Distributed Voltage Control in Distribution Networks: Online and Robust Implementations

Voltage regulation in distribution networks is increasingly challenged by the penetration of distributed energy resources (DERs). This paper develops a distributed voltage control (DVC) scheme to achieve the globally optimal settings of reactive power provided by DERs' power electronic interfaces. Based on unbalanced network flow modeling, the alternating direction method of multipliers algorithm is used to develop the proposed distributed design. To simplify the communication network, the power flow coupling is linearized to involve only neighboring buses. Interestingly, this linear approximation model enjoys a satisfactory performance and allows to exchange information only between neighboring buses. The DVC design is further improved for online implementations that can efficiently adapt to time-varying operating conditions. Last, to cope with cyber resource constraints, we slightly change the DVC design using a "freezing strategy" for unavailable variables due to link failures with guaranteed convergence. Numerical simulations using realistic multi-phase feeders and daily generation/load time-series have validated our analytical results and demonstrated the performance improved by the proposed DVC designs.