Human platelet activation by Escherichia coli: roles for FcγRIIA and integrin αIIbβ3

Gram-negative Escherichia coli cause diseases such as sepsis and hemolytic uremic syndrome in which thrombotic disorders can be found. Direct platelet–bacterium interactions might contribute to some of these conditions; however, mechanisms of human platelet activation by E. coli leading to thrombus formation are poorly understood. While the IgG receptor FcγRIIA has a key role in platelet response to various Gram-positive species, its role in activation to Gram-negative bacteria is poorly defined. This study aimed to investigate the molecular mechanisms of human platelet activation by E. coli, including the potential role of FcγRIIA. Using light-transmission aggregometry, measurements of ATP release and tyrosine-phosphorylation, we investigated the ability of two E. coli clinical isolates to activate platelets in plasma, in the presence or absence of specific receptors and signaling inhibitors. Aggregation assays with washed platelets supplemented with IgGs were performed to evaluate the requirement of this plasma component in activation. We found a critical role for the immune receptor FcγRIIA, αIIbβ3, and Src and Syk tyrosine kinases in platelet activation in response to E. coli. IgG and αIIbβ3 engagement was required for FcγRIIA activation. Moreover, feedback mediators adenosine 5’-diphosphate (ADP) and thromboxane A₂ (TxA₂) were essential for platelet aggregation. These findings suggest that human platelet responses to E. coli isolates are similar to those induced by Gram-positive organisms. Our observations support the existence of a central FcγRIIA-mediated pathway by which human platelets respond to both Gram-negative and Gram-positive bacteria

Assessment of grid-connected wind turbines with an inertia response by considering internal dynamics

This paper presents a small-signal analysis of different grid side controllers for full power converter wind turbines with inertia response capability. In real wind turbines, the DC link controller, the drivetrain damping controller and the inertial response might present contradictory control actions in a close bandwidth range. This situation might lead to reduced control performance, increased component stress and non-compliance of connection agreements. The paper presents an analysis of the internal wind turbine dynamics by considering different grid-side converter control topologies: standard current control used in the wind industry, standard current control with inertia emulation capabilities and virtual synchronous machines. Comments are made on the similarities between each topology and the negative effects and limits, and possible remedies are discussed. Finally, the conclusion poses that the inclusion of a DC link voltage controller reduces the ability of a converter to respond to external frequency events without energy storage. The degradation increases with the DC link voltage control speed

PN admittance characterisation of grid supporting VSC controller with negative sequence regulation and inertia emulation

This work presents an analysis of converter output admittance for grid supporting VSC controllers in the positive – negative frame (pn-frame). Previously discovered issues in other reference frames are explored to prove the efficacy of analysis in the pn-frame The effect of negative sequence control is often overlooked and the pn-frame offers a useful method for observing the result. The impact of control parameters such as PLL bandwidth was explored which decreased network damping and increased regions of negative incremental impedance. Reduction of unwanted admittance components was achieved by the addition of appropriately tuned voltage feedforward filters. The equivalence of inertia and droops has been documented previously but not utilising converter impedance. Analogous traces of impedances were obtained for each structure with a similar response obtained when changing the respective associated gain indicating an equivalence

Analysis of optimal grid-forming converter penetration in AC connected offshore wind farms

The modern electricity network is seeing a trend in the replacement of fossil fuel power plants with converter interfaced generation as worldwide efforts are made to combat climate change. New converter control structures such as grid-forming are seen as a key building block for maintaining the stability of the future power system. Moreover, wind power is the fastest growing renewable technology in the UK with ambitious targets set for installed capacity in the coming decade. While the benefits and drawbacks of the technology have been explored, little attention has been given to how many grid-forming converters will be needed to stabilise the modern network. Is there such a thing as too much grid-forming? This paper utilises an impedance-based windfarm model with the capability to include unique control systems on each turbine to present a small-signal based methodology for determining the penetration limits of grid-forming technology. Key stability and screening metrics are applied to identify the penetration that provides the strongest and most stable system. Three key points are specified: the critical, optimal and maximum penetrations. Moreover, findings suggest providing enhanced system strength via converters is only applicable to a certain extent where further interactions cause increased stability issues

