The use of solar energy is an obvious choice; the energy of the sun is not only indispensable for most processes in nature but it is also a clean, abundant, sustainable, and—most importantly—universally available resource. Although the further spread of photovoltaic systems, which make use of this source of energy, is expected in the future all around the world, no comprehensive investigation has been conducted into the current situation of the small-scale photovoltaic power plants in Hungary, where this type of photovoltaic system is the most popular. By means of a case study, whose novelty lies in its focus on small-scale power plants and their complex examination, including economic and geographic indicators, this paper analyzes their status in Hungary. The study endeavors to establish the reasons for the popularity of this type of power plant and to identify some typical geographical locations with well-illustrated photovoltaic density. Residential, as well as business prosumers, w... [more]

The increasing amount of renewable energy sources in the electrical energy system leads to an increasing number of converter-based generators connected to the electrical power grid. Other than conventional power plants that are often connected to the grid via synchronous generators, converter-based generators do not provide mechanical inertia intrinsically. Therefore, ensuring frequency stability in the electrical power grid might become even more difficult in the future. With the concept of synthetic inertia, the converter-based generators partially imitate the behavior of conventional generators. By implementing such a concept in converters, they are capable of contributing to frequency stability as well. This paper compares two strategies to realize synthetic inertia by modeling converter-based generators in MATLAB/SIMULINK and simulating their behavior in a small Microgrid. The results prove that any kind of realization of synthetic inertia helps to improve frequency stability. Eac... [more]

The use of power electronic converters is essential for the operation of Switched Reluctance Machines (SRMs). Many topologies and structures have been developed over the last years considering several specific applications for this kind of machine, improving the control strategies, performance range, fault-tolerant operation, among other aspects. Thus, due to the great importance of power electronic converters in such applications, this paper is focused on a detailed review of main structures and topologies for SRM drives. The proposed study is not limited to the classic two-level power converters topologies dedicated to the SRMs; it also presents a review about recent approaches, such as multilevel topologies and based on impedance source network. Moreover, this review is also focused on a new class of topologies associated to these machines, namely the ones with fault-tolerant capability. This new category of topologies has been a topic of research in recent years, being currently co... [more]

Renewable energies are often subject to stochastic resources and daily cycles. Energy storage systems are consequently applied to provide a solution for the mismatch between power production possibility and its utilization period. In this study, a solar integrated thermo-electric energy storage (S-TEES) is analyzed both from an economic and environmental point of view. The analyzed power plant with energy storage includes three main cycles, a supercritical CO2 power cycle, a heat pump and a refrigeration cycle, indirectly connected by sensible heat storages. The hot reservoir is pressurized water at 120/160 °C, while the cold reservoir is a mixture of water and ethylene glycol, maintained at −10/−20 °C. Additionally, the power cycle’s evaporator section rests on a solar-heated intermediate temperature (95/40 °C) heat reservoir. Exergo-economic and exergo-environmental analyses are performed to identify the most critical components of the system and to obtain the levelized cost of elect... [more]

Wind Power Plants (WPPs) are generally located in remote areas with weak distribution connections. Hence, the value of Short Circuit Capacity (SCC), WPP size and the short circuit impedance angle ratio (X/R) are all very critical in the voltage stability of a distribution system connected WPP. This paper presents a new voltage stability model based on the mathematical relations between voltage, the level of wind power penetration, SCC and X/R at a given Point of Common Coupling (PCC) of a distribution network connected WPP. The proposed model introduces six equations based on the SCC and X/R values seen from a particular PCC point. The equations were developed for two common types of Wind Turbine Generators (WTGs), including: the Induction Generator (IG) and the Double Fed Induction Generator (DFIG). Taking advantage of the proposed equations, design engineers can predict how the steady-state PCC voltage will behave in response to different penetrations of IG- and DFIG-based WPPs. In a... [more]

Distribution networks with high electric vehicle (EV) penetration levels can experience transformer overloading and voltage instability issues. A charge scheduling approach is proposed to mitigate against these issues that suits smart home settings in residential areas. It comprises measurement systems located at distribution transformers that communicate directly with fuzzy logic controller (FLC) systems embedded within EV supply equipment (EVSE). This realizes a reduction in data processing requirements compared to more centralized control approaches, which is advantageous for distribution networks with large numbers of transformers and EV scheduling requests. A case study employing the proposed approach is presented. Realistic driver behavior patterns, EV types, and multivariate probabilistic modeling were used to estimate EV charging demands, daily travel mileage, and plug-in times. A Monte Carlo simulation approach was developed to obtain EV charging loads. The effectiveness of mi... [more]

