Solving the issue of energy security for geographical islands presents a one-of-a-kind problem that has to be tackled from multiple sides and requires an interdisciplinary approach that transcends just technical and social aspects. With many islands suffering in terms of limited and costly energy supply due to their remote location, providing a self-sustainable energy system is of utmost importance for these communities. In order to improve upon the status quo, novel solutions and projects aimed at increasing sustainability not only have to consider optimal utilization of renewable energy potentials in accordance with local conditions, but also must include active community participation. This paper analyzes both of these aspects for island communities and brings them together in an optimization scenario that is utilized to determine the relationship between supposed demand flexibility levels and achievable savings in a setting with variable renewable generation. The results, specifica... [more]

In recent years, the integration of the high-power static synchronous compensator (STATCOM) and energy storage in the same device has gained interest. Such a system is referred to as ES-STATCOM. Modular multilevel converter (MMC) topologies constitute a promising converter family for ES-STATCOM realization, providing a modular and scalable solution with a high efficiency that handles high-power and high-voltage ratings in grid applications. There is a gap in technical literature discussing the design and the comparison of MMC-based ES-STATCOMs while utilizing batteries to find the most suitable MMC topology for ES-STATCOMs. Therefore, this paper benchmarks MMC family members for ES-STATCOM realization. Both centralized and distributed energy storage approaches are investigated. The proposed design flowcharts can be employed for comparison and optimization purposes. In total, seven topologies are compared in terms of number of cells, required silicon area and total battery volume. Diffe... [more]

By replacing conventional supplies such as fossil fuels or internal combustion engines (ICEs), this paper presents a new configuration of hybrid power sources (HPS) based on the integration of a proton-exchange membrane fuel cell (PEMFC) with batteries (BATs) and supercapacitors (SCs) for hydraulic excavators (HEs). In contrast to conventional architectures, the PEMFC in this study functions as the main power supply, whereas the integrated BAT−SC is considered as an auxiliary buffer. Regarding shortcomings existing in the previous approaches, an innovative energy management strategy (EMS) was designed using a new mapping fuzzy logic control (MFLC) for appropriate power distribution. Comparisons between the proposed strategy with available approaches are conducted to satisfy several driving cycles with different load demands and verify the strategy’s effectiveness. Based on the simulation results, the efficiency of the PEMFC when using the MFLS algorithm increased up to 47% in compariso... [more]

The spread of near-Zero Energy Buildings (nZEB) involves the employment of high performant air-conditioning plants where renewable sources can be integrated easily. In this context, heat pumps appear as a promising solution given their ability to exploit aerothermal, hydrothermal and geothermal sources and to supply both heating and cooling loads with the same device. In order to evaluate the energy performances in transient conditions, the actual winter (COP) and summer (EER) performance indexes, in the function of the sources’ temperatures and the capacity ratio (CR), have to be available. Nevertheless, heat pump manufactures often provide the trend of the performance indexes in the function of the temperatures of the sources specifically for nominal conditions, whereas the dependence of the performance indexes in the function of CR, that takes into account the part-load operation, is almost always not provided. Alternatively, specific technical standards suggest the use of a correct... [more]

The dynamic test-bed is a powerful tool for the powertrain integration and control strategy development of a hybrid electric vehicle (HEV). This paper focuses on developing a test-bed controller with driver simulation, road load simulation (RLS), and engine simulation. The main factors that influence the RLS accuracy are analyzed, especially inertia of test-bed and torque signal sampling frequency, and the RLS algorithm with penalty function based on a forward model is proposed. The engine model is developed and permanent magnet synchronous motor (PMSM) is adopted to realize engine start-up/stop, torque control, and inertia simulation. The simulation platform was built in MATLAB/Simulink to verify its accuracy. The simulation results present the developed RLS with a penalty function based on a forward model that can reduce the speed and torque error. The developed controller is applied to the single-axis parallel HEV test-bed. The experiment results show that the developed test-bed con... [more]

