The Method Of Security-Constrained Unit Commitment With Wind Power Generators

Security-constrained unit commitment is the foundation of the economic scheduling and security assess of power system. This problem has extremely important effect on the optimal short-term operation. The study on unit commitment problem has important economic and social benefit. There is abundant wind energy in the nature which becomes one of the most important ways to cope with the worldwide increasing environmental and energy problems. As wind power is widely used, more wind power generators will be drawn into when deal with generate program. Allow for the biggish effect of the wind generator in unit commitment, it is necessary to analyze the security-constrained unit commitment in wind power integrated system. In this dissertation, the problem of security-constrained unit commitment in wind power integrated system is studied.Firstly, linearization is used for changing the objective function to a set of linear equations and inequalities by interval subsection of the unit output. The integer variables in unit commitment have their own specialty. By calculating the slacked security-constrained unit commitment model and referring to the proposed rules form the specialty, the collection of all the units whose status stays the same during all periods can be obtained. Based on this method, the optimization range is narrowed efficiently and the calculation speeds up. For the sake of computational efficiency, the problem will be decomposed into two layers. The upper-layer is unit commitment without network constrain. The sub-layer is optimal power flow problem with AC constraints whose objective function is to minimize the network loss. If some variables are out of limitation, the method will add some new constraint conditions to the upper-layer and circulates. Two IEEE test systems were tested and the outcome is compared with other literatures*. The results show the effectiveness and efficiency of proposed method.Secondly, three practical wind generators were compared which showed the asynchronous generator makes the biggest impact to unit commitment. The impact contains the uncertainty of the wind power and the decline of voltage after absorbing reactive power. So this paper concentrates the unit commitment with asynchronous generator units. The asynchronous power generator is different from thermal power generator. Asynchronous generator will absorb reactive power so that the Q-V model should be brought to the AC security constrain conditions for the sake of voltage limit. The volatility of wind power is frequent because of the active power assessed by wind speed. This paper used Weibull distribution to estimate the confidence interval of wind speed so that the active power assessed can be acquired.At last the wind power was put into the unit commitment model as an interval variable. Commutation and extremal scenes need to solve the interval variable and network security constrains was modified to insure the security of system. The integer variables and continuous variables of upper-layer unit commitment without network security constrains were solved by Benders decomposition method. The sub-layer model was solved by interior point method. An IEEE-57system with a wind power generator is tested with this method. The high efficiency calculate software CPLEX assisted the solution of upper-layer model. Simulation results show that the proposed method is effective.