Voltage stability improvement is a challenging issue in planning and security assessment of power systems. As modern systems are being operated under heavily stressed conditions with reduced ...stability margins, incorporation of voltage stability criteria in the operation of power systems began receiving great attention. This study presents a novel voltage stability constrained optimal power flow (VSC-OPF) approach based on static line voltage stability indices to simultaneously improve voltage stability and minimise power system losses under stressed and contingency conditions. The proposed methodology uses a voltage collapse proximity indicator (VCPI) to provide important information about the proximity of the system to voltage instability. The VCPI index is incorporated into the optimal power flow (OPF) formulation in two ways; first it can be added as a new voltage stability constraint in the OPF constraints, or used as a voltage stability objective function. The proposed approach has been evaluated on the standard IEEE 30-bus and 57-bus test systems under different cases and compared with two well proved VSC-OPF approaches based on the bus voltage indicator L-index and the minimum singular value. The simulation results are promising and demonstrate the effectiveness of the proposed VSC-OPF based on the line voltage stability index.
This paper proposes an adaptive dc-link voltage control method for the two-stage photovoltaic inverter during the low voltage ride-through (LVRT) operation period. The dc-link voltage will be ...controlled to follow the change of grid voltage during the LVRT operation to maintain the high modulation ratio so that the high frequency harmonics injected into the grid can be attenuated significantly. Besides, when suffering the asymmetrical grid faults, the proposed control method could to some extent attenuate the double-line-frequency dc-link voltage ripple to keep the dc-link voltage in the safe operational range by shifting the double-line-frequency power ripple to the front-end dc input source, which can be achieved by intentionally fluctuating the dc input power or employing a bidirectional dc-dc converter depending on the voltage drop ratio and the input power level. The theoretical findings were verified by MATLAB simulations and the constructed experimental prototype.
The tremendous therapeutic potential of voltage-gated sodium channels (Navs) has been the subject of many studies in the past and is of intense interest today. Nav1.7 channels in particular have ...received much attention recently because of strong genetic validation of their involvement in nociception. Here we summarize the current status of research in the Nav field and present the most relevant recent developments with respect to the molecular structure, general physiology, and pharmacology of distinct Nav channel subtypes. We discuss Nav channel ligands such as small molecules, toxins isolated from animal venoms, and the recently identified Nav1.7-selective antibody. Furthermore, we review eight characterized ligand binding sites on the Nav channel α subunit. Finally, we examine possible therapeutic applications of Nav ligands and provide an update on current clinical studies.
The future grid is evolving into a smart distribution network that integrates multiple distributed energy resources ensuring at the same time reliable operation and increased power quality. In recent ...years, many research papers have addressed the voltage violation problems that arise from the high penetration of distributed generation. In view of the transition to active network management and the increase in the quantity of collected data, distributed control schemes have been proposed that use pervasive communications to deal with the complexity of smart grid. This paper reviews the recent publications on distributed and decentralized voltage control of smart distribution networks, summarizes their control models, and classifies the solution methodologies. Moreover, it comments on issues that should be addressed in the future and the perspectives of industry applications.
Voltage fluctuations are common disturbances in power grids. Initially, it is necessary to selectively identify individual sources of voltage fluctuations to take actions to minimize the effects of ...voltage fluctuations. Selective identification of disturbing loads is possible using a signal chain consisting of demodulation, decomposition, and assessment of the propagation of component signals. The accuracy of such an approach is closely related to the applied decomposition method. The paper presents a new method for decomposition by approximation with pulse waves. The proposed method allows for a correct identification of selected parameters, that is, the frequency of changes in the operating state of individual sources of voltage fluctuations and the amplitude of voltage changes caused by them. The article presents results from numerical simulation studies and laboratory experimental studies, based on which the estimation errors of the indicated parameters were determined by the proposed decomposition method and other empirical decomposition methods available in the literature. The real states that occur in power grids were recreated in the research. The metrological interpretation of the results obtained from the numerical simulation and experimental research is discussed.
