In this work, the concept of an energy conversion system for wind turbines based on the modified permanent magnet synchronous generator (PMSG) is presented. In the generator, a pair of three-phase windings is used, one of which is connected in a “star” and the second in a “delta” configuration. At the outputs of both windings, two six-pulse uncontrolled (diode) rectifiers are included. These rectifiers are mutually coupled by a specially designed pulse transformer, whose primary winding is powered by the power electronics converter—the so-called “current modulator”—which, in this case, operates as a magnetic flux modulator, in the generator. The modulator provides a quasi-sinusoidal magnetomotive force (mmf) in the stator of the machine. The whole system is connected to the power grid via a dedicated voltage source inverter (VSI) converter. The main objective of the elaborated solution is to provide high efficiency conversion of mechanical (wind) energy into electricity by means of a r... [more]

This article presents the results from research performed on the implementation of restructuring policies of Polish mining enterprises. The study sought to verify whether the changes planned in Poland since the 1990s have been successfully introduced. The main objective of the restructuring of the Polish mining industry was to transform it into a profitable, cost-effective sector, which would be able to survive in a competitive market. The study also allowed the determination of a ratio giving a clear and synthetic outcome—called the indicator of the ability to change (WZZ). This indicator included criteria for assessing the efficiency of a company during the process of change, the fundamental errors committed during the change process, and the reasons for a low level of ability to change. The WZZ indicator achieved only an average level of 30%. The main errors committed during the change process are the mining enterprises’ lack of experience in change management and a lack of executiv... [more]

The comprehensive exploitation of geothermal fields has an impact on the productivity of the reservoirs. To realize sustainable steam production, changes in the rock temperature need to be predicted and controlled. A coupled thermo-hydro-mechanical (THM) model employing COMSOL Multiphysics was proposed to study the characteristics of heat transfer, fluid flow, and solid deformation at the Lahendong geothermal field, in North Sulawesi, Indonesia. The numerical results were compared with analytical and measured data in order to validate the numerical simulation. Based on the results, the predicted temperatures of the production wells showed significant decrease with the production time. In addition, a reduction in the reservoir temperature leads to lower specific gross electrical power within the production well, which should significantly reduce the sustainability of the power plant.

A cubic-spring restoring function with high-deformation stiffening is introduced to passively improve the harnessed marine hydrokinetic power by using flow-induced oscillations/vibrations (FIO/V) of a cylinder. In these FIO/V experiments, a smooth, rigid, single-cylinder on elastic end-supports is tested at Reynolds numbers ranging from 24,000 < Re < 120,000. The parameters of the tested current energy converter (CEC) are cubic stiffness and linear damping. Using the second generation of digital virtual spring-damping (Vck) controller developed by the Marine Renewable Energy Laboratory (MRELab), the cubic modeling of the oscillator stiffness is tested. Experimental results show the influence of the parameter variation on the amplitude, frequency, energy conversion, energy efficiency, and power of the converter. All experiments are conducted in the low turbulence-free surface water (LTFSW) channel of the MRELab of the University of Michigan. The main conclusions are: (1) The nonli... [more]

A hydrobiotite (HBT) clay contains more cesium (Cs)-specific adsorption sites than illitic clay, and the capacity of frayed edge sites can increase as the weathering of micaceous minerals proceeds. Thus, Cs can be selectively adsorbed to HBT clay. In this study, we investigated the removal efficiency of non-radioactive (133Cs) and radioactive (137Cs) Cs from HBT, using oxalic acid. We found the minimum optimal concentration of 0.15 M oxalic acid removed more than 90% of Cs. Subsequently, cations and Cs ions were removed using Ca(OH)2 and sodium tetraphenylborate (NaTPB) to treat the washing wastewater generated at the optimum concentration of the desorbent (0.15 M oxalic acid). In order to remove cations and heavy metal ions in the waste solution, Ca(OH)2 was treated at a mass ratio of 0.025 g/mL and pH 9−10 to derive optimal conditions. As a final step, to remove Cs, NaTPB was treated with a mass ratio of 2 mg/mL and reduced to below 0.1 mg/L Cs to find the optimal dose. The novelty o... [more]

