BACKGROUND The growing disparity between the rising demand for liver transplantation(LT)and the limited availability of donor organs has prompted a greater reliance on older liver grafts.Traditionally,utilizing livers...BACKGROUND The growing disparity between the rising demand for liver transplantation(LT)and the limited availability of donor organs has prompted a greater reliance on older liver grafts.Traditionally,utilizing livers from elderly donors has been associated with outcomes inferior to those achieved with grafts from younger donors.By accounting for additional risk factors,we hypothesize that the utili-zation of older liver grafts has a relatively minor impact on both patient survival and graft viability.AIM To evaluate the impact of donor age on LT outcomes using multivariate analysis and comparing young and elderly donor groups.METHODS In the period from April 2013 to December 2018,656 adult liver transplants were performed at the University Hospital Merkur.Several multivariate Cox propor-tional hazards models were developed to independently assess the significance of donor age.Donor age was treated as a continuous variable.The approach involved univariate and multivariate analysis,including variable selection and assessment of interactions and transformations.Additionally,to exemplify the similarity of using young and old donor liver grafts,the group of 87 recipients of elderly donor liver grafts(≥75 years)was compared to a group of 124 recipients of young liver grafts(≤45 years)from the dataset.Survival rates of the two groups were estimated using the Kaplan-Meier method and the log-rank test was used to test the differences between groups.RESULTS Using multivariate Cox analysis,we found no statistical significance in the role of donor age within the constructed models.Even when retained during the entire model development,the donor age's impact on survival remained insignificant and transformations and interactions yielded no substantial effects on survival.Consistent insigni-ficance and low coefficient values suggest that donor age does not impact patient survival in our dataset.Notably,there was no statistical evidence that the five developed models did not adhere to the proportional hazards assumption.When comparing donor age groups,transplantation using elderly grafts showed similar early graft function,similar graft(P=0.92),and patient survival rates(P=0.86),and no significant difference in the incidence of postoperative complications.CONCLUSION Our center's experience indicates that donor age does not play a significant role in patient survival,with elderly livers performing comparably to younger grafts when accounting for other risk factors.展开更多
This paper deals with reduction of losses in electric power distribution system through a dynamic reconfiguration case study of a grid in the city of Mostar,Bosnia and Herzegovina.The proposed solution is based on a n...This paper deals with reduction of losses in electric power distribution system through a dynamic reconfiguration case study of a grid in the city of Mostar,Bosnia and Herzegovina.The proposed solution is based on a nonlinear model predictive control algorithm which determines the optimal switching operations of the distribution system.The goal of the control algorithm is to find the optimal radial network topology which minimizes cumulative active power losses and maximizes voltages across the network while simultaneously satisfying all system constraints.The optimization results are validated through multiple simulations(using real power demand data collected for a few characteristic days during winter and summer)which demonstrate the efficiency and usefulness of the developed control algorithm in reducing the grid losses by up to 14%.展开更多
As the development of new power systems progresses,the inherent inertia of power systems continues to diminish.Centralized frequency regulation,which relies on rapid communication and real-time control,can enable inve...As the development of new power systems progresses,the inherent inertia of power systems continues to diminish.Centralized frequency regulation,which relies on rapid communication and real-time control,can enable inverter-based thermostatically controlled load(ITCL)clusters to provide virtual inertia support to the power grid.However,ITCL clusters exhibit significant discrete response characteristics,which precludes the direct integration of load-side inertia support into the synchronous unit side.To address this issue,this paper elaborates on the existing technical framework and analyzes the underlying causes of the problem.It proposes a timestamp allocation mechanism for ITCL cluster control instructions,ensuring that many ITCL terminals can be triggered at staggered times,thereby allowing the load cluster power to adhere to the inertia analog control law at any moment.Building on this foundation,the paper further examines the impact of the inertia response delay of ITCL clusters,which is based on centralized frequency regulation,on the stability of the power system.A design scheme for inertia analog control parameters is proposed,taking into account dual constraints,frequency stability and load cluster regulation capacity.Finally,the feasibility and applicability of the proposed mechanism and parameter design scheme are investigated through simulations conducted via MATLAB/Simulink.展开更多
Various regulations, aimed at the protection of human beings and electrical equipment against possible adverse effects resulting from exposure to electromagnetic fields, have been issued in many countries. Most of the...Various regulations, aimed at the protection of human beings and electrical equipment against possible adverse effects resulting from exposure to electromagnetic fields, have been issued in many countries. Most of them are based on safety guidelines published by international expert groups. In this paper, electric and magnetic fields are calculated in the vicinity of 25 kV traction line supplying railway traction systems. Calculation results are compared to exposure limits specified by safety guidelines and regulations. Possible countermeasures for reduction of electromagnetic fields are proposed. Also, this paper presents a method for calculation of the induced voltages to an underground gas pipeline from a neighbouring 25 kV electric traction overhead line in case of short circuit. Calculations are performed with EMTP-ATP software. Possible countermeasures for reduction of induced voltages are proposed.展开更多
