Static Security Analysis Based On Stochastic Load Flow

Static security analysis is a fundamental problem in power system planning and operation. In the traditional static security analysis of power system, the power flow caleulation has used certain methods. But as the interconnection structure of regional power grid becoming increasingly close and the renewable energy such as wind power and solar power injecting continuously, the uncertain feature in power system has been increased severely, the weakness of the classical node-to-node analysis method is exposed, and the uncertain analysis method, especially stochastic load flow begins to catch people’s attention. Stochastic load flow considering the influence of uncertain factors on the system, such as the stochastic change of generator power and load power, could give stochastic distribution of the nodal voltages and the line flows, which could provide more comprehensive information to the planning and operation people.After the study of stochastic load flow based on cumulant and Gram-Charlier series expansion, this paper applys it in the static security analysis. Firstly, the paper introduces the theory of cumulant and Gram-Charlier series expansion. A Von Mises method is adopted to avoid the shortages of Gram-Charlier series expansion method in solving the discrete distribution, and the results are satisfied.Then, stochastic models of generator power, load power, wind power, DC power flow and AC power flow are built. Considering the assumed condition of standard DC power flow, correction factors are given to reducing the error, and tested by the standard IEEE14 systems and a real power system in a certain province.Considering the existing behavioral index of static security assessment could not apply to the situation existing uncertain factors, a behavioral index of contingency ranking is put forward, which combines the influence of uncertain factors on the line power with the load factor of lines. Then, according the behavioral index, an approach of the automatic contingency selection and ranking combining improved DC power flow algorithm with branch outage simulation based on compensation method is adopted, and the list of contingency is gained. Next, linearized stochastic load flow is adopted in accurate N-1 verification which is used to verify the list of contingency in turn. Finally, tested by the standard IEEE 14 systems and a real power system in a certain province. The results show that the method described in this paper could reflect the influence of serious contingency to power system comprehensively, has much higher running speed, validity and practicability of the proposed approach could be also proved.