Modelling and control for bounded synchronization in multi-terminal VSC-HVDC transmission networks

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The extension and size of the power grid is expected to increase in the near future. Managing such a system presents challenging control problems that, so far, have been approached with classical control techniques. However, large scale systems of interconnected nodes fall within the framework of the emerging field of complex networks. This paper models multi-terminal VSC-HVDC systems as a complex dynamical network, and derives conditions ensuring bounded synchronization of its trajectories for a family of controllers. The obtained results are validated via numerical simulations.Postprint (author's final draft

Control of MTDC Transmission Systems under Local Information

High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper a distributed controller for multi-terminal high-voltage direct current (MTDC) transmission systems is considered. Sufficient conditions for when the proposed controller renders the closed-loop system asymptotically stable are provided. Provided that the closed loop system is asymptotically stable, it is shown that in steady-state a weighted average of the deviations from the nominal voltages is zero. Furthermore, a quadratic cost of the current injections is minimized asymptotically

Power balancing and dc fault ride through in DC grids with dc hubs and wind farms

Acknowledgment This project was funded by European Research Council under the Ideas program in FP7; grant no 259328, 2010.Peer reviewedPostprin

Distributed Controllers for Multi-Terminal HVDC Transmission Systems

High-voltage direct current (HVDC) is an increasingly commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper the voltage-droop method (VDM) is reviewed, and three novel distributed controllers for multi-terminal HVDC (MTDC) transmission systems are proposed. Sufficient conditions for when the proposed controllers render the equilibrium of the closed-loop system asymptotically stable are provided. These conditions give insight into suitable controller architecture, e.g., that the communication graph should be identical with the graph of the MTDC system, including edge weights. Provided that the equilibria of the closed-loop systems are asymptotically stable, it is shown that the voltages asymptotically converge to within predefined bounds. Furthermore, a quadratic cost of the injected currents is asymptotically minimized. The proposed controllers are evaluated on a four-bus MTDC system.Comment: arXiv admin note: substantial text overlap with arXiv:1406.5839, arXiv:1311.514

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

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

Passivity - Based Control and Stability Analysis for Hydro-Solar Power Systems

Los sistemas de energía modernos se están transformando debido a la inclusión de renovables no convencionales fuentes de energía como la generación eólica y fotovoltaica. A pesar de que estas fuentes de energía son buenas alternativas para el aprovechamiento sostenible de la energía, afectan el funcionamiento y la estabilidad del sistema de energía, debido a su naturaleza inherentemente estocástica y dependencia de las condiciones climáticas. Además, los parques solares y eólicos tienen una capacidad de inercia reducida que debe ser compensada por grandes generadores síncronos en sistemas hidro térmicos convencionales, o por almacenamiento de energía dispositivos. En este contexto, la interacción dinámica entre fuentes convencionales y renovables debe ser estudiado en detalle. Para 2030, el Gobierno de Colombia proyecta que el poder colombiano El sistema integrará en su matriz energética al menos 1,2 GW de generación solar fotovoltaica. Por esta razón, es necesario diseñar controladores robustos que mejoren la estabilidad en los sistemas de energía. Con alta penetración de generación fotovoltaica e hidroeléctrica. Esta disertación estudia nuevas alternativas para mejorar el sistema de potencia de respuesta dinámica durante y después de grandes perturbaciones usando pasividad control basado. Esto se debe a que los componentes del sistema de alimentación son inherentemente pasivos y permiten formulaciones hamiltonianas, explotando así las propiedades de pasividad de sistemas eléctricos. Las principales contribuciones de esta disertación son: una pasividad descentralizada basada control de los sistemas de control de turbinas hidráulicas para sistemas de energía de múltiples máquinas para estabilizar el rotor acelerar y regular el voltaje terminal de cada sistema de control de turbinas hidráulicas en el sistema como, así como un control basado en PI pasividad para las plantas solares fotovoltaicas

Simulation and optimization of an HVDC network connecting offshore windfarms with the mainland

In this project an algorithm capable of simulating a network connecting offshore wind farms HVDC points with consumers has been created. This simulation takes into account the analytical model that HVDC network is based on. The simulation also takes into account the control that is applied in such cases. In addition, the control of the system calculates the optimum working point to optimise the network energy transfer