Mechanical stimulation of plants can be caused by various abiotic and biotic environmental factors.Apart from the negative consequences,it can also cause positive changes,such as acclimatization of plants to stress co...Mechanical stimulation of plants can be caused by various abiotic and biotic environmental factors.Apart from the negative consequences,it can also cause positive changes,such as acclimatization of plants to stress conditions.Therefore,it is necessary to study the physiological and biochemical mechanisms underlying the response of plants to mechanical stimulation.Our aim was to evaluate the response of model plant Arabidopsis thaliana to a moderate force of 5 N(newton)for 20 s,which could be compared with the pressure caused by animal movement and weather conditions such as heavy rain.Mechanically stimulated leaves were sampled 1 h after exposure and after a recovery period of 20 h.To study a possible systemic response,unstimulated leaves of treated plants were collected 20 h after exposure alongside the stimulated leaves from the same plants.The effect of stimulation was assessed by measuring oxidative stress parameters,antioxidant enzymes activity,total phenolics,and photosynthetic performance.Stimulated leaves showed increased lipid peroxidation 1 h after treatment and increased superoxide dismutase activity and phenolic oxidation rate after a 20-h recovery period.Considering photosynthetic performance after the 20-h recovery period,the effective quantum yield of the photosystem II was lower in the stimulated leaves,whereas photochemical quenching was lower in the unstimulated leaves of the treated plants.Nonphotochemical quenching was lower in the stimulated leaves 1 h after treatment.Our study suggested that plants sensed moderate force,but it did not induce pronounced change in metabolism or photosynthetic performance.Principal component analysis distinguished three groups–leaves of untreated plants,leaves analysed 1 h after stimulation,while stimulated and unstimulated leaves of treated plants analysed 20 h after treatment formed together the third group.Observed grouping of stimulated and unstimulated leaves of treated plants could indicate signal transduction from the stimulated to distant leaves,that is,a systemic response to a local application of mechanical stimuli.展开更多
In this paper, a new control method for synchronous motor with excitation and damper windings is presented. It is based on one type of nonlinear control; feedback linearization control. To make a realization in the se...In this paper, a new control method for synchronous motor with excitation and damper windings is presented. It is based on one type of nonlinear control; feedback linearization control. To make a realization in the sense of electric drive, symmetricM space vector PWM （pulse width modulation） is applied. Estimation of damper winding currents via Lyapunov function for the whole estimated system is done. The aim of control is to make tracking system for rotor speed and square of stator flux. Simulation of motor starting to predefined operating points is done, and also maintaining these points during step change of load torque is obtained. Simulations give good results.展开更多
Modeling of ancillary services market can be described as institutional arrangements for establishing ancillary services management in deregulated electricity market. Models of the national ancillary services markets ...Modeling of ancillary services market can be described as institutional arrangements for establishing ancillary services management in deregulated electricity market. Models of the national ancillary services markets are market models which offer transmission system operator efficient procurement of ancillary services, reducing the system management risk, more competitive electricity market, better utilization of production facilities and complete deregulation of electricity markets. This paper deals with current mode of ancillary services market and potential market development in Croatia. Described models are used for establishing market of ancillary services which should occur in parallel with the electricity market.展开更多
Electricity price forecasting plays a vital role inthe strategy decision making for almost all power marketparticipants. This article investigates statistical background andpotential relations between different power ...Electricity price forecasting plays a vital role inthe strategy decision making for almost all power marketparticipants. This article investigates statistical background andpotential relations between different power market products (e.g.day-ahead prices, intraday prices, etc.). Danish and Croatianpower markets are used for the purpose of the case studyto present the methods used in this article. First, Danish andCroatian power market structures are shortly explained to clarifythe context of the problem. The data collection and preprocessingmethods are described, followed by the core focus of the study:statistical analysis. In addition to the presented histograms ofrespective power market components, we examine interrelationships through statistical analysis, demonstrating significantcorrelations both numerically and graphically. Furthermore,price spreads are investigated as a logical next step of the noticedcorrelations. Our comparative analysis of Danish and Croatianmarket peculiarities reveals three key findings: i) statisticallysignificant relationships between specific market components,ii) distinct behavioral patterns among observed factors, and iii) anopen-access analytical tool with accompanying dataset for futureresearch. Finally, the findings of this article present to marketparticipants an efficient tool to adjust business strategies andincrease profit.展开更多
The voltage uprating of existing overhead lines is an interesting solution for increasing the transmission of electricity, especially in areas where it is difficult to build new lines. If a line is uprated with minor ...The voltage uprating of existing overhead lines is an interesting solution for increasing the transmission of electricity, especially in areas where it is difficult to build new lines. If a line is uprated with minor changes of its design and without improvement of the grounding electrodes of towers, its lightning performance remains unchanged. The consequence is that the uprated line will have a lightning flashover rate very high compared to an overhead line of same nominal voltage but of standard design. One attractive solution to solve this problem is to use line arresters. The goal of this paper is to study the use of line arresters to achieve a satisfactory lightning performance of an overhead line uprated from 225 kV to 400 kV without major design modifications. In order to compare different strategies of line arrester installation the flashover rate is calculated based on a software able to launch automatically EMTP-RV. The software named LIPS has been developed under the cover of a partnership between Hydro-Quebec, RTE and EDF.展开更多
