bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Inertia Reserve and Inertia Control Strategy for Wind Farms
Authors: Cai Youming , Li Zheng , Cai Xu
Published: March 2020

It is important to reduce the impact of the high penetration of wind power into the electricity supply for the purposes of the security and stability of the power grid. As such, the inertia capability of wind farms has become an observation index. The existing control modes cannot guarantee the wind turbine to respond to the frequency variation of the grid, hence, it may lead to frequency instability as the penetration of wind power gets much higher. For the stability of the power grid, a simple and applicable method is to realize inertia response by controlling wind farms based on a high-speed communication network. Thus, with the consideration of the inertia released by a wind turbine at its different operating points, the inertia control mechanism of a doubly-fed wind turbine is analyzed firstly in this paper. The optimal exit point of inertia control is discussed. Then, an active power control strategy for wind farms is proposed to reserve the maximum inertia under a given power output constraint. Furthermore, turbines in a wind farm are grouped depending on their inertia capabilities, and a wind farm inertia control strategy for reasonable extraction of inertia is then presented. Finally, the effectiveness of the proposed control strategy is verified by simulation on the RT-LAB (11.3.3, OPAL-RT TECHNOLOGIES, Montreal, Quebec, Canada) platform with detailed models of the wind farm.
Effect of UV-Light Treatment on Efficiency of Perovskite Solar Cells (PSCs)
Authors: Kim Sangmo , Quy Hoang Van , Choi Hyung Wook , Bark Chung Wung
Published: March 2020

We employed ultra-violet (UV) light treatment on the TiO2 layer prior to coating the perovskite layer to improve the solar conversion efficiency of perovskite solar cells (PSCs). A laboratory-made UV treatment system was equipped with various UV light sources (8 W power; maximum wavelengths of 254, 302, and 365 nm). The UV light treatment improved the power conversion efficiency (PCE) while coating the uniformity layer and removing impurities from the surface of cells. After the PSCs were exposed to UV light, their PCE developed approximately 10% efficiency; PBI2 decreased without changing the structure.
Numerical Study on Effects of Air Return Height on Performance of an Underfloor Air Distribution System for Heating and Cooling
Authors: Fan Yaming , Li Xiangdong , Zheng Minfeng , Weng Rengui , Tu Jiyuan
Published: March 2020

The exhaust/return-split configuration is regarded as an important upgrade of traditional under-floor-air-distribution (UFAD) systems due to its higher energy efficiency. Moreover, existing studies are mostly focused on the effect of the return vent height on the performance of an UFAD system under cooling conditions. Knowledge of the performance under heating conditions is sorely lacking. This paper presents a numerical evaluation of the performance characteristics of an UFAD system with six different heights of the return vents in heating operation by comprehensively considering thermal comfort, air quality, and energy consumption. The results show that, in the heating mode, the general thermal comfort (predicted mean vote-predicted percentage dissatisfied (PMV-PPD) values) and indoor air quality indices (mean age of air and volatile organic compounds (VOCs) concentration) were greatly improved and energy consumption was slightly reduced with a lower return vent height. Although these were opposite to the findings of our previous study regarding the performance in cooling mode, an optimal return vent height in terms of the comprehensive all-year performance can be recommended. This method provides insight into the design and optimization of the return vent height of UFAD for space heating and cooling.
The Composition and Properties of Polish Waste Focused on Biostabilisation in MBT Plants during the Heating Season
Authors: Jędrczak Andrzej , Myszograj Sylwia , Połomka Jacek
Published: March 2020

This paper presents the morphological composition of fraction <80 mm, being separated from municipal solid waste (MSW) and delivered in the winter season to the 21 mechanical-biological treatment (MBT) plants throughout several regions of Poland. This fraction is hereinafter referred to as OFMSW (organic fraction of municipal solid waste). Their properties are considered while using parameters such as: moisture, loss on ignition and organic carbon content, as well as moisture and loss on ignition of screen fractions <10 mm and 10–20 mm that are found within. The main aim of this research was to test waste from 21 industrial installations, and to prove that ash content (fine fractions) in waste intended for MBT was about 1/3 of the mass of overall OFMSW mass. These quantities exceed the limits that were approved for the correct operation of MBT installations. The effect of their high content in MSW during the heating season is low moisture (from 25.4% to 58.3%) and the low loss on ignition (from 23.1% to 54.3% DM [dry matter]), which might even determine their inaptness in terms of biological treatment and incineration. The <10 mm fraction contained on average 31.7 ± 7.5% of water and showed a loss on ignition of 29.8 ± 7.1% DM. These values for the 10–20 mm fraction were respectively: 36.6 ± 12.5% DM and 37.3 ± 8.8% DM, respectively.
Optimal Dispatch Strategy for a Flexible Integrated Energy Storage System for Wind Power Accommodation
Authors: Zhou Yunhai , Zhao Pinchao , Xu Fei , Cui Dai , Ge Weichun , Chen Xiaodong , Gu Bo
Published: March 2020

