This paper investigates the nonlinear modeling and stability of a doubly-fed variable speed pumped storage power station (DFVSPSPS). Firstly, the mathematical model of DFVSPSPS with surge tank considering nonlinear pump turbine characteristics was derived and established. Then, Hopf bifurcation analysis of DFVSPSPS was performed. The stable region was identified and verified by example analysis. Moreover, the effect mechanism of nonlinear pump turbine characteristics on the stability of DFVSPSPS was explored. Finally, the influence of factors on the stability and dynamic response of DFVSPSPS was studied. The results indicate that the emerged Hopf bifurcation of DFVSPSPS is supercritical and the region on the low side of the bifurcation line is the stable region. Nonlinear head characteristics have a significant influence on the stability and dynamic response of DFVSPSPS. Nonlinear speed characteristics have an obvious effect on the stability and dynamic response of DFVSPSPS only under... [more]

The phase-synchronized rotation of a pair of closely spaced vertical-axis wind turbines has been found in wind tunnel experiments and computational fluid dynamics (CFD) simulations. During phase synchronization, the two wind turbine rotors rotate inversely at the same mean angular velocity. The blades of the two rotors pass through the gap between the turbines almost simultaneously, while the angular velocities oscillate with a small amplitude. A pressure drop in the gap region, explained by Bernoulli’s law, has been proposed to generate the interaction torque required for phase synchronization. In this study, an analytical model of the interaction torques was developed. In our simulations using the model, (i) phase synchronization occurred, (ii) the angular velocities of the rotors oscillated during the phase synchronization, and (iii) the oscillation period became shorter and the amplitude became larger as the interaction became stronger. These observations agree qualitatively with t... [more]

In order to deal with many influence factors of electric vehicles in driving under complex conditions, this paper establishes the system state equation based on the longitudinal dynamics equation of vehicle. Combined with the improved Sage−Husa adaptive Kalman filter algorithm, the road slope estimation model is established. After the driving speed and rough slope observation are input into the slope estimation model, the accurate road slope estimation at the current time can be obtained. The road slope estimation method is compared with the original Sage−Husa adaptive Kalman filter road slope estimation method through three groups of road tests in different slope ranges, and the accuracy and stability advantages of the proposed algorithm in road conditions with large slopes are verified.

In order to study the impact of a renewable energy quota and green power certificate system on the strategies of energy suppliers, this paper constructs a multi-stage game model of renewable energy power investment and production from the renewable energy interest chain and its stakeholders. Through the calculation and solution of the model, the optimal renewable energy utilization level, pricing and production strategies of renewable energy power of energy suppliers are calculated under the scenarios of direct sale of power and purchase and sale by power grids. The results show that the quota ratio, green certificate price and investment cost are the key influencing factors of energy suppliers’ strategies, and changes in the values of the three factors will completely change the renewable energy investment, pricing and production levels of energy suppliers in equilibrium. In addition, the study found that the impact of the renewable energy quota on renewable energy utilization levels... [more]

With the development of More/All-Electric Aircraft, especially the progress of hybrid electrical propulsion or electrical propulsion aircraft, the problem of optimizing the energy system design and operation of the aircraft must be solved regarding the increasing electrical power demand-limited thermal sink capability. The paper overviews the state of the art in architecture optimization and an energy management system for the aircraft power system. The basic design method for power system architecture optimization in aircraft is reviewed from the multi-energy form in this paper. Renewable energy, such as the photo-voltaic battery and the fuel cell, is integrated into the electrical power system onboard which can also make the problem of optimal energy distribution in the aircraft complex because of the uncertainty and power response speed. The basic idea and research progress for the optimization, evaluation technology, and dynamic management control methods of the aircraft power syst... [more]

Currently, the primary method for determining the object coordinates is positioning using Global Navigation Satellite Systems (GNSS) supported by Inertial Navigation Systems (INS). The main goal of this solution is to ensure high positioning availability, particularly when access to satellite signals is limited (in tunnels, areas with densely concentrated buildings and in forest areas). The aim of this article is to determine whether the GNSS/INS system supported by the RTK receiver is suitable for the implementation of selected geodetic and construction tasks in railway engineering, such as determining the place and extent of rail track deformations (1 cm (p = 0.95)), the process of a rapid stocktaking of existing rail tracks (3 cm (p = 0.95)) and for design and construction works (10 cm (p = 0.95)), as well as what the impact of various terrain obstacles have on the obtained positioning accuracy of the tested system. During the research, one INS was used, the Ekinox2-U by the SBG Sys... [more]

