Terms Of System Stability Research Articles

Modeling and Integrating PV Stations into IEC 61850 XMPP Intelligent Edge Computing Gateway

Distributed energy resources (DERs) are being widely interconnected to electrical power grids. The dispersed and intermittent generational mixes bring technical and economic challenges to the power systems in terms of stability, reliability, and interoperability. In practice, most of the communication technologies in DER are provided by proprietary communication protocols, which are not designed for the prevention of cyber security over a wide area network, and methodology of DER integration is not unified. This has made it technically difficult for power utilities and aggregators to monitor and control the DER systems after they are interconnected with the electrical grids. Moreover, peer to peer communication between DER systems as well as local intelligent computation is required to reduce decision latency and enhance the stability of the smart grid or microgrid. In this paper, the first, novel architecture of IEC 61850 XMPP (extensible messaging and presence protocol) of the edge computing gateway, involving advanced concepts and technologies, was developed and completely studied to counter the abovementioned challenges. The results show that the proposed architecture can enhance the DER system’s effective integration, security in data communication and transparency for interoperability. The novel and advanced concepts involve first modeling the topology of the photovoltaic (PV) station to IEC 61850 information models according to the IEC 61850-7-4 logical nodes and the DER-specific logical nodes defined in IEC 61850-7-420. This guarantees the interoperability between DER and DER, DER and utility and DER and the energy service operator. The second step was to map the information models to IEC 61850-8-2 XMPP for the specific communication protocol in DER applications. XMPP protocol, a publish/subscribe communication mechanism, is recommended in DER applications because of its characteristics of cybersecurity and authenticated encryption. After that we enabled the edge computing capability for data processing and the analytics of the DER side for time-critical missions. The aggregated data was then sent to the control center in the cloud. By applying the edge computing architecture, the system reduced decision latency, improved data privacy and enhanced security. The goal of this paper was to introduce the practical methodologies of these novel concepts to academics and industrial engineers.

Uniform eventual practical stability of impulsive differential system in terms of two measures

Uniform eventual practical stability of impulsive differential system in terms of two measures

A Review on Anaerobic Co-Digestion with a Focus on the Microbial Populations and the Effect of Multi-Stage Digester Configuration

Recent studies have shown that anaerobic co-digestion (AnCoD) is superior to conventional anaerobic digestion (AD). The benefits of enhanced bioenergy production and solids reduction using co-substrates have attracted researchers to study the co-digestion technology and to better understand the effect of multi substrates on digester performance. This review will discuss the results of such studies with the main focus on: (1) generally the advantages of co-digestion over mono-digestion in terms of system stability, bioenergy, and solids reduction; (2) microbial consortia diversity and their synergistic impact on biogas improvement; (3) the effect of digester mode, i.e., multi-stage versus single stage digestion on AnCoD. It is essential to note that the studies reported improvement in the synergy and diverse microbial consortia when using co-digestion technologies, in addition to higher biomethane yield when using two-stage mode. A good example would be the co-digestion of biodiesel waste and glycerin with municipal waste sludge in a two-stage reactor resulting in 100% increase of biogas and 120% increase in the methane content of the produced biogas with microbial population dominated by Methanosaeta and Methanomicrobium.

Design and Control of Coupled Inductor DC–DC Converters for MVDC Ship Power Systems

This paper deals with the design and control aspects of modern ship power systems within the paradigm of an all-electric ship. The widespread use of power electronic converters is central in this context due to the technological advances in automation systems and the integration of the electrical propulsion systems and other components, such as electrical energy storage systems and renewable energy sources. The issue to address in this scenario is related to the request of increased performances in dynamic operation while pursuing advantages in terms of energy savings and overall system security. In addition, the presence of large load changes requires providing robustness of the control in terms of system stability. This paper is focused on medium voltage direct current (MVDC) ship power systems and the design and control of coupled inductor DC–DC converters. The load is handled in terms of a constant power model, which generally is considered the most critical case for testing the stability of the system. The robustness of the design procedure, which is verified numerically against large and rapid load variations, allowed us to confirm the feasibility and the attractiveness of the design and the control proposal.

Image analysis applied to Brillouin images of tissue-mimicking collagen gelatins.

