Load Sharing Research Articles

EEG-Based Mental Workload Estimation.

Knowledge of the level of mental workload induced by any task is essential for optimizing load share among the operators. This helps in assessing their capability; besides, helping in task allocation. Since a persistently high workload experienced by operators such as aircraft pilots and automobile drivers many times compromises their performance and safety. Despite the availability of various mental workload evaluation techniques such as heart rate variability, pupil dilation, sac-cades, etc., assessment of mental workload is still a challenging task. In this work, we aim to evaluate the workload of the operator involved in long duration tasks. For this, experiments have been carried out in a working environment which provides tasks to be done simultaneously, tasks with a pause or break in activity and cross-functional tasks. The experiment data is recorded continuously in different modes and analyzed in segments to show the change in mental workload. The artificial neural network (ANN) architecture classified the workload data with an accuracy of 96.6%. The brain connectivity analysis shows the efficacy of the proposed approach.

Distributed Load Sharing Among Converters in an Autonomous Microgrid Including PV and Wind Power Units

The ability to manage energy within an autonomous microgrid, which enables system optimization, requires coordinated control of the connected power sources. This generally involves coordination of active and reactive power generation. To increase energy management capability, coordination of converter connected power sources can be extended to other tasks such as harmonic compensation and load balancing. However, some units in microgrids, such as wind and photovoltaic (PV) power sources, have local criteria such as maximum power point tracking that determines the reference value for active power generation. In this paper, a distributed control structure for independent sharing of tasks among sources is introduced where units with local active current reference can contribute to generation of only non-active current components in coordination with other units while their active current is generated autonomously. For task-sharing among units, an objective function based on current components is presented. In order to verify the proposed method, optimization of a microgrid with a PV unit is simulated.

Droop Control of Bi-Directional DC-DC Converter for Improved Voltage Regulation and Load Sharing in DC Microgrid

Droop Control of Bi-Directional DC-DC Converter for Improved Voltage Regulation and Load Sharing in DC Microgrid

Mitigation of Power and Frequency Instability to Improve Load Sharing Among Distributed Inverters in Microgrid Systems

This paper presents the design of a power system stabilizer (PSS) for stability improvement of a droop-controlled inverter-based microgrid systems. For faster power sharing, high droop gains are required, but increasing the droop gains degrades the system stability. Hence, there is a tradeoff between the faster load sharing and system stability. An answer to the given problem is presented in this paper by developing a PSS for inverter-based microgrid. The proposed stabilizer provides sufficient damping to the low-frequency oscillation even at higher value of droop gains which are usually unstable otherwise. The PSS designed in this paper is a generalized one and a step-by-step method to select the PSS parameters is also presented. Time domain simulation, experimental results, and eigenvalue analysis are presented for verification of the proposed controller.

Influence of Backlash on Load Sharing and Dynamic Load Characteristics of Twice Split Torque Transmission System

Based on the characteristics of the helicopter main reduction gearbox, and combined with the advantages of face gear and cylindrical gear power dividing, a new configuration of helicopter main gearbox with twice split paths is proposed. A bending–torsional coupled dynamic model of the system is developed through the lumped parameter method, and the influence of stiffness, damping and backlash are considered. The dynamic equation is solved by Runge–Kutta method, and the load sharing and the dynamic load coefficients are obtained, as well as their variation with the backlash. Results show that with the increase of the backlash, the load-sharing coefficient decreases, the dynamic load coefficient increases, but the other drive stages are almost unaffected. Compared with split torque stages and power confluence stages, the load sharing and dynamic load coefficient of power input stages are the most sensitive to the backlash of the power input stage, and the appropriate increase of the backlash can effectively improve the dynamic properties. Therefore, in order to obtain better dynamic performance, it is necessary to allocate the backlash reasonably.

The Predictive Value of the Load Sharing Classification Concerning Sagittal Collapse and Posterior Instrumentation Failure: A Systematic Literature Review.

