Continuous Approach To Reactive Power Optimization Of Power System Based On Sigmoid And Ncp Function

Reactive power optimization of power system is to optimize the appointed objective function of the system by adjusting the active and reactive power output of generators, the transformer taps and the reactive compensations, with precondition of all the constrains under the conditions of the configuration parameters and loads given. It is a powerful tool to ensure the operation of power system safely, stably and economically.Taking into account the discrete feature of transformer taps and switching capacitor/reactor banks, reactive power optimization is actually a large-scale of nonlinear mixed integer programming. The key and difficulty to solve this problem is how to handle discrete variables accurately and quickly. Till now, we haven’t found a perfect method to solve such complex problem. Moreover, with the expansion of the grid size, voltage quality requirement enhance, as well as the increasingly grim situation of energy conservation and emission reduction, higher requirements for solving reactive power optimization are needed. Therefore, it is of great important theoretic significance and practical value to research the algorithm with high computational accuracy and efficiency for reactive power optimization.In recent years, continuous approach has become a kind of new trend for researching the mixed integer programming. The advantage of this approach is that it can avoid solving the discrete variables directly. Thus the calculation time is not sensitive to the system size. Therefore, we introduce two continuous functions:Sigmoid function and NCP function, for handling discrete variables in reactive power optimization. And then we can model the new continuous reactive power optimization with the continuous functions, and solve the problem by modern interior point method, which is designed to coordinate the precision and efficiency effectively. Since there are multiple values for the discrete variables in reactive power optimization, we firstly considered the continuous reactive power optimization without taking into account discrete variables, to quickly obtain the discrete values around the continuous optimal solutions of discrete variables. Then, based on the solutions of pre-calculation, a continuous treatment to the discrete variables is given by the continuous functions.The numerical results of test systems ranging in size from30to1780buses show that the proposed method possesses high computational efficiency and good convergence. It is available to solve the large-scale nonlinear mixed integer programming.