The application of the large-capacity energy storage and heat storage devices in an integrated energy system with a high proportion of wind power penetration can improve the flexibility and wind power accommodation capacity of the system. However, the efficiency and cost of the flexible resource should also be taken into consideration when improving the new energy accommodation capacity. Based on these considerations, the authors try to construct a joint optimal scheduling model for day-ahead energy storage and heat storage that considers flexibility. The power supplies and devices will be modeled separately, which enables a universal applicability. The objective function is the minimum cost and wind curtailment. Various practical constraints are taken into account. The mixed integer programming and software GLPK is used to program and solve. The actual operation data of a provincial power grid in northern China is used to conduct simulation analysis in four different working conditions. The results show that the model can maintain economical efficiency under different working conditions. In addition, it can adjust and dispatch various power supplies and devices efficiently, significantly improving wind power accommodation of the system.
Energy Efficiency of Linear Electromagnetic Actuators for Flapping Wing Micro Aerial Vehicles
Authors: McIvor Blake , Chahl Javaan
Published: March 2020

The development of flapping wing systems has been restricted by high power density requirements, comparatively large forces and the requirement for light weight. The use of linear electromagnetic actuators has had a small presence in the flapping wing literature when compared to other actuator types. This has been due to the high power consumption and low power output of this system when compared to resonant systems. This work assesses linear electromagnetic actuators presented in the literature and demonstrates the performance improvements achieved when the mechanism natural frequency is appropriately tuned. This process shows a reduction of input power consumption to 13% of the original power consumption. This improvement, combined with appropriate power electronic design, can reduce the perceived gap between linear electromagnetic actuators and solid-state actuators.
Wind Turbine Performance in Very Large Wind Farms: Betz Analysis Revisited
Authors: West Jacob R. , Lele Sanjiva K.
Published: March 2020

The theoretical limit for wind turbine performance, the so-called Betz limit, arises from an inviscid, irrotational analysis of the streamtube around an actuator disk. In a wind farm in the atmospheric boundary layer, the physics are considerably more complex, encompassing shear, turbulent transport, and wakes from other turbines. In this study, the mean flow streamtube around a wind turbine in a wind farm is investigated with large eddy simulations of a periodic array of actuator disks in half-channel flow at a range of turbine thrust coefficients. Momentum and mean kinetic energy budgets are presented, connecting the energy budget for an individual turbine to the wind farm performance as a whole. It is noted that boundary layer turbulence plays a key role in wake recovery and energy conversion when considering the entire wind farm. The wind farm power coefficient is maximized when the work done by Reynolds stress on the periphery of the streamtube is maximized, although some mean kinetic energy is also dissipated into turbulence. This results in an optimal value of thrust coefficient lower than the traditional Betz result. The simulation results are used to evaluate Nishino’s model of infinite wind farms, and design trade-offs described by it are presented.
Review of Trends and Targets of Complex Systems for Power System Optimization
Authors: Vysocky Jan , Misak Stanislav
Published: March 2020

Optimization systems (OSs) allow operators of electrical power systems (PS) to optimally operate PSs and to also create optimal PS development plans. The inclusion of OSs in the PS is a big trend nowadays, and the demand for PS optimization tools and PS-OSs experts is growing. The aim of this review is to define the current dynamics and trends in PS optimization research and to present several papers that clearly and comprehensively describe PS OSs with characteristics corresponding to the identified current main trends in this research area. The current dynamics and trends of the research area were defined on the basis of the results of an analysis of the database of 255 PS-OS-presenting papers published from December 2015 to July 2019. Eleven main characteristics of the current PS OSs were identified. The results of the statistical analyses give four characteristics of PS OSs which are currently the most frequently presented in research papers: OSs for minimizing the price of electricity/OSs reducing PS operation costs, OSs for optimizing the operation of renewable energy sources, OSs for regulating the power consumption during the optimization process, and OSs for regulating the energy storage systems operation during the optimization process. Finally, individual identified characteristics of the current PS OSs are briefly described. In the analysis, all PS OSs presented in the observed time period were analyzed regardless of the part of the PS for which the operation was optimized by the PS OS, the voltage level of the optimized PS part, or the optimization goal of the PS OS.
On the Role of Regulatory Policy on the Business Case for Energy Storage in Both EU and UK Energy Systems: Barriers and Enablers
Authors: Gailani Ahmed , Crosbie Tracey , Al-Greer Maher , Short Michael , Dawood Nashwan
Published: March 2020