The thermodynamic aspect of a compression type heat pump （HP） is briefly described and special attention is given to investigation of condensing temperature influence on heat pump efficiency in heating mode, express...The thermodynamic aspect of a compression type heat pump （HP） is briefly described and special attention is given to investigation of condensing temperature influence on heat pump efficiency in heating mode, expressed by its coefficient of performance （COP）. Heat pumps are usually applied for the purposes of heating and cooling of energy efficient buildings where they have advantages in low-temperature systems, as it is well documented in the paper. The comparison of real thermodynamic processes with thermodynamically most favorable Camot＇s process is made. The results in the paper show that COP is diminishing with increasing of condensing temperature and also depends on real properties of working fluids. The impact of compressor efficiency for two real working media is also analyzed in the paper. There is significant diminishing of COP with diminishing of compressor efficiency. The intension of the paper is to help better understanding of this very effective and prosperous technology, and to encourage its development, production, and efficient application.展开更多
Accurate and reliable information about the temperature of the synchronous generators excitation winding hot spot is necessary to determine the dynamic limit caused by excitation winding overheating in the PQ diagram....Accurate and reliable information about the temperature of the synchronous generators excitation winding hot spot is necessary to determine the dynamic limit caused by excitation winding overheating in the PQ diagram. For good estimation of a position and the hot spot temperature it is decided to mount 19 temperature probes on one pole of the 6-pole, 400 kVA. 50 llz synchronous generator. Due to a large number of the probes and because the probes should be glued with the metal epoxy it was assumed that mounting of the probes will disrupt the temperature field of the excitation winding. To get the answer to this question the excitation winding resistance was measured betbre and after mounting the probes, in a hot and a cold state. Temperature rise can be estimated if the resistance ratio in the hot and the cold state is known. The paper also addresses the analysis of the measurement accuracy. The result shows that, there is no significant influence on the temperature when mounting the 19 temperature probes which covered 10% of the pole excitation winding surface.展开更多
This paper addresses some of the problems related to direct surface temperature measurement of a salient pole synchronous generator excitation winding in rotation. Excitation winding temperature is used for determinin...This paper addresses some of the problems related to direct surface temperature measurement of a salient pole synchronous generator excitation winding in rotation. Excitation winding temperature is used for determining the dynamic limit in a PQ diagram. The paper also addresses procedures of improving the accuracy of surface temperature measurement using the contact DS 18B20 digital temperature probes. The paper also provides experimental results of direct temperature measurement of the excitation winding surface conducted in the salient pole synchronous generator in the rotation.展开更多
Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for power...Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for powering induction furnaces, in audio technique. Spectrum of signals sampled by pulse amplitude modulation and output voltage spectrum of the converter with pulse width modulation have similar properties. Spectrum of signals sampled by pulse amplitude modulation contains a harmonic of frequency equal to the frequency of the modulating signal and the harmonics of frequencies equal to the sum of frequency of the modulating signal and multiples of the sampling frequency. The output voltage spectrum of the converter with bipolar pulse width modulation contains harmonic of frequency equal to the frequency of the modulating signal and harmonics of frequencies equal to sum of the frequency of the modulating signal and multiples of the frequency of the carrier signal. It also contains harmonics of frequencies equal to the sum of the multiples of the frequency of the modulating signal and the multiples of the carrier signal. The comparison analysis was carried out for the harmonics of the output voltage of the converter with bipolar pulse width modulation in time domain. The dependency of the amplitudes and frequency spectrum on the wave forms of the carrier signal and modulating signal was shown. Similarity of the output voltage spectrum of the converter and signal spectrum sampled by the pulse width modulation was also shown. Key words： Output voltage converter with bipolar pulse width modulation, spectral analysis, Fourier series, carrier signal, reference signal.展开更多
In this paper a fast output sampling （FOS） estimator is designed for estimation of state-space variables of DC-DC boost converter. Estimated state-space variables are output voltage of the converter and its first de...In this paper a fast output sampling （FOS） estimator is designed for estimation of state-space variables of DC-DC boost converter. Estimated state-space variables are output voltage of the converter and its first derivative, which are suitable for model reference adaptive controllers and sliding mode controllers design. Estimator is designed for operation in continuous and discontinuous conduction modes. The simulation results show that proposed FOS estimator provides good estimation of state-space variables despite the voltage ripple caused by high frequency switching in converter and disturbances （change of load and input voltage）.展开更多
Results of the 2007/08 survey ＂Energy--the present and the future＂ conducted on a population of 1439 students from Zagreb University have shown that after school and television, internet is the third major source of...Results of the 2007/08 survey ＂Energy--the present and the future＂ conducted on a population of 1439 students from Zagreb University have shown that after school and television, internet is the third major source of knowledge for the participants. Therefore, ＂NEMIS＂ web site （www.nemis.zpf.fer.hr） was launched at the end of the 2008. NEMIS is a Croatian acronym for ＂Nuclear Energy--Mysticism and Reality＂. The site was envisioned as a place where interested visitors could get information, prepared by experts, on all the issues relating to nuclear energy. The main objectives of the work reported in this paper are to present the structure of the NEMIS web site and to analyze the activity on the site during the last three years. Based on the performed analysis, future activities on the site are set and discussed.展开更多