Brillouin spectroscopy is an emerging analytical tool in biomedical and biophysical sciences. It probes viscoelasticity through the propagation of thermally induced acoustic waves at gigahertz frequencies. Brillouin light scattering (BLS) measurements have traditionally been performed using multipass Fabry-Pérot interferometers, which have high contrast and resolution, however, as they are scanning spectrometers they often require long acquisition times in poorly scattering media. In the last decade, a new concept of Brillouin spectrometer has emerged, making use of highly angle-dispersive virtually imaged phase array (VIPA) etalons, which enable fast acquisition times for minimally turbid materials, when high contrast is not imperative. The ability to acquire Brillouin spectra rapidly, together with long term system stability, make this system a viable candidate for use in biomedical applications, especially to probe live cells and tissues. While various methods are being developed to improve system contrast and speed, little work has been published discussing the details of imaging data analysis and spectral processing. Here we present a method that we developed for the automated retrieval of Brillouin line shape parameters from imaging data sets acquired with a dual-stage VIPA Brillouin microscope. We applied this method for the first time to BLS measurements of collagen gelatin hydrogels at different hydration levels and cross-linker concentrations. This work demonstrates that it is possible to obtain the relevant information from Brillouin spectra using software for real-time high-accuracy analysis.

A low noise stable radiometer front-end for passive microwave tissue thermometry

ABSTRACTA low noise, high gain, stable radiometer front-end is presented for non-invasive tissue thermometry using custom designed narrow band low noise amplifiers (LNAs) and band pass filter (BPF) with 1.3 GHz centre frequency and − 20 dB pass band of 332 MHz. The fabricated LNAs have >15 dB gain, unconditional gain stability and noise figure (NF) < 1.45 dB in the pass band. The maximum insertion loss of the BPF is <1 dB over 1.2–1.4 GHz with 50 dB suppression in the surrounding communication bands. The cascaded radiometer front-end has measured gain of 45–50 dB, NF < 1.75 dB in the pass band and > 30 dB suppression in the adjacent personal communication bands. The Allan deviation of the total power radiometer indicates long term system stability and presence of Gaussian thermal noise for integration time, . Radiometer measurements of a matched load at room temperature for indicate acceptably low influence of external electromagnetic interference (EMI) and system noise equivalent temperature of 145 K. The brightness temperature measured by the total power radiometer using a resonant slot antenna demonstrates the ability to detect a 0.3°C change in the test load temperature with better than 0.1°C accuracy.

Dynamic output-feedback RMPC for systems with polytopic uncertainties under Round-Robin protocol

This paper is concerned with the dynamic output-feedback robust model predictive control (RMPC) problem for systems with polytopic uncertainties under the Round-Robin (RR) protocol. In the backward channel, i.e., from the sensors to the controller, several sensors share a communication network to transmit the data to the remote controller, and thus data collision might happen if these sensors start transmissions together. In order to prevent data from collisions, a so-called RR protocol is utilized to orchestrate the data transmission order, where only one node with token is allowed to send data at each transmission instant. The aim of the problem addressed is to design a set of controllers in the framework of dynamic output-feedback RMPC (OFRMPC) so as to guarantee the asymptotical stability of the closed-loop system in terms of the token-dependent Lyapunov-like approach. By taking the influence of the underlying RR protocol into consideration, sufficient conditions with less conservatism are obtained by solving a time-varying terminal constraint set of an auxiliary optimization problem. Furthermore, an algorithm including both off-line and online parts is provided to find a sub-optimal solution. Finally, a numerical simulation result is exploited to illustrate the usefulness and effectiveness of the proposed RMPC strategy.

Understanding flash crash contagion and systemic risk: A micro–macro agent-based approach

The purpose of this paper is to advance the understanding of the conditions that give rise to flash crash contagion, particularly with respect to overlapping asset portfolio crowding. To this end, we designed, implemented, and assessed a hybrid micro–macro agent-based model, where price impact arises endogenously through the limit order placement activity of algorithmic traders. Our novel hybrid microscopic and macroscopic model allows us to characterise systemic risk not just in terms of system stability, but also in terms of the speed of financial distress propagation over intraday timescales. We find that systemic risk is strongly dependent on the behaviour of algorithmic traders, on leverage management practices, and on network topology. Our results demonstrate that, for high-crowding regimes, contagion speed is a non-monotone function of portfolio diversification. We also find the surprising result that, in certain circumstances, increased portfolio crowding is beneficial to systemic stability. We are not aware of previous studies that have exhibited this phenomenon, and our results establish the importance of considering non-uniform asset allocations in future studies. Finally, we characterise the time window available for regulatory interventions during the propagation of flash crash distress, with results suggesting ex ante precautions may have higher efficacy than ex post reactions.