Buildings play a significant role in terms of energy consumption and polluting emissions production across Europe and this huge contribution to consumption and environmental impact becomes even more alarming when attention is switched from single buildings to entire urban systems. Although great efforts have been made to support energy efficiency investments, distrust and suspicion are shared attitudes among private investors (and stakeholders in general) towards large-scale implementation of these kinds of projects. Within this framework, on-bill schemes were implemented in the United States more than 30 years ago. In particular, on-bill energy efficiency is a method of financing energy efficiency improvements that uses the utility bill as the repayment vehicle. A detailed analysis of on-bill schemes is currently addressed by the H2020 RenOnBill project, which focuses on these schemes to enhance and support large-scale investments for energy efficiency and deep residential stock renov... [more]

This paper investigates the interrelations between stock returns and crude oil prices for European oil-importing/exporting countries. A vector autoregression (VAR) model is applied to estimate the significance of stock market responses to changes in oil prices during the pandemic period 2019−2021. A Granger causality test is applied to find the direction and the intensity of the relation between crude oil and the indices of the European stock markets. The findings of this paper hold with or without the COVID-19 pandemic episode and reveal the interaction between the European stock markets and the crude oil prices. The results indicate that in steady periods, before the COVID-19 outbreak and after the announcement of vaccinations, there is no interdependence between crude oil and stock prices, whereas in high volatility periods, the causality from stock markets to oil prices increases and both oil-exporting and -importing countries are equally influenced. These findings have implication... [more]

Based on the energy storage type of hydraulic wind turbines (HWTs) and in view of the unit frequency drop problem under high wind power proportion conditions, this paper proposes a method of primary frequency control under maximum power point tracking (MPPT). HWT power output is affected by wind speed randomness and volatility. In addition, traditional wind turbines do not have inertial adjustment ability, leading to a decrease in the frequency stability of the power system caused by the increase in wind power permeability. In the paper, a hydraulic energy storage system and synchronous generator are combined to carry out primary frequency modulation, and a mathematical model of the hydraulic energy storage system, the hydraulic main transmission system, and the generator active power regulation system after grid connection is established. By analyzing the load changing rules of power systems and frequency fluctuation caused by the power system load after the wind turbine is grid-conne... [more]

The effect of three kinds of fuels used to supply a diesel engine on its characteristics, fuel consumption, and emissions was studied. The fuels comprised pure diesel, a blend of diesel with 6% of methyl ester of yellow grease in the form of rapeseed oil, and a blend of diesel with methyl ester of brown grease in the form of goose fat. The chromatographic analysis was conducted for these fuels, and the results are presented. Two tests, comprising measurement of fuel consumption and engine emissions, were conducted on a vehicle with a diesel engine operating under zero load and under full load. The engine’s characteristics, including both power and torque versus speed, were determined under full engine load. The results of these tests are presented in this paper. The results indicated that the use of different methyl ester-based biodiesel blends with the same content of diesel to supply the diesel engine resulted in different fuel consumption and emissions of the engine not only in comp... [more]

Modern ships discharge large amounts of energy into the environment. More specifically, internal combustion engines (ICE) of commercial and passenger ships waste significant amounts of thermal energy at high temperature through their exhaust gases that are discharged to the atmosphere. A practical approach of recovering some amount of this energy is by using thermoelectric generator systems, which can convert thermal into electrical energy, given that there is a significant temperature difference. It is the aim of this work to propose a thermoelectric generator to recover energy from the exhaust gases of marine ICEs. The proposed thermoelectric generator uses the outside surface of the ICE manifold as the hot side of the thermoelectric module, while the cold side is maintained at a low temperature through a heat sink and induced water flow. The goal of this work is to design this thermoelectric generator and identify the configuration that produces the maximum electric power. The analy... [more]

The year 2021 brought a significant increase in CO2 emissions despite the rapid growth of new renewable energy sources (RES) installations being commissioned [...]

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications... [more]

Fischer−Tropsch synthetic (FT) fuels are expected to be an ideal alternative for diesel fuel to achieve higher thermal efficiency and reduction in exhaust emissions because of their characteristics of being aromatic-free, sulfur-free, and high cetane number. In this study, the effects of chemical compositions and cetane number of FT fuels on diesel engine performance were investigated by using a commercial GTL (Gas-to-Liquids) diesel fuel synthesized by the FT method and blended paraffinic hydrocarbon fuels made to simulate FT fuels with different chemical compositions and cetane numbers. At first, a commercial diesel fuel (JIS No.2) and GTL were examined by varying the intake oxygen concentrations with cooled EGR. Compared with diesel fuel, GTL shows shorter premixed combustion, smaller heat release peak, and longer diffusion combustion duration at both high and medium conditions due to the higher cetane number. Further, by using the GTL, a limited improvement in thermal efficiency an... [more]