We present an extensive study of the electronic properties and carrier transport in phosphorene nanoribbons （PNRs） with edge defects by using rigorous atomistic quantum transport simulations. This study reports on t...We present an extensive study of the electronic properties and carrier transport in phosphorene nanoribbons （PNRs） with edge defects by using rigorous atomistic quantum transport simulations. This study reports on the size- and defect-dependent scaling laws governing the transport gap, and the mean free path and carrier mobility in the PNRs of interest for future nanoelectronics applications. Our results indicate that PNRs with armchair edges （aPNRs） are more immune to defects than zig-zag PNRs （zPNRs）, while both PNR types exhibit superior immunity to defects relative to graphene nanoribbons （GNRs）. An investigation of the mean free path demonstrated that even in the case of a low defect density the transport in PNRs is diffusive, and the carrier mobility remains a meaningful transport parameter even in ultra-small PNRs. We found that the electron-hole mobility asymmetry （present in large-area phosphorene） is retained only in zPNRs for W 〉 4 nrn, while in other cases the asymmetry is smoothed out by edge defect scattering. Furthermore, we showed that aPNRs outperform both zPNRs and GNRs in terms of carrier mobility, and that PNRs generally offer a superior mobility-bandgap trade-off, relative to GNRs and monolayer MoS2. This work identifies PNRs as a promising material for the extremely scaled transistor channels in future posbsilicon electronic technology, and presents a persuasive argument for experimental work on nanostructured phosphorene.展开更多
A climate relevant and immediately available proven light water nuclear strategy with a potential to contribute essentially and timely to reduction of carbon dioxide emission to the year 2065 was assumed. The perspect...A climate relevant and immediately available proven light water nuclear strategy with a potential to contribute essentially and timely to reduction of carbon dioxide emission to the year 2065 was assumed. The perspective of fission energy after that year is considered. Two technologies with long term perspective which need no or small amounts of uranium, i.e. fast breeders and molten salt thorium reactors were singled out. The main technical and safety characteristics were considered. In both of these technologies it is essential to have starter nuclides as neither U238 nor Th232 are fissile. It was investigated whether plutonium from spent fuel of light water reactors generated to the year 2065 would be present in quantities sufficient to continue operation on the same or similar level in both technologies. However, taking into account operational safety, proliferation risks, and waste production preference must be given to thorium technology.展开更多
A threat of global warming should convince the public to accept a nuclear fission energy contribution to climate change mitigation, at least for the climate critical years up to 2065. The nuclear fission energy is ava...A threat of global warming should convince the public to accept a nuclear fission energy contribution to climate change mitigation, at least for the climate critical years up to 2065. The nuclear fission energy is available now, with proven reactors, such as advanced LWR （light water reactors）. Nuclear strategy in this paper outlines a proposal to replace all coal power plants （without carbon and capture storage system） with nuclear power plants in the period 2025-2065. Assuming once through advanced LWR technology, one would need nuclear capacity of 1,600 GW to replace coal power plants in that period. Corresponding reduction of emission would amount to 11.8 Gt of CO2. This energy strategy would reduce carbon emission by approximately 22% in the year 2065 and would be covered by projected uranium resources. An estimation of replacement costs showed that future carbon tax has a considerable potential to offset higher costs of nuclear replacement power.展开更多
Deep geothermal energy presents large untapped renewable energy potential could significantly contribute to global energy needs. However, developing geothermal projects involves uncertainties regarding adequate geothe...Deep geothermal energy presents large untapped renewable energy potential could significantly contribute to global energy needs. However, developing geothermal projects involves uncertainties regarding adequate geothermal brine extraction and huge costs related to preparation phases and consequently drilling and stimulation activities. Therefore, evaluating utilization alternatives of such projects is a complex decision-making problem effectively addressed using multi-criteria decision-making (MCDM) methods. This study introduces the MCDM method utilizing analytic hierarchy process (AHP) and weighted decision matrix (WDM) to assess different utilization alternatives (electricity generation, direct heat use and cogeneration). The AHP method determines the weight of each criterion and sub-criterion, while the WDM calculates the final project grade. Five criteria groups - technological, geological, economic, societal and environmental – comprising twenty-eight influencing factors were selected and used for the assessment of investment in Enhanced Geothermal Systems (EGS) projects. The AHP-WDM method was used by 38 experts from six categories: industry, educational institution, research and technology organization (RTO), small- and medium-sized enterprises (SME), local community and other. These diverse expert inputs aimed to capture varying perspectives and knowledge influence investment decisions in geothermal energy. The results were analysed accordingly. The results underscore the importance of incorporating different viewpoints to develop robust, credible, and effective investment strategies for EGS projects. Therefore, this method will contribute to more efficient EGS project development, enabling thus a greater penetration of the EGS into the market. Additionally, the proposed AHP-WDM method was implemented for a case study examining two locations. Locations were assessed and compared on scenario-based evaluation. The results confirmed the method's adequacy for assessing various end uses and comparing project feasibility across different locations.展开更多
Virtual power plant(VPP)aggregates large amounts of distributed energy and controllable loads.The comprehensive consideration of carbon emissions and electricity transactions has great significance in improving the VP...Virtual power plant(VPP)aggregates large amounts of distributed energy and controllable loads.The comprehensive consideration of carbon emissions and electricity transactions has great significance in improving the VPP operation’s economic efficiency.In this paper,the bidding strategy of the VPP by considering the carbon-electricity integration trading in an auxiliary service(AS)market is studied.First of all,the basic structure and operating features of the VPP are briefly introduced.Then,the bidding strategy model of carbon-electricity integration trading in an auxiliary service market is proposed and the corresponding objective function and the constraint conditions are also analyzed.Furthermore,the GAMS solver is utilized to give the optimal solution of the bidding strategy model.Finally,the effectiveness of the bidding strategy of a VPP based on the consideration of carbon-electricity integration trading is verified through simulation cases.展开更多
基金Supported by the European Regional Development Fund(DATACROSS),No.KK.01.1.1.01.0009.
