When integrating multi-grid renewable energy systems, modular multi-level converters (MMCs) are promising for high-voltage DC (HVDC) transmission. Because of the characteristics of the system, however, it is more difficult to prevent a fault at the DC terminal than at the AC terminal of the MMC. Accordingly, a fault ride-through (FRT) strategy for the operation of the MMC in the DC terminal is required for stable system operation. In this paper, a solution for closed-circuit overcurrent caused by a permanent line-to-line DC fault is proposed. This method is able to reduce the fault current through the adjustment of the slope of the total voltage in the system by operating a sub-module having lower switching losses and fewer passive devices compared with existing topologies. Additionally, through the equivalent circuit of the proposed scheme in a sub-module in case of a fault, the FRT mechanism for the fault current is explained. The feasibility of this proposed technique was verified t... [more]

Sustainability and energy efficiency have become important factors for many industrial processes, including chemical pulping. Recently complex back-end heat recovery solutions have been applied to biomass-fired boilers, lowering stack temperatures and recovering some of the latent heat of the moisture by condensation. Modern kraft recovery boiler flue gas offers still unutilized heat recovery possibilities. Scrubbers have been used, but the focus has been on gas cleaning; heat recovery implementations remain simple. The goal of this study is to evaluate the potential to increase the power generation and efficiency of chemical pulping by improved back-end heat recovery from the recovery boiler. Different configurations of heat recovery schemes and different heat sink options are considered, including heat pumps. IPSEpro simulation software is used to model the boiler and steam cycle of a modern Nordic pulp mill. When heat pumps are used to upgrade some of the recovered low-grade heat, u... [more]

Deep low-frequency earthquakes (LFEs) are known to occur in dehydration phenomena from the subducting hydrous slab and in magmatic phenomena beneath Quaternary volcanoes in Japan. To realize the spatial and temporal characteristics of the magmatic deep low-frequency earthquakes, their hypocenters along with those of ordinary overhead high-frequency earthquakes are analyzed beneath six volcanic fields in northeastern Japan. This trial clarifies the rising basaltic magma conduits and rheological profiles of the lithosphere. Deep low-frequency earthquakes tend to form three vertical clusters corresponding to the rheological strength peak of the peridotite upper mantle, gabbroic lower crust, and granitic upper crust. Interactive aseismic gaps between low- and high-frequency earthquakes reveal the brittle−plastic transition as an isothermal indicator in the lithosphere. This relationship provides a tool to monitor the thermal evolution of the lithosphere and to explore sustainable geotherma... [more]

Inductive power transfer (IPT) systems have become more and more popular recently. To improve transient responses and load disturbance responses, this paper proposes a predictive controller design for a three-winding inductive power transfer (IPT) system. First, a three-winding IPT is presented. Next, a predictive controller is designed based on augmented variables and a performance index. Finally, a digital signal processor, TMS 320F2808, made by Texas Instrument, is used to execute the predictive control algorithms and to control the switching states of the power devices. An IPT system, with DC 220 V input, DC 130 V output, and a rated power of 2 kW, is implemented. A buck converter is used to provide an adjustable output voltage and output current to charge a battery set. Experimental results show that the proposed predictive controllers of the IPT system have better performance than proportional-integral (PI) controllers, including faster transient responses and better load disturb... [more]

The most efficient energy management strategies for hybrid vehicles are the “Optimization-Based Strategies”. These strategies require a preliminary knowledge of the driving cycle, which is not easy to predict. This paper aims to combine Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC) low section short trips with real traffic levels for vehicle energy and fuel consumption prediction. Future research can focus on implementing a new strategy for Hybrid Electric Vehicle (HEV) energy optimization, taking into account WLTC and Google Maps traffic levels. First of all, eight characteristic parameters are extracted from real speed profiles, driven in urban road sections in the city of Messina at different traffic conditions, and WLTC short trips as well. The minimum distance algorithm is used to compare the parameters and assign the three traffic levels (heavy, average, and low traffic level) to the WLTC short trips. In this way, for each route assigned from Google maps, vehicle’s e... [more]

The expansion on the use of Electric Vehicles demands new mechanisms to ease the charging process, making it autonomous and with a reduced user intervention. This paper reviews the technologies applied to the wireless charge of Electric Vehicles. In particular, it focuses on the technologies based on the induction principle, the capacitive-based techniques, those that use radiofrequency waves and the laser powering. As described, the convenience of each technique depends on the requirements imposed on the wireless power transfer. Specifically, we can state that the power level, the distance between the power source and the electric vehicle or whether the transfer is executed with the vehicle on the move or not or the cost are critical parameters that need to be taken into account to decide which technology to use. In addition, each technique requires some complementary electronics. This paper reviews the main components that are incorporated into these systems and it provides a review... [more]