This paper presents a SWOT analysis of the impact of recent EU regulatory changes on the business case for energy storage (ES) using the UK as a case study. ES technologies (such as batteries) are key enablers for increasing the share of renewable energy generation and hence decarbonising the electricity system. As such, recent regulatory changes seek to improve the business case for ES technologies on national networks. These changes include removing double network charging for ES, defining and classifying ES in relevant legislations, and clarifying ES ownership along with facilitating its grid access. However, most of the current regulations treat storage in a similar way to bulk generators without paying attention to the different sizes and types of ES. As a result, storage with higher capacity receives significantly higher payment in the capacity market and can be exempt from paying renewable energy promotion taxes. Despite the recent regulatory changes, ES is defined as a generation device, which is a barrier to a wide range of revenue streams from demand side services. Also, regulators avoid disrupting the current energy market structure by creating an independent asset class for ES. Instead, they are encouraging changes that co-exist with the current market and regulatory structure. Therefore, although some of the reviewed market and regulatory changes for ES in this paper are positive, it can be concluded that these changes are not likely to allow a level playing field for ES that encourage its increase on energy networks.
Magnetic Positioning Technique Integrated with Near-Field Communication for Wireless EV Charging
Authors: Qian Zhongnan , Yan Rui , Cheng Zeqian , Wu Jiande , He Xiangning
Published: March 2020

For wireless electric vehicle charging, the relative position of the primary and secondary coils has significant impacts on the transferred power, efficiency and leakage magnetic flux. In this paper, a magnetic positioning method using simultaneous power and data transmission (SWPDT) is proposed for power coil alignment. Four signal coils are installed on the primary coil to detect the secondary coil position. By measuring the positioning signal amplitudes from the four signal coils, the power coil relative position can be obtained. Moreover, all the communication needed in the positioning process can be satisfied well by SWPDT technology, and no extra radio frequency (RF) communication hardware is needed. The proposed positioning method can work properly both in power transfer online condition and in power transfer offline condition. Thus, a highly integrated wireless charging system is achieved, which features simultaneous power transfer, data transmission and position detection. A positioning experimental setup is built to verify the proposed method. The experimental results demonstrate that the positioning resolution can be maintained no lower than 1 cm in a 1060 mm × 900 mm elliptical region for a pair of 510 mm × 410 mm rectangular power coils. The three-dimensional positioning accuracy achieves up to 1 cm.
A Review and Evaluation of Predictive Models for Thermal Conductivity of Sands at Full Water Content Range
Authors: Wang Jiaming , He Hailong , Dyck Miles , Lv Jialong
Published: March 2020

The effective thermal conductivity (λeff) of sands is a critical parameter required by applications in geothermal energy resources, geo-technique and geo-environment and in science disciplines. However, the availability of the reliable λeff data is not sufficient and predictive models are usually used in practice to estimate λeff. These predictive models may vary in complexity, flexibility, accuracy and applications. There is no universal model that can be applied to all soil types and full water content range. The choice of different models may result in distinctive estimates of λeff. The objectives of this study were to conduct an extensive review of the thermal conductivity models of sands and evaluate their performance with a large dataset consisting of various sand types from dry to saturation. A total of 14 models to predict λeff of sands were evaluated with a large compiled dataset consisting of 1025 measurements on 62 sands from 20 studies. The results show that the models of Chen 2008 (CS2008) and Zhang et al. 2016 (ZN2016) give the best estimates of thermal conductivity of sands, with Nash–Sutcliffe efficiency = 0.9 and RMSE = 0.3 W m−1 °C−1. These two models are potentially applied to accurately estimate thermal conductivity of sands of different types.
Sequence Impedances of Land Single-Core Insulated Cables: Direct Formulae and Multiconductor Cell Analyses Compared with Measurements
Authors: Benato Roberto , Dambone Sessa Sebastian , Poli Michele , Sanniti Francesco
Published: March 2020

The paper deals with the sequence impedances (positive/negative and zero sequences) of high- and extra-high-voltage land single-core insulated cables. In particular, it presents the comparisons between sequence impedance measurements and computations. The computations of the sequence impedances are carried out by means of the most important international normative and council references (IEC/Cigré) and of multiconductor cell analysis which is a consolidated and powerful tool developed by University of Padova in order to analyse power frequency regimes of multiconductor asymmetric power systems. The comparisons are presented with reference to four high- and extra-high voltage insulated cables, even if the available ones are much higher: however, the conclusions derived from these four reference cases are general and can be useful for transmission system operators and for power electric system engineers involved in insulated cables. The paper demonstrates, for the first time in technical literature, that direct formulae cannot correctly evaluate the sequence impedances of installed single-core land cable systems. Extensive on-field measurement campaigns have served to this purpose.
Cluster-Based Prediction for Batteries in Data Centers
Authors: Haider Syed Naeem , Zhao Qianchuan , Li Xueliang
Published: March 2020

Prediction of a battery’s health in data centers plays a significant role in Battery Management Systems (BMS). Data centers use thousands of batteries, and their lifespan ultimately decreases over time. Predicting battery’s degradation status is very critical, even before the first failure is encountered during its discharge cycle, which also turns out to be a very difficult task in real life. Therefore, a framework to improve Auto-Regressive Integrated Moving Average (ARIMA) accuracy for forecasting battery’s health with clustered predictors is proposed. Clustering approaches, such as Dynamic Time Warping (DTW) or k-shape-based, are beneficial to find patterns in data sets with multiple time series. The aspect of large number of batteries in a data center is used to cluster the voltage patterns, which are further utilized to improve the accuracy of the ARIMA model. Our proposed work shows that the forecasting accuracy of the ARIMA model is significantly improved by applying the results of the clustered predictor for batteries in a real data center. This paper presents the actual historical data of 40 batteries of the large-scale data center for one whole year to validate the effectiveness of the proposed methodology.
Analysis of the Thermodynamic Consistency of the Richardson–Duhmann Model for Thermionic Converters
Authors: Martí Antonio
Published: March 2020