文摘BACKGROUND The growing disparity between the rising demand for liver transplantation(LT)and the limited availability of donor organs has prompted a greater reliance on older liver grafts.Traditionally,utilizing livers from elderly donors has been associated with outcomes inferior to those achieved with grafts from younger donors.By accounting for additional risk factors,we hypothesize that the utili-zation of older liver grafts has a relatively minor impact on both patient survival and graft viability.AIM To evaluate the impact of donor age on LT outcomes using multivariate analysis and comparing young and elderly donor groups.METHODS In the period from April 2013 to December 2018,656 adult liver transplants were performed at the University Hospital Merkur.Several multivariate Cox propor-tional hazards models were developed to independently assess the significance of donor age.Donor age was treated as a continuous variable.The approach involved univariate and multivariate analysis,including variable selection and assessment of interactions and transformations.Additionally,to exemplify the similarity of using young and old donor liver grafts,the group of 87 recipients of elderly donor liver grafts(≥75 years)was compared to a group of 124 recipients of young liver grafts(≤45 years)from the dataset.Survival rates of the two groups were estimated using the Kaplan-Meier method and the log-rank test was used to test the differences between groups.RESULTS Using multivariate Cox analysis,we found no statistical significance in the role of donor age within the constructed models.Even when retained during the entire model development,the donor age's impact on survival remained insignificant and transformations and interactions yielded no substantial effects on survival.Consistent insigni-ficance and low coefficient values suggest that donor age does not impact patient survival in our dataset.Notably,there was no statistical evidence that the five developed models did not adhere to the proportional hazards assumption.When comparing donor age groups,transplantation using elderly grafts showed similar early graft function,similar graft(P=0.92),and patient survival rates(P=0.86),and no significant difference in the incidence of postoperative complications.CONCLUSION Our center's experience indicates that donor age does not play a significant role in patient survival,with elderly livers performing comparably to younger grafts when accounting for other risk factors.
基金supported in part by the European Regional Development Fund under Grant KK.01.1.1.01.0009(DATACROSS).
文摘This paper deals with reduction of losses in electric power distribution system through a dynamic reconfiguration case study of a grid in the city of Mostar,Bosnia and Herzegovina.The proposed solution is based on a nonlinear model predictive control algorithm which determines the optimal switching operations of the distribution system.The goal of the control algorithm is to find the optimal radial network topology which minimizes cumulative active power losses and maximizes voltages across the network while simultaneously satisfying all system constraints.The optimization results are validated through multiple simulations(using real power demand data collected for a few characteristic days during winter and summer)which demonstrate the efficiency and usefulness of the developed control algorithm in reducing the grid losses by up to 14%.
基金supported by the Key Scientific and Technological Projects(2024KJGG27)of Tianfu Yongxing Laboratorythe Experimental Platform Open Innovation Funding(209042025003)of Sichuan Energy Internet Research Institute,Tsinghua University.
文摘As the development of new power systems progresses,the inherent inertia of power systems continues to diminish.Centralized frequency regulation,which relies on rapid communication and real-time control,can enable inverter-based thermostatically controlled load(ITCL)clusters to provide virtual inertia support to the power grid.However,ITCL clusters exhibit significant discrete response characteristics,which precludes the direct integration of load-side inertia support into the synchronous unit side.To address this issue,this paper elaborates on the existing technical framework and analyzes the underlying causes of the problem.It proposes a timestamp allocation mechanism for ITCL cluster control instructions,ensuring that many ITCL terminals can be triggered at staggered times,thereby allowing the load cluster power to adhere to the inertia analog control law at any moment.Building on this foundation,the paper further examines the impact of the inertia response delay of ITCL clusters,which is based on centralized frequency regulation,on the stability of the power system.A design scheme for inertia analog control parameters is proposed,taking into account dual constraints,frequency stability and load cluster regulation capacity.Finally,the feasibility and applicability of the proposed mechanism and parameter design scheme are investigated through simulations conducted via MATLAB/Simulink.