Short-Term Load Prediction (STLP) is an important part of energy planning. STLP is based on the analysis of historical data such as outdoor temperature, heat load, heat consumer configuration, and the seasons. This research aims to forecast heat consumption during the winter heating season. By preprocessing and analyzing the data, we can determine the patterns in the data. The results of the data analysis make it possible to form learning algorithms for an artificial neural network (ANN). The biggest disadvantage of an ANN is the lack of precise guidelines for architectural design. Another disadvantage is the presence of false information in the analyzed training data. False information is the result of errors in measuring, collecting, and transferring data. Usually, trial error techniques are used to determine the number of hidden nodes. To compare prediction accuracy, several models have been proposed, including a conventional ANN and a wavelet ANN. In this research, the influence of... [more]

Due to the inappropriate treatment of dairy wastewater, which can easily cause underground water pollution, there is an increasing need for a novel approach to reuse dairy wastewater. The technology of microbially induced calcium carbonate precipitation with environmentally friendly characteristics and high efficiency has been widely used for underground infrastructure remediation. However, there is a lack of in-depth research on the application of this technology under extreme underground environments, such as the borehole of oil wells with high temperature, high pressure, alkaline, and aerobic conditions. In addition, to reduce the cost of this technology when applied on a large scale, we adopted dairy wastewater to cultivate bacteria. Then, we put the bacterial solution into cement slurry in the borehole to improve the cementing quality. In this paper, the rheology properties, mechanical strength, permeability, porosity, and pore distribution of microbial cementing slurry were studi... [more]

In October 2014, EU leaders agreed upon three key targets for the year 2030: a reduction of at least 40% in greenhouse gas emissions, a saving of at least a 27% share for renewable energy, and at least a 27% improvement in energy efficiency [...]

Microalgae are currently considered to be a promising feedstock for biodiesel production. However, significant research efforts are crucial to improve the current biomass and lipid productivities under real outdoor production conditions. In this context, batch, continuous and semi-continuous operation regimes were compared during the Spring/Summer seasons in 2.6 m3 tubular photobioreactors to select the most suitable one for the production of the oleaginous microalga Nannochloropsis oceanica. Results obtained revealed that N. oceanica grown using the semi-continuous and continuous operation regimes enabled a 1.5-fold increase in biomass volumetric productivity compared to that cultivated in batch. The lipid productivity was 1.7-fold higher under semi-continuous cultivation than that under a batch operation regime. On the other hand, the semi-continuous and continuous operation regimes spent nearly the double amount of water compared to that of the batch regime. Interestingly, the bioch... [more]

The Breeding Blanket (BB) is one of the key components of the European Demonstration (EU-DEMO) fusion reactor. Its main subsystems, the Breeder Zone (BZ) and the First Wall (FW), are cooled by two independent cooling circuits, called Primary Heat Transfer Systems (PHTS). Evaluating the BB PHTS performances in anticipated transient and accident conditions is a relevant issue for the design of these cooling systems. Within the framework of the EUROfusion Work Package Breeding Blanket, it was performed a thermal-hydraulic analysis of the PHTS during transient conditions belonging to the category of “Decrease in Coolant System Flow Rate”, by using Reactor Excursion Leak Analysis Program (RELAP5) Mod3.3. The BB, the PHTS circuits, the BZ Once Through Steam Generators and the FW Heat Exchangers were included in the study. Selected transients consist in partial and complete Loss of Flow Accident (LOFA) involving either the BZ or the FW PHTS Main Coolant Pumps (MCPs). The influence of the loss... [more]

This paper proposes a Hybrid Microgrid (HμG) model including distributed generation (DG) and a hydrogen-based storage system, controlled through a tailored control strategy. The HμG is composed of three DG units, two of them supplied by solar and wind sources, and the latter one based on the exploitation of theProton Exchange Membrane (PEM) technology. Furthermore, the system includes an alkaline electrolyser, which is used as a responsive load to balance the excess of Variable Renewable Energy Sources (VRES) production, and to produce the hydrogen that will be stored into the hydrogen tank and that will be used to supply the fuel cell in case of lack of generation. The main objectives of this work are to present a validated dynamic model for every component of the HμG and to provide a strategy to reduce as much as possible the power absorption from the grid by exploiting the VRES production. The alkaline electrolyser and PEM fuel cell models are validated through real measurements. Th... [more]

