This paper presents a novel three-port high-step-up/step-down bidirectional DC/DC converter with a coupled inductor for photovoltaic (PV) systems. The proposed converter combines a high-step-up converter, which is used to step-up the PV module to DC bus 200 V, and a battery charge/discharge bidirectional converter to form a three-port bidirectional converter. When sufficient energy is supplied from the PV modules, the converter can step-up the output of the PV modules and provide energy to the DC bus while charging the battery simultaneously. However, when no energy is supplied from the PV modules, the DC bus voltage is provided by the battery. Moreover, the energy stored in the leakage inductor is recycled to the DC-blocking capacitor, and synchronous rectification is conducted in the switch during the step-up mode to reduce switch loss and thereby increase the system’s overall efficiency. Finally, a 500 W three-port bidirectional converter is implemented to verify the feasibility and... [more]

Off-grid power systems are often used to supply electricity to remote households, cottages, or small industries, comprising small renewable energy systems, typically a photovoltaic plant whose energy supply is stochastic in nature, without electricity distributions. This approach is economically viable and conforms to the requirements of the European Green Deal and the Fit for 55 package. Furthermore, these systems are associated with a lower short circuit power as compared with distribution grid traditional power plants. The power quality parameters (PQPs) of such small-scale off-grid systems are largely determined by the inverter’s ability to handle the impact of a device; however, this makes it difficult to accurately forecast the PQPs. To address this issue, this work compared prediction models for the PQPs as a function of the meteorological conditions regarding the off-grid systems for small-scale households in Central Europe. To this end, seven models—the artificial neural netwo... [more]

For high-speed permanent magnet machines (HSPMMs), many design schemes of rotor length−diameter ratios can satisfy the constraints of multiple physical fields during the motor design period. The rotor length−diameter ratio greatly impacts the comprehensive performances of multiple physical fields. However, these analyses are missing in the existing literature. Therefore, this paper focuses on the influence of the rotor length−diameter ratio on comprehensive performances. Firstly, finite element models (FEM) of multiple physical fields are built by ANSYS Workbench platform and Motor-CAD software. Then, the comprehensive performances of multiple physical fields are comparatively analyzed. Finally, the designed HSPMM is implemented, based on one prototype of 60 kW, 30,000 rpm to verify the results of comparative analysis. Based on the comparative analysis above, the influent laws of rotor length−diameter ratios on comprehensive performances of multiple physical fields are discussed and su... [more]

This paper presents the energy potential of biogas obtained from the anaerobic digestion (AD) of sewage sludge (SS) preceded by thermal hydrolysis (THP) using Cambi THP® technology. The presented data are for the Tarnów (Poland) wastewater treatment plant for the year 2020. A detailed energy balance of biogas and its use in the cogeneration process and in the production of heat in the water boiler and the steam boiler is presented. The article contains data on the amount of processed SS and the content of dry matter and dry organic matter at different stages of the technological process. The annual plant operation resulted in the production of 3,276,497 Nm3 of biogas as a result of processing 8684 tonnes of dry solids (tDS) of municipal SS from the Tarnów wastewater treatment plant (WWTP) and regional WWTPs. The energy potential of the produced biogas was 75,347.06 GJ. The average calorific value of biogas was 23,021 kJ/Nm3.. The obtained biogas production allowed us to cover the therm... [more]

To stabilize the electrical mode of an arc steelmaking furnace in the initial stages of melting, it is advisable to use a high-speed current-limiting system, in addition to the traditional electrode movement control system. This system is implemented by including the primary winding of the furnace transformer choke, controlled by thyristors. The use of such a system, on the one hand, reduces the negative impact of the arc steel furnace on the the power supply network operation and, on the other, affects the operation of the electrode movement system, built on the principle of an impedance regulator. In order to analyze the mutual influences between such systems, a mathematical model for the power supply and control system of the arc steelmaking furnace was created. The developed model can work in real time, which corresponds to the world trends of modern control system synthesis for complex technological objects. In the created model, the work of the combined control system with differ... [more]