In the present study, experimental analyses were conducted by using biodiesel derived from second-generation feedstock. In terms of cost and accessibility, second-generation feedstock has gained more attention due to its environmental approach. Waste-cooking-oil-derived methyl ester was produced through a transesterification reaction in the presence of a synthesized magnesium zirconate (Mg2Zr5O12) heterogeneous catalyst. This trans-esterified waste cooking oil (WCO) was used as biodiesel and was blended with diesel in 10%, 20%, 30%, 40%, and 50% by volume ratio for further analysis. The fuel properties of pure and blended biodiesel were investigated in terms of flash point, density, kinematic viscosity, and lower heating value as per the American Society for Testing and Materials (ASTM) D-6751 standards. For each blended fuel, the engine performance and gaseous emissions trend with engine loads of 0, 3, 6, 9, and 12 kg were measured on a Kirloskar TV1 IC engine. The results indicated t... [more]

Hydrogen is a versatile vector for heat and power, mobility, and stationary applications. Steam methane reforming and coal gasification have been, until now, the main technologies for H2 production, and in the shorter term may remain due to the current costs of green H2. To minimize the carbon footprint of these technologies, the capture of CO2 emitted is a priority. The in situ capture of CO2 during the reforming and gasification processes, or even during the syngas upgrade by water−gas shift (WGS) reaction, is especially profitable since it contributes to an additional production of H2. This includes biomass gasification processes, where CO2 capture can also contribute to negative emissions. In the sorption-enhanced processes, the WGS reaction and the CO2 capture occur simultaneously, the selection of suitable CO2 sorbents, i.e., with high activity and stability, being a crucial aspect for their success. This review identifies and describes the solid sorbents with more potential for... [more]

Bangladesh has a rapidly increasing population and coupled with healthy economic growth, is resulting in a rising energy demand. The country also aims to increase its renewable share of electricity to 10% by 2030. However, due to limited wind resources, solar energy seems to be most appropriate to deliver such a target. However, in a land-scarce country, this presents a major challenge, which this work aims to partially address. Being a globally leading producer of commodities, Bangladesh has a considerable number of large manufacturing plants with appropriate roofs that could be used for deploying solar energy conversion systems at scale. A methodology is presented which identified and assessed 6045 such plants, which have roof areas ranging from 100 m2 to 50,000 m2, and modelled the deployment of solar photovoltaic (PV) technology that can provide power through site available grid infrastructure. Such deployment takes advantage of net metering regulations to enhance the case for such... [more]

In order to clearly understand the air flow resistance characteristics in vertical tanks for sinter waste heat recovery in the steel industry, experimental research on the air flow pressure drop (FPD) performance in a sinter bed layer (BL) was conducted. Based on a self-made experimental device, the measurement values of air FPD for different experimental conditions were determined firstly, and then the concept of Euler number (Eu) in heat exchangers was introduced into the study of air FPD in BL; the change rules of Eu under different particle diameters were analyzed. Finally, the air FPD correlation in sinter BL was obtained and described in the form of Eu, and the error analysis of obtained air FPD correlation was performed. The results show that, the air FPD increases as a second power relationship with the increase in air superficial velocity when the particle diameter is constant. The decrease amplitude of Eu gradually dwindles when increasing the Reynolds number (Re), and the de... [more]

The development of high-performance nonprecious metal catalysts for oxygen reduction reactions is critical for the commercialization of fuel cells. In this paper, we report a non-precious catalyst with high-performance, in which Fe and Fe3C is embedded in nitrogen-doped carbon nanofibers (MIL-N-CNFs) by co-electrospinning Fe-MIL and polyacrylonitrile (PAN) and pyrolyzing. The mass ratio of Fe-MIL to PAN in the precursors and the pyrolysis temperature were optimized to be 1.5 and treated at 800 °C, respectively. The optimized catalyst exhibited an onset potential of 0.950 V and a half-wave potential of 0.830 V in alkaline electrolytes, thanks to the improved mass transfer kinetics in a meso-porous structure and enhanced reaction kinetics by confined Fe and Fe3C particles. Additionally, the optimized catalyst showed a better methanol tolerance than the commercial 20 wt.% Pt/C, indicating a potential application in direct methanol fuel cells. Serving as the cathode in CCM, the anion-excha... [more]

