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  • Articles  (409)
  • Copernicus  (235)
  • Institute of Physics  (113)
  • Institute of Physics (IOP)  (61)
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  • Articles  (409)
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  • 1
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    Design of a high-power density energy system for solar powered aircraft (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-10-31
    Description: Maximum energy utilization and high-power density are critical to solar powered aircraft energy system. SiC devices have the advantages of high frequency and high temperature and it is very promising in the aspect of the development of high temperature and high-power density converter. This paper designed a 1.2 kW SiC based power controller using interleaved two-switch buck-boost converter, analyzed the working process of the converter, put forward small signal model and discussed three mode control strategy, and achieved smooth switching among all modes and maximum utilization of power energy. Experimental results demonstrate that the converter module has the power density of 2.4 kW/kg.
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 2
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    Improved control strategy for PI-R current of DFIG considering voltage and current harmonics compensation (2016)
    Institute of Physics (IOP)
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    Publication Date: 2016-09-27
    Description: With the rapid development of wind power generation, the related research of wind power control and integration issues has attracted much attention, and the focus of the research are shifting away from the ideal power grid environment to the actual power grid environment. As the main stream wind turbine generator, a doubly-fed induction generator (DFIG) is connected to the power grid directly by its stator, so it is particularly sensitive to the power grid. This paper studies the improvement of DFIG control technology in the power grid harmonic environment. Based on the DFIG dynamic model considering the power grid harmonic environment, this paper introduces the shortcomings of the common control strategy of DFIG, and puts forward the enhanced method. The decoupling control of the system is realized by compensating the coupling between the rotor harmonic voltage and harmonic current, improving the control performance. In addition, the simulation experiments on PSCAD/EMTDC are ca...
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  • 3
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    Effect of unbalanced magnetic pull and hydraulic seal force on the vibration of large rotor-bearing systems (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: The influence of unbalanced magnetic pull (UMP) and hydraulic seal force on the vibration of large rotor-bearing systems is studied. The UMP caused by rotor eccentricity imposes important effects on rotating machinery, especially for large generators such as water turbine generator sets, because these machines operate above their first critical speed in some instances and are supported by oil film bearings. A magnetic stiffness matrix for studying the effects of the UMP is proposed. The magnetic stiffness matrix can be generated by decomposing the expression of air gap magnetic field energy. Two vibration models are constructed using the Lagrange equation. The difference between the two models lies in the boundary support condition: one has rigid support and the other has elastic bearing support. The influence of the magnetic stiffness and elastic support on the critical speed of the rotor is studied using Lyapunov nonlinear vibration stability theory. The vibration amplitude of...
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  • 4
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    Estimating soil total nitrogen contents from visible/near-infrared reflectance based on successive projections algorithm (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-03-19
    Description: The Visible/near-infrared reflectance (Vis/NIR) spectroscopy combined with multiple regression methods have been employed to assess various soil properties quantitatively. However, useless or irrelevant information in some bands worsen the performances of the calibrated models. Successive projections algorithm (SPA) is an effective technique for selecting informative variables, and its application potential in estimating soil contents using visible/near-infrared reflectance (Vis/NIR) spectroscopy has not been explored. This paper aimed to explore the effect of SPA combined with support vector machine regression (SVMR) on soil total nitrogen (TN) contents estimation using Vis/NIR spectroscopy. For this purpose, SPA-SVMR was compared with full spectrum based SVMR (FS-SVMR) for soil total nitrogen (TN) estimation, respectively. The results showed that the SPA-SVMR model (R 2 v = 0.58, RMSEV = 0.364) performed better than the FS-SVMR model (R 2 ...
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  • 5
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    The impact of climate change on summer maize phenology in the northwest plain of Shandong province under the IPCC SRES A1B scenario (2014)
    Institute of Physics (IOP)
    Details
    Publication Date: 2014-03-19
    Description: Climate change will affect agricultural production. Combining a climate model and a crop growth model furnishes a good approach for analyzing this effect quantitatively. The purpose of this study is to analyze the effect of climate change on summer maize phenology in northwest Shandong province under the A1B climate scenario using a regional climate model and the CERES-Maize growth model. The results showed that the temperature would increase significantly during the maize growth season in the study region, that the increased temperature would shorten the maize growth stage and result in a potential yield loss using the current cultivar, and that it is critical to breed a heat-resistant and late-maturing cultivar to maintain the yield.