Demystifying inertial specifications : supporting the inclusion of grid-followers

Inertia provision from converters is often separated into two categories according to the control approach. Inertia from grid-followers (GFLs) is deemed to be "synthetic" due to a slow response. In contrast, grid-forming (GFM) inertia is deemed to be "true", and more useful for frequency stability, due its faster provision. This paper analyses the distinctions between GFM and GFL inertia by carrying out parametric sweeps of each approach at different operating conditions. The analysis aims to assist the ongoing efforts to quantify grid stabilising phenomena, particularly the recent adaptation of the GB grid code to incorporate GFM converters. The optimal tuning configurations are identified, showing that the GFL can achieve fast inertial provision that can contain the grid frequency as effectively as GFM inertia on strong grids, despite the opposing consensus in the literature. The simulations also highlight the importance of voltage-source behaviours in determining the initial evolution of grid frequency, that these features should be considered more explicitly by system operators, and that GFLs should not be excluded so readily. Neglecting GFL control could limit the assets available to support the grid and inhibit the rate that the net zero transition can occur

Grid strength impedance metric : an alternative to SCR for evaluating system strength in converter dominated systems

Short circuit ratio is an outdated measure of system strength in converter dominated systems as the useful behaviour of inverter-based resources is not represented. While still useful for determining fault current provision, converter connected generation contributes to short circuit level and system strength in a different way to traditional synchronous generation. Additionally, traditional measures only account for system strength at the fundamental frequency while converters possess complex interactions across a frequency range. A novel method of determining system strength across this frequency range from the network impedances is proposed in this paper. The approach known as the Grid Strength Impedance Metric, calculates the system strength independently from short circuit level. The unique contribution of grid-following and grid-forming converters is represented by including the multiple-input multiple-output converter output impedances in the calculation. Small-signal impedance models are employed, and the metric is largely concerned with short-term voltage stability, but some inferences can be made for longer timescales. The approach is validated using time domain simulations to check for any identified areas of weakness in the frequency range. The Grid Strength Impedance Metric successfully represents the useful behaviour of grid-forming converters, indicating an enhancement in voltage stiffness in locations of deployment

Inertia and frequency support from Britain's AC powered trains

The penetration of converter connected generation is increasing globally, bringing with it valid concerns over the stability of the modern electricity network. In terms of frequency stability, the provision of inertia and frequency support from converter interfaced generation has been the topic of significant research with a wide range of systems considered. One resource that has avoided significant attention is the GB rail electrical rolling stock. Everyday thousands of trains run on a strict schedule, travelling at high speeds with considerable mass all acting as one large energy store. The AC connected trains possess regenerative braking systems allowing for this energy to be harvested. With simple software modifications this energy can be extracted during large frequency events. This article investigates the power available for inertia and frequency response throughout a working day. A sensitivity analysis of parameters is conducted and the work looks to the future by considering increasing penetration of AC trains. A response between 300 – 850 MW is estimated for a one-minute frequency response. The calculated energy and response profile was then used to investigate the effect that the trains would have had on the 9th of August power cut that occurred in the UK in 2019

Exploring an impedance-based SCR for accurate representation of grid-forming converters

The strength of an electrical network connection point is often characterized by the short circuit ratio. Analysis of the fault current contribution at the node can provide information on system impedance, voltage stability, maximum power transfer and system recovery time. However, the introduction of more power converter connected generation decreases the validity of the current short circuit ratio definition. Mainly, the parameters that determine the strength of a connection point cannot be inferred from the fault level contribution. This article presents a discussion on the pitfalls of quantifying the strength of an electrical network using fault current contribution. The limitations of the method for converter dominated networks are presented and alternative definitions from literature are discussed with drawbacks explored. Further considerations for a new index are described, and the article suggests utilizing system impedances for investigation of different stability components. Varying converter control algorithms are explored in terms of impedance, both grid-following and grid-forming. Grid-forming structures without a current loop were found to provide the greatest improvement in voltage stiffness