The development and implementation of strategies to assist safe and effective transport and storage of pellets in containers and indoor facilities without heating systems are challenging. This study primarily aimed to reshape the organic fraction of municipal solid waste into a liquid-state binder in order to develop freezing−defrosting-proof non-wood pellets. The introduction of the standard solution of food waste into the process of pelleting consisted of stirring it together with the residual biomass from distillation of cellulosic bioethanol or alternatively spraying very fine droplets on the layer of the starting material before it entered the pilot-scale automatic machine at 200 MPa and 125 °C. The addition by spraying of carbohydrate-rich supplement boiled for five minutes caused the pellets to show increases in apparent density (1250.8500 kg·m−3), durability (99.7665%), and hydrophobicity (93.9785%), and consistently prevented them from suffering severe mechanical fracture by t... [more]

In this work, a synchronous model for grid-connected and islanded microgrids is presented. The grid-connected model is based on the premise that the reference frame is synchronized with the AC bus. The quadrature component of the AC bus voltage can be cancelled, which allows to express output power as a linear equation for nominal values in the AC bus amplitude voltage. The model for the islanded microgrid is developed by integrating all the inverter dynamics using a state-space model for the load currents. This model is presented in a comprehensive way such that it could be scalable to any number of inverter-based generators using inductor−capacitor−inductor (LCL) output filters. The use of these models allows designers to assess microgrid stability and robustness using modern control methods such as eigenvalue analysis and singular value diagrams. Both models were tested and validated in an experimental setup to demonstrate their accuracy in describing microgrid dynamics. In addition... [more]

The nitrogen (N2) expander and single mixed refrigerant (SMR) liquefaction processes are recognized as the most favorable options to produce liquefied natural gas (LNG) at small-scale and offshore sites. These processes have a simple and compact design that make them efficient with respect to their capital costs. Nevertheless, huge operating costs, mainly due to their lower energy efficiency, remains an ongoing issue. Utilization of design variables having non-optimal values is the primary cause for the lower energy efficiency; which, in turn, leads to exergy destruction (i.e., entropy generation), and ultimately the overall energy consumption is increased. The optimal execution of the design variables of LNG processes can be obtained through effective design optimization. However, the complex and highly non-linear interactions between design variables (refrigerant flowrates and operating pressures) and objective function (overall energy consumption) make the design optimization a diff... [more]

The objective of this research was to evaluate the stress corrosion cracking (SCC) of X-70 micro-alloyed steel in contact with bio-ethanol and E-50 gasohol. Environmental factors, including water (1%, 3% and 5%) and NaCl (10 mg/L and 32 mg/L), as well as two aging treatments were studied. Experimental values were obtained by the Slow Strain Rate Test (SSRT) technique, X-ray fluorescence (XRF), and tensile test according to the information reported in the literature. The results of the SSRT for the SCC determination showed that this steel in these conditions did not show evidence of SCC, which was attributed to the formation of an oxide (Fe2O3) not soluble in ethanol. The oxide layer acts as a protector preventing the formation of pitting, one of the main causes of cracks initiation in SCC.

Reducing the weight of a wind turbine blade is a major issue. Wind turbines have become larger in size to increase power generating efficiency. The blade has also grown in length to take more wind energy. A fabric-based wind turbine blade, introduced by General Electric Co., reduced the blade weight. In this study, a small fabric-covered blade for a 10 kW wind turbine was developed to verify structural ability. The blade was designed on the cross-section using variational asymptotic beam sectional analysis (VABS), structural analysis was carried out using MSC.Nastran for the design loads. A modal analysis was performed to compare the modal frequency and mode shapes. Static structural testing and modal testing were fulfilled. The analysis results were compared with the testing results. The fabric-covered structure was confirmed to reduce the blade mass with sufficient strength.