The article evaluates the reduction of carbon dioxide emission due to the partial substitution of coal with alternative fuels in clinker manufacture. For this purpose, the calculations were performed for seventy waste-derived samples of alternative fuels with variable calorific value and variable share in the fuel mixture. Based on annual clinker production data of the Polish Cement Association and the laboratory analysis of fuels, it was estimated that the direct net CO2 emissions from fossil fuel combustion alone were 543 Mg of CO2 per hour. By contrast with the full substitution of coal with alternative fuels (including 30% of biomass), the emission ranged from 302 up to 438 Mg of CO2 per hour, depending on fuel properties. A reduction of 70% in the share of fossil fuels resulted in about a 23% decrease in net emissions. It was proved that the increased use of alternative fuels as an additive to the fuel mix is also of economic importance. It was determined that thanks to the combus... [more]

The worldwide consumption of fossil hydrocarbons in the road transport sector in 2020 corresponded to roughly half of the overall consumption. However, biofuels have been discreetly contributing to mitigate gaseous emissions and participating in sustainable development, and thus leading to the extending of the commercial utilization of internal combustion engines. In this scenario, the present work aims at exploring the effects of alternative fuels containing a blend of 15% ethanol and 35% biodiesel with a 50% fossil diesel (E15D50B35) or 50% Fischer−Tropsch (F-T) diesel (E15FTD50B35) on the engine combustion, exhaust emissions (CO, HC, and NOx), particulate emissions characteristics as well as the performance of an aftertreatment system of a common rail diesel engine. It was found that one of the blends (E15FTD50B35) showed more than 30% reduction in PM concentration number, more than 25% reduction in mean particle size, and more than 85% reduction in total PM mass with respect to con... [more]

Buildings in hot climate areas are responsible for high energy consumption due to high cooling load requirements which lead to high greenhouse gas emissions. In order to curtail the stress on the national grid and reduce the atmospheric emissions, it is of prime importance that buildings produce their own onsite electrical energy using renewable energy resources. Photovoltaic (PV) technology is the most favorable option to produce onsite electricity in buildings. Installation of PV modules on the roof of the buildings in hot climate areas has a twofold advantage of acting as a shading device for the roof to reduce the cooling energy requirement of the building while producing electricity. A high ground coverage ratio provides more shading, but it decreases the efficiency of the PV system because of self-shading of the PV modules. The aim of this paper was to determine the optimal value of the ground coverage ratio which gives maximum overall performance of the roof-mounted PV system by... [more]

Recent researches on behavioral finance have tested for, among others, evidence for the relations between weather, investors’ mood, and investment decisions. Many of the researches related to the influence of some weather factors, such as sunshine duration on stock exchange returns, but there is no complex research taking into account a wide group of weather factors determining investors’ mood. The main goal of the article is to verify the influence of weather factors on basic market parameters of energy sector companies quoted on the Warsaw Stock Exchange. Rates of return, trading volumes, and values of trading volume are taken into account during the research. All analyses are based on econometric models assuming the existence of typical problems of estimation such as: autocorrelation of residuals, heteroskedasticity, or abnormality of residuals. The best approximation of models was obtained for GARCH (Generalized Autoregressive Conditional Heteroskedasticity) type models.

A good design of the ice rink floor could save a great deal of capital and operational costs for hockey arenas. This ice rink floor design focuses on a cost-effective tube arrangement and an optimal concrete coverage over the tubes that could provide sufficient heat transfer rate between the coolant and the freezing ice. This paper reports a theoretical model to simulate the heat transfer characteristic of a different tube diameter, spacing distance, and thickness of the concrete coverage of the tubes of an ice rink. In addition, calcium chloride and ethylene glycol with water solutions are compared to figure out the pros and cons of these two secondary coolants. This model prediction is compared to the typical ice floor arrangement in order to determine the best floor construction scenario.

Clean energy for all, as listed in the United Nation’s SDG7, is a key component for sustainable environmental development. Therefore, it is imperative to uncover the environmental implications of alternative energy technologies. SustainableGAS project simulates different process chains for the substitution of natural gas with renewable energies in the German gas market. The project follows an interdisciplinary approach, taking into account techno-social and environmental variabilities. However, this research highlights the project results from the environmental perspective. So far, a detailed assessment of the environmental costs of alternative gas technologies with a focus on the process of energy transition has remained rare. Although such data constitute key inputs for decision-making, this study helps to bridge a substantial knowledge gap. Competing land-use systems are examined to secure central ecosystem services. To fulfill this obligation, an Integrated Valuation of Ecosystem S... [more]

