Distributed Frequency Control through MTDC Transmission Systems

TL;DR

This paper introduces distributed controllers for frequency and voltage regulation in asynchronous AC systems connected via MTDC grids, ensuring stability, cost minimization, and voltage regulation with minimal communication.

Contribution

It presents novel distributed dynamic controllers that achieve frequency and voltage regulation, stability, and cost optimization in MTDC-connected AC systems, including a communication-free variant.

Findings

Controllers ensure AC frequency convergence to nominal values.

Voltage deviations are minimized through quadratic cost functions.

Controllers perform effectively in high-order dynamic system simulations.

Abstract

In this paper we propose distributed dynamic controllers for sharing both frequency containment and restoration reserves of asynchronous AC systems connected through a multi-terminal HVDC (MTDC) grid. The communication structure of the controller is distributed in the sense that only local and neighboring state information is needed, rather than the complete state. We derive sufficient stability conditions, which guarantee that the AC frequencies converge to the nominal frequency. Simultaneously, a global quadratic power generation cost function is minimized. The proposed controller also regulates the voltages of the MTDC grid, asymptotically minimizing a quadratic cost function of the deviations from the nominal DC voltages. The results are valid for distributed cable models of the HVDC grid (e.g. $\pi$-links), as well as AC systems of arbitrary number of synchronous machines, each modeled by the swing equation. We also propose a decentralized, communication-free version of the controller. The proposed controllers are tested on a high-order dynamic model of a power system consisting of asynchronous AC grids, modelled as IEEE 14 bus networks, connected through a six-terminal HVDC grid. The performance of the controller is successfully evaluated through simulation.