In distribution networks, there are slow controlling devices and fastcontrolling devices for Volt-VAR regulation. These slow controlling devices,such as capacitors or voltage regulators, cannot be operated frequently andshould be scheduled tens of minutes ahead (Hereafter named as slow control).Since of the uncertainties in predicting the load and distributed generation,the voltage violations cannot be eliminated by fast controlling devices withimproper schedule of the slow controlling devices. In this paper we proposedual time-scale coordination for the Volt-VAR control scheme, corresponding toslow and fast control. In the case of slow control, a robust voltage andreactive power optimization model is developed. This guarantees that subsequentfast controls can maintain the system's voltage security if the uncertainparameters vary within predefined limits. This nonconvex optimization problemis relaxed to a mix integer second order conic problem, and the dual form ofits sub-problem is also derived. Then a column-and-constraint generationalgorithm was used to solve the robust convexified model. A conventionaldeterministic optimization model can be used to determine the fast controlmechanism. Numerical tests were conducted on a real distribution feeder inChina, a balanced IEEE 69-bus and unbalanced 123-bus benchmark distributionnetworks. The simulation results show that solving the deterministic model isnot always feasible and voltage violation may occur. The robust model was shownto be effective with respect to all possible scenarios in the uncertainty set,with little compromise in terms of network losses.
展开▼