Input-to-State Stabilization of Uncertain Parabolic PDEs Using an Observer-Based Fuzzy Control

This paper presents an observer-based fuzzy controller for one-dimensional parabolic partial differential equations with distributed bounded disturbance using discrete point measurements. Sufficient conditions are derived to guarantee the input-to-state stability of the closed-loop system in terms of linear matrix inequalities. A numerical simulation example is given to demonstrate the efficiency of the results.

First beam tests of prototype silicon modules for the CMS High Granularity Endcap Calorimeter

The High Luminosity phase of the Large Hadron Collider will deliver 10 times more integrated luminosity than the existing collider, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry. As part of its upgrade program, the Compact Muon Solenoid collaboration is designing a high-granularity calorimeter (HGCAL) to replace the existing endcap calorimeters. It will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 cm2 cell size, with the remainder of the hadronic section being based on highly-segmented scintillators with silicon photomultiplier readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. First hexagonal silicon modules, using the existing Skiroc2 front-end ASIC developed for CALICE, have been tested in beams at Fermilab and CERN in 2016. We present results from these tests, in terms of system stability, calibration with minimum-ionizing particles and resolution (energy, position and timing) for electrons, and the comparisons of these quantities with GEANT4-based simulation.

Sanitation of blackwater via sequential wetland and electrochemical treatment

The discharge of untreated septage is a major health hazard in countries that lack sewer systems and centralized sewage treatment. Small-scale, point-source treatment units are needed for water treatment and disinfection due to the distributed nature of this discharge, i.e., from single households or community toilets. In this study, a high-rate-wetland coupled with an electrochemical system was developed and demonstrated to treat septage at full scale. The full-scale wetland on average removed 79 ± 2% chemical oxygen demand (COD), 30 ± 5% total Kjeldahl nitrogen (TKN), 58 ± 4% total ammoniacal nitrogen (TAN), and 78 ± 4% ortho-phosphate. Pathogens such as coliforms were not fully removed after passage through the wetland. Therefore, the wetland effluent was subsequently treated with an electrochemical cell with a cation exchange membrane where the effluent first passed through the anodic chamber. This lead to in situ chlorine or other oxidant production under acidifying conditions. Upon a residence time of at least 6 h of this anodic effluent in a buffer tank, the fluid was sent through the cathodic chamber where pH neutralization occurred. Overall, the combined system removed 89 ± 1% COD, 36 ± 5% TKN, 70 ± 2% TAN, and 87 ± 2% ortho-phosphate. An average 5-log unit reduction in coliform was observed. The energy input for the integrated system was on average 16 ± 3 kWh/m3, and 11 kWh/m3 under optimal conditions. Further research is required to optimize the system in terms of stability and energy consumption.

Encapsulation of babchi essential oil into microsponges: Physicochemical properties, cytotoxic evaluation and anti-microbial activity

Babchi essential oil (BEO) is a valuable essential oil reported to possess a variety of biological activities such as antitumor, anti inflammatory, immunomodulatory, antioxidant, antifungal and antibacterial properties. Due to its anti-microbial properties, this oil possesses an immense potential for the treatment of dermatological disorders. Further, it has minimal tendency to develop resistance, a common issue with most of the antibiotics. However, its highly viscous nature and poor stability in the presence of light, air and high temperature, limits its practical applications. To surmount these issues, this research aims to encapsulate BEO in ethyl cellulose (EC) microsponges for enhanced stability, antibacterial effect and decreased dermal toxicity. The quasi emulsion solvent evaporation technique was used for fabrication of the BEO microsponges employing EC as polymer, polyvinyl alcohol (PVA) as stabilizer and dichloro methane (DCM) as solvent. The effect of formulation variables such as the amount of EC and PVA were also investigated. The prepared microformulations were evaluated for production yield, encapsulation efficiency, particle size and in vitro release. In vitro cytotoxicity was also checked to assess dermal safety of BEO microsponges. Results revealed that all the dispersions were in micro size range (20.44 ± 3.13 μm to 41.75 ± 3.65 μm), with good encapsulation efficiency (87.70 ± 1.20% of F2) and controlled release profile (cumulative drug release 73.34 ± 1.76%). Field emission scanning electron microscopy results showed that the microsponges possessed a spherical uniform shape with a spongy structure. Results of cytotoxicity study indicated that the prepared microsponges were safer on dermal cells in comparison to pure BEO. The optimized formulation was also evaluated for in vitro antimicrobial assay against dermal bacteria like Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, which confirmed their enhanced antibacterial activity. Furthermore, the results of photostability and stability analysis indicated improved stability of BEO loaded microsponges. Hence, encapsulation of BEO in microsponges resulted in efficacious carrier system in terms of stability as well as safety of this essential oil alongwith handling benefits.