Distributed generation inverters have become a key element to improve grid efficiency and reliability, particularly during grid faults. Under these severe perturbations, inverter-based power sources ...should accomplish low-voltage ride-through requirements in order to keep feeding the grid and support the grid voltage. Also, rated current can be required to better utilize reactive power provisions. This paper presents a reference generator capable to accomplish these two objectives: to keep the injected currents within safety values and to compute the power references for a better utilization of the inverter power capacity. The reference generator is fully flexible since positive and negative active and reactive powers can be simultaneously injected to improve ride-through services. Selected experimental results are reported to evaluate the performance of the proposed reference generator under different control strategies.
In this study, a new method is proposed to analyse steady-state voltage stability under load variations. This method combines a weighted sum of two voltage stability indices: one derived from power ...flow equations, and another from the decay of voltage magnitudes. The weight value of each index is updated using an algorithm based on a backwards Euler approximation. In addition, the impact of uncertainty related to voltage measurements on the prediction of voltage instability is mathematically quantified using this new index. The obtained formula shows a reduction in the capability of the proposed stability index in predicting voltage instability when the amplitude of measurement uncertainties increases. Thus, an appropriate filtering technique is added in parallel to the developed index, which proves to reduce the adverse impacts due to uncertain measurements. Simulation studies are performed using four test cases: 5-bus, IEEE 14-bus, IEEE 57-bus, and IEEE 118-bus systems. The obtained results show that the proposed index, named as global voltage stability index, is effective when compared to other voltage stability indices such as voltage collapse prediction index, voltage collapse index, and local Thévenin index.
Power quality and voltage control are among the most important aspects of the grid-connected power converter operation under faults. Nonsinusoidal current may be injected during unbalanced voltage ...sag, and active or/and reactive power may include double frequency content. This paper introduces a novel control strategy to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected photovoltaic (PV) inverters during unbalanced faults. With the proposed control method, PV inverter injects sinusoidal currents under unbalanced grid faults. In addition, an efficient and easy-to-implement current limitation method is introduced, which can effectively limit the injected currents to the rated value during faults. In this case, the fault-ride-through operation is ensured, and it will not trigger the overcurrent protection. A non-maximum power point tracking (non-MPPT) operation mode is proposed for the dc-dc converter. The mode is enabled under severe faults when the converter cannot handle the maximum PV power. Finally, experimental validation is provided by implementing a method in an experimental setup, including a 2 kW PV inverter.
With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs ...and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3>hNaV1.2>hNaV1.1>hNaV1.6>hNaV1.3>hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel.
Display omitted
•We analysed thermostability of solubilised voltage-gated sodium channels (VGSCs).•VGSCs are the most thermostable in CHAPS or LMNG within detergents tested.•VGSCs from electric eel and ratNaV1.3 are more stable than human VGSCs tested.•NaV1.2 was found to be the most thermostable within human VGSCs tested.•VGSCs can be stabilised by tetrodotoxin and by sea anemone toxin.
Voltage-gated sodium (NaV) channels are pore-forming transmembrane proteins that play essential roles in excitable cells, and they are key targets for antiepileptic, antiarrhythmic, and analgesic ...drugs. We implemented a heterobivalent design strategy to modulate the potency, selectivity, and binding kinetics of NaV channel ligands. We conjugated μ-conotoxin KIIIA, which occludes the pore of the NaV channels, to an analogue of huwentoxin-IV, a spider-venom peptide that allosterically modulates channel gating. Bioorthogonal hydrazide and copper-assisted azide–alkyne cycloaddition conjugation chemistries were employed to generate heterobivalent ligands using polyethylene glycol linkers spanning 40–120 Å. The ligand with an 80 Å linker had the most pronounced bivalent effects, with a significantly slower dissociation rate and 4–24-fold higher potency compared to those of the monovalent peptides for the human NaV1.4 channel. This study highlights the power of heterobivalent ligand design and expands the repertoire of pharmacological probes for exploring the function of NaV channels.
PDF
