Research Of Static Voltage Stability Analysis And Wide Area Control Strategy Based On The External Network Equivalence

With the development of the power technology, the expansion of the system size and the increasing complication of the network structure, power systems are operated more close to their limit conditions under the restriction of environmental and economic factors. And the security and stability problems occur continually which may even cause the system collapse. Consequently, power system stability and security problem has been an important research issue and the static voltage stability problem is paid more and more attention.Load shedding is considered as an effective measure to the voltage stability problem. The existing control strategies are all formulated based on information of the whole network. The implement of control measures may miss the opportunity when power system is operated close to its limit. Then the expected control purpose cannot be achieved. So a method for analyzing the static voltage stability of regional grid and a wide-area control strategy, which is based on external network equivalence method are proposed. The efficiency of static voltage stability analysis and wide-area control should be improved after taking account the external network equivalence method.The main contexts are listed as follows:â‘ A least square Thevenin equivalence model taking account of measurement error is proposed based on the single-bus external network equivalence method, which can not only consider the change of equivalent voltage phase angle, but also filter the measurement error effectively. Continuation power flow method is adopted to analysis the static voltage stability margin based on the proposed equivalence model. Numerical tests on the modified IEEE14 bus system illuminate that static voltage stability is more accuracy with the proposed equivalence model.â‘¡A wide-area load shedding strategy based on Thevenin equivalence is proposed according the specialty of regional grids. The proposed strategy takes the effect of external system into account according to the Thevenin equivalence method. The requirement of static voltage stability is considered reasonably by taking the power flow equations with increasing load as static voltage stability constraints. Then a minimizing load shedding optimal model, which is quadratic, is established by considering the power flow equations with load margin as the static voltage stability constraints and the semi-smooth Newton method is used to solve the optimal model. The calculation speed can be increased by using the quadratic model, whose Hiaasen matrix is formed only at the first iteration. The validity and the efficiency of the proposed load shedding strategy are tested in the modified IEEE14 bus system and IEEE30 bus system.