Decomposed three-phase power flow solution using the sequence component frame

Abstract

With new developments in power systems, system unbalance is somewhat aggravated. Three-phase analysis of power systems is necessary both for planning and for monitoring. In the paper, a decomposed three-phase AC power flow algorithm using the sequence component frame is developed, in which a three-phase unbalanced power flow problem is decomposed into three separate subproblems with weak mutuality. By introducing new definitions of bus types, the subproblem corresponding to the positive sequence component (positive sequence power flow) is solved by using the Newton-Raphson iterative scheme, and the other two subproblems are formulated into two sets of linear simultaneous equations. The mutuality is included by putting the three subproblems into an iterative process. Simulation tests have verified that the approach can give an accurate solution with much less computational time and storage requirements than the existing methods and can converge reliably under any conditions of unbalance in the system loading and networks. The number of iterations needed is approximately proportional to the degree of the system unbalance. In practice, the algorithm could be used to replace the normal single-phase power flow programs because, in addition to its functions of solving unbalanced power flow problems and analysing abnormal system operations, it can solve balanced power flow problems at nearly exactly the same computational cost as single-phase tones.