Study design:Systematic review.Objective:In 1994, the Load Sharing Classification (LSC) was introduced to aid the choice of surgical treatment of thoracolumbar spine fractures. Since that time this classification system has been commonly used in the field of spine surgery. However, current literature varies regarding its use and predictive value in relation to implant failure and sagittal collapse. The objective of this study is to assess the predictive value of the LSC concerning the need for anterior stabilization to prevent sagittal collapse and posterior instrumentation failure.Methods:An electronic search of PubMed, Medline, Embase, and the Cochrane Library was performed. Inclusion criteria were (1) cohort or clinical trial (2) including patients with thoracolumbar burst fractures (3) whose severity of the fractured vertebrae was assessed by the LSC.Results:Five thousand eighty-two articles have been identified, of which 21 articles were included for this review. Twelve studies reported no correlation between the LSC and sagittal collapse or instrumentation failure in patients treated with short-segment posterior instrumentation (SSPI). Seven articles found no significant relation; 5 articles found no instrumentation failure at all. The remaining 9 articles experienced failure in patients with a high LSC or recommended a different surgical technique.Conclusions:Although the LSC was originally developed to predict the need for anterior stabilization in addition to SSPI, many studies show that SSPI only can be sufficient in treating thoracolumbar fractures regardless of the LSC. The LSC might have lost its value in predicting sagittal collapse and posterior instrumentation failure.

On the capabilities and limitations of predictive, multi-zone combustion models for hydrogen-diesel dual fuel operation

Compared with traditional hydrocarbon fuels, hydrogen provides a high-energy content and carbon-free source of energy rendering it an attractive option for internal combustion engines. Co-combusting hydrogen with other fuels offers significant advantages with respect to thermal efficiency and carbon emissions.This study seeks to investigate the potential and limitations of multi-zone combustion models implemented in the GT-Power software package to predict dual fuel operation of a hydrogen-diesel common rail compression ignition engine. Numerical results for in-cylinder pressure and heat release rate were compared with experimental data. A single cylinder dual-fuel model was used with hydrogen being injected upstream of the intake manifold. During the simulations low (20 kW), medium (40 kW) and high (60 kW) load conditions were tested with and without exhaust gas recirculation (EGR) and at a constant engine speed of 1500 rpm. Both single and double diesel injection strategies were examined with hydrogen energy share ratio being varied from 0 to 57% and 0–42 respectively. This corresponds to a range in hydrogen air-equivalence ratios of approximately 0–0.29.The results show that for the single-injection strategy, the model captures in-cylinder pressure and heat release rate with good accuracy across the entire load and hydrogen share ratio range. However, it appears that for high hydrogen content in the charge mixture and equivalence ratios beyond the lean flammability limit, the model struggles to accurately predict hydrogen entrainment leading to underestimated peak cylinder pressures and heat release rates. For double-injection cases the model shows good agreement for hydrogen share ratios up to 26%. However, for higher energy share ratios the issue of erroneous hydrogen entrainment into the spray becomes more accentuated leading to significant under-prediction of heat release rate and in-cylinder pressure.

Performance Modeling of Representative Load Sharing Schemes for Clustered Servers in Multiaccess Edge Computing

Due to their limited functionality, ubiquitous connected devices in the Internet of Things rely heavily on the computational and storage resources of the cloud. However, mainstream cloud systems always require high network bandwidth and cannot satisfy the delay requirement of real-time applications. Therefore, a new paradigm called multiaccess edge computing has emerged to offload the computation and storage needs of end user devices to the edge cloud servers located in the radio access networks of 5G mobile networks. In this paper, we study and compare three load sharing schemes, namely, no sharing, random sharing, and least loaded sharing, which exploit the collaboration between clustered servers in different degrees. We develop computationally efficient analytical models to evaluate the performance of these schemes. These models are validated by simulation, and then used to compare the performances of the three load sharing schemes under various system parameters. Comparison results show that the least loaded sharing scheme is most suitable to fully exploit the collaboration between the servers and achieve load balance among them. It contributes to reducing the blocking probability and waiting time experienced by users.

