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Abstract The accidental outages of generating units are increasing in power systems, which can bring huge power shortage suddenly and lead to severe system oscillations. The secure operation of power systems sometimes cannot be guaranteed only by regulating traditional generating units, due to the rapid regulation requirement of making up for power shortage. To address this issue, this paper proposes using emergency demand response (DR) to provide contingency reserve capacities by adjusting the power consumption of flexible loads (FLs). Firstly, in order to analyze the dynamic regulation process of power systems in accidental outages, the power system model in faulty condition is reconstructed to obtain the regulation power from well-running generators. On this basis, FLs are modelled and integrated into the novel reconstructed power system model to be as an alternative method of making up for the fast regulation capacities. Considering that the inevitable communication time-delay probably leads to the slowdown of response speed and endangers the system security, an adaptive time-delay control (ATDC) scheme is proposed and integrated into the control process of aggregated FLs. In this manner, the regulation speed of FLs can be accelerated, the control precision of response capacities can be improved, and the power system frequency deviations caused by time-delay can be decreased. Finally, the proposed models and methods are verified by numerical studies. The results in the test system show that the frequency deviations can be decreased effectively from −0.3276 Hz to −0.1337 Hz in accidental outages by using the ATDC scheme of FLs.

Abstract Modern transportation requires advanced powertrain systems to reduce the production of greenhouse gas CO2. Partially premixed combustion (PPC) is one of the most promising methods to achieve low emission and low fuel consumption of internal combustion engines. The present paper evaluated the effects of the calibration parameters on the efficiency and emissions of a multi-cylinder engine using PPC during stable operations, and the performance of the engine during transient operations. The peak gross indicated efficiency of 51.5% and the peak net indicated efficiency of 48.7% were achieved under stable operating conditions. The transient results also demonstrate an average net indicated efficiency of 47.5%. The nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbon (HC) conform with the Euro VI emission legislation in the case of most transient operations except some low load points.

Artículos en revistas Islands are facing considerable challenges in meeting their energy needs in a sustainable, affordable and reliable way. The present paper develops an integrated approach to economically assess initiatives that can transform island power systems into smart ones. Single and multi-action initiatives fostering the deployment of renewable energy sources (RES), energy storage systems (ESS), demand-side management (DSM), and electric vehicle (EV) are considered. An hourly unit commitment on a weekly basis is proposed to assess the impact of the initiatives on the system operation costs of five prototype island power systems, which have been identified by applying clustering techniques to a set of sixty islands power systems. The different investment costs of the initiatives are accounted for determining their corresponding internal rate of return (IRR) through their lifetime. The economic assessment of single and multi-action initiatives for five prototype islands representing sixty island power systems quantifies which initiatives are most suitable for which type of island power system. The assessment shows that islands of different sizes and features require different initiatives. Larger islands tend to DSM initiatives, whereas smaller islands tend to RES initiatives. Multi-action initiatives achieve highest system operation cost reduction, whereas single action initiatives yield to highest IRR. info:eu-repo/semantics/publishedVersion

This paper proposes a simple behavioural model for photovoltaic modules. This model can be used to characterise current–voltage and power–voltage outputs of photovoltaic modules as a function of solar module temperature and solar radiation intensity. Such a model cannot only serve as a tool to study the I–V curve and its maximum power point characteristics but also to design photovoltaic power systems and power converters used for PV applications. It can also be used for performance rating. This model has first been developed to study the maximum power point characteristics by exploring the existing similarity between the photovoltaic module I–V characteristic and the step response of a first-order system. It has the advantage to use only parameters that are available on the data sheet. To construct the proposed model, measured I–V curves at different working conditions (solar radiation intensity and ambient temperature) were used, then other I–V characteristics corresponding to different working conditions have been used to validate it. The obtained results show a high degree of correspondence between the real outdoor measured I–V characteristics and those given by the developed model.

Abstract Average Sherwood numbers based on experimental results were determined for a sublimating naphthalene cylinder subjected to a crossflow of air. The range of Reynolds numbers for all tested cylinders was from 4700 to 141 000. The nominal diameters of the tested cylinders were 25·4, 50·8 and 76·2 mm (i.e. 1, 2 and 3 inches respectively). The average uncertainty of the reported data was estimated to be ±9·7%. The experiments were performed using an open-loop wind tunnel. The test cylinders were cast using molten naphthalene and the test method involved naphthalene sublimation. The resultant expression is given in dimensionless form.

Abstract In this paper, different particle sizes of kaolin were employed to incorporate paraffin via vacuum impregnation method. The paraffin/kaolin composites were characterized by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimeter (DSC) and Thermogravimetry (TG). The results showed that the paraffin/kaolin composite with the largest particle size of kaolin (K4) has the highest thermal conductivity (0.413 W/(m K) at 20 °C) among the diverse composites. The latent heat capacity of paraffin/K4 is 119.49 J/g and the phase change temperature is 62.4 °C. In addition, the thermal properties and thermal conductivities of paraffin/K4 with different mass fraction of K4 (0–60%) were investigated. The thermal conductivities of the composites were explained in microcosmic field. The phonon mean free path determines the thermal conductivity, and it can be significantly affected by temperature and the contact surface area. The leaks, thermal storage and release properties of pure paraffin and paraffin/kaolin composites were investigated and the composites presented good thermal stabilities.

High penetration of distributed generation (DG) in secondary (low-voltage) distribution networks (SDN) is one of the primary challenges of network operators. Particularly in radial LV networks, renewable intermittency and bidirectional power flow may cause critical problems such as under/over voltages, line overloads and high energy losses. System operators usually consider the worst-case scenarios for the assessment of the impacts of new integrations and usually they prefer passive methods to mitigate the negative effects. However, analysis of daily operation with high resolution, stochastic DG supply and residential demand profiles can reveal both the occurrence rates and the severities of the critical events, while paving the way for the development of active mitigation methods. This study is focused on detailed daily operation analysis of SDNs with renewable-based microgrids. Seasonal DG output and residential demand profiles throughout a day were simulated using a virtual test bed to investigate the critical cases.

Abstract The hydrothermal liquefaction (HTL) of microalgae produces water-soluble biocrude (WSB) and water-insoluble biocrude (WISB) simultaneously. The effects of heterogeneous catalysts (i.e. Pt/C, Ru/C, and Pt/C + Ru/C) on the properties of the two types of biocrudes derived from Chlorella HTL were explored for the first time. The results show that the addition of catalyst (Pt/C, Ru/C, or Pt/C + Ru/C) and/or the increase of residence time (from 10 to 30 min) could decrease the WSB fraction in total biocrude (WSB + WISB) mainly due to the improvement of the WISB yield. The catalytic effects on the WISB yield primarily occurred at the low algae loading (i.e., 1:10 of algae/water) condition, and there was a certain synergetic catalytic effect between Pt/C and Ru/C at this condition. The catalytic effect of Pt/C on the yields of WISB and total biocrude reduced as residence time increased. At the HTL conditions of 350 °C, 0.3 MPa H2, and 1:5 of algae/water for 30 min, Pt/C and Ru/C separately led to WSB and WISB with the highest C (63.57 and 74.16 wt%), H (7.34 and 8.44 wt%) contents and the lowest N (12.19 and 7.06 wt%), O (14.06 and 9.15 wt%) contents, and the highest HHVs (29.73 and 35.60 MJ/kg). The WISB produced with Pt/C mainly consisted of amides, hydrocarbons, organic acids and phenols. Pt/C could promote the cracking of high-molecular-weight compounds in WSB to form more low-boiling-point compounds.