This research work focuses on investigating the lubricity and analyzing the engine characteristics of diesel−biodiesel blends with fuel additives (titanium dioxide (TiO2) and dimethyl carbonate (DMC)) and their effect on the tribological properties of a mineral lubricant. A blend of palm−sesame oil was used to produce biodiesel using ultrasound-assisted transesterification. B30 (30% biodiesel + 70% diesel) fuel was selected as the base fuel. The additives used in the current study to prepare ternary fuel blends were TiO2 and DMC. B30 + TiO2 showed a significant reduction of 6.72% in the coefficient of friction (COF) compared to B30. B10 (Malaysian commercial diesel) exhibited very poor lubricity and COF among all tested fuels. Both ternary fuel blends showed a promising reduction in wear rate. All contaminated lubricant samples showed an increment in COF due to the dilution of combustible fuels. Lub + B10 (lubricant + B10) showed the highest increment of 42.29% in COF among all contami... [more]

The integration of renewable resources is quickly growing in the Nordic power system (NPS), and it has led to increasing challenges for the operation and control of the NPS. Nordic countries require that the first-generation power plants have a more flexible operation regime to overcomes power imbalances coming from fluctuations of the demand and supply. This paper assesses optimal frequency support of variable-speed hydropower plants installed in Telemark and Vestfold, Norway, considering future scenarios of NPS. The total kinetic energy of the NPS is expected to be significantly reduced in the future. This paper looks into the implementation of hydropower units with a variable-speed operation regime and battery energy storage systems (BESS), equipped with fast-active power controller (FAPC) technology, to provide fast frequency response after a system frequency disturbance. The frequency support was formulated as an optimization process; therefore, the parameter of the FAPC was optim... [more]

Synchronization and islanding detection represent some of the main issues for grid-connected photovoltaic systems (PVSs). The synchronization technique allows to achieve PVS high power factor operation and it provides grid voltage monitoring. The islanding detection control function ensures safe operation of the PVS. Focusing on low-power single-stage PVSs, in this study the most adopted and the highest performance synchronization and islanding detection methods are discussed. The role of the synchronization system is fundamental to detect the grid conditions, for the islanding detection purpose, and to manage the reconnection to the grid after a PVS trip. Hence a combined review is advantageous.

This paper aims at presenting and describing a dimensioning methodology for energy storage systems (ESS), in particular for one based on flywheels, applied for the specific application of reducing power oscillation in a wave energy conversion (WEC) plant. The dimensioning methodology takes into account the efficiency maps of the storage technology as well as the effect of the filtering control techniques. The methodology is applied to the case study of a WEC plant in operation in Spain, using real power generation profiles delivered into the electric grid. The paper firstly describes the calculation procedure of the efficiency maps for the particular technology of flywheels, although it could be extended to other storage technologies. Then, the influence of using future data values in the dimensioning process and the control of the ESS operation is analysed in depth. A moving average filter (MAF) is defined to compensate for power oscillations, studying the difference between consideri... [more]

The lack of synchronous inertia, associated with the relevant penetration of variable speed wind turbines (VSWTs) into isolated power systems, has increased their vulnerability to strong frequency deviations. In fact, the activation of load shedding schemes is a common practice when an incident occurs, i.e., the outage of a conventional unit. Under this framework, wind power plants should actively contribute to frequency stability and grid reliability. However, the contribution of VSWTs to frequency regulation involves several drawbacks related to their efficiency and equipment wear due to electrical power requirements, rotational speed changes, and subsequently, shaft torque oscillations. As a result, wind energy producers are not usually willing to offer such frequency regulation. In this paper, a new control technique is proposed to optimize the frequency response of wind power plants after a power imbalanced situation. The proposed frequency controller depends on different power sy... [more]

