Modeling and Control of High-Voltage Direct-Current Transmission Systems: From Theory to Practice and Back

TL;DR

This paper develops a unified port-Hamiltonian modeling framework for multi-terminal HVDC systems, proves stability with decentralized PI control, identifies intrinsic performance limits, and proposes an outer-loop solution validated through simulations.

Contribution

It introduces a physically motivated port-Hamiltonian modeling approach, establishes stability with decentralized PI control, and proposes an outer-loop to overcome PI limitations, with validation on a benchmark example.

Findings

Decentralized PI control stabilizes the system globally.

Intrinsic performance limitations of PI control are identified.

Outer-loop control significantly improves transient performance.

Abstract

The problem of modeling and control of multi-terminal high-voltage direct-current transmission systems is addressed in this paper, which contains five main contributions. First, to propose a unified, physically motivated, modeling framework - based on port-Hamiltonian representations - of the various network topologies used in this application. Second, to prove that the system can be globally asymptotically stabilized with a decentralized PI control, that exploits its passivity properties. Close connections between the proposed PI and the popular Akagi's PQ instantaneous power method are also established. Third, to reveal the transient performance limitations of the proposed controller that, interestingly, is shown to be intrinsic to PI passivity-based control. Fourth, motivated by the latter, an outer-loop that overcomes the aforementioned limitations is proposed. The performance limitation of the PI, and its drastic improvement using outer-loop controls, are verified via simulations on a three-terminals benchmark example. A final contribution is a novel formulation of the power flow equations for the centralized references calculation.