Robust reactive power optimisation and voltage control method for active distribution networks via dual time-scale coordination

In distribution networks, there are slow controlling devices and fast controlling devices for Volt-VAr regulation. These slow controlling devices, such as capacitors or voltage regulators, cannot be operated frequently and should 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 with improper schedule of the slow controlling devices. In this paper we propose dual time-scale coordination for the Volt-VAr control scheme, corresponding to slow and fast control. Slow control guarantees that subsequent fast controls can maintain the system's voltage security if the uncertain parameters vary within predefined limits. A column-and-constraint generation algorithm was used to solve the robust convexified model. A conventional deterministic optimization model can be used to determine the fast control mechanism. The simulation results show that solving the deterministic model is not always feasible and voltage violation may occur. The robust model was shown to be effective with respect to all possible scenarios in the uncertainty set, with little compromise in terms of network losses.