The Research Of BX Type Fast Decoupled Method For Load Flow With Low Impedance Branches

In the present, Newton method and fast decoupled method are two main methods of power flow calculation, fast decomposition method has some characteristics which including fast speed of computation, less occupied memory and good convergence, so that it has been widely used in the power flow calculation of actual power system.With the increasing scale of power grid, the electric power network will become more complex. More and more ill-condition power flow emerge, including ill-condition power flow of low impedance branch system which is a relatively common condition. While dealing the problem with this power flow, these two methods may emerge disconvergence.There are two kinds of typical fast decoupled method called BX type and improved XB, which can be used to deal with the ill-condition power flow including low impedance branch system. The improved XB fast decomposition method has a great tackling performance about low impedance branch system of x ≈ r, however it can’t handle with the situation of r ≥ x. The BX type fast decoupled method has a great convergence performance in dealing with normal power flow, but for the ill-condition power flow with low impedance branch, this method will disconverge.Even if adopting a similar improvement with XB fast decomposition method, the effect is not desiredBased on the characteristics of above BX method and improved XB method, these two methods are combined in this paper so as to form a new method, namely improve BX method. When solving power flow, BX method is used in the normal branch and improved XB method is used in the small impedance branch. At the same time, improved BX method will emerge larger number of iterations even disconvergence in dealing with the low impedance branch of the r ≥ x. The coefficientof this method is corrected in this paper, namely reactance x multiplied by a coefficient that make this low impedance branch convergence and convergence times has been greatly reduced.Numerical example results show that Improved BX type fast decoupled method obtain a good convergence in the power flow calculation of low impedance branch system of x ≥ r, r≥ x and x ≈ r.