Given that the issue of variations in geometrical parameters of the borehole heat exchanger (BHE) revolves around the phenomenon of thermal resistance, a thorough understanding of these parameters is beneficial in enhancing thermal performance of BHEs. The present study seeks to identify relative changes in the thermal performance of double U-tube BHEs triggered by alterations in circuit arrangements, as well as the shank spacing and the borehole length. The thermal performance of double U-tube BHEs with different configurations is comprehensively analyzed through a 3D transient numerical code developed by means of the finite element method. The sensitivity of each circuit configuration in terms of the thermal performance to variations of the borehole length and shank spacing is investigated. The impact of the thermal interference between flowing legs, namely thermal short-circuiting, on parameters affecting the borehole thermal resistance is addressed. Furthermore, the energy exchange... [more]

This paper assesses the application of the second-law of thermodynamics in a military Environmental Control Unit (ECU) to evaluate the exergy destruction (or irreversibility) in each component when operating at high ambient temperature. Experimental testings were conducted on three ECUs, 1.5 (5.3 kW), 3 (10.6 kW), and 5 (17.6 kW) tons of refrigeration (RT), to assess the potential contribution of each component to enhance the overall energy efficiency of the system, and to determine the feasibility of the thermodynamic model presented herein. The analysis provided for extreme high ambient conditions up to 51.7 °C (125 °F). The results yielded that the highest irreversibility was associated with compressors (32.4% to 42.5%). This is followed by the heat exchanges (19.6% to 32.9%) in the case of 1.5-RT and 3-RT units, whereas for the 5-RT unit, the highest irreversibility was associated with the evaporator followed by the one of the compressors. In the 3-RT ECU, the condenser’s second-la... [more]

The article presents a novel on-line partial discharge (PD) monitoring system for power transformers, whose functioning is based on the simultaneous use of three unconventional methods of PD detection: high-frequency (HF), ultra-high frequency (UHF), and acoustic emission (AE). It is the first monitoring system equipped in an active dielectric window (ADW), which is a combined ultrasonic and electromagnetic PD sensor. The article discusses in detail the process of designing and building individual modules of hardware and software layers of the system, wherein the most attention was paid to the PD sensors, i.e., meandered planar inverted-F antenna (MPIFA), high-frequency current transformer (HFCT), and active dielectric window with ultrasonic transducer, which were optimized for detection of PDs occurring in oil-paper insulation. The prototype of the hybrid monitoring system was first checked on a 330 MVA large power transformer during the induced voltage test with partial discharge mea... [more]

The coordinated heat-electricity dispatch of the urban integrated energy system (UIES) helps to improve the system flexibility, thereby overcoming the adverse effects caused by the random fluctuations of renewable energy (RE) and promoting the penetration of RE. Among them, the dynamic characteristics of the urban heat network (UHN) are important features that need to be considered for the operating scheduling of the UIES. This paper aims to establish a flexibility scheduling model for UIES based on the dynamic characteristics of the UHN. First, the typical structure and key equipment model of the urban integrated heat and power system (UIHPS) with the dynamic characteristics of the UHN is proposed. Then, the definition and model of the UIHPS flexibility and the assessment index of the flexibility are developed. Moreover, a flexibility scheduling model for a UIHPS that considers the dynamic characteristics of a UHN is established. Finally, the validity of the proposed model is validate... [more]

Today, hydrogen production plays an important part in the industry due to the increasing use of hydrogen in significant domains, such as chemistry, transportation, or energy. In this paper, we aim to design a numerical control solution based on the thermodynamic analysis of the pyrolysis reactions for hydrogen production and to present novel research developments that highlight industrial applications. Beginning with the evaluation of the technological aspects for the pyrolysis chemical process, the paper studies the thermodynamic evaluation of the system equilibrium for the pyrolysis reactions set, to recommend an appropriate automatic control solution for hydrogen pyrolysis installations. The numerical control architecture is organized on two levels, a control level dedicated to key technological parameters, and a supervisory decision level for optimizing the conversion performances of the pyrolysis process. The data employed for modelling, identification, control, and optimization t... [more]