To improve the resource recovery efficiency of mining face in thick coal seams, the correlation between deformation failure of bottom coal in the gob-side entry and coal pillar width was analyzed by theoretical analysis, numerical calculation, and similar simulation experiments. The results showed that, when the coal pillar was strong, with the decrease of pillar width, the failure depth of the bottom coal in the gob-side entry and floor heave increased. The deformation failure depth of the bottom coal in the entry was inversely related to the width of the coal pillar. The bottom coal was further fractured and dispersed under the action of tension, shear, and extrusion in the process of floor heave. Based on the floor heave induced by the narrow coal pillar, a recovery technique of the bottom coal with thick coal seams in the gob-side entry was developed. The width of the narrow pillar to be reserved was obtained by theoretical calculation and revised by numerical simulation; ultimatel... [more]

At the moment of writing, in Italy, there is an ongoing pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Its outbreak is leading to severe global socioeconomic disruptions impacting on all economic sectors from tourism, industry and the tertiary sector, up to the operational and opening of public offices, the closure of schools and the organization of families. Measures adopted by the Italian government to deal with the COVID-19 emergency have had direct effects both on people’s daily lives and on the activity of most industrial and commercial production companies. These changes have been unequivocally reflected also on the Italian electricity system, which has shown unprecedented behavior in terms of both energy consumption and volume—and subsequently, in the observed share of renewable and conventional production technologies. The goal of this study is to show the impact on the power industry of all the restricti... [more]

A novel analytical model is proposed and validated in this paper to predict the velocity deficit in the wake downwind of a wind turbine. The model is derived by employing mass and momentum conservation and assuming a cosine-shaped distribution for the velocity deficit. In this model, a modified wake growth rate rather than a constant one is chosen to take into account the effects of the ambient turbulence and the mechanical turbulence generated. The model was tested against field observations, wind-tunnel measurements in different thrust operations and high-resolution large-eddy simulations (LES) for two aerodynamic roughness lengths. It was found that the normalized velocity deficit predicted by the proposed model shows good agreement with experimental and numerical data in terms of shape and magnitude in the far wake region ( x / d 0 > 3 ). Based on the proposed model, predictions from multiple views and at different locations are demonstrated to show the spatial distribution... [more]

In search of sustainable business models, product innovation must fulfil a double objective: the new product must have a higher (market) value, and at the same time a lower eco-burden. To achieve this objective, it is an imperative that the value, the total costs of ownership, and the eco-burden of a product are analysed at the beginning of the design process (idea generation and concept development). The design approach that supports such a design objective, is called Eco-efficient Value Creation (EVC). This approach is characterised by a two-dimensional representation: the eco-burden at the y-axis and the costs or the value at the x-axis. The value is either the Willingness to Pay or the market price. The eco-burden is expressed in eco-costs, a monetised single indicator in LCA (Life Cycle Assessment): an app for IOS and Android, and excel look-up tables at the internet, enable quick assessment of eco-costs. A practical example is given: the design of a new concept of domestic street... [more]

The organic Rankine cycle (ORC) is widely used to recover industrial waste heat. For an ORC system using industrial waste hot water as a heat source, a novel hot water split-flow dual-pressure organic Rankine cycle (SFD-ORC) system is developed to improve the performance of the ORC. The maximum net power output was selected to compare three ORC systems, including basic ORC (B-ORC), conventional dual-pressure ORC (CD-ORC) and SFD-ORC. A genetic algorithm (GA) was used to optimize the parameters to search the maximum net power output of ORCs. The maximum net output power was taken as the standard of performance evaluation. The results show that, under the same hot water inlet temperature condition, the optimal hot water outlet temperature of B-ORC is much higher than that of CD-ORC and SFD-ORC, which indicates that less thermal energy could be utilized to convert to power in B-ORC. The optimal hot water temperature at the outlet of evaporator 1 in SFD-ORC is higher than that in CD-ORC, w... [more]