Lithium-rich layered oxides are recognized as promising materials for Li-ion batteries, owing to higher capacity than the currently available commercialized cathode, for their lower cost. However, their voltage decay and cycling instability during the charge/discharge process are problems that need to be solved before their practical application can be envisioned. These problems are mainly associated with a phase transition of the surface layer from the layered structure to the spinel structure. In this paper, we report the AlF3-coating of the Li-rich Co-free layered Li1.2Ni0.2Mn0.6O2 (LLNMO) oxide as an effective strategy to solve these problems. The samples were synthesized via the hydrothermal route that insures a very good crystallization in the layered structure, probed by XRD, energy-dispersive X-ray (EDX) spectroscopy, and Raman spectroscopy. The hydrothermally synthesized samples before and after AlF3 coating are well crystallized in the layered structure with particle sizes of... [more]

Microgrids have emerged as a solution to address new challenges in power systems with the integration of distributed energy resources (DER). Inverter-based microgrids (IBMG) need to implement proper control systems to avoid stability and reliability issues. Thus, several researchers have introduced multi-objective control strategies for distributed generation on IBMG. This paper presents a review of the different approaches that have been proposed by several authors of multi-objective control. This work describes the main features of the inverter as a key component of microgrids. Details related to accomplishing efficient generation from a control systems’ view have been observed. This study addresses the potential of multi-objective control to overcome conflicting objectives with balanced results. Finally, this paper shows future trends in control objectives and discussion of the different multi-objective approaches.

This paper presents a novel integrated permanent magnet (PM) in-wheel motor (IWM) driving system for electric vehicles (EVs), in order to overcome the disadvantages of electromagnetic vibration and cogging torque in the topology scheme, on the basis of maintaining high output torque. Firstly, the transient magnetic field of the integrated PM motor is analyzed using the improved analytical subdomain model and finite element (FE) model. The harmonic component of magnetic force density (MFD) is obtained with no-load condition. Furthermore, the vertical dynamic model for the dynamic vibration absorber is established to investigate the influence of the magnetic force harmonic on the vibration response of the stator and rotor. On this basis, the multi-objective optimization design of the pole−slot structure parameters is carried out by using the adaptive weighted particle swarm optimization (AWPSO) algorithm. Finally, the optimization results are compared and verified by FE analysis. The inv... [more]

Wireless power transfer with multiple transmitters can have several advantages, including more robustness against misalignment and extending the mobility and range of the receiver(s). In this work, the efficiency maximization problem is analytically solved for a capacitive wireless power transfer system with multiple coupled transmitters and a single receiver. It is found that the system efficiency can be increased by adding more transmitters. Moreover, it is proven that the cross-coupling between the transmitters can be eliminated by adding shunt susceptances at the input ports. Optimal values for the input currents and receiver load are determined to achieve maximum efficiency. As well the optimal load, the optimal input currents and the maximum efficiency are independent on the cross-coupling. By impedance-matching the internal conductances of the generators, the maximum-efficiency solution also becomes the one that provides the maximum output power. Finally, by expressing each tran... [more]

This research work puts forward a hybrid AC/DC microgrid with renewable energy sources pertaining to consumer’s residential area for meeting the demand. Currently, the power generation and consumption have experienced key transformations. One such tendency would be integration of microgrids into the distribution network that is characterized by high penetration of renewable energy resources as well as operations in parallel. Traditional droop control can be employed in order to get an accurate steady state averaged active power sharing amongst parallel inverters pertaining to hybrid AC/DC microgrid. It is presumed that there would be similar transient average power responses, and there would be no circulating current flowing between the units for identical inverters possessing the same droop gain. However, the instantaneous power could be affected by different line impedances considerably and thus resulting in variation in circulating power that flows amongst inverters, especially duri... [more]

This paper provides an overview of islanding fault detection in microgrids. Islanding fault is a condition in which the microgrid gets disconnected from the microgrid unintentionally due to any fault in the utility grid. This paper surveys the extensive literature concerning the development of islanding fault detection techniques which can be classified into remote and local techniques, where the local techniques can be further classified as passive, active, and hybrid. Various detection methods in each class are studied, and advantages and disadvantages of each method are discussed. A comprehensive list of references is used to conduct this survey, and opportunities and directions for future research are highlighted.