In this work, we develop the general theory for analyzing the thermodynamic consistency of the Richardson–Duhmann model for vacuum thermionic energy converters. In addition to the electron fluxes from emitter to collector and vice versa, we calculate the energy and entropy fluxes associated to them. The calculation of the entropy fluxes is what allows us to conclude that the model is consistent by verifying that both at the emitter and at the collector the entropy generation rate is positive. In the process, we review the Richardson–Duhmann model in order to assure that the assumptions we make for calculating the energy and entropy fluxes are consistent. We also generalize the Richardson–Duhmann model in order to consider Fermi–Dirac statistics.
The Energy Transition: Democracy, Justice and Good Regulation of the Heat Market
Authors: Vitéz Blanka , Lavrijssen Saskia
Published: March 2020

This paper discusses whether the concepts of energy democracy, energy justice and the principles of good market regulation could play a role in developing a more consistent approach towards the regulation of the energy sector. It is concluded that the principles of good regulation can provide a useful framework within which advantages and disadvantages can be weighed of regulatory choices to be made when modernizing the regulation of the energy markets. A case study of the Dutch heat market is used as an example, showing that a lot remains to be gained in terms of flexible regulation and supervision and the facilitation of citizen participation. Both energy democracy and energy justice call for this. The lack of flexibility in the current regulatory framework could lead to ineffective and disproportionate regulation, hindering a sustainable, reliable and affordable development of the heat market. A larger need for flexibility is justified because of the differences between the types of heat networks. Customized solutions regarding unbundling and third-party access, including the modernization of the heat market, also require sufficient discretionary powers for the independent regulator that do not hinder but in fact stimulate the development of the heat market. Furthermore, increased citizen-participation is important in light of energy justice and energy democracy, which are energy specific concepts that overarch the principles of good regulation in the energy sector. Both concepts are based on the awareness that the energy transition is a matter for all citizens of the European Union and should not be ignored by policymakers and independent regulators. Since it is likely that most heat consumers will remain locked in for a relatively long time in natural monopolies facilitated by older generation heat networks and a lack of alternatives, substantive citizen-participation could yield positive results regarding community engagement in heat network management and heat supply.
Dual Closed-Loop Linear Active Disturbance Rejection Control of Grid-Side Converter of Permanent Magnet Direct-Drive Wind Turbine
Authors: Ma Youjie , Yang Xia , Zhou Xuesong , Yang Luyong , Zhou Yongliang
Published: March 2020

In the permanent magnet direct-drive wind power grid-connected system, in order to solve the coupling problem between d -axis and q -axis currents and to improve the disturbance rejection performance of direct current (DC) bus voltage under grid faults, a new dual closed-loop structure based on linear active disturbance rejection control (LADRC) is proposed. This new dual closed-loop control includes current inner loop decoupling control and DC bus voltage outer loop control with first-order LADRC. As the LADRC has the advantages of decoupling and disturbances rejection, it is applied to the control of wind power grid-connected inverter. Through analysis, it is demonstrated that the current decoupling control is simpler than proportional integral (PI) control algorithm, the dynamic response speed is faster, and the DC bus voltage control has better anti-disturbance. Finally, a 1.5 MW direct-drive permanent magnet wind power system was established through digital simulation, and the control effects of the two control modes under different working conditions are compared. The simulation results verify that the proposed dual closed-loop control based on first-order LADRC is superior to PI double closed-loop control in terms of decoupling performance and disturbance rejection performance under grid faults.
Active Shock Absorber Control Based on Time-Delay Neural Network
Authors: Alyukov Alexander , Rozhdestvenskiy Yuri , Aliukov Sergei
Published: March 2020

A controlled suspension usually consists of a high-level and a low-level controller. The purpose the high-level controller is to analyze external data on vehicle conditions and make decisions on the required value of the force on the shock absorber rod, while the purpose of the low-level controller is to ensure the implementation of the desired force value by controlling the actuators. Many works have focused on the design of high-level controllers of active suspensions, in which it is considered that the shock absorber can instantly and absolutely accurately implement a given control input. However, active shock absorbers are complex systems that have hysteresis. In addition, electro-pneumatic and hydraulic elements are often used in the design, which have a long response time and often low accuracy. The application of methods of control theory in such systems is often difficult due to the complexity of constructing their mathematical models. In this article, the authors propose an effective low-level controller for an active shock absorber based on a time-delay neural network. Neural networks in this case show good learning ability. The low-level controller is implemented in a simplified suspension model and the simulation results are presented for a number of typical cases.
Rolling Bearing Fault Prediction Method Based on QPSO-BP Neural Network and Dempster–Shafer Evidence Theory
Authors: Wan Lanjun , Li Hongyang , Chen Yiwei , Li Changyun
Published: March 2020

