Research On Optimal Power Flow Of High Voltage AC/DC Hybrid Power Grid

HVDC has great advantages for long distance and large-scale transmission of electric energy.With the proposal and development of the global energy interconnection,it can be foreseen that more and more HVDC/UHVDC projects will be put into construction to connect the cross-regional and transnational power grid.Therefore,improving the stability and economy of AC/DC hybrid system is becoming an important problem.The optimal power flow of AC/DC hybrid power grid has attracted widespread attention.When the national/regional power grids are interconnected by DC lines,the active power delivered by the transmission lines will affect the power flow of itself,the sending-end and receiving-end,but the traditional research lacks the detailed analysis of this impact.In addition,the transmission capacity of DC lines are usually determined according to equal network loss ratio for the whole grid,and then optimal reactive power dispatching will be done at the sending-end and receiving-end respectively.This two-stage isolated scheduling also has its shortcomings.Based on this,the Stackelberg game optimization model of AC/DC hybrid power grid is established in this paper firstly,which takes the interest of DC transmission lines and the network loss of the sending-end and receiving-end as different players.Four possible game modes of AC/DC hybrid system is discussed.Secondly,the power distribution of DC transmission lines and reactive power optimization schemes under different game modes and its effects on the interests of all parties and the loss of the whole network are analyzed.Then,a modified particle swarm optimization(MPSO)algorithm is used to determine the power distribution of DC lines and reactive power optimization schemes of the sending-end and receiving-end,the effect of active power dispatching and reactive power optimization on the AC/DC hybrid power system are compared afterwards.Finally,the validity of the proposed model is verified by two IEEE 9-node systems which are connected by DC transmission lines.As for the AC/DC hybrid power grid inside the nation/region,because the control variables of AC and DC side can be dispatched comprehensively,this paper will focus on finding more appropriate algorithm to achieve the optimal power flow of the AC/DC system.Inspired by the exploratory behavior of navigators in Age Discovery in fifteenth and sixteenth centuries,a novel meta-heuristic intelligent algorithm,called Navigator Optimization Algorithm(NOA),is proposed.The concept of “search cycle” was first put forward in the new algorithm to balance the degree of "exploration" and "exploitation" in iterative process and can achieve better performance.The proposed algorithm is applied to the optimal power flow calculation of AC/DC hybrid system and the superiority of NOA is verified by comparing the simulation results with some other intelligent algorithms presented recently.Finally,considering the actual power system often need to handle many-objective(having four or more objectives)optimization problems,a many-objective optimal power flow model of AC/DC hybrid power system is established in this paper,which takes generator cost,voltage deviation,voltage stability and active power loss as the targets.NSGA-III algorithm is first applied to obtain the Pareto optimal solution set and the final scheme is determined as reference of the decision maker by technique for order preference by similarity to ideal solution(TOPSIS)method.