Refrigerant maldistribution severely deteriorates the heat transfer performance of a microchannel evaporator. Compared with the refrigerant distribution among flat tubes along the header, refrigerant distribution among microchannels in the flat tube in the airflow direction has barely been paid attention. In this paper, a heat transfer mathematical model of a microchannel evaporator’s flat tube composed of vertically placed parallel microchannels in the airflow direction was developed. The Refrigerant distribution among the microchannels was evaluated and its influence on heat transfer between air and refrigerant was analyzed. The results showed that the refrigerant distribution and heat transfer performance between air and refrigerant were interrelated and interacted with each other. The temperature of the air leaving the microchannel evaporator changed along the microchannel because of uneven refrigerant distribution among the microchannels, and the air temperature difference between... [more]

The wireless power transmission (WPT) of an autonomous underwater vehicle (AUV) tends to have non-negligible eddy current loss with increasing frequency or coil current due to the conductivity of seawater. In this paper, the inductor-capacitor-capacitor and parallel (LCC-P) topology and the magnetic coupler with an H-shaped receiver structure are chosen to achieve a compact system on the receiving side. The conditions for constant current output of the LCC-P topology are analyzed based on the cascaded circuit analysis method. The traditional parameter design method does not consider the influence of eddy current loss on the system circuit model, by introducing the equivalent eddy current loss resistance at both the transmitting side and receiving side, a modified circuit model of the WPT system in the seawater condition was obtained. Afterward, a nonlinear programming model with the optimal efficiency of the constant current mode as the objective function is established, and the geneti... [more]

Studying the thermal decomposition of wood pellets is an important subject in order to understand the behavior of wood pellets during the combustion process. In fact, wood pellets have become an important fuel used in boiler combustion. The objective of this study is to investigate the mass loss and elemental analysis of pine wood pellets at various times and temperatures. Commercial pellets with a diameter of 6 mm were used. The experiment was conducted in the laboratory of the Engineering University of Minho. The pellets were burned in a small reactor of 1.36 kW with a maximum temperature range of 1150 °C. The data were observed at different temperatures: 264, 351, 444, 541, 650, and 734 °C, and at time intervals of 30, 60, 120, 180, 240, 300, 600, 900, 1200, and 3600 s. The results of the experiment revealed that the reaction rate increases with the temperature, and the higher the combustion temperature applied, the higher the mass loss of all substances observed. The remaining mass... [more]

In recent years, a rapid increase in the adoption of renewable energy sources and in the transition from a centralized electricity generation system to an increasingly distributed one has occurred. Within this scenario, in line with the European directives for achieving the objectives in the field of energy transition and climate change, energy communities are seen as potential contributors. The purpose of this work is to analyze the application potential of the energy community concept associated with district heating networks, leading to better overall energy-economic performance. This was demonstrated for a specific energy community in Italy, and it can be achieved by maximizing internal energy sharing—resulting from the electricity surplus generated by the photovoltaic system—and adopting different strategies that include heat pumps in order to maximize self-consumption and self-sufficiency, as well as to evaluate the most efficient investment in economic terms by exploiting the in... [more]

The onset of rotating stall and surge in compressors limits the operating range of aero-engines. Accurately predicting the key features during these events is critical in the engine design process. In this paper, a three-dimensional computational model for transient simulation of multi-stage axial compressors during stall is proposed. The kinetic equations describing the dynamic process of the compression system are constructed, with a 3D through-flow model for the compression part and a 1D gas collector model for the outlet part. The calculation of the source term is performed using the developed body-force model, which realizes the correlation between the deviation angle and the loss coefficient with the inlet parameters in various flow regions. Validated on a single-stage compressor and a single-rotor fan, the results show that the method is capable of capturing the stall and surge features correctly and that the three-dimensional structure of the stall cell can be captured. In addi... [more]