The increasing share of volatile, renewable energies, such as wind and solar power, leads to challenges in the stabilization of power grids and requires more flexibility in future energy systems. This article addresses the flexibilization of the consumer side and presents a simulation-based method for the technical and economic investigation of energy flexibility measures in industrial steam supply systems. The marketing of three different energy-flexibility measures—bivalence, inherent energy storage and adjusting process parameters—both at the spot market and at the balancing power market, are investigated from a technical as well as an economic point of view. Furthermore, the simulation-based methodology also considers pressure and temperature fluctuation induced by energy-flexibility measures. First, different energy-flexibility measures for industrial steam supply systems are introduced. Then, the physical modeling of the steam generation, distribution, and consumption as well as... [more]

The article presents an experimental laboratory setup used for the empirical determination of the gasification of coal samples in the form of solid rock, cut out in the form of a cylinder. An experimental laboratory set enabled a series of experiments carried out at 700 °C with steam as the gasification agent. The samples were prepared from the coal seam, the use of which can be planned in future underground and ground gasification experiments. The result of the conducted coal gasification process, using steam as the gasification agent, was the syngas, including hydrogen (H2) with a concentration between 46% and 58%, carbon dioxide (CO2) with a concentration between 13% and 17%, carbon monoxide (CO) with a concentration between 7% and 11.5%, and methane(CH4) with a concentration between 9.6% and 20.1%.The results from the ex-situ experiments were compared with the results of numerical simulations using computational fluid dynamics (CFD) methods. A three-dimensional numerical model for... [more]

The method of increasing the efficiency of using one of the most common means of auxiliary transport in underground coal mines—suspended monorails—is presented. Increase of velocity is one of the key parameters to improve the efficiency and economical effect related with the underground auxiliary transport. On the other hand, increasing the velocity results in bigger value of force acting on the suspended monorail route and its suspensions. The most important issue during increasing the velocity is ensuring the required safety for the passengers and not overloading the infrastructure. In order to analyze how increasing velocity influences the level of loads of the route suspension and the steel arch loads, the computational model of suspended monorail was developed. The computational model included both the physical part (embedded in the program environment based on the Multi-Body System method) and the components of the monorail control system. Two independent software environments we... [more]

While frequency response analysis (FRA) is a well matured technique widely used by current industry practice to detect the mechanical integrity of power transformers, interpretation of FRA signatures is still challenging, regardless of the research efforts in this area. This paper presents a method for reliable quantitative and qualitative analysis to the transformer FRA signatures based on a decision tree classification model and a fully connected neural network. Several levels of different six fault types are obtained using a lumped parameter-based transformer model. Results show that the proposed model performs well in the training and the validation stages, and is of good generalization ability.

The power delivered by photovoltaic (PV) arrays is dependent on environmental factors, and hence the availability and quality of power delivered by the PV array is low. These issues can be mitigated by integrating a battery energy storage system (BESS) with PV arrays. The integration of the BESS with PV arrays requires controller circuits to regulate power flow between the BESS, PV array, and the load. In this paper, a boost converter-based controller is proposed. The proposed controller has higher reliability and efficiency, and lower operational complexity. It improves the power quality and availability by adjusting the power flow to/from the BESS while delivering the required load power. A simulation study was performed to validate the proposed controller under varying irradiance and temperature of the PV array. The controller was validated against both lithium-ion and lead-acid BESSs.

Several types of high voltage direct current (HVDC) breakers have been introduced and commercialized. Each of them has advantages and disadvantages. Among them, the hybrid HVDC breaker is highly successful. One of the most important concerns that the hybrid HVDC breaker has faced is high power loss throughout its fault current breaking process. The hybrid HVDC breaker comprises a high voltage bidirectional main HVDC breaker. A significant number of electronic switches need to be connected in a series where anti-parallel diodes are essentially embraced. During fault inception, a number of series solid-state switches and a number of series diodes dramatically increase the power loss of the main breaker. This study, firstly, studies the power loss of the hybrid HVDC breaker and later develops a structure of a full-bridge hybrid breaker (FBHB) to reduce the losses of the current structure both in the normal and fault protection states. In this paper simulations are done based on PSCAD. In... [more]

Brazil is currently undergoing changes to regulations on distributed generation (DG), specifically for solar energy micro-generation. The changes proposed by the Brazilian Regulatory Agency suggest that only the cost of energy be compensated to investors. The service costs and other charges related to energy tariffs must be divided among consumers. Investors with existing installations and class entities have contested these proposals, calling them “sun-fees”. To date, no scientific papers have been published discussing these changes. The new regulations propose an end to cross subsidies, where all consumers (even those who do not have DG) pay for the transmission and distribution systems. This study compares the economic feasibility of micro-generation before and after implementing the new standards proposed by the regulatory agency. We used data on average electrical energy demand, energy price, and solar radiation in different regions. The national averages were used as a base compa... [more]