Primary and secondary power control of multiterminal HVDC grids

Postprint (published version

Aggregating sequences that occur in many proteins constitute weak spots of bacterial proteostasis

Aggregation is a sequence-specific process, nucleated by short aggregation-prone regions (APRs) that can be exploited to induce aggregation of proteins containing the same APR. Here, we find that most APRs are unique within a proteome, but that a small minority of APRs occur in many proteins. When aggregation is nucleated in bacteria by such frequently occurring APRs, it leads to massive and lethal inclusion body formation containing a large number of proteins. Buildup of bacterial resistance against these peptides is slow. In addition, the approach is effective against drug-resistant clinical isolates of Escherichiacoli and Acinetobacterbaumannii, reducing bacterial load in a murine bladder infection model. Our results indicate that redundant APRs are weak points of bacterial protein homeostasis and that targeting these may be an attractive antibacterial strategy

Predicting effective diffusion coefficients in mudrocks using a fractal model and small-angle neutron scattering measurements

The determination of effective diffusion coefficients of gases or solutes in the water‐saturated pore space of mudrocks is time consuming and technically challenging. Yet reliable values of effective diffusion coefficients are important to predict migration of hydrocarbon gases in unconventional reservoirs, dissipation of (explosive) gases through clay barriers in radioactive waste repositories, mineral alteration of seals to geological CO2 storage reservoirs, and contaminant migration through aquitards. In this study, small‐angle and very small angle neutron scattering techniques have been utilized to determine a range of transport properties in mudrocks, including porosity, pore size distributions, and surface and volume fractal dimensions of pores and grains, from which diffusive transport parameters can be estimated. Using a fractal model derived from Archie's law, we calculate effective diffusion coefficients from these parameters and compare them to laboratory‐derived effective diffusion coefficients for CO2, H2, CH4, and HTO on either the same or related mudrock samples. The samples include Opalinus Shale from the underground laboratory in Mont Terri, Switzerland, Boom Clay from a core drilled in Mol, Belgium, and a marine claystone cored in Utah, USA. The predicted values were compared to laboratory diffusion measurements. The measured and modeled diffusion coefficients show good agreement, differing generally by less than factor 5. Neutron or X‐ray scattering analysis is therefore proposed as a novel method for fast, accurate estimation of effective diffusion coefficients in mudrocks, together with simultaneous measurement of multiple transport parameters including porosity, pore size distributions, and surface areas, important for (reactive) transport modeling

Frequency-domain modeling and assessment of AC and DC electromagnetic stability in MMC-based VSC HVDC links

© 2018 IEEE. In this paper, an analysis of electromagnetic instability is presented for Voltage Source Converter High Voltage Direct Current (VSC HVDC) systems. In recent years, the interaction between electromagnetic modes of the system and the converter dynamics has shown to give rise to instability problems in the AC network, up to the kHz range. This paper extends the analysis of the problem to the DC side and investigates to what extent similar problems can be expected in future HVDC installations.status: publishe

Assessment of AC network modeling impact on small-signal stability of AC systems with VSC HVDC converters

status: publishe

Optimal DC reference voltage in HVDC grids

In a HVDC grid, power energy equilibrium must be guaranteed at every moment to prevent DC voltage to increase or decrease to unacceptable values. Contrary to the frequency in an AC power system, the DC voltage cannot be assumed to be the same throughout the system, since a DC voltage difference is necessary to have a current flow. To operate HVDC grids as far as possible from DC voltage stability limits, the selection of the DC reference voltage and DC reference node are crucial factors. This paper introduces a method to find the optimal DC voltage in a HVDC grid based on power flow and line resistances. The method is implemented in the open-source software MatACDC and the results are verified by dynamic simulations in DIgSILENT, using a one area DC voltage restoration controller.status: publishe

Towards standardisation of survey outcome categories and response rate calculations

Survey response rates are important process quality indicators and are used for many purposes. However, attempts to compare response rates — across surveys, years, organisations and countries — are severely hampered by inconsistencies in the use of survey outcome categories and in the calculation of response rates based upon these categories. In this article, we highlight some of the main issues. With regard to outcome categories, these include the structure of the coding schema, the definitions of the categories and field implementation. With regard to response rate calculation, main issues include the suitability of different rates for different purposes, how to treat uncertainty regarding eligibility of sample units and whether or not to weight the data. We illustrate some of these issues using data from UK surveys and we suggest the possible form of some solutions

Robustness evaluation of fast breaker failure backup protection in bipolar HVDC grids

To ensure a reliable fault clearing, a backup protection scheme is required for selective HVDC grid protection. One way to achieve this is to use both voltage and current measurements to distinguish uncleared faults from cleared ones during the fault clearing process of the primary protection. This paper studies the applicability of such a backup protection algorithm in meshed bipolar HVDC grids and evaluates the robustness of the algorithm against system operating conditions and breaker opening delays. The influence of different operating conditions on the fault waveforms is analysed using a three-terminal bipolar test system. The robustness of the fast breaker failure backup protection algorithm is evaluated via simulation studies on the bipolar test system in PSCAD. The simulation results show that the fast breaker failure backup protection algorithm can distinguish between uncleared and cleared faults with sufficient margin for all considered operating conditions.status: publishe