•This paper proposes a distance relay in time domain based on the R-L differential-equation algorithm which is suitable for wind power integration system. Especially, this paper proposes a solution ...during zero-voltage fault conditions.•The instantaneous value equivalent model of DFIG is established and characteristics of the transient EMF of DFIG after the fault are also analyzed, which shows that the EMF of DFIG has the inertia within a short time after the faults.•The memory voltage drop and actual voltage drop on equivalent impedance from relay location to back-side and opposite-side equivalent power sources are introduced in this paper to detect the fault direction.•Simulation results shows that the proposed fault direction method is easy to implement and can detect the fault direction within a short data window.
This paper proposes a distance relay in time domain based on the R-L differential-equation algorithm which is suitable for wind power integration system. However, the conventional R-L differential-equation algorithm cannot detect the correct fault direction if the fault point is very close to the relay location. Therefore, this paper mainly focuses on this problematic conditions and proposes a solution. The instantaneous value equivalent model of DFIG is established and characteristics of the transient electromotive force (EMF) of DFIG after the faults are also analyzed, which shows that the EMF of DFIG has the inertia within a short time after the faults. The memory voltage drop and actual voltage drop on equivalent impedance from relay location to back-side and opposite-side equivalent power sources are introduced in this paper to detect the fault direction. Meanwhile, the characteristics of the memory voltage drop and actual voltage drop under forward and reverse fault conditions are deduced, respectively. With the differentiated correlation coefficient between the memory voltage drop and actual voltage drop under different fault conditions (forward and reverse fault), the fault direction identification criterion is formed accordingly. Finally, an extensive performance evaluation using PSCAD/EMTDC simulation corroborates the effectiveness of the proposed method. Results show that the proposed method can detect the fault direction quickly with high sensitivity during zero-voltage fault conditions.
The Li-rich and Mn-based material xLi2MnO3·(1–x)LiMO2 (M = Ni, Co, and Mn) is regarded as one of the new generations of cathode materials for Li-ion batteries due to its high energy density, low ...cost, and less toxicity. However, there still exist some drawbacks such as its high initial irreversible capacity, capacity/voltage fading, poor rate capability, and so forth, which seriously limit its large-scale commercial applications. In this paper, the Ta–Mo codoped Li1.2Ni0.13Co0.13Mn0.54O2 with high energy density is prepared via a coprecipitation method, followed by a solid–state reaction. The synthetic mechanism and technology, the effect of charge–discharge methods, the bulk doping and the surface structure design on the structure, morphology, and electrochemical performances of the Li1.2Ni0.13Co0.13Mn0.54O2 cathode are systematically investigated. The results show that Ta5+ and Mo6+ mainly occupy the Li site and transition-metal site, respectively. Both the appropriate Ta and Ta–Mo doping are conductive to increase the Mn3+ concentration and suppress the generation of Li/Ni mixing and the oxygen defects. The Ta–Mo codoped cathode sample can deliver 243.2 mA h·g–1 at 1 C under 2.0–4.8 V, retaining 80% capacity retention after 240 cycles, and decay 1.584 mV per cycle in 250 cycles. The capacity retention can be still maintained to 80% after 410 cycles over 2.0–4.4 V, and the average voltage fading rate is 0.714 mV per cycle in 500 cycles. Compared with the pristine, the capacity and voltage fading of Ta–Mo codoped materials are effectively suppressed, which are mainly ascribed to the fact that the highly valence Ta5+ and Mo6+ that entered into the crystal lattice are favorable for maintaining the charge balance, and the strong bond energies of Ta–O and Mo–O can help to maintain the crystal structure and relieve the corrosion from the electrolyte during the charging/discharging process.
The 9LiFePO4·Li3V2(PO4)3/C composite cathode material is synthesized by spray-drying and post-calcining method based on citrate. The composite is well crystallized, and contains olivine-type LiFePO4 ...and monoclinic Li3V2(PO4)3 phases. The composite material exhibits spherical particles in the size of 0.5–5μm, and shows a high tap-density of 1.64gcm−3. The electrochemical performance of the material is excellent. At 5C and 10C rates, the sample exhibits the initial discharge capacities of 135.3 and 109.6mAhg−1 and capacity retentions of 96.2% and 93.7% after 100cycles, respectively. The homogenous mixing of the LiFePO4 and fast ion conductor additive Li3V2(PO4)3, which is resulted from spray-drying, can be the reason why the composite has good rate capability.