To effectively predict the rolling bearing fault under different working conditions, a rolling bearing fault prediction method based on quantum particle swarm optimization (QPSO) backpropagation (BP) neural network and Dempster–Shafer evidence theory is proposed. First, the original vibration signals of rolling bearing are decomposed by three-layer wavelet packet, and the eigenvectors of different states of rolling bearing are constructed as input data of BP neural network. Second, the optimal number of hidden-layer nodes of BP neural network is automatically found by the dichotomy method to improve the efficiency of selecting the number of hidden-layer nodes. Third, the initial weights and thresholds of BP neural network are optimized by QPSO algorithm, which can improve the convergence speed and classification accuracy of BP neural network. Finally, the fault classification results of multiple QPSO-BP neural networks are fused by Dempster–Shafer evidence theory, and the final rolling bearing fault prediction model is obtained. The experiments demonstrate that different types of rolling bearing fault can be effectively and efficiently predicted under various working conditions.
In-Stream Energy by Tidal and Wind-Driven Currents: An Analysis for the Gulf of California
Authors: Magar Vanesa , Godínez Victor M. , Gross Markus S. , López-Mariscal Manuel , Bermúdez-Romero Anahí , Candela Julio , Zamudio Luis
Published: March 2020

We analyzed the peak spring tidal current speeds, annual mean tidal power densities ( T P D ) and annual energy production ( A E P ) obtained from experiment 06.1, referred as the “HYCOM model” throughout, of the three dimensional (3D), global model HYCOM in an area covering the Baja California Pacific and the Gulf of California. The HYCOM model is forced with astronomical tides and surface winds alone, and therefore is particularly suitable to assess the tidal current and wind-driven current contribution to in-stream energy resources. We find two areas within the Gulf of California, one in the Great Island Region and one in the Upper Gulf of California, where peak spring tidal flows reach speeds of 1.1 m per second. Second to fifth-generation tidal stream devices would be suitable for deployment in these two areas, which are very similar in terms of tidal in-stream energy resources. However, they are also very different in terms of sediment type and range in water depth, posing different challenges for in-stream technologies. The highest mean T P D value when excluding TPDs equal or less than 50 W m−2 (corresponding to the minimum velocity threshold for energy production) is of 172.8 W m−2, and is found near the town of San Felipe, at (lat lon) = (31.006–114.64); here energy would be produced during 39.00% of the time. Finally, wind-driven currents contribute very little to the mean T P D and the total A E P . Therefore, the device, the grid, and any energy storage plans need to take into account the periodic tidal current fluctuations, for optimal exploitation of the resources.
Comparative Study on Optimization Solvers for Implementation of a Two-Stage Economic Dispatch Strategy in a Microgrid Energy Management System
Authors: Lee Gi-Ho , Park Jae-Young , Ham Seung-Jun , Kim Young-Jin
Published: March 2020

A microgrid energy management system (MEMS) optimally schedules the operation of dispatchable distributed energy resources to minimize the operation costs of microgrids (MGs) via an economic dispatch (ED). Actual ED implementation in the MEMS relies on an optimization software package called an optimization solver. This paper presents a comparative study of optimization solvers to investigate their suitability for ED implementation in the MEMS. Four optimization solvers, including commercial as well as open-source-based ones, were compared in terms of their computational capability and optimization results for ED. Two-stage scheduling was applied for the ED strategy, whereby a mixed-integer programming problem was solved to yield the optimal operation schedule of battery-based energy storage systems. In the first stage, the optimal schedule is identified one day before the operating day; in the second stage, the optimal schedule is updated every 5 min during actual operation to compensate for operational uncertainties. A modularized programming strategy was also introduced to allow for a comparison between the optimization solvers and efficient writing of codes. Comparative simulation case studies were conducted on three test-bed MGs to evaluate the optimization results and computation times of the compared optimization solvers.
CFD Analysis on the Heat Transfer and Fluid Flow of Solar Air Heater having Transverse Triangular Block at the Bottom of Air Duct
Authors: Choi Hwi-Ung , Choi Kwang-Hwan
Published: March 2020

In this study, a two-dimensional CFD (computational fluid dynamics) analysis was performed to investigate the heat-transfer and fluid-friction characteristics in a solar air heater having a transverse triangular block at the bottom of the air duct. The Reynolds number, block height (e), pitch (P), and length (l) were chosen as design parameters. The results are validated by comparing the Nusselt number predicted by simulation with available experimental results. Renormalization-group (RNG) k - ε model with enhanced wall-treatment was selected as the most appropriate turbulence model. From the results, it was found that the presence of a transverse triangular block produces a higher Nusselt number than that of smooth air duct. The enhancement in Nusselt number varied from 1.19 to 3.37, according to the geometric conditions investigated. However, the use of transverse triangular block also results in significantly higher friction losses. The thermohydraulic performance (THPP) was also estimated and has a maximum value of 1.001 for height (e) of 20 mm, length (l) of 120 mm, and pitch (P) of 150 mm, at Reynolds number of 8000. Furthermore, in the present study, correlations of the Nusselt number and friction factor were developed as a function of geometrical conditions of the transverse triangular block and Reynolds number, which can be used to predict the value of Nusselt number and friction factor with the absolute percentage deviations of 3.29% and 7.92%, respectively.
Semi-Analytical Model for Heat and Mass Transfer Evaluation of Vapor Bubbling
Authors: Starace Giuseppe , Carrieri Lorenzo , Colangelo Gianpiero
Published: March 2020