文摘Various regulations, aimed at the protection of human beings and electrical equipment against possible adverse effects resulting from exposure to electromagnetic fields, have been issued in many countries. Most of them are based on safety guidelines published by international expert groups. In this paper, electric and magnetic fields are calculated in the vicinity of 25 kV traction line supplying railway traction systems. Calculation results are compared to exposure limits specified by safety guidelines and regulations. Possible countermeasures for reduction of electromagnetic fields are proposed. Also, this paper presents a method for calculation of the induced voltages to an underground gas pipeline from a neighbouring 25 kV electric traction overhead line in case of short circuit. Calculations are performed with EMTP-ATP software. Possible countermeasures for reduction of induced voltages are proposed.
基金supported by the University of Zagreb Research Grant.
文摘Mechanical stimulation of plants can be caused by various abiotic and biotic environmental factors.Apart from the negative consequences,it can also cause positive changes,such as acclimatization of plants to stress conditions.Therefore,it is necessary to study the physiological and biochemical mechanisms underlying the response of plants to mechanical stimulation.Our aim was to evaluate the response of model plant Arabidopsis thaliana to a moderate force of 5 N(newton)for 20 s,which could be compared with the pressure caused by animal movement and weather conditions such as heavy rain.Mechanically stimulated leaves were sampled 1 h after exposure and after a recovery period of 20 h.To study a possible systemic response,unstimulated leaves of treated plants were collected 20 h after exposure alongside the stimulated leaves from the same plants.The effect of stimulation was assessed by measuring oxidative stress parameters,antioxidant enzymes activity,total phenolics,and photosynthetic performance.Stimulated leaves showed increased lipid peroxidation 1 h after treatment and increased superoxide dismutase activity and phenolic oxidation rate after a 20-h recovery period.Considering photosynthetic performance after the 20-h recovery period,the effective quantum yield of the photosystem II was lower in the stimulated leaves,whereas photochemical quenching was lower in the unstimulated leaves of the treated plants.Nonphotochemical quenching was lower in the stimulated leaves 1 h after treatment.Our study suggested that plants sensed moderate force,but it did not induce pronounced change in metabolism or photosynthetic performance.Principal component analysis distinguished three groups–leaves of untreated plants,leaves analysed 1 h after stimulation,while stimulated and unstimulated leaves of treated plants analysed 20 h after treatment formed together the third group.Observed grouping of stimulated and unstimulated leaves of treated plants could indicate signal transduction from the stimulated to distant leaves,that is,a systemic response to a local application of mechanical stimuli.
文摘In this paper, a new control method for synchronous motor with excitation and damper windings is presented. It is based on one type of nonlinear control; feedback linearization control. To make a realization in the sense of electric drive, symmetricM space vector PWM （pulse width modulation） is applied. Estimation of damper winding currents via Lyapunov function for the whole estimated system is done. The aim of control is to make tracking system for rotor speed and square of stator flux. Simulation of motor starting to predefined operating points is done, and also maintaining these points during step change of load torque is obtained. Simulations give good results.
文摘Modeling of ancillary services market can be described as institutional arrangements for establishing ancillary services management in deregulated electricity market. Models of the national ancillary services markets are market models which offer transmission system operator efficient procurement of ancillary services, reducing the system management risk, more competitive electricity market, better utilization of production facilities and complete deregulation of electricity markets. This paper deals with current mode of ancillary services market and potential market development in Croatia. Described models are used for establishing market of ancillary services which should occur in parallel with the electricity market.
基金supported in part by the Croatian Science Foundation and the European Union through the European Social Fund under the Project of Flexibility of Converter-based Micro-grids—FLEXIBASE(PZS-2019-02-7747)in part by the European Structural and Investment Funds under KK.01.2.1.02.0066 Electric Vehicle Charging Station with Integrated Battery Storage.
文摘Electricity price forecasting plays a vital role inthe strategy decision making for almost all power marketparticipants. This article investigates statistical background andpotential relations between different power market products (e.g.day-ahead prices, intraday prices, etc.). Danish and Croatianpower markets are used for the purpose of the case studyto present the methods used in this article. First, Danish andCroatian power market structures are shortly explained to clarifythe context of the problem. The data collection and preprocessingmethods are described, followed by the core focus of the study:statistical analysis. In addition to the presented histograms ofrespective power market components, we examine interrelationships through statistical analysis, demonstrating significantcorrelations both numerically and graphically. Furthermore,price spreads are investigated as a logical next step of the noticedcorrelations. Our comparative analysis of Danish and Croatianmarket peculiarities reveals three key findings: i) statisticallysignificant relationships between specific market components,ii) distinct behavioral patterns among observed factors, and iii) anopen-access analytical tool with accompanying dataset for futureresearch. Finally, the findings of this article present to marketparticipants an efficient tool to adjust business strategies andincrease profit.
