Modeling PV/PQ switching in security constrained optimal power flow

In general, the generator terminal voltage in Security-Constrained Optimal Power Flow (SCOPF) is scheduled as a constant value. However, when the reactive power output of generator reaches its limit, the generator cannot keep the setting value and the bus will switch from PV bus to PQ bus. In this paper, to model the PV/PQ switching in SCOPF, four equivalence formulations are introduced, i.e. equivalence formulation with logical constraints, equivalence formulation with min and max functions, equivalence model with discrete auxiliary variable, equivalence model with continuous auxiliary variable. We then assess these techniques by comparing their computation performance on a 57-bus and a 118-bus system. The results show that the PV/PQ switching model is more economic than that without PV/PQ switching. Besides, it can be seen that Model 3 is more robust to find a feasible solution, while Model 4 is faster but its performance depends on the solver's ability.