Air source heat pumps (ASHPs) are widely recognized as energy-saving and environmentally friendly heating and air-conditioning equipment with broad applications. However, when conventional ASHPs are operated at a low ambient temperature, they suffer from problems such as high discharge temperature and low heating efficiency. To address these problems, this study designed a new type of dual evaporator combined with a compressor casing thermal storage heat pump system (DE-CCTS) on the basis of a low-temperature air source heat pump water heater with enhanced vapor injection (EVI). The proposed DE-CCTS used thermal storage phase change material (PCM), which was filled in the secondary evaporator (the thermal storage heat exchanger), to recover the waste heat of the compressor casing. Unlike that in the original system under different ambient temperatures, the suction temperature increased by 0.1−1 °C, the discharge temperature decreased by 0.1−0.5 °C, and the coefficient of performance (C... [more]

This paper proposes an enhanced energy management system (EEMS) for a residential AC microgrid. The renewable energy-based AC microgrid with hybrid energy storage is broken down into three distinct parts: a photovoltaic (PV) array as a green energy source, a battery (BT) and a supercapacitor (SC) as a hybrid energy storage system (HESS), and apartments and electric vehicles, given that the system is for residential areas. The developed EEMS ensures the optimal use of the PV arrays’ production, aiming to decrease electricity bills while reducing fast power changes in the battery, which increases the reliability of the system, since the battery undergoes fewer charging/discharging cycles. The proposed EEMS is a hybrid control strategy, which is composed of two stages: a state machine (SM) control to ensure the optimal operation of the battery, and an operating mode (OM) for the best operation of the SC. The obtained results show that the EEMS successfully involves SC during fast load and... [more]

The integration of smart grid technologies in interconnected power system networks presents multiple challenges for the power industry and the scientific community. To address these challenges, researchers are creating new methods for the validation of: control, interoperability, reliability of Internet of Things systems, distributed energy resources, modern power equipment for applications covering power system stability, operation, control, and cybersecurity. Novel methods for laboratory testing of electrical power systems incorporate novel simulation techniques spanning real-time simulation, Power Hardware-in-the-Loop, Controller Hardware-in-the-Loop, Power System-in-the-Loop, and co-simulation technologies. These methods directly support the acceleration of electrical systems and power electronics component research by validating technological solutions in high-fidelity environments. In this paper, members of the Survey of Smart Grid International Research Facility Network task on... [more]

This paper describes an innovative method to evaluate energy access in any of size population by applying fuzzy logic. The obtained results allow ranking regions of Mexico according to their overall energy access. The regions were determined by the country’s political division (32 states). The results presented herein are in close correspondence with other studies undertaken. This method is recommended because it is possible to use as an assessment tool due to its representativeness—that is, it poses a heuristic alternative to quantify the level of Energy Access in a particular region through qualitative data. It is also efficient and cost-effective in terms of computer resources. This is extremely important to public policy makers that require more accurate, faster and cheaper methodologies to assess energy access as an indicator of well-being.

Experimental research was conducted on a rapid compression and expansion machine (RCEM) that has characteristics similar to a gasoline compression ignition (GCI) engine, using two gasoline−biodiesel (GB) blends—10% and 20% volume—with fuel injection pressures varying from 800 to 1400 bar. Biodiesel content lower than GB10 will result in misfires at fuel injection pressures of 800 bar and 1000 bar due to long ignition delays; this is why GB10 was the lowest biodiesel blend used in this experiment. The engine compression ratio was set at 16, with 1000 µs of injection duration and 12.5 degree before top dead center (BTDC). The results show that the GB20 had a shorter ignition delay than the GB10, and that increasing the injection pressure expedited the autoignition. The rate of heat release for both fuel mixes increased with increasing fuel injection pressure, although there was a degradation of heat release rate for the GB20 at the 1400-bar fuel injection rate due to retarded in-cylinder... [more]