This paper addresses a comprehensive evaluation of a bearing fault evolution and its consequent prediction concerning the remaining useful life. The proper prediction of bearing faults in their early stage is a crucial factor for predictive maintenance and mainly for the production management schedule. The detection and estimation of the progressive evolution of a bearing fault are performed by monitoring the amplitude of the current signals at the time domain. Data gathered from line-fed and inverter-fed three-phase induction motors were used to validate the proposed approach. To assess classification accuracy and fault estimation, the models described in this paper are investigated by using Artificial Neural Networks models. The paper also provides process flowcharts and classification tables to present the prognostic models used to estimate the remaining useful life of a defective bearing. Experimental results confirmed the method robustness and provide an accurate diagnosis regardl... [more]

In many energy-intensive industrial process plants, significant improvements in energy efficiency can be achieved through increased heat recovery. However, retrofitting plants for heat integration purposes can affect process operability. The aim of this paper is to present a comprehensive overview of such issues by systematically relating different types of heat recovery retrofit measures to a range of technical barriers associated with process operability and practical implementation of the measures. The paper presents a new approach for this kind of study, which can be applied in the early-stage screening of heat integration retrofit measures. This approach accounts for the importance of a number of selected operability factors and their relative significance. The work was conducted in the form of a case study at a large oil refinery. Several conceptual heat exchanger network retrofit design proposals were prepared and discussed during semi-structured interviews with technical staff... [more]

The increasing energy demand encourages the use of photovoltaic solar systems coupled to organic rankine cycle (ORC) systems. This paper presents a model of an ORC system coupled with a concentrating photovoltaic and thermal (CPV/T) system. The CPV/T-ORC combined system, described and modeled in this paper, is sized to match the electrical load of a medium industrial user located in the South of Italy. A line-focus configuration of the CPV/T system, constituted by 16 modules with 500 triple-junction cells, is adopted. Different simulations have been realized evaluating also the direct normal irradiance (DNI) by means of the artificial neural network (ANN) and considering three input condition scenarios: Summer, winter, and middle season. Hence, the energy performances of the CPV/T-ORC system have been determined to evaluate if this integrated system can satisfy the industrial user energy loads. In particular, the peak power considered for the industrial machines is about 42 kW while ot... [more]

Anaerobic digestion (AD) of chicken litter (CL) is a viable alternative to disposal. However, methane yields from this primarily organic waste are quite low when mono-digested. This paper discusses the effect of an enzyme cocktail, trace element (TE) supplementation and selenium (Se) addition in small-scale batch biomethane potential (BMP) assays to enhance the AD of CL. Eleven different assays were set up in triplicate including assays containing only inoculum (blank), only CL (negative control) and cellulose and inoculum (positive control). The results indicate that both enzyme treatment and trace element supplementation enhanced the biogas and methane yield. The highest specific biogas and methane yields were noted for 1% enzyme-treated CL of 835.2 L/kg volatile solids (VS) and 460.8 L/kg VS, respectively. Usually, mono-digestion of CL is low due to high nitrogen content and the presence of recalcitrant lignocellulosic material from the bedding material. Enzyme treatment performed b... [more]

This paper proposes an asymmetrical pulse-width modulation (PWM) strategy for current-fed dual-active bridge (CFDAB) converters applied to energy storage systems (ESS). The ESS application considers low-voltage and high-capacity batteries, for low-power applications, such as data centers, residential photovoltaic systems (PV), and uninterruptable power supplies (UPS). The proposed modulation permits the use of an isolation transformer with negligible leakage inductance and, therefore, avoids the use of auxiliary circuits such as snubbers, active-clamp, or resonant cells. Hence, the converter implementation is simplified. The modulation also benefits the design of the control system because the converter can be modeled and controlled using simple strategies. A straightforward, large-signal model for the battery charge mode, which is valid over all the operation range of the converter, is obtained. Also, the converter operates with a fixed dc bus voltage on both charge and discharge mode... [more]

Due to changes in wind, the torque obtained from the wind turbine always fluctuates. Here, the wind turbine and the rotor of the generator are connected by a shaft that is one elastic body, and each rotating body has different inertia. The difference in inertia between the wind turbine and the generator causes a torsion between the wind generator and the generator; metal fatigue and torsion can damage the shaft. Therefore, it is necessary to consider the axial torsional vibration suppression of a geared wind power generator using a permanent magnet synchronous generator (PMSG). In addition, errors in axis system parameters occur due to long-term operation of the generator, and it is important to estimate for accurate control. In this paper, we propose torque estimation using H ∞ observer and axial torsional vibration suppression control in a three inertia system. The H ∞ controller is introduced into the armature current control system (q-axis current control system) of... [more]

The park and ride (P&R) parking type is usually located near peripheral public transport stops. These parking places are dedicated to people who, after leaving their vehicle in the parking, continue their journey to the city center using some form of public transport such as bus, metro, rail or tram systems. This article aims to examine the features associated with P&R parking locations in use in Cracow (Poland). The analysis included the number of entries and exits to and from parking during particular periods of the day, week and year, parking time of vehicles, and parking space use. A parking peak hour factor was also calculated, which expresses the crowding degree of vehicle entries/exits in/out parking during a particular period. In addition, the paper presents an analysis of factors determining users to P&R parking use. In the modeling process, logit models were used, which, as stated after analyzing the literature on the subject, were already used in various countries around the... [more]