Distribution of joints and fissures under hydraulic coupling condition is particularly critical to the stability of surrounding rock masses in underground engineering construction. In this paper, DDARF (Discontinuous Deformation Analysis for Rock Failure) and RFPA (Rock Failure Process Analysis) are compared and analyzed firstly based on laboratory tests. Then using preferred software RFPA, the failure process, stress state, acoustic emission characteristics and energy dissipation laws of rock masses with different joint locations are analyzed under the hydraulic coupling condition. Results show that a large tensile stress region is generated on both ends of the original joint with the micro-cracks’ propagation, water pressure in cracks promotes the generation of tensile stress to a certain extent, damage effect angle increases gradually from the rock specimen with the middle joint to that with the marginal joint; the same water pressure has a certain auxiliary effect on the main crack... [more]

The aim of this work was to develop the design of a direct liquid cooling system for a battery pack of a high-performance plug-in hybrid vehicle. The cooling system of the battery pack is of an innovative type, with the direct cooling of the power busbars and the poles of the lithium cells. In order to obtain preliminary information for the dimensioning and verification of the battery pack cooling system, a simulation model of the whole vehicle and its powertrain was developed. In this way, the current profiles to which the storage system will be subjected can be estimated and can be used to fine-tune the cooling system. The use of a simulation model of the entire vehicle was necessary because the vehicle is still at the design stage, and only experimental data on the specific consumption of the internal combustion engine and experimental characterization data of the lithium cells used, as well as data provided by the manufacturers of the electric motors and inverters, are currently av... [more]

Increased efforts toward climate change mitigation and achieving net zero (NZ) are occurring globally. This research addresses three challenges to meeting the target NZ goals: (1) quantifying energy use reduction approaches, including energy efficiency and renewable power; (2) obtaining measured data to verify NZ achievements; and (3) providing NZ definitions to a globally understandable concept. To do so, a reorganized NZ concept (NZX%) is proposed that is practical, measurable, and adaptable to different regions and requirements. The “X%” presents the fraction of renewable energy to the total energy used, and the “ORG” defines the organization’s NZ definition that a project uses. The objective of this proposal is to create a universally NZ concept and method, using measured utility power data, by (1) determining a baseline NZX%; (2) projecting an optimized NZX%; (3) measuring and reporting the actual NZX%. This application is extendable from a building level to the community, city, a... [more]

Cahora Bassa, a thyristor-based High Voltage Direct (HVDC) link, transmits 1920 MW of power from a hydro-power plant in Zambezi River, north of Mozambique, to Apollo Substation in Johannesburg, South Africa. The high degree of harmonics distortion that is transferred into the AC side of the transmission network and the continuous increase in the rate at which commutation failure occurs during systems disturbance are both flaws in the utilization of this HVDC converter technology. AC and DC filters with rugged controllers are often used to minimize this effect but are limited in scope. Modern converter technology, such as the Voltage Source Converter (VSC), was proposed in this study to reduce harmonics content level, increase power transfer capabilities, enhance network stability, and reduce the rate of commutation failure occurrence. This paper, therefore, evaluates the performance analysis of the Cahora Bassa HVDC link and its level of harmonic distortion in the line commutated conve... [more]

Pumped storage units improve the stability of the power grid, and the key component is the pump−turbine. A pump−turbine usually needs to start and shutdown frequently, and the operating head varies greatly due to changes in the water level of the reservoir, which makes the dynamic behavior of a pump−turbine runner extremely complex. This paper investigates the effects of operating head on the dynamic response characteristics of a pump−turbine runner in turbine mode. The flow characteristics of the pump−turbine at maximum head, rated head and minimum head are analyzed, and the dynamic response characteristic of the pump−turbine runner are numerically studied. The results show that operating head can affect the pressure pulsation and dynamic stress characteristics of the pump−turbine runner, but it has little effect on the frequency spectra. The conclusions of this paper intend to improve understanding of the effects of the operating head on the dynamic behavior of the pump−turbine runne... [more]

Crude oil price volatility impacts the global economy in general, as well as the economies of Europe and the United States in particular; it is supremely difficult to describe its tendency precisely, hence it leads to a forecasting methodology. This study aims to use the autoregressive integrated moving average (ARIMA), and seasonal autoregressive integrated moving average (SARIMA) approaches to cope with this problem in the United States and Europe. The data was gathered from the U.S. Energy Information Administration and federal research economic data (FRED) from January 2017 to September 2021. Simultaneously, values from January 2017 to March 2021, with 51 observations accounting for 90% of the total samples, were employed for the training phase, and the rest were used for the testing phase. The forecast result also indicated that the root mean square error (RMSE) and mean absolute percentage error (MAPE) values, applied by ARIMA models in Europe and the United States, have higher a... [more]