| 1. |
- Akinbomi, Julius, et al.
(författare)
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Evaluation of Fermentative Hydrogen Production from Single and Mixed Fruit Wastes
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:5, s. 4253-4272
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Tidskriftsartikel (refereegranskat)abstract
- The economic viability of employing dark fermentative hydrogen from wholefruit wastes as a green alternative to fossil fuels is limited by low hydrogen yield due to theinhibitory effect of some metabolites in the fermentation medium. In exploring means ofincreasing hydrogen production from fruit wastes, including orange, apple, banana, grapeand melon, the present study assessed the hydrogen production potential of singly-fermentedfruits as compared to the fermentation of mixed fruits. The fruit feedstock was subjected tovarying hydraulic retention times (HRTs) in a continuous fermentation process at 55 °C for47 days. The weight distributions of the first, second and third fruit mixtures were 70%,50% and 20% orange share, respectively, while the residual weight was shared equally bythe other fruits. The results indicated that there was an improvement in cumulativehydrogen yield from all of the feedstock when the HRT was five days. Based on the resultsobtained, apple as a single fruit and a fruit mixture with 20% orange share have the mostimproved cumulative hydrogen yields of 504 (29.5% of theoretical yield) and 513 mL/gvolatile solid (VS) (30% of theoretical yield ), respectively, when compared to other fruits.
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| 2. |
- Dyachuk, Eduard, et al.
(författare)
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Measurements of the Aerodynamic Normal Forces on a 12-kW Straight-Bladed Vertical Axis Wind Turbine
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:8
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Tidskriftsartikel (refereegranskat)abstract
- The knowledge of unsteady forces is necessary when designing vertical axis wind turbines (VAWTs). Measurement data for turbines operating at an open site are still very limited. The data obtained from wind tunnels or towing tanks can be used, but have limited applicability when designing large-scale VAWTs. This study presents experimental data on the normal forces of a 12-kW straight-bladed VAWT operated at an open site north of Uppsala, Sweden. The normal forces are measured with four single-axis load cells. The data are obtained for a wide range of tip speed ratios: from 1.7 to 4.6. The behavior of the normal forces is analyzed. The presented data can be used in validations of aerodynamic models and the mechanical design for VAWTs.
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| 3. |
- Forslund, Johan, 1985-, et al.
(författare)
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Experimental Results of a DC Bus Voltage Level Control for a Load-Controlled Marine Current Energy Converter
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:5, s. 4572-4586
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates three load control methods for a marine current energy converter using a vertical axis current turbine (VACT) mounted on a permanent magnet synchronous generator (PMSG). The three cases are; a fixed AC load, a fixed pulse width modulated (PWM) DC load and DC bus voltage control of a DC load. Experimental results show that the DC bus voltage control reduces the variations of rotational speed by a factor of 3.5 at the cost of slightly increased losses in the generator and transmission lines. For all three cases, the tip speed ratio can be kept close to the expected . The power coefficient is estimated to be 0.36 at ; however, for all three cases, the average extracted power was about \%. A maximum power point tracking (MPPT) system, with or without water velocity measurement, could increase the average extracted power.
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| 4. |
- Gong, Mei, 1967-, et al.
(författare)
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Exergy Analysis of the Supply of Energy and Material Resources in the Swedish Society
- 2016
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Ingår i: Energies. - Basel : M D P I AG. - 1996-1073. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- Exergy is applied to the Swedish energy supply system for the period 1970–2013. Exergy flow diagrams for the systems of electricity and district heating as well as for the total supply system of energy and material resources for 2012 are presented. The share of renewable use has increased in both electricity and district heat production. The resource use is discussed in four sectors: residential and service, transportation, industry and agriculture. The resource use is also analyzed with respect to exergy efficiency and renewable share. The total exergy input of energy and material resources amounts to about 2700 PJ of which about 530 PJ was used for final consumption in 2012. The results are also compared with similar studies. Even though the share of renewable resource use has increased from 42% in 1980 to 47% in 2012, poor efficiency is still occurring in transportation, space heating, and food production. A strong dependence on fossil and nuclear fuels also implies a serious lack of sustainability. A more exergy efficient technology and a higher renewable energy share are needed in order to become a more sustainable society.
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| 5. |
- Hui, Zhang, et al.
