Backup Protection Algorithm for Failures in Modular DC Circuit Breakers

Funding: 10.13039/100010661-Horizon 2020 Framework ProgrammePeer reviewedPostprin

Power-System Level Classification of Voltage-Source HVDC Converter Stations Based Upon DC Fault Handling Capabilities

status: publishe

The Kasterlee Formation and its relation with the Diest and Mol Formations in the Belgian Campine

Stratigraphic analysis of cored and geophysically logged boreholes in the Kasterlee-Geel-Retie-Mol-Dessel area of the Belgian Campine has established the presence of two lithostratigraphic units between the classical Diest and Mol Formations, geometrically related to the type Kasterlee Sand occurring west of the Kasterlee village and the study area. A lower 'clayey Kasterlee' unit, equivalent to the lithology occurring at the top of the Beerzel and Heist-op-den-Berg hills, systematically occurs to the east of the Kasterlee village. An overlying unit has a pale colour making it lithostratigraphically comparable to Mol Sand although its fine grain size, traces of glauconite and geometrical position have traditionally led stratigraphers to consider it as a lateral variety of the type Kasterlee Sand; it has been named the 'lower Mol' or 'Kasterlee-sensu-Gulinck' unit in this study. In the present analysis, the greenish glauconitic Kasterlee Sand in its hilly stratotype area evolves eastwards into the lower 'clayey Kasterlee' unit and possibly also into an overlying 'lower Mol' or `Kasterlee-sensu-Gulinck' unit, although it is equally possible that the latter unit has an erosive contact and therefore is stratigraphically slightly younger than the type Kasterlee Sand west of the Kasterlee village. A lateral extension of this detailed stratigraphic succession into the faulted one of east Limburg is proposed

Modeling and Control of DC Grids (Modellering en controle van DC netten)

The European Union's energy policy strives for a competitive, sustainable and secure energy supply. One of the most obvious results of this policy is the ongoing strong increase of renewable energy sources in the energy supply. The transmission grid updates required to accommodate this envisaged massive amount of renewable energy sources in the transmission system go well beyond standard system reinforcements used in the past: in the coming decades, a North-Sea grid interconnecting various offshore wind farms is expected to be built. This grid can gradually evolve into a European overlay supergrid connecting the offshore wind resources with the demand centers on the continent. Also solar energy, concentrated in the south of Europe, will require similar solutions. Voltage Source Converter High Voltage Direct Current (VSC HVDC) is the most suitable technological candidate to build such a grid.One of the challenges to use this technology relates to the control of the DC voltage in case of DC system contingencies, such as a converter outage. This thesis deals with the modeling and control of VSC HVDC in a meshed DC grid and multi-terminal DC systems in general. Models are developed to address both the interactions with the AC system and the control of the DC system. The main contributions of the work include a detailed comparison of different DC voltage control strategies for multi-terminal DC systems, the development of detailed dynamic and steady-state models as well as an open-source Matlab-based power flow software program, MatACDC, which enables the study of the influence of the DC voltage control on the power flows in the AC and DC systems. Furthermore, the impact of a distributed DC voltage control on the AC system transient stability is investigated, as well as the influence of the DC system layout on the DC voltage control after a contingency.nrpages: 237status: publishe

Modeling and Control of DC grids - KBVE/SRBE Robert Sinave Award 2013

This paper discusses the background and main contributions of my PhD thesis entitled “modeling and control of DC grids”. The expected advent of multi-terminal HVDC systems and meshed DC grids poses major challenges to the control and operation of our power system. The article describes these challenges and explains how the work has contributed in the field of the development of steady-state and dynamic models to study the future power grid. Furthermore, the article describes new fundamental insights in system interactions that have been analyzed in the thesis.status: publishe

A Comprehensive Modeling Framework for Dynamic and Steady-State Analysis of Voltage Droop Control Strategies in HVDC Grids

