Reactive Power Optimization Of AC/DC System Considering Voltage Stability Index

High voltage direct current power transmission is developing quickly with the research of the control device as thyristor.At the same time,its advantages of economy and technology determine the necessity and broad prospects of the construction of the DC transmission.Meanwhile,the DC and AC hybrid transmission also brings a series of security problems to the whole network.Fault of system generator and input of heavy load can cause more serious consequences in voltage decline because of the consumption of a lot of reactive power in converter station.So it is very important to study the reactive power optimization method and voltage stability of AC/DC hybrid system.This paper first analyzes the advantages and disadvantages of the existing method of AC/DC system power flow calculation.Those papers don’t consider that the actual converter control mode will change with the operating state of the system changing.So that the AC control mode is converted automatically is added into the power flow iteration based on the new AC/DC steady state model.Then the paper establishes the improved static voltage stability index based on an alternating iterative method calculating system flow which is applicable to AC/DC system.Used the genetic algorithm,the optimal load shedding strategy is solved based on the objective function which makes the load loss cost minimum.The simulation results show that the new algorithm can optimize the control strategy,maintain the stability of the system,and reduce the loss cost.Finally,considering the correlation between reactive power optimization and voltage stability,especially when the system is put into heavy load or generator fault causes the voltage drops,the conventional reactive power optimization method is unable to meet the requirements of the system.We give the AC/DC power system of reactive power optimization model whose objective function make the network loss and power economic cost minimum.And the model considers thetransformation ratio of DC converter,the control angle,node voltage limits and flow constraints.Then the steps of using simulated annealing genetic algorithm to solve the model are presented.The results show that the method has better astringency and better performance in the IEEE30 system which includes of DC transmission line.