文摘The voltage uprating of existing overhead lines is an interesting solution for increasing the transmission of electricity, especially in areas where it is difficult to build new lines. If a line is uprated with minor changes of its design and without improvement of the grounding electrodes of towers, its lightning performance remains unchanged. The consequence is that the uprated line will have a lightning flashover rate very high compared to an overhead line of same nominal voltage but of standard design. One attractive solution to solve this problem is to use line arresters. The goal of this paper is to study the use of line arresters to achieve a satisfactory lightning performance of an overhead line uprated from 225 kV to 400 kV without major design modifications. In order to compare different strategies of line arrester installation the flashover rate is calculated based on a software able to launch automatically EMTP-RV. The software named LIPS has been developed under the cover of a partnership between Hydro-Quebec, RTE and EDF.
文摘The thermodynamic aspect of a compression type heat pump （HP） is briefly described and special attention is given to investigation of condensing temperature influence on heat pump efficiency in heating mode, expressed by its coefficient of performance （COP）. Heat pumps are usually applied for the purposes of heating and cooling of energy efficient buildings where they have advantages in low-temperature systems, as it is well documented in the paper. The comparison of real thermodynamic processes with thermodynamically most favorable Camot＇s process is made. The results in the paper show that COP is diminishing with increasing of condensing temperature and also depends on real properties of working fluids. The impact of compressor efficiency for two real working media is also analyzed in the paper. There is significant diminishing of COP with diminishing of compressor efficiency. The intension of the paper is to help better understanding of this very effective and prosperous technology, and to encourage its development, production, and efficient application.
文摘Accurate and reliable information about the temperature of the synchronous generators excitation winding hot spot is necessary to determine the dynamic limit caused by excitation winding overheating in the PQ diagram. For good estimation of a position and the hot spot temperature it is decided to mount 19 temperature probes on one pole of the 6-pole, 400 kVA. 50 llz synchronous generator. Due to a large number of the probes and because the probes should be glued with the metal epoxy it was assumed that mounting of the probes will disrupt the temperature field of the excitation winding. To get the answer to this question the excitation winding resistance was measured betbre and after mounting the probes, in a hot and a cold state. Temperature rise can be estimated if the resistance ratio in the hot and the cold state is known. The paper also addresses the analysis of the measurement accuracy. The result shows that, there is no significant influence on the temperature when mounting the 19 temperature probes which covered 10% of the pole excitation winding surface.
文摘This paper addresses some of the problems related to direct surface temperature measurement of a salient pole synchronous generator excitation winding in rotation. Excitation winding temperature is used for determining the dynamic limit in a PQ diagram. The paper also addresses procedures of improving the accuracy of surface temperature measurement using the contact DS 18B20 digital temperature probes. The paper also provides experimental results of direct temperature measurement of the excitation winding surface conducted in the salient pole synchronous generator in the rotation.
文摘Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for powering induction furnaces, in audio technique. Spectrum of signals sampled by pulse amplitude modulation and output voltage spectrum of the converter with pulse width modulation have similar properties. Spectrum of signals sampled by pulse amplitude modulation contains a harmonic of frequency equal to the frequency of the modulating signal and the harmonics of frequencies equal to the sum of frequency of the modulating signal and multiples of the sampling frequency. The output voltage spectrum of the converter with bipolar pulse width modulation contains harmonic of frequency equal to the frequency of the modulating signal and harmonics of frequencies equal to sum of the frequency of the modulating signal and multiples of the frequency of the carrier signal. It also contains harmonics of frequencies equal to the sum of the multiples of the frequency of the modulating signal and the multiples of the carrier signal. The comparison analysis was carried out for the harmonics of the output voltage of the converter with bipolar pulse width modulation in time domain. The dependency of the amplitudes and frequency spectrum on the wave forms of the carrier signal and modulating signal was shown. Similarity of the output voltage spectrum of the converter and signal spectrum sampled by the pulse width modulation was also shown. Key words： Output voltage converter with bipolar pulse width modulation, spectral analysis, Fourier series, carrier signal, reference signal.
文摘In this paper a fast output sampling （FOS） estimator is designed for estimation of state-space variables of DC-DC boost converter. Estimated state-space variables are output voltage of the converter and its first derivative, which are suitable for model reference adaptive controllers and sliding mode controllers design. Estimator is designed for operation in continuous and discontinuous conduction modes. The simulation results show that proposed FOS estimator provides good estimation of state-space variables despite the voltage ripple caused by high frequency switching in converter and disturbances （change of load and input voltage）.
文摘Results of the 2007/08 survey ＂Energy--the present and the future＂ conducted on a population of 1439 students from Zagreb University have shown that after school and television, internet is the third major source of knowledge for the participants. Therefore, ＂NEMIS＂ web site （www.nemis.zpf.fer.hr） was launched at the end of the 2008. NEMIS is a Croatian acronym for ＂Nuclear Energy--Mysticism and Reality＂. The site was envisioned as a place where interested visitors could get information, prepared by experts, on all the issues relating to nuclear energy. The main objectives of the work reported in this paper are to present the structure of the NEMIS web site and to analyze the activity on the site during the last three years. Based on the performed analysis, future activities on the site are set and discussed.
