Investigation of reactive power limit induced voltage collapse

Voltage instability is caused by the inability of the system to meet reactive power demand. The problem of voltage instability is even more critical for an isolated microgrid, which only has generators with limited reactive power capacities. In this paper, we investigated what happens if all generators in the system hit their reactive power limit. To simplify the analysis, a simple two-bus example was used. Analytical power flow solutions was derived, and the corresponding physical interpretation was discussed. The physical constraints of the generator determined whether the power flow solution is feasible. It was found that when the reactive power limit of the generators is hit, even though there is a power flow solution, due to the physical limitation of the generator, no feasible solution exists. This causes the system to experience voltage collapse.