The 9LiFePO4·Li3V2(PO4)3/C composite cathode material exhibits spherical particles in the size of 0.5–5μm. The small particles fill in the gaps between large particles, which are helpful to improve the tap-density of material. The tap-density of the as-prepared powders is as high as 1.64gcm−3, which is remarkably higher than those of irregularly-shaped or nano-sized LiFePO4, Li3V2(PO4)3 and xLiFePO4·yLi3V2(PO4)3. Display omitted
► Spherical 9LiFePO4·Li3V2(PO4)3/C is prepared by spray-drying and calcining method. ► The composite shows a high tap-density of 1.64gcm−3. ► The composite shows excellent rate capability and cycle performance.
Platinum (Pt)-based heterogeneous catalysts are promising for electrocatalytic hydrogen evolution reaction (HER); considerable efforts, however, are devoted to reducing Pt usage by maximizing ...catalytic efficiency due to its high price and scarcity. Herein, we report Pt single-atom and cluster catalyst anchored on functionalized multiwall carbon nanotubes (Pt/f-MWCNTs) by photodeposition. The Pt/f-MWCNTs catalyst with Pt loading of 0.323 wt% exhibits exceptionally high activity and decent stability for HER in acid condition, whose mass activity is 74.7 times higher than that of state-of-the-art commercial Pt/C catalyst at an overpotential of 50 mV vs. RHE. This work paves a novel way to realize controllable synthesis of Pt-based catalysts with ultrahigh activity and long-term stability for electrocatalytic HER.
F-MWCNTs play triple roles of photoelectron generator, supporter, and conductor to uniformly disperse Pt single atoms and clusters, solving the problems of electron conductivity, active site density, intrinsic activity and stability simultaneously, whose mass activity is 74.7 times higher than that of 20 wt% Pt/C catalyst. Display omitted
•Single atoms and clusters dispersion state of Pt anchored on the surface of MWCNTs.•Mass efficiency is twice the highest performance of Pt-based HER catalysts reported so far.•Pt loading is as low as 0.323 wt%.
Iron phosphide as anode material for lithium ion batteries (LIBs) attracts a lot of attention because of large theoretical capacity. Nevertheless, the inherent disadvantages of huge volume expansion ...and low electrical conductivity inhibit its further application. In this work, FeP@C/reduced graphene oxide (rGO) anode material with unique polyhedral structure was synthesized by a simple solvothermal and low temperature phosphiding method. Metal organic framework MIL-101(Fe) was used as the precursor and anchored on the surface of graphene oxide (GO). The organic ligand of MIL-101(Fe) was transformed to polyhedral carbon skeleton, which combined with GO to form a three-dimensional conductive network that provides efficient channels for electrons and ions, and attenuates volume expansion during the insertion/extraction of lithium ions, and avoids partial pulverization and improves cycle stability. The optimized FeP@C/rGO anode material showed a discharge capacity of 414.7 mAh g−1 at the current density of 8 A g−1, and reached a capacity of 949.7 mAh g−1 after 100 cycles at 0.1 A g−1; even cycled at the current density of 1 A g−1, it provided a capacity of 737.7 mAh g−1 after 450 cycles. In virtue of ingenious microstructure design and structural optimization, FeP@C/rGO exhibited outstanding electrochemical properties in LIBs.
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•Metal organic framework MIL-101(Fe) was used as the precursor.•A stable three-dimensional conductive network was formed in the composite.•FeP@C composite was anchored on rGO sheets.•The conductivity of ions and electrons of FeP@C/rGO were obviously improved.•FeP@C/rGO composite showed excellent electrochemical properties.
