Optimal Configuration And Coordinated Control Of Volt/Var Sources In Active Distribution Networks

With shrinking petroleum resource and enviroment pollution becase worse,distributed generation(DG),which is based on renewable resource,has become the key research and advanced technology.traditional distribution network have been upgraded to an active distribution network with high penetration of DGs.However,the intermittencies of DGs,including wind turbine and photovolatic,cause uncertainties of injected active and reactive power injected,which challenge security operation of power grid.Therefore,active distribution networks must be able to accommodate high penetration of DGs.This paper analyzed optimal configuration and coordinated control in active distribution networks.(1)Analyzed the time sequence characteristic and uncertainties of DGs and loads,developed multistate models in different period of uncontrolled DGs such as wind turbine,photovoltaic and loads.Analyzed the effect of r/x ratio on node voltages in distribution networks,and calculated the probability node voltage violation based on semi-invariant stochastic power flow.(2)Proposed generlized sources which including devices that can supply active and reactive power in distribution networks.Developed an optimal configuration model of generlized sources based on chance constrain programming and bi-level programming.reactive power output of DG is also considered,as well as its regulation with loads.Simulation results show that utilization of DGs is increased,annual cost is decreased and accuracy of objective is improved.(3)Developed a volt/var multi-period framework of active distribution network,including a day-ahead schedule,a short-term refine and a real-time refine parts.Optimal model and its algorithm in each period is proposed considering adjust characteristic,based on which time decouple can be achieved,and the effect of forecast errors on volt/var control can be mitigated.(4)Analyzed the forecast error distribution of DG real power and its effect on DG reactive power output.Proposed a pre-coarse-fine dynamic volt/var optimal model,based on which a coordinated optimal result can be obtained through iteration between continuous and discrete variables.(5)Developed a multi-objective partitioning method,in which reactive power ballance,reserve and couple degree are considered.Analyzed a distributed control strategy according to the results of partition,based on which the switching number of OLTC is reduced.(6)Proposed to convert some AC lines to DC ones and formed a hybrid AC/DC distribution network through voltage source converter(VSC).Analyzed the effect of different VSC configuration and control strategy on the transfer capacity of distribution networks.An optimal model including a normal state and a risk state is developed,and the control capability of VSC is fully used.