd cha llenge from power engineering and academic research. In order to boost the security and sta bility of power system’s operation, the effective coordination control via w ide-area measurement control(WAMS) is one of the future possible solutions. However, the extensive time-dela ys in WAMS inevitably give rise to adverse effects on power syste m’s stability and involved controllers’ performance. In this thesis, the power system sma ll signa l sta bility w ith time-dela y has been fully studied, and the main research work is illustrated as follows:(1) On the basis of detaile d mathe matical models of cruc ia l components and devices in power system, the time-invariant mode ls are constructed via linearization technique for the research on power system small signa l stability with time de lay, which inc lude the typica l second-order system, single-ge nerator-infinite-bus system, WSCC-3-generator-9-bus system and IEEE-10-generator-39-bus system.(2) An effective measure to solve the de lay sta bility region in a large scale is proposed. Initia lly, the parameter transform is utilized to convert the solution to stability boundary into the operations of search, translation and inverse-translation within a bounded interva l, thereby greatly curta iling the calculation; furthermore, the structure and feature of stability region boundary are solve d via four-point interpolation and perturbation; finally, the effective ness of this method is va lidated via a typical second-order system and WSCC-3-generator-9-bus system.(3) A mode l reduction method is proposed so as to simplify the mode l of power grid w ith single de lay and a nove l linear matrix ine qua lity criterion is constructed. This reduction method initia lly genera lizes the linearize d power system mode l w ith single de lay to a state-space with input and output; subsequent ly, the state-spacebased mode l reduction algorithms are utilized to simplify the generalized mode l. Hence a simplifie d mode l can be obta ined w ith less unknown variables and unchanged cruc ia l dynamical features. In the meanwhile, a LMI stability criterion is put forward to carry out the numerical comparison of stability margins via original and simplifie d syste ms. The numerica l illustrations of WSCC-3-generator-9-bus system and IEEE-10-generator-39-bus system indicate that the simplified mode l of time-de lay syste m generates errors fewer than 6%, but the effic iency is at least 4 times of the model without simplification.(4) A novel LMI stability criterion w ith better effic iency is proposed, and this criterion can address the multi-de lay situation. Firstly, this criterion builds up a new Lyapunov-Krasovskii functiona l and seeks the maximum derivative of this functional via variationa l calculus, thereby constructing the criterion w ithout the introduction of free-weighting matrix(FWM) and with less unknow n variables; in addition, the mathematica l equivale nce between new criterion’s extremum condition and existing FWM criteria’s optima l condition is proved. Lastly, the numerical examples of the typical second-order system, single-generator-infinite-bus system and WSCC-3-generator-9-bus system verify the correctness of matrix construction, and the remarkable efficiency boost of the proposed criterion.