The Research On Multiterminal AC/DC Hybrid Power System State Estimation

The development of VSC-multiterminal hybrid AC/DC power system helps improve the reliability of unban distribution system,which will relieve the intense situation to some degree that the urban land resource is squeezed by uban corridor.At the same time,the distributed energy sources such as wind as well as solar energy,and the vehicle charging stations,need voltage source converter to connect the grid.This is a general trend that the multiterminal hybrid AC/DC system will be formed in grid at city.In order to develop the further study and research of mulititerminal hybrid AC/DC system,the real-time and accurate state of multiterminal hybrid system and the bad data filtering is necessary,which underlines the emphasis of state estimationThe development and basic methods of state estimation about the hybrid AC/DC system is introduced at first,then,the importance of the study in multiterminal hybrid AC/DC system is discussed appropriately.Based on the mathematical model of two-terminal hybrid AC/DC system is established,the mathematical modeling methods of AC system,DC system and AC/DC coupling lines in multi-terminal hybrid AC/DC system are further studied respectively,especially the equations of voltage-controlled mode and the constant power-controlled mode are introduced.Then power loss in coverter's both ends are detailled in the whole coupling part,which facilitate the whole model being extended to any number of node and the control mode adopted.Combined with the power flow algorithm of two-terminal hybrid AC/DC system,the power flow equations of AC system,DC system and AC/DC coupling lines in multi-terminal hybrid AC/DC system are deduced.The power flow calculation is performed for the three decoupled parts,and the power distributionof slack bus and droop bus which is controlled by node voltage are also included.Then a simulation results contained with five AC nodes and three DC nodes proves the convergency of the algorithm.Finally,the weighted least square power flow state estimation applied in traditional power system is introduced in multi-terminal hybrid AC/DC system,then the power flow estimation algorithm combined with the sequeatial iterative method is carried out on hybrid system.Particularly,an improved generalized least square estimation methods is proposed.After compared with the simulation results of the power flow calculation and weighted least square estimation algorithm,the conclusion that the accuracy of generalized least square estimation algorithm is exactly improved can be demonstrated.