Multi-stage refrigeration systems cover a wide range of possibilities and are diffusing more and more. The idea that inspired this work derived from the need to have a tool to model the energy behavior of the intercooler inside a multi-stage refrigeration system. In this work, a semi-analytical model of a single bubble, injected into the liquid of an intercooler of a multi-stage system, has been developed. The developed model is a set of equations derived from the Fourier equation for heat conduction in defined conditions and includes the effects of sensible and latent heat. The vapor bubble is supposed to be injected in the saturated liquid contained in a tank at a defined depth, at an intermediate pressure. The model has been implemented in Matlab and the results show the influence of the liquid surface tension, the injection depth and the thermal diffusivity of the vapor. The model developed here is a useful low-cost tool for evaluating heat transfer optimization of a separator/intercooler of a multi-stage refrigeration system.
Off-Design Performances of an Organic Rankine Cycle for Waste Heat Recovery from Gas Turbines
Authors: Carcasci Carlo , Cheli Lapo , Lubello Pietro , Winchler Lorenzo
Published: March 2020

This paper presents an off-design analysis of a gas turbine Organic Rankine Cycle (ORC) combined cycle. Combustion turbine performances are significantly affected by fluctuations in ambient conditions, leading to relevant variations in the exhaust gases’ mass flow rate and temperature. The effects of the variation of ambient air temperature have been considered in the simulation of the topper cycle and of the condenser in the bottomer one. Analyses have been performed for different working fluids (toluene, benzene and cyclopentane) and control systems have been introduced on critical parameters, such as oil temperature and air mass flow rate at the condenser fan. Results have highlighted similar power outputs for cycles based on benzene and toluene, while differences as high as 34% have been found for cyclopentane. The power output trend with ambient temperature has been found to be influenced by slope discontinuities in gas turbine exhaust mass flow rate and temperature and by the upper limit imposed on the air mass flow rate at the condenser as well, suggesting the importance of a correct sizing of the component in the design phase. Overall, benzene-based cycle power output has been found to vary between 4518 kW and 3346 kW in the ambient air temperature range considered.
Fabrication of Skutterudite-Based Tubular Thermoelectric Generator
Authors: Jang Hanhwi , Kim Jong Bae , Stanley Abbey , Lee Suhyeon , Kim Yeongseon , Park Sang Hyun , Oh Min-Wook
Published: March 2020

The conversion efficiency of the thermoelectric generator (TEG) is adversely affected by the quality of thermal contact between the module and the heat source. TEGs with the planar substrate are not suitable for the curved heat sources. Several attempts have been made to tackle this issue by fabricating complex tubular-shaped TEGs; however, all efforts have been limited to low-temperature applications. Furthermore, the electrical contact resistance of the module is critical to achieving a high-power output. In this work, we developed the tubular TEG with significantly low specific contact resistance by optimizing the joining process. We show that the modified resistance welding (MRW) performed by spark plasma sintering (SPS) is an efficient joining method for the fabrication of the TE module, with high feasibility and scalability. This research seeks to suggest important design rules to consider when fabricating TEGs.
Anti-Agglomeration Effects of Biodegradable Surfactants from Natural Sources on Natural Gas Hydrate Formation
Authors: Kang Seong-Pil , Lee Dongwon , Lee Jong-Won
Published: March 2020

Kinetic hydrate inhibitors (KHI) and anti-agglomerants (AA) rather than thermodynamic hydrate inhibitors (THI) are often used for flow assurance in pipelines. This is because they require much lower dosages than thermodynamic inhibitors. Although the hydrate-phase equilibria are not affected, KHI and AA prevent the formed hydrate crystals from growing to a bulky state causing pipeline blockage. However, these KHIs might have huge environmental impact due to leakages from the pipelines. In this study, two biodegradable AA candidates from natural sources (that is, lecithin and lanolin) are proposed and their performances are evaluated by comparing them with and without a conventional AA (Span 80, sorbitan monooleate). At 30% and 50% water cut, the addition of AA materials was found to enhance the flow characteristics substantially in pipelines and hardly affected the maximum value of the rotational torque, respectively. Considering the cost-effective and environmental advantages of the suggested AA candidates over a conventional AA such as Span 80, the materials are thought to have potential viability for practical operation of oil and gas pipelines. However, additional investigations will be done to clarify the optimum amounts and the action mechanisms of the suggested AAs.
A High-Gain Observer-Based Adaptive Super-Twisting Algorithm for DC-Link Voltage Control of NPC Converters
Authors: Shen Xiaoning , Liu Jianxing , Marquez Abraham , Luo Wensheng , Leon Jose I. , Vazquez Sergio , Franquelo Leopoldo G.
Published: March 2020

