Global Optimal Control And Slack Optimal Control Of Reactive Power And Voltage Considering Model Errors

With the development of the power system,the uncertainty in sources,power grids and loads become more and more significant.It is hard to evaluate and predict the operation state of the power system with large uncertainty.Therefore,the operation and control of the power system are greatly influenced by the uncertainty.The equivalent model of the power system cannot be formulated accurately because of the increase of the increase of the uncertain elements,which is a big challenge of the reactive power and voltage control.This thesis focuses on the optimal reactive power dispatch with model errors resulting form the uncertainty in sources,power grids and loads.Detailed works on the theories and applications are as follows:(1)An optimal reactive power dispatch(ORPD)mehod considering the uncertainty of the transmission line parameters is proposed to fill the gap existed in the studies on ORPD.Based on the robust optimization theory,a robust ORPD model is presented,where the uncertainty of transmission line parameters is modeled by using an uncertainty set.Moreover,indicators,including robustness indicator,optimality indicator and composite indicator,are proposed to evaluate the performance of the proposed models in terms of robustness and optimality quantitatively.And the master-sub problem framework is utilized to solve the robust ORPD model and to obtain the value of the robustness indicator.The simulation results show that the proposed ORPD method advoids the infeasiblity proplem resulting from the uncertainty of the transmission line parameters,and verifies the effectiveness of the indicators on evaluating the ORPD methods.(2)Motivated by the situation that the robus optimization method tends to return an over conservative solution,an improved robust optimization method is presented.The increment form of the inequality constraint is presented,and its mechanism for reducing conservativeness is analysed.Based on the analysis,feedback and correction procedures are introduced to the formulation of the constraints.With the feedback and correction procedures the excessively strict constraints are replaced by the constraints represented by increment,therefore a robust optimization model with feedback and correction(FCRO)is constructed.The proposed method takes account both the robustness and optimality.It improves the feasibility region of robust optimization,and thus improves the effect of robust optimization,while it does not harm the safety of reactive power and voltage control.(3)An expanded stochastic roubst optimization(ESRO)method for ORPD is presented to deal with multiple uncertain elements,which have different characteristics.First,the uncertain elements are classified into four categories according to the time-varying/time-invariant characteristics and the information of the probabilitiy distribution.And then the ESRO model is formulated by the integration the existing processing methods of uncertain elements and the feedbacek and correction procedures.Finally,the solution is given.The proposed method takes full advantage of the characteristics of different uncertain elements.It can effectly manage uncertain elements of different types in one model,and keep best control performance under different operation conditions.(4)A slack optimal control method for reactive power and voltage is proposed from a new perspective,in order to cope with the difficulty and deficiency of global reactive power optimization.The control theory and technical measures are provided.On the aspect of control theory,the multi-dimension architecture,control objective and trigger mechanism of the slack optimal control of reactiove power and voltage are proposed.And on the aspect of technical measures,decoupled optimization,slack control and dynamic moving are provided.The proposed theory and measures effectively advoid the difficulty and deficiency of global reacitive power optimization,and improve the praciticability of ORPD greatly.(5)Coordination methods for the reactive power compensation of different substations and the voltage and reactive power control between power plants and substations are proposed.the reactive power compensation of different substations is coordinated by substation grouping and reactive power interval moving.And the transfer characteristic of the Schmitt trigger is ultilized to advoid regulation oscillation.The voltage control of power plants and the reactive power compensaton of substations are managed by a hierarchical-disributed architecture.The proposed coordination methods achieve the cooperation of reactive power resources.Researches of the thesis provide models,algorithms and instruction rules for the reactive power and voltage control of power systems considering model errors.In addition,the conclusions of the thesis can be used to cope with the difficulty of global reactive power optimization.This work was supported by National Natural Science Foundation of China under Grant No.51377060.