Voltage Stability Corrective Control Based On OPF Model

As interconnection of the power system become larger and larger,as well as the increasing booming electric load,the operation of power system actually is not far from the collapse especially if not enough attention is paid to it.Voltage instability,one of very important issues of power system security,has become the culprit of several big blackouts in these years.Owing to this,it attracts unbelievable interest recently.In this paper,the basic voltage stability mechanism and latest research on static voltage stability indices are introduced,besieds,from this point,the voltage collapse proximity index is derived.Then both weakness and strength of VCPI are illustrated with simulation cases on IEEE 9-bus system.At last,another new static voltage stability index—voltage alarm index is proposed,based on the priniciple of voltage instability mechnism,which could be regarded as the best complementary choice of VCPI.Thanks to the cooperation of these two,a relative complete voltage stability constraint is built,which could monitor and control system voltage stability.In the third part of paper,the forgoing voltage stability constraint is added into the traditional optimal power flow model,forming VSC-OPF(voltage stability constrained optimal power flow).Via VSC-OPF,we could act in the maximum economic benefit under safe condition.Or we could say a little amount of economic benefit is sarcrificed in order to preventive control voltage stability.However,there is a flaw in this theory,which is when the stability condition is extremely severe,it is very possible question can’t converge.In order to solve this problem,the optimal load shedding strategy based on voltage stability constraint is proposed.Just as its name,the forgoing voltage stability constraint is added into it either,then some other methods,such as output of generators could cooperate with load shedding to minimize shedding amount.Moreover,every bus is defined as a weight value,so those important loads could get more protect in shedding process,which could minimize side effect of load shedding.After load shedding,we could use VSC-OPF again to acquire the maximum economic benefit.Although overal voltage stability will change,the extent is so little that we could neglect it with no side effect.In a word,we could say the load shedding strategy complements the VSC-OPF method very well.The promising effects of all methods in this paper are verified by IEEE standard cases,so they could be applied in transmission part to gain safe benefit.