OA101] Assessment of dose efficiency of a modern X-ray fluoroscopy system using a model observer

Purpose The aim of this work was to measure image quality in terms of the square of the accumulation rate of the signal to noise ratio of low-contrast details, SNR rate 2 , kerma area product rate, P KA , rate and to quantify dose efficiency, SNR rate 2 / P KA , rate on a modern fluoroscopy system while varying the imaging conditions such as contrast detail size, X-ray beam size, dose rate, and object thickness. Methods The methodology derived by Tapiovaara et al. (Phys. Med. Biol., 38, 1761–1788, 1993, and STUK-A196, 2003) was used and implemented in MatlabTM. Measurement of model observer SNR rate 2 and P KA , rate were derived from stored fluoroscopy image sequences and the built-in kerma-area product reading on a Siemens Axiom Artis Zee MP system, respectively. 1024 image frames with and without the contrast detail were stored and subsequently analyzed by a model observer. SNR was calculated from the mean and standard deviation of the distributions of the decision variable. Finally, the long-term stability of the imaging system in terms of dose efficiency and the usefulness of the method as a quality control measure was evaluated. Results The precision in SNR rate 2 estimate was proportional to the inverse square root of the number of frames and SNR rate 2 was proportional to the area and squared thickness of the low-contrast detail. The dose efficiency increased with a factor of three with decreasing X-ray beam size from 242 cm2 to 182 cm2 and object thickness from 25 cm to 20 cm, hence quantifying the large dose efficiency gains by collimation and compression. The dose efficiency increased by 50% using the reduced dose rate compared to high dose rate. While the long-term stability of dose efficiency was measured with an uncertainty of ± 8%, the method is presently too time-consuming for routine quality control, mainly due to the slow data transfer of the large data files to the analysis server. Conclusions The results of the dose efficiency measurements under varying imaging conditions, agree with common radiological protection knowledge and allows changes in dose efficiency to be quantified which facilitate dose optimization in interventional procedures.

A comprehensive LVRT strategy of two-stage photovoltaic systems under balanced and unbalanced faults

The increase in penetration of photovoltaic (PV) systems into utility grid poses great challenges in terms of system stability, thus, force several countries to update their grid codes to accommodate the low voltage ride-through (LVRT) capability of PV systems to stay connected to the grid and supply the reactive current to support grid voltage during grid faults. In line with this, a comprehensive LVRT strategy is proposed in this paper for grid-connected PV systems under balanced and unbalanced grid faults. The proposed strategy includes the power references calculation method to meet the requirements of grid codes, the active power reduction method to avoid the overvoltage of the dc-link, the peak current limiting method to avoid the overcurrent of the inverter, and three current reference generators implemented by the proposed current reference formulations to ensure the reliable operation of PV systems under different grid faults. The effectiveness of the proposed strategy has been verified in MATLAB/SIMULINK simulation platform and the results show that the proposed LVRT strategy has good performance under different grid faults.

Process Filtration of Liquid Methane Radiation Products Using Centrifugal Separation

The radiation chemistry of methane is relatively well known and the creation of hydrogen and long chain hydrocarbons (in the form of oils, waxes and even solid carbon-like deposits) in the presence of a neutron source has presented a challenge to the ISIS liquid methane moderator operation since first start up. The rapid build-up of gaseous hydrogen leads to pressure fluctuation and circulation failure as the pipework becomes gas-locked. Current operational practice sees us replace the methane charge every single day which, while proving effective at removing the built up hydrogen gas, leads to temperature instability and periods where the system is unavailable to the users. Additionally, this approach does very little to curtail hydrocarbon build-up; previous attempts to remove the hydrocarbons using mesh filters have also proved ineffective and instead the system must be regularly flushed with solvent, while the moderator vessel requires complete replacement after only 2 or 3 operational cycles.We intend to investigate the possibility of using centrifugal separation in order to constantly remove heavy hydrocarbons and hydrogen gas from the process stream of liquid methane. If successful this could realise great benefits in terms of system stability, maintenance costs and beam time available to users. This paper will provide details of the proposed changes to be incorporated as part of the Target Station 1 (TS1) upgrade project.