(författare)
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Limitations and constraints of eddy-current loss models for interior permanent-magnet motors with fractional-slot concentrated windings
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes and compares models for predicting average magnet losses in interior permanent-magnet motors with fractional-slot concentrated windings due to harmonics in the armature reaction (assuming sinusoidal phase currents). Particularly, loss models adopting different formulations and solutions to the Helmholtz equation to solve for the eddy currents are compared to a simpler model relying on an assumed eddy-current distribution. Boundaries in terms of magnet dimensions and angular frequency are identified (numerically and using an identified approximate analytical expression) to aid the machine designer whether the more simple loss model is applicable or not. The assumption of a uniform flux-density variation (used in the loss models) is also investigated for the case of V-shaped and straight interior permanent magnets. Finally, predicted volumetric loss densities are exemplified for combinations of slot and pole numbers common in automotive applications.
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| 6. |
- Loncarski, Jelena, 1983-, et al.
(författare)
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Comparison of Output Current Ripple in Single and Dual Three-Phase Inverters for Electric Vehicle Motor Drives
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:5, s. 3832-3848
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Tidskriftsartikel (refereegranskat)abstract
- The standard solution for the traction system in battery powered electric vehicles (EVs) is a two-level (2L) inverter feeding a three-phase motor. A simple and effective way to achieve a three-level (3L) inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding connection of standard three-phase ac motors. The 3L inverter solution can be usefully adopted in EVs since it combines several benefits such as current ripple reduction, increment of phase motor voltage with limited voltage ratings of the two battery banks, improvement in system reliability, etc. The reduction in current ripple amplitude is particularly relevant since it is a source of electromagnetic interference and audio noise from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single-2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole modulation range of the inverter, and the theoretical results are verified with experimental tests carried out by an inverter-motor drive prototype.
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| 7. |
- Mahmood, Farhan, et al.
(författare)
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Extracting Steady State Components from Synchrophasor Data Using Kalman Filters
- 2016
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Data from phasor measurement units (PMUs) may be exploited to provide steady state information to the applications which require it. As PMU measurements may contain errors and missing data, the paper presents the application of a Kalman Filter technique for real-time data processing. PMU data captures the power system’s response at different time-scales, which are generated by different types of power system events; the presented Kalman Filter methods have been applied to extract the steady state components of PMU measurements that can be fed to steady state applications. Two KF-based methods have been proposed, i.e., a windowing-based KF method and “the modified KF”. Both methods are capable of reducing noise, compensating for missing data and filtering outliers from input PMU signals. A comparison of proposed methods has been carried out using the PMU data generated from a hardware-in-the-loop (HIL) experimental setup. In addition, a performance analysis of the proposed methods is performed using an evaluation metric.
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| 8. |
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| 9. |
- Wegener, Moritz, et al.
(författare)
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3E-Analysis of a Bio-Solar CCHP System for theAndaman Islands, India—A Case Study
- 2019
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Ingår i: Energies. - Basel, Switzerland : MDPI. - 1996-1073. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Energy services are especially expensive on remote islands due to longer and more unstable fuel supply chains. In this paper, different renewable energy systems utilizing locally available biomass and solar energy are proposed as alternatives for a hotel resort on Neil Island, India. Based on local demand data, commercial information, and scientific literature, four cases are modelled with the simulation software HOMER and their economic, energetic, as well as ecological (3E) performances are compared. The robustness of each case configuration is tested with a sensitivity analysis. The results show that a biomass-based, solar-assisted combined cooling, heating, and power (CCHP) system offers an economic saving potential of more than 500,000 USD over twenty years and could decrease CO2 emissions by 365 t per year. When not applying CCHP measures, system performance is significantly worsened. A solar and battery-assisted diesel generator system shows similar economic outcomes as the CCHP system but worse ecological performance. Implementing the biomass-based CCHP system could improve the ecological footprint of the island, substantially decrease expenditure for the hotel owner, and generate a new source of income for surrounding farmers through biomass selling.
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| 10. |
- Yang, Weijia, et al.
(författare)
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A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:9, s. 10260-10275
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a mathematical model of hydro power units, especially the governor system model for different operating conditions, based on the basic version of the software TOPSYS. The mathematical model consists of eight turbine equations, one generator equation, and one governor equation, which are solved for ten unknown variables. The generator and governor equations, which are different under various operating conditions, are presented and discussed in detail. All the essential non-linear factors in the governor system (dead-zone, saturation, rate limiting, and backlash) are also considered. Case studies are conducted based on one Swedish hydro power plant (HPP) and three Chinese plants. The simulation and on-site measurements are compared for start-up, no-load operation, normal operation, and load rejection in different control modes (frequency, opening, and power feedback). The main error in each simulation is also discussed in detail. As a result, the model application is proved trustworthy for simulating different physical quantities of the unit (e.g., guide vane opening, active power, rotation speed, and pressures at volute and draft tube). The model has already been applied effectively in consultant analyses and scientific studies.
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