Commande non-linéaire et analyse de stabilité de réseaux multi-terminaux haute tension à courant continu

This dissertation was devoted to the study of multi-terminal high voltage direct current (MTDC) networks. The main contributions were in the field of nonlinear automatic control, applied to power systems, power electronics and renewable energy sources. The research work was started with the intention of filling some gaps between the theory and the practice, in particular: 1) to investigate various control approaches for the purpose of improving the performance of MTDC systems; 2) to establish connections between existing empirical control design and theoretical analysis; 3) to improve the understanding of the multi-time-scale behavior of MTDC systems characterized by the presence of slow and fast transients in response to external disturbances. As a consequence, this thesis work can be put into three areas, namely nonlinear control design of MTDC systems, analysis of MTDC system's dynamic behaviors and application of MTDC systems for frequency control of AC systems.Cette thèse a été consacrée à l'étude des réseaux multi-terminaux haute tension à courant continu (MTDC). Les principales contributions étaient dans le domaine du contrôle automatique non linéaire, appliquées aux systèmes électriques, électronique de puissance et les sources d'énergie renouvelables. Le travail de recherche a été lancé avec l'intention de combler certaines lacunes entre la théorie et la pratique, en particulier: 1) d'enquêter sur diverses approches de contrôle pour le but d'améliorer la performance des systèmes MTDC; 2) d'établir des connexions entre la conception du contrôle empiriques existantes et analyse théorique; 3) d'améliorer la compréhension du comportement multi-échelle de temps des systèmes MTDC caractérisés par la présence de transitoires lents et rapides en réponse aux perturbations externes. En conséquence, ce travail de thèse peut être mis en trois domaines, à savoir la conception non linéaire de commande de systèmes MTDC, analyse des comportements dynamiques de système MTDC et l'application de systèmes MTDC pour le contrôle de fréquence des systèmes de climatisation

Power and frequency control of an offshore wind farm connected to grid through an HVDC link with LCC-based rectifier

Mención Internacional en el título de doctorThere is an increasing interest in the use of line-commutated converter (LCC) technology to connect large offshore wind farms (OWFs) placed far from the coast by means of a high voltage direct current (HVDC) link. This is due to the better features of LCCs compared to voltage-source converters in terms of cost, reliability and efficiency. However, this technology requires a frequency control in the OWF to allow the operation of both the wind turbine generator systems (WTGSs) and the LCC rectifier. Therefore, this Thesis presents two frequency control proposals. First, a centralized voltage and frequency control for an OWF connected through LCC-rectifier-based HVDC link is proposed. It is derived from an enhanced LCC-rectifier station average-value model which indicates that the active power balance at the point of common coupling drives the OWF voltage while the corresponding reactive power balance drives the OWF frequency. Even though voltage control cannot be applied in case of using a diode rectifier, the voltage magnitude variation is clamped between acceptable values. As a second proposal, a decentralized frequency control for the diode-rectifier-based HVDC link connection of OWFs is also presented. This control is based on a reactive power / frequency droop which allows the WTGSs to reach synchronous operation and equally share the reactive power without the need of communications among the WTGSs. Moreover, the control proposals do not rely on a phase-locked loop, so controls are not subject to grid disturbances or measurement noise. Another important specification of the proposed control strategies is that they do not modify the active power control channel of the WTGSs. Finally, the stability and the simulation results to assess the performance of both control proposals are studied.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Alireza Nami.- Secretario: Oriol Gomis Bellmunt.- Vocal: Ana Belén Morales Martíne

Complex networks-based control strategies for multi-terminal HVDC transmission lines

The work proposes and analizes complex network-based controllers for HVDC transmission lines. Two different control approaches are studied: Distributed PID strategies, which take into account just local information of the state of each single node, and Global PID algorithms, in which the control action for each node depends on the state of the whole network. Both control techniques are tested and numerically validated on a model of the North Sea Transnational Grid, which is a project of connecting already existing off-shore power plants in northern Europe countries with each other and with mainland distribution stations. The thesis is structured in seven chapters: the first chapter is an introducion about HVDC transmission lines, the second contains the main theoretical aspects of complex networks, the third and fourth chapter are more technical and they are about the study case. The above indicated control strategies are compared and discussed along with the simulation results in chapters five and six. Finally conclusions and suggestions for further research works are drawn in chapter seven.Incomin