Distributed Secondary Frequency Control through MTDC Transmission Systems

TL;DR

This paper introduces distributed control strategies for sharing frequency control reserves across asynchronous AC grids connected via multi-terminal HVDC systems, ensuring stability, fair power sharing, and quantifiable voltage and frequency errors.

Contribution

It proposes novel distributed controllers for primary and secondary frequency regulation in multi-terminal HVDC-connected AC systems, with proven stability and power sharing properties.

Findings

Controllers achieve global asymptotic stability.

Voltage and frequency errors are bounded and quantified.

Fair power sharing among AC systems is demonstrated.

Abstract

In this paper, we present distributed controllers for sharing primary and secondary frequency control reserves for asynchronous AC transmission systems, which are connected through a multi-terminal HVDC grid. By using Lyapunov arguments, the equilibria of the closed-loop system are shown to be globally asymptotically stable. We quantify the static errors of the voltages and frequencies, and give upper bounds for these errors. It is also shown that the controllers have the property of power sharing, i.e., primary and secondary frequency control reserves are shared fairly amongst the AC systems. The proposed controllers are applied to a high-order dynamic model of of a power system consisting of asynchronous AC grids connected through a six-terminal HVDC grid.