Zero-voltage ride through (ZVRT) is the extreme case of low-voltage ride through (LVRT), which represents the optimal grid-connection capability of wind turbines (WTs). Enforcing ZVRT will improve the dynamic performance of WTs and therefore significantly enhance the resiliency of renewable-rich grids. A control scheme that includes a pitch system is an essential control aspect of WTs riding through voltage dips; however, the existing control scheme with a pitch system for LVRT cannot distinguish between a ZVRT status and a power-loss condition, and, consequently, does not meet the ZVRT requirements. A system-level control scheme with a pitch system for ZVRT that includes pitch system modeling, control logic, control circuits, and overspeed protection control (OPC) is proposed in this paper for the first time in ZVRT research. Additionally, the field data are shared, a fault analysis of an overspeed accident caused by a voltage dip that describes the operating status at the WT-collapse... [more]

Electric vehicles (EVs) are characterized by a significant variety of possible powertrain configurations, ranging from one to four electric machines, which can have an on-board or in-wheel layout. Multiple models of production EVs have recently been introduced on the market, with 4-wheel-drive (4WD) architectures based on a central motor within each axle, connected to the wheels through a gearbox, a differential, and half-shafts. In parallel, an important body of research and industrial demonstrations have covered the topic of 2-speed transmission systems for EVs, with the target of enhancing longitudinal acceleration and gradeability performance, while increasing the operating efficiency of the electric powertrain. Although several recent studies compare different electric powertrain architectures, to the best of the authors’ knowledge the literature misses a comparison between 2-wheel-drive (2WD) and 4WD configurations for the same EV, from the viewpoint of drivability and energy con... [more]

Global energy systems are undergoing a transition process towards renewable energy and energy efficiency practices. Induction motors play an important role in this energy transformation process since they are widely used as industrial loads, representing more than 53% of global energy consumption. With more countries adopting minimum energy performance standards through more efficient induction motors, comparisons between these new technologies in the presence of electrical disturbances must be systematically evaluated before adopting a substitution policy in the industry. To this end, this work presents a comparative analysis of the impact of harmonic voltages on the performance and temperature rise of electric motors classes IE2, IE3 and IE4 in the same operational conditions in view of future substitutions. The results show that under ideal operating conditions the IE4 class permanent magnet motor has better performance in terms of consumption and temperature, however presenting non... [more]

The crystallization of hydrogenated amorphous silicon (a-Si:H) is essential for improving solar cell efficiency. In this study, we analyzed the crystallization of a-Si:H via excimer laser annealing (ELA) and compared this process with conventional thermal annealing. ELA prevents thermal damage to the substrate while maintaining the melting point temperature. Here, we used xenon monochloride (XeCl), krypton fluoride (KrF), and deep ultra-violet (UV) lasers with wavelengths of 308, 248, and 266 nm, respectively. Laser energy densities and shot counts were varied during ELA for a-Si:H films between 20 and 80 nm thick. All the samples were subjected to forming gas annealing to eliminate the dangling bonds in the film. The ELA samples were compared with samples subjected to thermal annealing performed at 850−950 °C for a-Si:H films of the same thickness. The crystallinity obtained via deep UV laser annealing was similar to that obtained using conventional thermal annealing. The optimal pass... [more]

Although the power system usually always appears stable and reliable to consumers, a lot of work and research goes into keeping the power system both stable and reliable under constantly changing conditions and in these increasingly demanding times. One of the key issues in the power system is maintaining stability after large disturbances in order to prevent the loss of synchronicity of the generators in the system. Today’s generator protection systems mostly use measurements of impedance change to detect generator out of step. This article discusses the possibility of detecting the loss of synchronicity by using real time load angle measurements. The authors propose a real time load angle measurement algorithm and present the results of the algorithm’s testing performed on a real hydrogenerator. The results show that the developed algorithm gives highly accurate real time load angle measurements with the maximum possible resolution and that the load angle can be used for detecting th... [more]