On the load share between nailing and bone

On the load share between nailing and bone

Multi-Channel-Based Microgrid for Reliable Operation and Load Sharing

This paper presents a novel approach to distribute available power among critical and non-critical loads in microgrids. The approach is based on supplying power over a number of channels with distinguishable frequencies where loads could be served by these channels according to their level of importance. The multi-channel scheme not only offers flexibility to supply loads but also to share power among adjacent microgrids. The control system, which can deal with multi-channel scheme, is presented and different applications that can be offered whereby are discussed. The number of channels that can be supplied by any inverter is determined based on the parameters of the used filter. Moreover, the power exchange efficiencies over the active channels at various power levels are determined and approximated formulas for quick evaluation are presented. To verify the proposed solution performance, simulation and experimental studies were performed. The obtained results demonstrate the effectiveness of using multi-channel scheme for power exchange in microgrid and also confirm the accuracy of the provided formula related to power exchange efficiencies.

Analysis of Load Sharing Response and Prediction of Interaction Behaviour in Piled Raft Foundation

Piled raft foundation is anticipated to show high load carrying capacity through partial load sharing between the pile and the raft components. But this complex load sharing behaviour due to the presence of interaction effects is not well known, and there is a scarcity of proper illustration and correlation among the interaction and load sharing factors. In the present study, prediction models are developed to estimate and correlate the load sharing factors and the interaction factors. 3D finite element modelling is performed for different foundation types in clayey soil underlain by sandy soil taking various design parameters. The nonlinear behaviour of the piled raft foundation, the load sharing factors and the interaction factors for every foundation types are evaluated, and a predicted model is suggested. The predicted expressions are also validated with the calculated results from the numerical analysis to a better goodness of fit. A proposed model is then suggested for the design of the piled raft foundation considering both the safety and serviceability conditions. The proposed simplified model provides an easy solution for the design of the piled raft foundation subjected to vertical loading.

Numerical Evaluation of Foundation of Digester Tank of Sewage Treatment Plant

In the present study the foundation of digester tank, main part of sewage treatment plant, is reanalyzed analytically and numerically to check the adequacy of such foundation to support superstructure loading. The foundation of digester tank consists of raft foundation and bored piles. The diameter of raft is 33 m and thickness of 1 m, while the piles are bored type of diameter 0.6 m and length 15 m. After testing eleven working piles, it is found that three piles cannot support a load of 1.5 times the working load (1305 kN) safely or in other words the factor of safety of these failed piles is less than 1.5. The results of filed pile tests are reanalyzed using two well-known methods, Davisson’s method and Brinch-Hansen method to check the ultimate carrying capacity of tested piles. Also, this paper includes analysis of previous soil investigation report and conducting additional soil investigation by drilling three boreholes to secure the soil parameters used in the analytical and numerical analysis of digester tank foundation. SAFE 12 software is used to analysis the foundation of structure as piled-raft instead of pile group to interest from the interaction between soil and raft foundation. The results of analysis showed that the piles failed in the tests can support its share of the superstructure load by a factor of safety 1.8 and the piles success in the field tests can support its share of the superstructure load by a factor of safety not less than 2.86. Also, the settlement under structure will be less than 100 mm, where using piled-raft analysis reduces the settlement to be within allowable limits.

Filament flexibility enhances power transduction of F-actin bundles.

The dynamic behavior of bundles of actin filaments growing against a loaded obstacle is investigated through a generalized version of the standard multifilament Brownian Ratchet model in which the (de)polymerizing filaments are treated not as rigid rods but as semiflexible discrete wormlike chains with a realistic value of the persistence length. By stochastic dynamic simulations, we study the relaxation of a bundle of Nf filaments with a staggered seed arrangement against a harmonic trap load in supercritical conditions. Thanks to the time scale separation between the wall motion and the filament size relaxation, mimicking realistic conditions, this setup allows us to extract a full load-velocity curve from a single experiment over the trap force/size range explored. We observe a systematic evolution of steady nonequilibrium states over three regimes of bundle lengths L. A first threshold length Λ marks the transition between the rigid dynamic regime (L < Λ), characterized by the usual rigid filament load-velocity relationship V(F), and the flexible dynamic regime (L > Λ), where the velocity V(F, L) is an increasing function of the bundle length L at a fixed load F, the enhancement being the result of an improved level of work sharing among the filaments induced by flexibility. A second critical length corresponds to the beginning of an unstable regime characterized by a high probability to develop escaping filaments which start growing laterally and thus do not participate anymore in the generation of the polymerization force. This phenomenon prevents the bundle from reaching at this critical length the limit behavior corresponding to perfect load sharing.

