Primary and secondary power control of multiterminal HVDC grids

Postprint (published version

Disturbance Attenuation of DC Voltage Droop Control Structures in a Multi-Terminal HVDC Grid

DC voltage droop control is seen as the preferred control structure for primary voltage control of future multi-terminal HVDC systems. Different droop control structures have been proposed in literature which can be classified in eight categories. This paper contributes to an analysis of the disturbance rejection of these droop control structures. The approach is based on multi-variable frequency response analysis where both ac and dc grid dynamics are incorporated. In particular, the amplification of dc voltage oscillations due to wind power variations is analyzed using singular value analysis. Further, the impact of dc cable modeling on the results is discussed. In addition, it is shown that the maximum singular value limits, frequently used in literature for MIMO-analysis, are not sufficient to prove that the impact of certain disturbances on analyzed outputs is within a certain boundary. It is necessary to verify the results by a multiple input single output analysis of the transfer functions connecting the inputs with the highest amplified output.Postprint (author's final draft

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

Reconfiguration Algorithm to Reduce Power Losses in Offshore HVDC Transmission Lines

The race to increase the efficiency and reduce the power losses in transmission systems has resulted in the substantial growth of high-voltage direct current (HVDC) transmission systems. Moreover, the interconnection of these transmission systems significantly increases their reliability. However, the control of these meshed grids is a key problem that usually is managed through the control of the VSCs in those grids, but the control of the VSC can be complemented with a reconfiguration algorithm. This paper proposes the use of the particle swarm optimization algorithm, in order to reconfigure meshed HVDC transmission systems and reduce losses. The proposed algorithm has been tested in the CIGRE benchmark grid, which comprises of several offshore wind farms that generate energy sent to the grid through several HVDC transmission lines. The results show that as the energy generation changes due to wind changes, the grid topology must be reconfigured in order to achieve the maximum efficiency. Doing this reconfiguration, power savings around 18–19% could be achieve

Interaction of Droop Control Structures and its Inherent Effect on the Power Transfer Limits in Multi-terminal VSC-HVDC

Future multiterminal HVDC systems are expected to utilize dc voltage droop controllers, and several control structures have been proposed in the literature. This paper proposes a methodology to analyze the impact of various types of droop control structures using small-signal stability analysis considering all possible combinations of droop gains. The different control structures are evaluated by the active power transfer capability as a function of the droop gains, considering various possible stability margins. This reveals the flexibility and robustness against active power flow variations, due to disturbances for all of the implementations. A case study analyzing a three-terminal HVDC VSC-based grid with eight different kinds of droop control schemes points out that three control structures outperform the remaining ones. In addition, a multivendor case is considered where the most beneficial combinations of control structures have been combined in order to find the best performing combination

Hierarchical Control Implementation for Meshed AC/Multi-terminal DC Grids with Offshore Windfarms Integration

Although the integration of meshed multi-terminal direct current (MTDC) grids with the existing AC grid has some added economic advantages, significant challenges are encountered in such systems. One of the major challenges is ensuring secure and optimal operation of the combined AC/MTDC grid considering the stability requirements of AC and DC grids at different operating conditions. This paper presents the implementation of hierarchical control for the combined AC/MTDC grid. The hierarchical control is based on the well-established three-layered control of the AC power system, comprising primary, secondary, and tertiary controls. A set of appropriate control methods are proposed for the primary, secondary, and tertiary control layers to accomplish the identified requirements for secure and optimal operation of the combined AC/MTDC grid

A generalized approach for design of contingency versatile DC voltage droop control in multi-terminal HVDC networks

The non-deterministic nature of power fluctuations in renewable energy sources impose challenges to the design of DC voltage-droop controller in Multi-Terminal High-Voltage DC (MTDC) systems. Fixed droop control does not consider converters’ capacity and system operational constraints. Consequently, an adaptive droop controller is counseled for appropriate power demand distribution. The previous adaptive droop control studies based on the converters’ Available-Headroom (AH) have lacked the demonstration of the droop gain design during consecutive power disturbances. In this paper, the design of the adaptive DC voltage droop control is investigated with several approaches, based on the permitted converters’ global and/or local AH and Loading Factor (LF). Modified adaptive droop control approaches are presented along with a droop gain perturbation technique to achieve the power-sharing based on the converters’ AH and LF. In addition, the impact of Multi-Updated (MU), Single-Updated (SU), and Irregular-Updated (IU) droop gains is investigated. The main objective of the adaptive droop control design is to minimize the power-sharing burden on converters during power variations/consecutive disturbances while maintaining the constraints of the DC grid (i.e., voltage and power rating). The presented approaches are evaluated through case studies with a 4-terminal and 5-terminal radial MTDC networks.Qatar Foundation; Qatar National Research FundScopu

Modelització i control de parcs eòlics marins connectat amb VSC-HVDC

Aquest treball presenta un estudi de modelització, disseny de controladors, mètodes d'operació i simulació de xarxes multiterminals d'alta tensió en corrent continu HVDC (High Voltage Direct Current) que interconnecten parcs eòlics marins amb la xarxa terrestre principal. Les xarxes HVDC utilitzen convertidors Voltage Source Converters (VSC) per tal de mantenir les tensions constants i per transformar els corrents d’alterns a continus i viceversa. S’estudien tres casos particulars de xarxes HVDC. La primera presenta una configuració punt a punt. Les altres dues xarxes són multiterminals, la principal diferència entre elles és que la darrera té més d’un punt de connexió amb la xarxa elèctrica de potència. Es pretén controlar les xarxes de corrent continu sense l’ús de comunicacions entre convertidors. Per això, en operació ordinària, es regula la tensió des dels convertidors VSC de connexió a la xarxa mitjançant llaços de control de tensió o controladors droop. L’estudi de cada cas es fa mitjançant simulacions amb un software del tipus EMTP (ElectroMagnetic Transients Program), aquestes es poden emprar en un futur per fer altres estudis i simulacions amb el mateix programari

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