Operational factors are known to affect the health of an in-service power transformer and to reduce the capabilities and readiness for energy transmission and distribution. Hence, it is important to understand the degradation rate and corresponding behavioral aspects of different insulating fluids under various fault conditions. In this article, the behavior of mineral oil and two environmentally friendly fluids (a synthetic and a natural ester) are reported under arcing, partial discharges, and thermal fault conditions. Arcing, partial discharges and thermal faults are simulated by 100 repeated breakdowns, top oil electrical discharge of 9 kV for five hours, and local hotspots respectively by using different laboratory-based setups. Some physicochemical properties along with the gassing tendency of fresh and aged insulating liquids are investigated after the different fault conditions. UV spectroscopy and turbidity measurements are used to report the degradation behavior and dissolved... [more]

In response to climate change and environmental issues, many countries have gradually optimized carbon market management and improved the carbon market trading mechanism. Carbon price prediction plays a pivotal role in promoting carbon market management when investors are guided by prediction to conduct rational carbon trading. A novel carbon price prediction methodology is constructed based on ensemble empirical mode decomposition, improved bat algorithm, and extreme learning machine (EEMD-IBA-ELM) in this study. Firstly, the carbon price is decomposed into multiple regular intrinsic mode function (IMF) components by the ensemble empirical mode decomposition, and partial autocorrelation analysis (PACF) is used to find IMF historical data affecting the current value of IMF. Secondly, the improved bat algorithm (IBA) is used to heighten extreme learning machine (ELM) while adaptive parameters are obtained. Finally, EEMD-IBA-ELM was established to predict carbon price. Simultaneously, en... [more]

Intermetallic compounds are key materials for energy transition as they form reversible hydrides that can be used for solid state hydrogen storage or as anodes in batteries. ABy compounds (A = Rare Earth (RE); B = transition metal; 2 < y < 5) are good candidates to fulfill the required properties for practical applications. They can be described as stacking of [AB5] and [AB2] sub-units along the c crystallographic axis. The latter sub-unit brings a larger capacity, while the former one provides a better cycling stability. However, ABy binaries do not show good enough properties for applications. Upon hydrogenation, they exhibit multiplateau behavior and poor reversibility, attributed to H-induced amorphization. These drawbacks can be overcome by chemical substitutions on the A and/or the B sites leading to stabilized reversible hydrides. The present work focuses on the pseudo-binary Sm2MnNi7−x system (0 ≤ x < 0.5). The structural, thermodynamic and corrosion properties are analyz... [more]

Introducing integrated, automatic control to buildings operating with the environmental quality management (EQM) system, we found that existing energy models are not suitable for use in integrated control systems as they poorly represent the real time, interacting, and transient effects that occur under field conditions. We needed another high-precision estimator for energy efficiency and indoor environment and to this end we examined artificial neural networks (ANNs). This paper presents a road map for design and evaluation of ANN-based estimators of the given performance aspect in a complex interacting environment. It demonstrates that in creating a precise representation of a mathematical relationship one must evaluate the stability and fitness under randomly changing initial conditions. It also shows that ANN systems designed in this manner may have a high precision in characterizing the response of the building exposed to the variable outdoor climatic conditions. The absolute valu... [more]

Disposal of vast agricultural residues has been a nerve-wracking social problem in many agriculture-intensive regions. Open-field combustion both squanders those biomass resources and causes severe atmospheric pollution and hazards. In addition, wood industries yield residues such as sanding powders without value application. Production of biofuels out of these biomass provides a multiple beneficial solution. To that end, this work focused on fabrication of biomass fuels using rice straws (Calorific value: 14.7 MJ/Kg) and wood residues from OSB industries (Calorific value: 17.3 MJ/Kg). Biofuel sticks from various proportions of biomass residues were made using an 18.5 KW industrial biomass extruder without adding bonding agents, achieving densities of 1.0−1.6 g/cm3 and comparative calorific values. The biofuel sticks exhibit moisture sensitivity when subjected to a ten-day conditioning. Release of residual stresses that were created during the densification process led to structural de... [more]

This paper presents the results of laboratory tests of cellulose insulation drying with the use of synthetic ester. The effectiveness of the drying process was investigated depending on the initial moisture of cellulose samples (2%, 3%, and 4%), ester temperature (55, 70, and 85 °C), initial moisture of the ester (70, 140, and 220 ppm), drying time (48, 96, and 168 h), and the weight ratio of cellulosic materials to ester (0.067 and 0.033). A large influence of temperature and time of drying on the efficiency of the drying process was found. This is important information due to the application of the results in the transformers drying procedure. The heating and drying ester unit should provide the highest possible temperature. For the assumed experiment conditions the initial moisture of the ester had little effect on the drying efficiency. An ester with a moisture content below 140 ppm can still be considered as meeting the requirements for drying cellulose with significant moisture.... [more]