A methodology to prevent cascading contingencies using BESS in a renewable integrated microgrid

One of the key features of a microgrid is its capability to operate in an islanded mode when required. However, due to limited resources and bidirectional power flows, a microgrid in islanded mode is susceptible to different contingencies with extensive effects, e.g., cascading loss of distributed generators (also known as Distributed Energy Resources – DERs) due to unacceptable post-fault voltage recovery performance. In a renewable integrated microgrid, conventionally Battery Energy Storage System (BESS) is placed at the point of common coupling of distributed generators. However, such a placement approach does not prevent the cascading tripping of DERs following a fault, especially in the presence of a large share of induction motor loads. To address this challenge, this paper proposes a new placement methodology of BESS based on reactive power margin to prevent cascading contingencies and a subsequent blackout in a microgrid. The proposed methodology deploys an iterative technique. If the voltages at DERs terminals after a fault fail to recover within the stipulated time suggested by the grid code, BESS is placed at the bus with the lowest reactive power margin. It is known as the centralised placement approach of BESS. If this approach does not avert the DER tripping, the location of BESS is changed using the distributed placement scheme. In this scheme, several BESSs are placed on multiple buses, which have relatively lower values of reactive power margin. In a specific microgrid, either the centralised or the distributed BESS placement approach is eventually adopted. To explore the effectiveness of the proposed method, the IEEE 43 bus industrial test system integrated with renewable energy resources is considered as an islanded microgrid for simulations. It is found that the proposed approach results in the most appropriate placement of BESS to make the microgrid immune to cascading tripping of DERs.

A load share model for non-identical components of a k-out-of-m system

• A model for load sharing systems with non-identical components. • A new multivariate family of distributions for ordered random variables . • Inference procedure for the dependence parameter associated with load sharing effect. • Illustration of the proposed procedures on two component parallel system. We consider a k -out-of- m load sharing system when the lifetimes of the components are not necessarily identically distributed random variables. For such systems, a model for the load sharing phenomenon through the exponentiated conditional survival functions of ordered failure times is proposed. This model is more general than the load sharing model with identically distributed component lifetimes and leads to a different family of distributions for ordered random variables. A general expression for the reliability of the system is given. The computations of the reliability for a two component parallel load sharing system corresponding to the exponential and Weibull distributions are discussed. For illustrative purpose, we discuss the inference procedures for a two component parallel load sharing system corresponding to the exponential distributions . A simulation study is carried out to assess the proposed estimation and testing procedures. The applicability of the proposed load sharing model is shown through two data sets.

CFD analysis of hydrogen injection pressure and valve profile law effects on backfire and pre-ignition phenomena in hydrogen-diesel dual fuel engine

This paper focuses on optimizing the hydrogen TMI (timed manifold injection) system through valve lift law and hydrogen injection parameters (pressure, injection inclination and timing) in order to prevent backfire phenomena and improve the volumetric efficiency and mixture formation quality of a dual fuel diesel engine operating at high load and high hydrogen energy share. This was achieved through a numerical simulation using CFD code ANSYS Fluent, developed for a single cylinder hydrogen-diesel dual fuel engine, at constant engine speed of 1500 rpm, 90% of load and 42.5% hydrogen energy share. The developed tool was validated using experimental data. As a results, the operating conditions of maximum valve lift = 10.60 mm and inlet valve closing = 30 °CA ABDC (MVL10 IVC30) prevent the engine from backfire and pre-ignition, and ensure a high volumetric efficiency. Moreover, a hydrogen start of injection of 60 °CA ATDC (HSOI60) is appropriate to provide a pre-cooling effect and thus, reduce the pre-ignition sources and helps to quench any hot residual combustion products. While, the hydrogen injection pressure of 2.7 bar and an inclination of 60°, stimulate a better quality of hydrogen-air mixture. Afterwards, a comparison between combustion characteristics of the optimized hydrogen-diesel dual fuel mode and the baseline (diesel mode) was conducted. The result was, under dual fuel mode there is an increase in combustion characteristics and NOx emissions as well as a decrease in CO2 emissions. For further improvement of dual fuel mode, retarding diesel start of injection (DSOI) strategy was used.

