Reverse and Forward Engineering of Local Voltage Control in Distribution Networks

TL;DR

This paper analyzes local voltage control in distribution networks, revealing limitations of non-incremental methods and proposing incremental algorithms that improve convergence and regulation.

Contribution

It introduces a novel framework linking voltage control dynamics to optimization algorithms, and designs incremental control schemes with relaxed convergence conditions.

Findings

Non-incremental control has restrictive convergence conditions.

Incremental control schemes improve convergence and regulation.

The work advances understanding of network dynamics as optimization algorithms.

Abstract

The increasing penetration of renewable and distributed energy resources in distribution networks calls for real-time and distributed voltage control. In this paper we investigate local Volt/VAR control with a general class of control functions, and show that the power system dynamics with non-incremental local voltage control can be seen as distributed algorithm for solving a well-defined optimization problem (reverse engineering). The reverse engineering further reveals a fundamental limitation of the non-incremental voltage control: the convergence condition is restrictive and prevents better voltage regulation at equilibrium. This motivates us to design two incremental local voltage control schemes based on the subgradient and pseudo-gradient algorithms respectively for solving the same optimization problem (forward engineering). The new control schemes decouple the dynamical property from the equilibrium property, and have much less restrictive convergence conditions. This work presents another step towards developing a new foundation -- network dynamics as optimization algorithms -- for distributed realtime control and optimization of future power networks.