Urban metabolism has emerged over the past decades as an important new paradigm of regional and urban sustainability governance towards a Chinese national scheme of ‘carbon neutrality’ by 2060. Hebei province in China faces twin pressures related to its supply of water and energy resources, which has brought humans and nature into conflict. Overcoming this tension in the human-land relationship in Hebei and determining a suitable development path for the future has become a core issue for the achievement of coordinated development within the Beijing−Tianjin−Hebei region. This paper constructs a system to simulate the metabolism of water, energy, and human relationships, and uses this model to carry out simulations for Hebei province. The model establishes five scenarios: a natural development scenario, economic growth scenario, water conservation development scenario, energy conservation development scenario, and low carbon scenario. The simulation results show that, without interventi... [more]

Power converter technology has expanded into a wide range of low, medium, and high power applications due to the ability to manage electrical energy efficiently. In this regard, the modular multilevel converter has become a viable alternative to ensure an optimal harmonic profile with a sinusoidal voltage at the load side. Model predictive control (MPC) is a state-of-the-art technique that has been successfully used to control power electronic converters due to its ability to handle multiple control objectives. Nevertheless, in the classical MPC approach, the optimal vector is applied during the whole sampling period producing an output voltage. This solution causes an unbalanced switching frequency of the power semiconductor, which then causes unbalanced stress on the power devices. Modulation strategies have been combined with MPC to overcome these shortcomings. This paper introduces the experimental assessment of a 7-level converter combining a simple phase shift multicarrier pulse-... [more]

Best Estimate Plus Uncertainty (BEPU) approaches for nuclear reactor applications have been extensively developed in recent years. The challenge for BEPU approaches is to achieve multi-physics modeling with an acceptable computational cost while preserving a reasonable fidelity of the physics modeled. In this work, we present the core multi-physics computational framework developed for the efficient computation of uncertainties in Light Water Reactor (LWR) simulations. The subchannel thermal-hydraulic code CTF and the nodal expansion neutronic code PARCS are coupled for the multi-physics modeling (CTF-PARCS). The computational framework is discussed in detail from the Polaris lattice calculations up to the CTF-PARCS coupling approaches. Sampler is used to perturb the multi-group microscopic cross-sections, fission yields and manufacturing parameters, while Dakota is used to sample the CTF input parameters and the boundary conditions. Python scripts were developed to automatize and modu... [more]

Based on the square heat-generation body (HGB) with “arrow-shaped” high-thermal-conductivity channel (HTCC) model established in the previous literature, we performed multi-objective optimization (MOO) with maximum temperature difference (MTD) minimization and entropy-generation rate (EGR) minimization as optimization objectives for its performance. Pareto frontiers with optimal set were obtained based on NSGA-II. TOPSIS, LINMAP, and Shannon entropy decision methods were used to select the optimal results in Pareto frontiers, and the deviation index was used to compare and analyze advantages and disadvantages of the optimal results for each decision method. At the same time, multi-objective constructal designs of the “arrow-shaped” HTCC were carried out through optimization of single degree of freedom (DOF), two DOF, and three DOF, respectively, and the thermal performance of the square heat-generation body under optimizations of different DOF were compared. The results show that const... [more]

As a crucial factor in the improvement of energy efficiency for power-using electromechanical products, the flow, conversion and distribution of energy are closely related to design variables of products. Simultaneously, performance is the constraint of energy efficiency and is strongly affected by design variables. In order to improve a product’s energy efficiency without compromising performance, an energy flow model with a basic energy flow element (EFE) was built on a functional basis and its modelling procedure is presented in this paper. Containing function, design variable and characteristic energy in EFEs, as well as the interface parameters between EFEs and environment, the model contributes to logically clarifying the relationship between design variables and performance. With the refrigerator as an example, the effectiveness of the energy flow model is verified by a comparison between simulation, based on an energy flow model, and experimentation. Furthermore, five critical... [more]