Acting as an interface between the grid and many energy systems, the active front-end (AFE) has been widely used in a large variety of industrial applications. In this paper, in order to ensure the fast dynamic performance and good disturbance rejection ability of the AFE, a high-gain observer (HGO) plus adaptive super-twisting algorithm (STA) for the three-level neutral-point-clamped (NPC) converter is proposed. Comparing with the conventional PI control strategy, the proposed controller implements the adaptive STA in the voltage regulator to provide a faster transient response. The gains of the adaptive STA keep varying according to the rules being reduced in steady state but increasing in transient conditions. Therefore, the chattering phenomenon is mitigated and the dynamic response is guaranteed. Additionally, to undermine the impact of external disturbances on the dc-link voltage, a high-efficiency HGO is designed in the voltage regulation loop to reject it. Experimental results based on a three-level NPC prototype are given and compared with the conventional PI method to validate the fast dynamic performance and high disturbance rejection ability of the proposed approach.
The Catenary Method as an Alternative to the Horizontal Directional Drilling Trajectory Design in 2D Space
Authors: Wiśniowski Rafał , Skrzypaszek Krzysztof , Łopata Paweł , Orłowicz Grzegorz
Published: March 2020

An increase in demand for energy natural resources has stimulated the development of gas pipeline networks in Europe, as well as globally. Also, in Poland in recent years there has been a significant increase in natural gas consumption. Therefore, it is necessary to build new pipelines networks using dig and no–dig techniques. Horizontal Directional Drilling is one of the most popular trenchless technologies. The aim of this article is to present a new approach in the design of HDD trajectories in two–dimensional space (2D). A review of the trajectories used so far has been provided, offering calculation algorithms to determine their well path. Then, the original catenary method is proposed, taking into account natural deflection of casing pipes. Applicable formulas and computational algorithms have been given, together with a computational example which enables comparison of the classical design methodology with the new one. According to the authors, due to natural stress distribution, the catenary method allows the use of smaller pulling forces during installation and ensures longer pipeline life. Therefore, it should be used in industrial practice as an alternative to current designing methods.
Optimizing Energy Consumption in Transportation: Literature Review, Insights, and Research Opportunities
Authors: Corlu Canan G. , de la Torre Rocio , Serrano-Hernandez Adrian , Juan Angel A. , Faulin Javier
Published: March 2020

From airplanes to electric vehicles and trains, modern transportation systems require large quantities of energy. These vast amounts of energy have to be produced somewhere—ideally by using sustainable sources—and then brought to the transportation system. Energy is a scarce and costly resource, which cannot always be produced from renewable sources. Therefore, it is critical to consume energy as efficiently as possible, that is, transportation activities need to be carried out with an optimal intake of energetic means. This paper reviews existing work on the optimization of energy consumption in the area of transportation, including road freight, passenger rail, maritime, and air transportation modes. The paper also analyzes how optimization methods—of both exact and approximate nature—have been used to deal with these energy-optimization problems. Finally, it provides insights and discusses open research opportunities regarding the use of new intelligent algorithms—combining metaheuristics with simulation and machine learning—to improve the efficiency of energy consumption in transportation.
Alienation Coefficient and Wigner Distribution Function Based Protection Scheme for Hybrid Power System Network with Renewable Energy Penetration
Authors: Ram Ola Sheesh , Saraswat Amit , Goyal Sunil Kumar , Sharma Virendra , Khan Baseem , Mahela Om Prakash , Haes Alhelou Hassan , Siano Pierluigi
Published: March 2020

The rapid growth of grid integrated renewable energy (RE) sources resulted in development of the hybrid grids. Variable nature of RE generation resulted in problems related to the power quality (PQ), power system reliability, and adversely affects the protection relay operation. High penetration of RE to the utility grid is achieved using multi-tapped lines for integrating the wind and solar energy and also to supply loads. This created considerable challenges for power system protection. To overcome these challenges, an algorithm is introduced in this paper for providing protection to the hybrid grid with high RE penetration level. All types of fault were identified using a fault index (FI), which is based on both the voltage and current features. This FI is computed using element to element multiplication of current-based Wigner distribution index (WD-index) and voltage-based alienation index (ALN-index). Application of the algorithm is generalized by testing the algorithm for the recognition of faults during different scenarios such as fault at different locations on hybrid grid, different fault incident angles, fault impedances, sampling frequency, hybrid line consisting of overhead (OH) line and underground (UG) cable sections, and presence of noise. The algorithm is successfully tested for discriminating the switching events from the faulty events. Faults were classified using the number of faulty phases recognized using FI. A ground fault index (GFI) computed using the zero sequence current-based WD-index is also introduced for differentiating double phase and double phase to ground faults. The algorithm is validated using IEEE-13 nodes test network modelled as hybrid grid by integrating wind and solar energy plants. Performance of algorithm is effectively established by comparing with the discrete wavelet transform (DWT) and Stockwell transform based protection schemes.
Temporary Fault Ride-Through Method in Power Distribution Systems with Distributed Generations Based on PCS
Authors: Lee Jung-Hun , Jeon Seung-Gyu , Kim Dong-Kyu , Oh Joon-Seok , Kim Jae-Eon
Published: March 2020

