The Convergence Analysis Of Fast Decoupled Load Flow

Power flow is the most basic and core calculation in power system analysis,which is the basis of static stability analysis,dynamic stability analysis and short circuit calculation of power system.In a practical power system,power grid is larger and larger scale,especially added local small power grids and environmental factors restrict transmission corridor.All of these factors increase the complexity of power grids,the ill conditioned phenomenon increases too,small impedance branches ill-condition power flow generally exists in the practical power system.At present,the most widely used power flow algorithm is Newton method and fast decoupled load flow.Compared with Newton method power flow,fast decoupled load flow has faster calculation speed and more saving memory ability.An ill-condition power flow with small impedance,fast decoupled load flow has no ill-condition power flow of x>>r,which is its merit.While,if the reactance x as much as resistance r or r>>x,fast decoupled load flow has poor convergence.According to the fast decoupled load flow of its own characteristics,two kinds of improved fast decoupled load flow are put forward.These two improved algorithms get better convergence of power flow with various small impedance.The first improved algorithm uses the revised factor to revise the reactance value of the small impedance branch,so that it can deal with various types of small impedance branches.The second improved algorithm is proposed by using series compensation method to change the original branches structure of small impedance,which x is as much as resistance r or r>>x,by adding new virtual node,optimizing virtual node number.Small impedance branches of x?r and normal branches instead of the structure of small impedance branches,which x is as much as r or r>>x.The second improved algorithm can completely eliminate influence of various small impedance branches to the convergence of fast decoupled load flow,making it no difference with normal power flow convergence.By IEEE14,IEEE30,the practical northeast 445 bus bars power system example analysis,two kinds of improved algorithm have better convergence,when they are used to deal with various small impedance branches system.The fast decoupled load flow improved by series compensation method has important engineering practical values too.