Distributed Voltage Control for Three-Phase Unbalanced Distribution Systems With DERs and Practical Constraints

Traditional voltage control schemes in the power distribution system are typically centralized or local. Local control often gives nonoptimal solutions utilizing local measurements and lacks global coordination. Centralized control gives optimal solutions but lack scalability and robustness, especially with the increasing number of distributed energy resources (DERs). Recent advancement in power electronics with improved automation and digitalization in power grid control provides an opportunity to enable distributed optimization approaches for voltage control. This article proposes an optimal distributed voltage control algorithm based on augmented Lagrangian multiplier theory and primal-dual gradients for three-phase unbalanced distribution systems. In the developed algorithm, each node uses its own local measurements and neighboring nodes measurements to compute optimal reactive power setpoints, while meeting reactive power injection constraints for DERs. The proposed algorithm also considers practical constraints, such as communication delays, measurement noises, modeling errors, limited control devices, and infrequent switching required for field implementation. The proposed algorithm is validated for voltage control in an unbalanced, three-phase IEEE 123-bus feeder modeled in OpenDSS to demonstrate superior performance.