Nanosized spherical LiFePO4/C composite was synthesized from nanosized spherical FePO4·2H2O, Li2C2O4, aluminum oxide, titanium oxide, oxalic acid, and sucrose by binary sintering process. The phases ...and morphologies of LiFePO4/C were characterized using SEM, TEM, CV, EIS, EDS, and EDX as well as charging and discharging measurements. The results showed that the as-prepared LiFePO4/C composite with good conductive webs from nanosized spherical FePO4·2H2O exhibits excellent electrochemical performances, delivering an initial discharge capacity of 161.7 mAh·g−1 at a 0.1 C rate, 152.4 mAh·g−1 at a 1 C rate and 131.7 mAh·g−1 at a 5 C rate, and the capacity retention of 99.1%, 98.7%, and 95.8%, respectively, after 50 cycles. Meanwhile, the high and low temperature performance is excellent for 18650 battery, maintaining capacity retention of 101.7%, 95.0%, 88.3%, and 79.3% at 55°C, 0°C, −10°C, and −20°C by comparison withthat of room temperature (25°C) at the 0.5 C rate over a voltage range of 2.2 V to 3.6 V, respectively.
Nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) with layered crystal structure is regarded as a promising positive electrode material for lithium-ion batteries due to its relatively high specific capacity, ...outstanding rate performance, and remarkable cycle stability. Nevertheless, the challenges such as capacity attenuation and voltage decline have seriously hindered its large-scale applications. Significantly, the thermodynamic instability of the H3 phase inevitably triggers undesirable cationic disordering and oxygen evolution reaction, which further induce a series of problems. Herein, we have systematically reviewed the research progress of NCM811 from the perspective of chemical stabilization of lattice structure and kinetic hindrance of cathode-electrolyte interface, and summarized the relationship between performance fading mechanism and corresponding strategies. Moreover, new ideas for further modification of ameliorating crystal structure stability and further improvement of NCM811 electrochemical properties are provided, which shines a light on the development of Ni-rich materials in LIBs.
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•The adaptive cycle engine is an evolutional concept of variable cycle engine.•The advantages of the adaptive cycle engine depend on the matching principles.•The equilibrium running principles of the ...adaptive cycle engine are deduced.•A nonlinear component-based adaptive cycle engine performance model is built.•The application of the equilibrium running principles based on model is proposed.
As an evolutional concept of variable cycle engine, the adaptive cycle engine draws widely attention with high expectations. It combines a variable geometry schedule and component matching principles to demonstrate its advantages such as avoiding severe inlet spillage drag and the wide variable cycle characteristics. Thus, this paper aims at equilibrium running principle analysis on an adaptive cycle engine at variable operating modes, deriving the equilibrium running equations of an adaptive cycle engine for the first time, and exploring the physical essence of components matching principle on the basis of a newly developed nonlinear component-based adaptive cycle engine performance model. It uncovers the physical essence of components matching relationships and provides mathematical derivation of equilibrium running principles which lay theoretical foundation of the variable geometries modulation schedule and overall performance optimization on an adaptive cycle engine.
MoS3 nanoparticles as well as MoS3 on graphene and multiwalled carbon nanotubes were synthesized by a solvothermal method and the prepared samples were employed as cathode material in zinc-ion ...batteries. With distinct advantages like low price, high safety, no environmental pollution, and high power, these batteries have promising properties for future generation battery systems. The microstructure and electrochemical properties of the prepared composite cathodes were investigated by XRD, TG, and XPS. The MoS3/MWCNTs have a discharge specific capacity of 368 mAh g−1 at the current density of 500 mA g−1 and stable cycling performance, and the discharge specific capacity of MoS3/MWCNTs can still reach 321 mAh g−1 at the current density of 1 A g−1. Making use of the outstanding mechanical, electrochemical and electronic properties of MWCNTs, the coated composite of MoS3 nanoparticles on MWCNTs can significantly improve the electrical conductivity of the materials, and enhance the charge-discharge capacity and high rate characteristics of MoS3 as aqueous zinc-ion cathode material.
•MoS3, MoS3-G, and MoS3-MWCNT were synthesized by a simple solvothermal method.•Carbon-doped MoS3 were uniform growthed on the surface of graphene and MWCNTs.•MoS3-G, and MoS3-MWCNT show a more disordered and higher specific surface structure.•Disordered structure promote the transfer of zinc ions and enhance the charge-discharge capacity.
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