Research On Asynchronous Iteration Based Distributed Dynamic Power Flow Of AC/HVDC Interconnected Power Systems

Power grid interconnection is one trend of the power system.With the rapid development of HVDC transmission technology,projects that has HVDC transmission lines as tie-lines are increasing.Decomposition-coordination computing of the interconnected power grids can not only achieve integrated modelling and computation among multi control centers of the interconnected power system,but also guarantee the computing accuracy of all kinds of local analysis software of each subsystem when disturbances occur in the external network.At the same time,it is compatible with existing EMS modeling characteristics of control centers.Since the HVDC system has flexible control modes and these control modes have a major effect on the power flow result,control effect must be considered in the distributed dynamic power flow algorithm of AC/HCDC interconnected power system.Based on the distributed dynamic power flow algorithm of pure AC interconnected power grids and external network equivalence of HVDC lines,the paper proposes an asynchronous-iteration based distributed dynamic power flow algorithm that has HVDC tie-lines modeled in the coordinator.The proposed algorithm retains the habit that AC tie-lines be modeled in both subsystems of its two ends,at the same time,HVDC tie-lines are modeled by the coordinator independently.The coordinator is responsible for the calculation of dc power flow,thus adjusting and switching of HVDC control modes can be considered conveniently without changing the fixed-point iteration format of boundary bus states.The proposed algorithm is divided into two kinds based on whether or not the HVDC lines are equivalent to the AC lines.The two algorithms are tested on test systems and their effectiveness is validated.Process of unbalanced power caused by power disturbances in the distributed dynamic power flow algorithm is also analyzed in this paper.Unbalanced power is reasonably allocated among generators by revising equivalent power injection into external boundary buses.Test result shows that the proposed improvement could reduce outer iterations of the distributed dynamic power flow algorithm and thus improve the computation efficiency.