Design of Simulation Product for Stability of Electric Power System Using Power System Stabilizer and Optimal Control

This paper will discuss the use of optimal control and Power System Stabilizer (PSS) in improving the oscillation of electric power system. Oscillations in the electric power system can occur due to the sudden release of the load (Switcing-Off). The oscillation of an unstable system for a long time causes the equipment to work in an interruption. To overcome this problem, a control device is required that can work effectively in repairing the oscillation. The power system is modeled from the Single Machine Infinite Bus Model (SMIB). The state space equation is used to mathematically model SMIB. SMIB system which is a plant will be formed togetherness state variables (State-Space), using riccati equation then determined the optimal gain as controller plant. Plant is also controlled by Power Stabilizer System using phase compensation method. Using Matlab Software based simulation will be observed response of rotor speed change and rotor angle change for each of the two controlling methods. Simulation results using the Simulink-MATLAB 6.1 software will compare the analysis of the plant state in Open loop state and use the controller. The simulation response shows that the optimal control and PSS can improve the stability of the power system in terms of acceleration to achieve settling-time and Over Shoot improvement. From the results of both methods are able to improve system performance.

Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter

The stability of a modular multilevel converter connected to an ac grid can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. The converter control parameters have a strong impact on the admittance and they can be adjusted for achieving system stability. This paper focuses on the admittance-shaping effect produced by different current-control schemes, either designed on a per-phase basis or in the $dq$ frame using space vectors. A linear analytical model of the converter ac-side admittance is developed, including the different current-control schemes and the phase-locked loop. Different solutions for computing the insertion indices are also analyzed, showing that for a closed-loop scheme a compact expression of the admittance is obtained. The impact of the control parameters on the admittance is discussed and verified experimentally, giving guidelines for designing the system in terms of stability. Moreover, recommendations on whether a simplified admittance expression could be used instead of the detailed model are given. The findings from the admittance-shaping analysis are used to recreate a grid-converter system whose stability is determined by the control parameters. The developed admittance model is then used in this experimental case study, showing that the stability of the interconnected system can be assessed using the Nyquist stability criterion.

Implementation of Distributed Fuzzy Load Control to an Autonomous Wind Diesel System

Many autonomous power systems are powered by diesel generators alone, which results in greater operating costs than interconnected grids. It is therefore desirable to integrate renewable energy sources such as wind into these mini grids. However, due to the fluctuating power generation from the wind resource, the varying load profile and the relatively low system inertia, technical difficulties arise in terms of system stability and efficient operation. Typically the penetration of wind energy on such systems is limited to 30%. Distributed intelligent load control can be used to increase wind penetration and cut diesel fuel consumption, whilst maintaining system stability. This thesis describes the development and application of a distributed intelligent load control system. The development of a self-tuning fuzzy controller and the construction of a laboratory wind-diesel test rig are discussed. The development of a dynamic Wind-Diesel computer model is also described. Finally the results of tests carried out on a Wind-Diesel system consisting of a 45kW stall regulated wind turbine and a 48kW diesel generator are discussed. The results were encouraging demonstrating that distributed fuzzy load control is a low cost and effective technique, which can be applied to small or large hybrid systems. The simulation results are developed by MATLAB.

A lumped parameter vane pump model for system stability analysis

This paper presents a semi-empirical lumped parameter model developed for analysing the dynamic stability and performance limitations of a pressure compensated vane pump for an automotive application with low-cost components. The model calculates continuous displacement chamber pressure profiles and inertial effects for the determination of the internal forces acting on the vane pump's pivoting cam. Measurements conducted on a custom test stand were used to define a nonlinearly progressive bias spring model and a black box representation of the pump control system valves. Analysis of the complete model reveals that the performance limitations imposed by the control system valves, in terms of system stability and achievable controller bandwidth, are more restrictive than the limitations imposed by the low-cost vane pump and limit the that bandwidth to 1.84 Hz. The control system also imposes limitations to the system performance based on resonance phenomena which may be significant in some applications.

Optimization of Continuing Education of Marine Human Resources in China Based on System Stability

In view of the shortage of marine talents and the slow progress of academic backbones, this paper analyzed in details the status quo of marine human resources and deficiencies in the existing marine education in China, and then proposed a plan for continuing education optimization based on the marine system stability in terms of the teaching mode, cultivation mechanism, and incentives. This plan was put forward as a reference for the development of marine talent education in China so as to optimize the allocation of marine human resources and vigorously advance the marine industry.