Distributed Control of Photovoltaic Units in Unbalanced LV Distribution Networks to Prevent Overvoltages

As more and more photovoltaic units are being installed, some LV networks have already attained their maximum hosting capacity, i.e. the maximum amount of distributed energy resources that they can accommodate during regular operations without suffering problems, such as overvoltages. As an alternative to network reinforcement, active network management (ANM) can, to a certain extent, increase their hosting capacity by controlling the power flows. In the framework of ANM, a distributed control scheme was previously presented. It makes use of a distress signal sent by each participating unit, when its terminal voltage is higher than 1.1 p.u. All units then proceed to absorb the maximum reactive power available. If the problem is not resolved, the units proceed to active power curtailment. This paper extends this control scheme to the case of unbalanced three-phase four-wire distribution networks with single- and/or three-phase inverters. The control scheme works by first partitioning the inverters into four groups, three for the single-phase inverters (one for each phase), and one for the three-phase converters. Each group then independently applies a distributed algorithm similar to the one previously presented. Their performance are then compared to those of two reference schemes, an on-off algorithm that models the default behaviour of PV inverters when there is an overvoltage, and the other one based on an unbalanced OPF. Its resulting total curtailed energy always lies between the two, with the on-off algorithm presenting the poorest performance, and the proposed algorithm losing its edge when the network is strongly unbalanced.