A Novel Communication-Based Average Voltage Regulation Scheme for a Droop Controlled DC Microgrid

In a dc microgrid, enhanced voltage regulation (VR) and load sharing (LS) are necessary for the economic and reliable operation of the system. Traditionally, droop control is used for LS in microgrids. However, because of the nature of the droop control, good VR and accurate LS cannot be achieved simultaneously. To overcome this drawback, a low-bandwidth, communication-based average VR technique along with an algorithm for equal voltage correction factor is proposed in this paper. Here, precise LS is achieved via droop control using a high value of droop gain, while good VR is obtained through low-speed control area network (CAN) communication, which provides fault tolerance and expandability feature to the system. Only the local dc bus voltage information is exchanged over CAN by the grid connected converters, which ensure low communication traffic. Thus, sufficient bandwidth is available on the CAN bus that can be used for control and monitoring purpose—a highly desirable proposition for a smart grid application. Effect of communication delays on system stability has been modeled and analyzed. Simulation and experimental results are presented to validate the feasibility of the proposed scheme. Plug-n-play and fail-safe features of the proposed technique are highlighted.

Load Sharing and Wayside Battery Storage for Improving AC Railway Network Performance, With Generic Model for Capacity Estimation, Part 1

Load sharing between feeder stations has the ability to significantly improve the performance of ac electric railways by reducing the number of traction power network grid connections and minimizing losses and plant size. In this paper, the existing rail power conditioner technology, traditionally used for load balancing, is investigated from the new perspective of providing reactive voltage support and active power sharing between stations. The concept is validated through a feasibility study conducted for a heavy haul ac railway network.

An Implementation of Parallel Buck Converters for Common Load Sharing in DC Microgrid

The increase in demand for clean, safe, and environmentally friendly renewable energy sources faces several challenges such as system design and reliable operations. DC microgrid (MG) is a promising system due to higher efficiency and natural interface to renewable sources. In the hierarchical control of DC Microgrid, the V-I droop control is deployed usually in primary control level for common load sharing between converters. However, conventional droop control causes improper current sharing, voltage variations, and circulating current regulation due to the presence of droop and line resistance between converters. The aim of this paper is to presents the primary control level design of buck converters in current mode control according to the concepts of time constant and time delay, and secondary control design for parallel operations in distributed manners by combining methods, namely, low bandwidth communication (LBC), circulating current minimization techniques, and average voltage/current control. Moreover, different time delays are used for two converters to testify the effects of communication delays on current sharing and voltage restoration. The simulation is done for 2 × 2.5 KWdc parallel buck converters in PLECS (a Simulation software used for high speed simulation for power electronics) environment which shows excellent results in minimizing circulation currents, enhancing proportional current sharing, and restoring the grid voltage.

Effects of Non-torque Loads and Carrier Pinhole Position Errors on Planet Load Sharing of Wind Turbine Gearbox

The effects of carrier pinhole position errors and non-torque loads on the load sharing of planet gears in a conventional-type three-point suspension wind turbine gearbox were investigated. A 1/4 scale-down model of a 2-MW class wind turbine gearbox was used, and a parametric study was conducted using a three-dimensional analysis model capable of performing system-level analysis. Axial force, radial force, and bending moment were used as non-torque loads, and the mesh load factor was used as an index representing the load sharing characteristics of the planet gears. The results of the analysis showed that the radial force and the moment were major non-torque load elements that affect the load sharing of the planet gears. The magnitudes, positions, and phases of pinhole position errors also made a significant impact on the load sharing characteristics of the planet gears. When non-torque loads and pinhole position errors acted together, the influence of pinhole position errors was greater than that of the non-torque loads. Their combination effect will be different according to the characteristics of drive train system. Therefore, the analysis that reflects actual specifications and operating conditions of all the drive train system components is necessary to derive the planet load sharing characteristics accurately.