Robust Reactive Power Optimization and Voltage Control Method for Active Distribution Networks via Dual Time-scale Coordination

TL;DR

This paper introduces a dual time-scale coordination method for Volt-VAR control in distribution networks, combining robust optimization for slow controls with fast control strategies to ensure voltage stability amid uncertainties.

Contribution

It develops a robust voltage and reactive power optimization model for slow controls and integrates it with fast control mechanisms, addressing uncertainties in load and generation predictions.

Findings

Robust model guarantees voltage security under uncertainties.

Deterministic model may lead to voltage violations.

Robust approach maintains system stability with minimal loss increase.

Abstract

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. In the case of slow control, a robust voltage and reactive power optimization model is developed. This guarantees that subsequent fast controls can maintain the system's voltage security if the uncertain parameters vary within predefined limits. This nonconvex optimization problem is relaxed to a mix integer second order conic problem, and the dual form of its sub-problem is also derived. Then 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. Numerical tests were conducted on a real distribution feeder in China, a balanced IEEE 69-bus and unbalanced 123-bus benchmark distribution networks. 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.