This paper deals with the proposition of improvement in the performance of a heat source by modification of its structure and by deriving a dedicated control system. Traditional heat sources consist of a single heater of high nominal power, but slow dynamics, that is regulated by a single closed loop control system. In this paper, an existing heater serially-connected with a supplemental heater with low nominal power but fast dynamics is proposed. A dedicated control system was derived with two active disturbance rejection controllers (ADRC) implemented in the habituating control structure. The proposed solution was validated using a virtual commissioning procedure where the heating system was simulated in the SIEMENS® Simit v10.3 industrial software, and ADRC controllers were implemented in SIEMENS® PLCSIM Advanced using dedicated library function blocks. The results showed the superiority of the proposed approach in comparison with the traditional single closed loop solution. The pro... [more]

Biogas production is a process with great potential. It uses the biodegradable raw materials of animal, vegetable and municipal waste. The amount of municipal as well as agricultural waste is increasing every year. This waste is an unmanaged and nuisance waste, and using it in biogas plants reduces the amount of waste. Biogas production is part of the EU’s policy to reduce dependence on fossil fuels and use energy from renewable sources (diversification of energy sources). Its importance is certain to increase in the future as energy demand increases. This article deals with the economical use of biodegradable waste for biogas production in Poland and Germany. Both countries have a similar agricultural and municipal waste structure. An agricultural biogas plant is one way of obtaining energy based on renewable energy sources (RES). Energy production from agricultural biogas will allow Poland to meet the 32% obligation imposed by the EU and Germany to continue to be the market leader in... [more]

The brushless doubly fed induction machine (BDFIM) is being considered as a possible solution for low-speed wind energy generator applications. It has been proposed as an alternative to the doubly fed induction machine (DFIM) due to its robust rotor structure as well as low operational maintenance requirements. However, due to its complicated control philosophy, higher overall machine size due to the extra set of control windings in the stator, and slightly lower efficiency, it is yet to be adopted in commercial applications. In this paper, a simplified vector control scheme for the control winding of a cage+nested-loop (cage+NL) rotor BDFIM is proposed. Experimental results are compared with simulations to validate the effectiveness of the proposed control scheme.

Coal resources perform an important role in China’s energy structure. Hydraulic support is the main supporting equipment of fully mechanized mining face in coal mines. Because the hydraulic support frequently bears the impact pressure from the working face, it is very easy to cause failure of the balance jack. In order to solve the problem that the balance jack easily damaged by impact and improve the impact resistance of the hydraulic support, an improved fast response balance jack with multiple adaptive buffers was proposed in this paper. The energy dissipation characteristics of the balance jack were analyzed by establishing the mathematical model of the multiple buffering process of it. Based on ADAMS, the dynamic simulation model of the hydraulic support was constructed, and the mechanical response characteristics of the proposed balance jack and the traditional balance jack under different impact loads were compared and analyzed. By changing the equivalent stiffness of the novel... [more]

In Wireless Sensor Networks (WSNs), routing algorithms can provide energy efficiency. However, due to unbalanced energy consumption for all nodes, the network lifetime is still prone to degradation. Hence, energy efficient routing was developed in this article by selecting cluster heads (CH) with the help of adaptive whale optimization (AWOA) which was used to reduce time-consumption delays. The multi-objective function was developed for CH selection. The clusters were then created using the distance function. After establishing groupings, the supercluster head (SCH) was selected using the benefit of a fuzzy inference system (FIS) which was used to collect data for all CHs and send them to the base station (BS). Finally, for the data-transfer procedure, hop count routing was used. An Oppositional-based Whale optimization algorithm (OWOA) was developed for multi-constrained QoS routing with the help of AWOA. The performance of the proposed OWOA methodology was analyzed according to the... [more]

