Study On Coordinated Active And Reactive Power Optimization Considering Uncertainty In Active Distribution Network

With lots of distributed power sources,flexible loads,energy storage devices and continuous,discrete reactive power compensation devices connected to the distribution network,the traditional distribution network gradually turned into an active distribution network(ADN)with multiple power sources and controllable resources.On the other hand,high-permeability distributed resources bring uncertainties to the ADN due to its inherent power fluctuation characteristics,which will impact the operation safety and stablility of the distribution network.Therefore,how to coordinate a large number of active and reactive power control resources in the ADN to achieve the reduction of the system power loss while ensuring the voltage quality of the distribution network is the key issue to be solved.In this thesis,combined with the distribution network structure and the control ability of each controllable resource,researches on the reactive power optimization of ADN with distributed generations,dynamic active and reactive power coordination optimization and robust coordination optimization considering uncertainty are studied.The main research contents are as follows:1.The basic model related to optimization research in distribution network is established,including DG,ESS,SVC,OLTC,parallel capacitor and other power regulating equipment connected in distribution network system.The power regulation principles of these equipments are introduced,and their power adjustment models are analyzed and established.This section also involves the analysis of the load diversity and complexity,and builds the exponential load model.By introducing the branch power flow method of distribution network,the power flow equation can be achieved,which lays the model foundation for the subsequent research content.2.The reactive power optimization strategy of ADN is proposed.Taking the coordinated control of discrete and continuous reactive power compensation equipment into consideration,the reactive power optimization model aiming at economic optimization is established.For the non-convex constraints in the model,the second order cone programming method is introduced.The cone relaxation technique is used for convex processing to transform the problem into a second-order cone programming problem.Considering the nonlinear constraints imposed by adding OLTC to the system,an accurate linearization method is proposed.Then the final model becomes a mixed integer second-order cone scheme.The problem is solved in the simulation and the effectiveness of the proposed optimization strategy in the reactive power regulation of the distribution network is verified.3.Further research on the established reactive power optimization model is also studied.Considering the strong coupling relationship between active and reactive power in the distribution network,the coordinated active and reactive power optimization strategy of the ADN is proposed.Firstly,the influence of active and reactive power on the network loss and voltage of the distribution network as well as the necessity of constructing the coordinated active and reactive power optimization model are theoretically analyzed.The situation that the active power and reactive power are not decoupled in the distribution network system is fully considered.Since the DG output does not match with load demand,the energy storage device is needed to be added in the system to make up for the active power shortage in the system.And the space-time coupling characteristic of the energy storage decides the optimal model should be constructed in the dynamic form.Finally,after simulating and verifying the model,the optimized control strategies are achieved.At the same time,the simulation results show that the coordinated active and reactive power optimization can effectively reduce the system network loss and improve the voltage distribution,which means the model has a good performance in improving the economical and operational stability of the distribution network.4.Considering the uncertainty of distributed generation output and load demand,a coordinated active and reactive power optimization model for ADN with uncertainty is established.The sources of the main uncertain factors in the active distribution network system are analyzed and the form of uncertainty set is used to describe the uncertainty.The robust optimization theory is applicated in the field of active distribution network operation optimization,and a two-stage robust active and reactive power optimization model is established.The basic principle of C&CG robust solution algorithm is introduced and based on it,the two-stage robust active and reactive optimization model is given.The solution strategy of the optimal model is solved by C&CG algorithm,and the feasibility and effectiveness of the proposed method are verified by a numerical example.