Nonlinear complementarity formulation for including generator Q limits directly into the Newton Raphson load flow method

A new scheme for incorporating generator Q limit adjustments automatically in Newton Raphson (NR) load flow method is proposed. The current practice for handling this feature is to adopt bus type switching method after the solution (without these limits) converges to a reasonable extent. However, the precise details of this scheme are not well documented and they vary across implementations. A modified Newton-Raphson load flow method is proposed here which includes this adjustment feature at the problem formulation stage itself. In the proposed approach, the limit constraints at the generator buses are viewed as a set of complementary relations. A scheme is evolved to combine these complementary relations at the generator buses into a single equation and use it along with the real power equation of the corresponding generator bus by using the Nonlinear Complementarity Problem (NCP) framework. This scheme though similar to the Mixed Complementarity Problem (MCP) approach proposed recently for this problem, is basically different. This modified formulation in the complementarity framework succeeds in eliminating many of the ambiguities inherent in the earlier MCP formulation and exhibits high level of consistency in its performance. The proposed method has been extensively tested and its effectiveness has been compared with bus type switching scheme as well as the MCP approach through simulation studies.