Hydraulic fracturing has made the production of gas more economical. Shale gas possesses the potential to arise as a main natural gas source worldwide. It has been assessed that the top 42 countries, including the U.S., are predicted to own 7299 trillion cubic feet (tcf) of technically recoverable shale gas resources. The main goal of this paper is to serve as a guide of different shale gas extraction methods. The significance of these methods and possible pros and cons are determined. Each technique was explained with the support of literature review. Specifically, this paper revealed that some fracking methods such as pulsed arc electrohydraulic discharges (PAED), plasma stimulation and fracturing technology (PSF), thermal (cryogenic) fracturing, enhanced bacterial methanogenesis, and heating of rock mass are at the concept stage for conventional and other unconventional resources. Thus, these found to be significant for stimulating natural gas wells, which provides very good product... [more]

As the number of parallel battery connections in an energy storage system is increased to extend the energy capacity and second-life batteries are actively adopted, the battery is more prone to cell inconsistency issues. The difference in the internal impedance and the mismatched state-of-charge accelerates the self-balancing effect between the parallel branches to reduce cell utilization and eventually results in harmful effects, both to the lifetime and to the safety of the batteries. However, conventional methods only partially mitigate the parallel inconsistency issue. This paper proposes a dynamic resistance equalizer for parallel-connected battery configurations to improve equalization performance. The optimal design procedure is also presented to minimize the power loss and equalization time. The overall performance is experimentally verified by a sequence of tests for a Li-ion battery in a 2S-4P configuration. The experimental results show that the proposed method dissipates le... [more]

Coal gasification is the process that produces valuable gaseous mixtures consisting primarily of H2 and CO, which can be used to produce liquid fuel and various kinds of chemicals. The literature shows that the effect of particle size on coal gasification and fusibility of coal ash is not clear. In this study, the gasification kinetics and ash fusibility of three coal samples with different particle size ranges were investigated. Thermogravimetric results of coal under a CO2 atmosphere showed that the whole weight loss process consisted of three stages: the loss of moisture, the release of volatile matter, and char gasification with CO2. Coal is a heterogeneous material containing impurities. Different grinding fineness leads to different liberation degrees for impurities. As for the effect of particle size on TG (thermogravimetry) curves, we found that the final solid residue amount was the largest for the coal sample with the smallest particle size. The Miura-Maki isoconversional mod... [more]

Contingency Constrained Optimal Power Flow (CCOPF) differs from traditional Optimal Power Flow (OPF) because its generation dispatch is planned to work with state variables between constraint limits, considering a specific contingency. When it is not desired to have changes in the power dispatch after the contingency occurs, the CCOPF is studied with a preventive perspective, whereas when the contingency occurs and the power dispatch needs to change to operate the system between limits in the post-contingency state, the problem is studied with a corrective perspective. As current power system software tools mainly focus on the traditional OPF problem, having the means to solve CCOPF will benefit power systems planning and operation. This paper presents a Quadratically Constrained Quadratic Programming (QCQP) formulation built within the matpower environment as a solution strategy to the preventive CCOPF. Moreover, an extended OPF model that forces the network to meet all constraints un... [more]

To mitigate global warming, humankind has been forced to develop new efficient energy solutions based on renewable energy sources. Hydrothermal liquefaction (HTL) is a promising technology that can efficiently produce bio-oil from several biomass sources. The HTL process uses sub- or supercritical water for producing bio-oil, water-soluble organics, gaseous products and char. Black liquor mainly contains cooking chemicals (mainly alkali salts) lignin and the hemicellulose parts of the wood chips used for cellulose digestion. This review explores the effects of different process parameters, solvents and catalysts for the HTL of black liquor or black liquor-derived lignin. Using short residence times under near- or supercritical water conditions may improve both the quality and the quantity of the bio-oil yield. The quality and yield of bio-oil can be further improved by using solvents (e.g., phenol) and catalysts (e.g., alkali salts, zirconia). However, the solubility of alkali salts pr... [more]