The current practice of Distributed Generation (DG) disconnection for every fault in distribution systems has an adverse effect on utility and stable power trading when the penetration level of DGs is high. That is, in the process of fault detecting and Circuit Breaker (CB) reclosing when a temporary fault occurs, DGs should be disconnected from the Point of Common Coupling (PCC) before CB reclosing. Then all DGs should wait at least 5 minutes after restoration for reconnection and cannot supply the pre-bid power in power market during that period. To solve this problem, this paper proposes a control method that can keep operating without disconnection of DG. This control method is verified through modeling and simulation by the PSCAD/EMTDC software package for distribution systems with DGs based on PCS (Power Conditioning Systems) and CB reclosing protection.
Analysis of Intrinsic Switching Losses in Superjunction MOSFETs Under Zero Voltage Switching
Authors: Rogina Maria , Rodriguez Alberto , G. Lamar Diego , Roig Jaume , Gomez German , Vanmeerbeek Piet
Published: March 2020

Switching losses of power transistors usually are the most relevant energy losses in high-frequency power converters. Soft-switching techniques allow a reduction of these losses, but even under soft-switching conditions, these losses can be significant, especially at light load and very high switching frequency. In this paper, hysteresis and energy losses are shown during the charge and discharge of the output capacitance (COSS) of commercial high voltage Superjunction MOSFETs. Moreover, a simple methodology to include information about these two phenomena in datasheets using a commercial system is suggested to manufacturers. Simulation models including COSS hysteresis and a figure of merit considering these intrinsic energy losses are also proposed. Simulation and experimental measurements using an LLC resonant converter have been performed to validate the proposed mechanism and the usefulness of the proposed simulation models.
Numerical and Experimental Studies on the Effect of Surface Roughness and Ultrasonic Frequency on Bubble Dynamics in Acoustic Cavitation
Authors: Altay Rana , Sadaghiani Abdolali K. , Sevgen M. Ilker , Şişman Alper , Koşar Ali
Published: March 2020

With many emerging applications such as chemical reactions and ultrasound therapy, acoustic cavitation plays a vital role in having improved energy efficiency. For example, acoustic cavitation results in substantial enhancement in the rates of various chemical reactions. In this regard, an applied acoustic field within a medium generates acoustic streaming, where cavitation bubbles appear due to preexisting dissolved gas in the working fluid. Upon cavitation inception, bubbles can undergo subsequent growth and collapse. During the last decade, the studies on the effects of different parameters on acoustic cavitation such as applied ultrasound frequency and power have been conducted. The bubble growth and collapse mechanisms and their distribution within the medium have been classified. Yet, more research is necessary to understand the complex mechanism of multi-bubble behavior under an applied acoustic field. Various parameters affecting acoustic cavitation such as surface roughness of the acoustic generator should be investigated in more detail in this regard. In this study, single bubble lifetime, bubble size and multi-bubble dynamics were investigated by changing the applied ultrasonic field. The effect of surface roughness on bubble dynamics was presented. In the analysis, images from a high-speed camera and fast video recording techniques were used. Numerical simulations were also done to investigate the effect of acoustic field frequency on bubble dynamics. Bubble cluster behavior and required minimum bubble size to be affected by the acoustic field were obtained. Numerical results suggested that bubbles with sizes of 50 µm or more could be aligned according to the radiation potential map, whereas bubbles with sizes smaller than 10 µm were not affected by the acoustic field. Furthermore, it was empirically proven that surface roughness has a significant effect on acoustic cavitation phenomena.
Electromagnetic Immunity Performance of Intelligent Electronic Equipment in Smart Substation’s Electromagnetic Environment
Authors: Liu Guanchen , Zhao Peng , Qin Yang , Zhao Mingmin , Yang Zhichao , Chen Henglin
Published: March 2020

With the gradual increasing of the transmission voltage level, the situation of interference on secondary side equipment in smart substations is becoming more serious. The authors tested the interference waveforms caused by the circuit breaker’s operation at the smart substation, which showed the severity of the electromagnetic (EM) environment. This paper takes the electronic current transformer acquisition card as an example. The influence of EM interference sources on the reliability of the acquisition card is analyzed. Then, standardized electromagnetic compatibility (EMC) immunity tests of the international electrotechnical commission (IEC) for different interferences are implemented. Typical output characteristics of acquisition cards for different tests are analyzed. Innovatively, this paper proposes a quantitative evaluation method of output waveform disturbance to evaluate the acquisition card’s performance. This disturbance distortion is of great significance to the EM environment estimation of the acquisition card.