文摘We present an extensive study of the electronic properties and carrier transport in phosphorene nanoribbons （PNRs） with edge defects by using rigorous atomistic quantum transport simulations. This study reports on the size- and defect-dependent scaling laws governing the transport gap, and the mean free path and carrier mobility in the PNRs of interest for future nanoelectronics applications. Our results indicate that PNRs with armchair edges （aPNRs） are more immune to defects than zig-zag PNRs （zPNRs）, while both PNR types exhibit superior immunity to defects relative to graphene nanoribbons （GNRs）. An investigation of the mean free path demonstrated that even in the case of a low defect density the transport in PNRs is diffusive, and the carrier mobility remains a meaningful transport parameter even in ultra-small PNRs. We found that the electron-hole mobility asymmetry （present in large-area phosphorene） is retained only in zPNRs for W 〉 4 nrn, while in other cases the asymmetry is smoothed out by edge defect scattering. Furthermore, we showed that aPNRs outperform both zPNRs and GNRs in terms of carrier mobility, and that PNRs generally offer a superior mobility-bandgap trade-off, relative to GNRs and monolayer MoS2. This work identifies PNRs as a promising material for the extremely scaled transistor channels in future posbsilicon electronic technology, and presents a persuasive argument for experimental work on nanostructured phosphorene.
文摘A climate relevant and immediately available proven light water nuclear strategy with a potential to contribute essentially and timely to reduction of carbon dioxide emission to the year 2065 was assumed. The perspective of fission energy after that year is considered. Two technologies with long term perspective which need no or small amounts of uranium, i.e. fast breeders and molten salt thorium reactors were singled out. The main technical and safety characteristics were considered. In both of these technologies it is essential to have starter nuclides as neither U238 nor Th232 are fissile. It was investigated whether plutonium from spent fuel of light water reactors generated to the year 2065 would be present in quantities sufficient to continue operation on the same or similar level in both technologies. However, taking into account operational safety, proliferation risks, and waste production preference must be given to thorium technology.
文摘A threat of global warming should convince the public to accept a nuclear fission energy contribution to climate change mitigation, at least for the climate critical years up to 2065. The nuclear fission energy is available now, with proven reactors, such as advanced LWR （light water reactors）. Nuclear strategy in this paper outlines a proposal to replace all coal power plants （without carbon and capture storage system） with nuclear power plants in the period 2025-2065. Assuming once through advanced LWR technology, one would need nuclear capacity of 1,600 GW to replace coal power plants in that period. Corresponding reduction of emission would amount to 11.8 Gt of CO2. This energy strategy would reduce carbon emission by approximately 22% in the year 2065 and would be covered by projected uranium resources. An estimation of replacement costs showed that future carbon tax has a considerable potential to offset higher costs of nuclear replacement power.
基金funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 792037support from Department of Energy and Power Systems of University of Zagreb Faculty of Electrical Engineering and Computing.
文摘Deep geothermal energy presents large untapped renewable energy potential could significantly contribute to global energy needs. However, developing geothermal projects involves uncertainties regarding adequate geothermal brine extraction and huge costs related to preparation phases and consequently drilling and stimulation activities. Therefore, evaluating utilization alternatives of such projects is a complex decision-making problem effectively addressed using multi-criteria decision-making (MCDM) methods. This study introduces the MCDM method utilizing analytic hierarchy process (AHP) and weighted decision matrix (WDM) to assess different utilization alternatives (electricity generation, direct heat use and cogeneration). The AHP method determines the weight of each criterion and sub-criterion, while the WDM calculates the final project grade. Five criteria groups - technological, geological, economic, societal and environmental – comprising twenty-eight influencing factors were selected and used for the assessment of investment in Enhanced Geothermal Systems (EGS) projects. The AHP-WDM method was used by 38 experts from six categories: industry, educational institution, research and technology organization (RTO), small- and medium-sized enterprises (SME), local community and other. These diverse expert inputs aimed to capture varying perspectives and knowledge influence investment decisions in geothermal energy. The results were analysed accordingly. The results underscore the importance of incorporating different viewpoints to develop robust, credible, and effective investment strategies for EGS projects. Therefore, this method will contribute to more efficient EGS project development, enabling thus a greater penetration of the EGS into the market. Additionally, the proposed AHP-WDM method was implemented for a case study examining two locations. Locations were assessed and compared on scenario-based evaluation. The results confirmed the method's adequacy for assessing various end uses and comparing project feasibility across different locations.
文摘Virtual power plant(VPP)aggregates large amounts of distributed energy and controllable loads.The comprehensive consideration of carbon emissions and electricity transactions has great significance in improving the VPP operation’s economic efficiency.In this paper,the bidding strategy of the VPP by considering the carbon-electricity integration trading in an auxiliary service(AS)market is studied.First of all,the basic structure and operating features of the VPP are briefly introduced.Then,the bidding strategy model of carbon-electricity integration trading in an auxiliary service market is proposed and the corresponding objective function and the constraint conditions are also analyzed.Furthermore,the GAMS solver is utilized to give the optimal solution of the bidding strategy model.Finally,the effectiveness of the bidding strategy of a VPP based on the consideration of carbon-electricity integration trading is verified through simulation cases.