Slurry transport systems are often limited in run length by the life of the pump internals, especially the impeller. The present work investigated abrasive wear of the impeller of a Hayward Gordon XR2(7) Torus Recessed Impeller slurry pump in a flow loop. The stock stainless steel impeller was replaced by a set of plastic test impellers with the same nominal geometry, fabricated by additive manufacturing (3D printing). A parametric set of abrasive wear experiments was conducted at five pump rotational speeds and three solid concentrations of garnet slurry in a pipe flow loop. Pump performance tests were conducted using impellers with progressive wear conditions, to investigate how a worn impeller affects hydraulic power delivery. A parabolic fit was imposed to describe the relationship between head and flow rate, and an empirical model was proposed to predict the pump head with damaged impellers. When the rotational speed is high, the damaged impeller has a larger effect on the pump’s... [more]

An accurate management of the interactions among end user, electric vehicle, and charging station during recharge is fundamental for the diffusion of electric mobility. The paper proposes an extension of the Open Charge Point Protocol standard with the aim of including the user in the charging optimization process. The user negotiates with the central station a recharge reservation giving his/her preference and flexibility. The charging station management system provides different solutions based on user’s flexibility. This negotiation allows the optimization of the power grid management considering the user requests and constraints. The complete architecture has been designed, implemented on a web server and on a smartphone app, and tested. Results are reported in this work.

Without experiences of electric buses, public transport authorities and bus operators have faced questions about how to implement them in a cost-effective way. Simple cost modelling cannot show how costs for different types of electric buses differ between different routes and timetables. Tools (e.g., HASTUS, PtMS, and optibus) which can analyse such details are complicated, time consuming to use, and provide insufficient insights into the mechanisms that influence the cost. This paper therefore proposes a method for how to calculate total cost of ownership, for different types of electric buses, in a way which can predict how the cost varies based on route and timetable. The method excludes factors which cause minor cost variations in an almost random manor, in order to better show the fundamental mechanisms influencing different costs. The method will help in finding ways to reduce the cost and help to define a few cases which deserve a deep analysis with more complete tools. Testing... [more]

At present, renewable energies represent 25% of the global power generation capacity. The increase in clean energy facilities is mainly due to the high levels of pollution generated by the burning of fossil fuels to satisfy the growing electricity demand. The global capacity of generating electricity from solar energy has experienced a significant increase, reaching 505 GW in 2018. Today, multilevel inverters are used in PV systems to convert direct current into alternating current. However, the use of multilevel inverters in renewable energies applications presents different challenges; for example, grid-connected systems use a transformer to avoid the presence of leakage currents. The grid-connected systems must meet at least two international standards analyzed in this work: VDE 0126-1-1 and VDE-AR-N 4105, which establish a maximum leakage current of 300 mA and harmonic distortion maximum of 5%. Previously, DC/AC converters have been studied in different industrial applications. The... [more]

In the multi-load wireless power transfer (WPT) system, the output power and transfer efficiency will drop significantly with the change of distance between transmitter and receiver. Power distribution among multiple loads is also a major challenge. In order to solve these problems, a novel multi-load WPT system based on parity−time symmetry (PT-WPT) is proposed in this paper. Firstly, the multi-load PT-WPT system is modeled based on the circuit model. Then, the transmission characteristics of the multi-load PT-WPT system are analyzed. It is found that constant output power with constant transfer efficiency can be maintained against the variation of coupling coefficient, and the power distribution relationship among loads is only related to the coupling coefficient. Further, power distribution under different coupling situations is analyzed in detail to meet different power demands. Finally, taking a dual-load PT-WPT system as an example, the system parameters are designed and the circ... [more]