Robustness Evaluation Of Optimal Control Strategies For Electric Power Systems

Optimal control of power system has important significance for improving the performance of power system, for example, reactive power optimization control can effectively reduce the network loss and improve the voltage quality, economic/emission dispatch optimization can effectively achieve the purpose of energy saving and emission reduction and so on. Most of the literatures about the optimal control of power system are based on the deterministic model, which assumes that the load is constant and the control object can be strictly controlled. However, in fact, the load not only is fluctuant but also has a prediction error, the control precision of the control object can only guarantee its control roughly in line with expectations.Taking into account the uncertainty of the load and the possible deviation of the control, the optimal control strategy derived from the point of view of mathematical optimization may sometimes be too sensitive for the above uncertainties and deviations, thereby show poor performance in practice. Therefore, it is necessary to evaluate the robustness of the control strategy, and select the control strategy which is strong enough for the uncertainty and deviation.In order to evaluate robustness of optimal control strategies for electric power systems, an index of robustness evaluation considering control accuracy and uncertainty of state variables was established. Methodologies for identifying whether robustness was satisfied for optimization problems with single objective function and multi-objective function were described respectively. An approach based on sampling optimization to evaluate robustness of control strategies was put forward. Some methods were given to selecting the optimal solution of multi-objective optimization. In case that robustness of several control strategies could meet or not meet requirements, method for comparing robustness of control strategies was suggested. For the optimization problem of single performance index, reactive power control problem for IEEE-30 system and economic dispatch problem for 6 machine system were used as example, where some candidate control strategies were obtained with reactive power optimization approach and their robustness was evaluated with the proposed method respectively to find out the best strategy; Aiming at the optimization problem of multi performance index, economic/emission dispatch problem for 6 machine system was used as example, where some candidate control strategies were obtained with sampling optimization method and their robustness was evaluated with the proposed method respectively to find out the best strategy. The results show that the proposed method is feasible.