This paper presents a comprehensive modeling framework to analyze and compare the performance of different voltage droop control characteristics in an HVDC grid. All models are fully derived mathematically, both for dynamic simulations and for steady-state power flow analysis. The main contribution lies in the development of a common modeling and control approach for the different droop-based control schemes that have been presented in the literature. The discussion includes power- and current-based droop control, either in their standard form or combined with a deadband, a constant voltage control or consisting of different slopes. Dynamic simulations show that, when applying a comparable underlying dynamic converter control framework, similar dynamic responses can be expected from the different droop control schemes, while the steady-state voltage deviations and power sharing after a contingency are different. A comparison with results from a full-detailed power flow implementation shows that these voltage deviations and power sharing can accurately be predicted by the derived steady-state power flow models, thereby avoiding the need for time-consuming dynamic simulations.status: publishe

Analysis of Power Sharing and Voltage Deviations in Droop-controlled DC Grids

This paper analyzes the influence of the converter droop settings and the dc grid network topology on the power sharing in a dc grid based on voltage source converter high voltage direct current technology. The paper presents an analytical tool to study the effect of the droop control settings on the steady-state voltage deviations and power sharing after a converter outage, thereby accounting for dc grid behavior. Furthermore, an optimization algorithm is developed, taking into account two conflicting optimization criteria. The simulation results show that, when selecting appropriate values for the converter gains, a tradeoff has to be made between the power sharing and the maximum allowable dc voltage deviation after an outage.status: publishe

Application of Extrapolation Capability of Vector Fitting for Out-of-Band Dominant Modal Synthesis of Voltage-Source Converters

Conventional state-space-based stability assessment method of voltage-source converters (VSCs) can be hindered by the black-box feature. Black box-based state-space model identification method using the terminal admittance/impedance frequency responses has thus been drawing increasing research attentions recently. However, the estimation of out-of-band modes commonly suffers from narrow bandwidth of frequency responses. This article presents, for the first time, the potential identification of several critical out-of-band modes of an artificially created rational function and a grid-connected VSC. This identification is achieved through their band-limited frequency responses using the vector fitting (VF) algorithm. On its basis, a sensitivity index of a partial fraction term is derived to explain the out-of-band modal identification behavior of the VF. The effects of the pole, residue, and fitting frequency interval width on the sensitivity index are further investigated and demonstrated. The numerical analysis shows that, with the help of the proposed sensitivity index, the extrapolation behavior of the VF can be explained, and several invisible out-of-band modes can further be identified or synthesized from a band-limited frequency response. This extrapolation feature may strengthen the curve fitting capability of the VF, i.e., compared to the VSC’s band-limited frequency responses, more modal information can be obtained and further used for eigenvalue-based stability analysis

Classification and analysis of impact on small-signal dynamics and stability from expansion of VSC-HVDC systems to multi-terminal HVDC grids

This paper presents a structured approach for analysing the effect of HVDC transmission system expansion on the small signal dynamics. The methodology decomposes the expansion of the system into a sequence of steps and aims especially at identifying the eigenvalues associated with interactions between the initial system and an added converter terminal. The procedure is illustrated with an example of expanding a point-to-point HVDC connection to a three-terminal radial configuration. The modes highlighted as responsible for the interactions between the initial system and the added third terminal are compared to the interaction modes identified by participation factor analysis. The presented results demonstrate that these two approaches present an excellent correlation and reveal complementary information.acceptedVersio

MATACDC - an open source software tool for steady-state analysis and operation of HVDC grids

With the increased interest in HVDC grids and their steady-state interactions with existing AC systems, there is a growing need for the development of tools to study the power flows in these systems. In this paper, we present MATACDC, an open source software for the analysis of hybrid AC/DC systems. The tool is available for everyone to download and allows to study the power flows in complex hybrid AC/DC systems. Incorporation of different converter control strategies enables the study of their steady-state impact for different contingencies, such as line outages or converter outages. MATACDC has been fully integrated with the power flow routines of MATPOWER, the open source MATLAB toolbox for solving AC system power flow and optimal power flow problems. A case study of the CIGRE B4 DC grid test system shows that the tools can be used to analyse complex hybrid AC/DC systems.status: publishe