Voltage stability: analysis needs, modelling requirement, and modelling adequacy

The importance of representing power system dynamic loads by valid dynamic models in dynamic analyses of voltage stability is demonstrated. Several dynamic load models reported in the literature are reviewed. It is shown that, for loads with slow dynamics or when the system voltage may be assumed constant, small signal stability is independent of the load model used, provided the model parameter values are correctly chosen. The same results can also be predicted by steady-state analysis by appropriately modifying the conventional power flow model. In large disturbance situations, and when the load dynamics exhibit fast response characteristics, a detailed system modelling is needed. An argument is presented in favour of using the theoretically rigorous and well established models for loads with fast dynamic response, when detailed analyses are warranted