Lignocellulosic biomass is an abundant resource that can be valorized for the production of bioenergy. However, studies aiming to quantify the amount of biogas production potential per km forest road are scarce in the literature. In this study, fresh pine needles, pine needle litter, pine branches, and pine bark were digested in batch reactors under mesophilic conditions after a grinding/milling pre-treatment. All samples were collected from a low-altitude Mediterranean Pinus forest (North Greece) adjacent to a category G forest road with a gentle slope. The methane yield of fresh pine needles was between 115 and 164 NmL g−1 volatile solids (VS), depending on the Pinus tree size. Pine needle litter produced a significantly lower methane yield (between 58 and 77 NmL g−1 VS), followed by pine bark (85 NmL g−1 VS) and pine branches (138 NmL g−1 VS). Considering the quantity of pine needle litter accumulated on adjacent forest roads (600 ± 200 g m−2), it was possible to calculate the biome... [more]

The energy generated by a solar photovoltaic (PV) system depends on uncontrollable factors, including weather conditions and solar irradiation, which leads to uncertainty in the power output. Forecast PV power generation is vital to improve grid stability and balance the energy supply and demand. This study aims to predict hourly day-ahead PV power generation by applying Temporal Fusion Transformer (TFT), a new attention-based architecture that incorporates an interpretable explanation of temporal dynamics and high-performance forecasting over multiple horizons. The proposed forecasting model has been trained and tested using data from six different facilities located in Germany and Australia. The results have been compared with other algorithms like Auto Regressive Integrated Moving Average (ARIMA), Long Short-Term Memory (LSTM), Multi-Layer Perceptron (MLP), and Extreme Gradient Boosting (XGBoost), using statistical error indicators. The use of TFT has been shown to be more accurate... [more]

Accurate photovoltaic (PV) power forecasting is indispensable to enhancing the stability of the power grid and expanding the absorptive photoelectric capacity of the power grid. As an excellent nonlinear regression model, the relevance vector machine (RVM) can be employed to forecast PV power. However, the optimization of the free parameters is still a key problem for improving the performance of the RVM. Taking advantage of the strong global search capability, good stability, and fast convergence rate of the sparrow search algorithm (SSA), this paper optimizes the parameters of the RVM by using the SSA to develop an excellent RVM (called SSA-RVM). Consequently, a novel hybrid PV power forecasting model via the SSA-RVM is proposed to perform ultra-short-term (4 h ahead) prediction. In addition, the effects of seasonal distribution and weather type on PV power are fully considered, and different seasonal prediction models are established separately to improve the prediction capability.... [more]

The automobile sector is a promising avenue for enhancing energy security, economic opportunity, and air quality in India. Before penetrating a large number of electric vehicles (EV) into the power grid, a thorough investigation and assessment of significant parameters are required, as additional nonlinear and EV loads are linked to the decentralized market. Many automobile companies have already invested in electric vehicle research; hence, a detailed analysis on range anxiety and grid connectivity concerns are the important factors affecting the future of the electric vehicle industry. In this paper, the initial review is about the decentralized market in India and sustainable aspects of electric mobility based on the Indian context, as it is a developing nation with an enormous resource and scope for EV markets. With recent literature from the last three years, the substantial constraints observed in benefits and challenges are reviewed. The financial stability aspects and the incen... [more]

Power converters for wireless power transfer (WPT) and, in general, for electrical vehicle charging are evolving in terms of nominal power and performance, bringing along non negligible emissions in the supraharmonic range (2 kHz to 150 kHz). The large installed power and the high concentration with a relatively short separation distance can be addressed by feeding the converters through a DC grid for better dynamic response and lower impedance. The prediction of conducted emissions in real supply conditions requires carrying out measurements with low impedance values, lower than those available in line impedance stabilization networks (LISNs) for AC grids. This work proposes an approach to extrapolate converter emissions in an ideal 0 Ω condition, that together with the input impedance curve (determined by a least mean square approach) form a Norton equivalent circuit of the converter. The interaction of the converters with the DC grid and superposition of emissions can be then thorou... [more]