The invention discloses a rapid decomposing method load flow calculating method suitable for a
branch system comprising small impedance. The method comprises the step of inputting
original data and initializing
voltage, the step of forming a node
admittance matrix, the step of forming a
coefficient matrix B' and a
coefficient matrix B'' of a modified equation and decomposing a factor table, the step of setting iteration count and a convergence mark, the step of calculating the inactive power unbalance amount
delta Q, the step of judging whether the absolute value
delta Qmax is smaller than the convergence accuracy epsilon or not, the step of calculating the active power unbalance amount
delta P, the step of judging whether the absolute value delta Pmax is smaller than the convergence accuracy epsilon or not, the step of calculating the balance node power and the inactive power of a PV node, and the step of calculating the
branch power. Part of elements in the
coefficient matrix B' of the modified equation of a rapid decomposing method are modified, and the
convergence problem produced during analyzing the
branch system comprising the small impedance with the resistance not equal to zero in rapid decomposing load flow calculation is solved. When a convention method is adopted to calculate non-convergence, the rapid decomposing method load flow calculating method can carry out convergence reliably.