Evaluation of methods for measuring the insolvability of power flow

In the voltage stability assessment of power system, the post-fault load flow divergences are met frequently. Among them some divergent cases are associated to true unsolvable cases while other cases are false unsolvable cases which result from the purely numerical problems like a bad initial state. There are three basic requirements for those techniques of handling the unsolvable power flow problems. First of all, it should distinguish exactly between the true and false unsolvable cases. Secondly, it can measure accurately the severity of the power flow insolvability. Thirdly, it should provide the sensitivities for preventive or emergency controls. The Optimal Multiplier Newton Power Flow technique (OM-PF), the Hessian Matrix based Optimal Power Flow (HM-OPF) technique and the Contingency Parameterization Continuation Power Flow technique (CP-CPF) can be used to effectively handle the load flow insolvability problem. The closest critical points in the power injection space are obtained by both OM-PF and HM-OPF methods while the closest critical point in contingency parameter space is obtained by CP-CPF method. Evaluation of these methods is given with simulation of IEEE 118 buses test system. Simulation results show that CP-CPF is the best method for identifying the true unsolvable cases. The insolvability measures and ranking given by three methods have little bigger mismatches. However, the sensitivities can be provided by all of them for the control strategies.