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  • 6
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    Effect of gas volume fraction on vortex motion in hydraulic turbine (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-07-31
    Description: In order to analyze the vortex motion in the flow channel of the hydraulic turbine impeller during the gas volume fraction change. Now, the pump with a specific speed of 55.7 is chosen as hydraulic turbine. On the basis of considering the gas compressibility, to take numerical calculation on the model under different flow rates and different gas volume fraction, to analyze the influence of gas volume fraction on vortex motion law in the impeller flow channel. Findings: When the flow rate is small, the relative velocity distribution in the impeller flow channel is uneven, the velocity field is chaotic, and there are obvious vortices, with the increase of the gas volume fraction, the vortices in the impeller flow channel gradually move to the inlet direction of the blade; With the increase of the flow rate, the flow in the channel of the hydraulic turbine impeller is unstable. Both the pressure surface and the suction surface of the blade appear vortices, the vortex region in the ...
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  • 7
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    Effect of gas volume fraction on the vortex motion within the oil-gas multiphase pump (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-07-31
    Description: In order to research the regular pattern of the vortex within the oil-gas multiphase pump with the gas volume fraction changes, the standard K-epsilon turbulence model is selected, the gas-liquid two-phase flow field within the multiphase pump is calculated by the CFD software under the different gas volume fraction, the regular pattern of the vortex motion within the multiphase pump is analyzed under the different gas volume fraction. The results show that, from the impeller hub to the rim, the vortex in the guide vane is gradually become smaller, the vortex within the impeller is gradually obvious, and with the increase of the gas volume fraction, the flow separation, the backflow and the vortex phenomenon within the impeller and the guide vane are gradually increased. It is also found that the flow separation has a greater influence on the turbulent dissipation within the whole flow field, that is, the more serious the area of off flow, the greater the energy loss. The result...
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  • 8
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    Study on the distribution regularity of gas volume in multiphase pump (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-07-31
    Description: In order to reduce the phase separation, air plug and turbulence vortex in the multiphase pump. The two-fluid model and the standard k- ε turbulence model are selected, the distribution regularity of gas phase volume within the multiphase pump is researched using the CFD software about air-liquid two-phase under the different working conditions. The results of the study showed that the gas phase gathers at the rim when the gas-liquid two-phase enter into the impeller inlet, and the gas phase is gradually increased at the rim with the increase of the flow rate, the gas is concentrated in the hub at the second half of the impeller, and the most serious aggregation is the small flow rate condition. When the flow is constant, the gas obviously increases in the guide vane hub with the increase of the gas volume fraction. With the increase of the gas volume fraction, the uniformity of the gas phase in the circumferential direction is deteriorated in the inlet and the middle of impelle...
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  • 9
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    One-step synthesis of nitrogen and chlorine co-doped fluorescent carbon nanodots for the sensitive detection of Ag + (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-10-12
    Description: Nitrogen and chlorine co-doped fluorescent carbon nanodots (CDs) were prepared using a facile and eco-friendly solvothermal process in which N-Chlorosuccinimide(NCS) was used as a carbon source. The resulting CDs were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared and X-ray photoelectron spectroscopy (XPS). It shows emission of blue light at 410 nm when excited at 340 nm. High quantum yield of 21.7% and good biocompatibility were also observed. Importantly, the fluorescence intensity of CDs was selectively quenched after addition of Ag + . Based upon the aforementioned phenomenon, a new fluorescent biosensor for the detection of Ag + was proposed. The linear range and detection limit was 5-70 μM and 1.06 μM, respectively. Eventually, these superior properties demonstrated that the CDs have promising applications in the field of environmental a...
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  • 10
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    Optimal scheduling modelling for wind power accommodation with compressed air energy storage and price-based demand response (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-10-31
    Description: Nowadays, price-based demand response (PDR) programs with compressed air energy storage (CAES) systems have been rapidly developed in China for wind power generation propagation. Based on this development trend, an optimal scheduling model considering thermal power units (TUs), wind power plants, PDR mechanisms and CAES plants is studied in this paper. Considering the factors of uncertainties in PDR, wind power output and electricity demand, a fuzzy power system optimal scheduling model for minimizing the sum of TUs operation cost, CAES plants cost and wind curtailment penalty is proposed. According to the fuzzy scheduling theory, the fuzzy chance constrains are converted into their clear equivalent forms. The simulation study is implemented with using the data from the Huntorf CAES plant, which can verify the feasibility and effectiveness of the optimal scheduling model. It is found that the use of CAES and PDR results in 11.1% reduction in thermal power units operation cost an...
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