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Yinxiao Zhu,Huiqing Wen,Guanying Chu,Xingshuo Li 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
With consideration of instability in environmental conditions, the increasing installation of maximum power point (MPP) operational Photovoltaic systems (PVSs) injects an unstable power generation to the grid (such as, overloading). Aiming to reduce the instable generation during continuous peak power generation, an adaptive constant power generation (CPG) algorithm is proposed in this paper. With the proposed control, the system can operate at MPP tracking (MPPT) mode or CPG mode with the detection from system operators. When the operation mode is detected, the control will operate with self-judgment including regulate the initial mode during CPG with a simple MPP initial MPP estimation. With the estimation of MPP and internal step-size regulation, the response speed, an important factor in variable environments, can be improved. In order to evaluate the proposed scheme, simulation and experiment in different condition, such as changing irradiation and changing limit power level are carried out.
Zhan, Yinxiao,Park, Tae Seon Elsevier 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.97 No.-
<P><B>Abstract</B></P> <P>Oscillatory flows and heat transfer characteristics in a channel with inclined plates have been numerically investigated. For the fully developed channel flow of 10 ⩽ Re ⩽ 800 , the inclined plates as a vortex generator are installed at the upper wall. To examine the effects of inclined plates on flow bifurcation and attendant heat transfer rates, unsteady simulations are performed for various plate conditions. The resulting flows are classified into three vortical structures of recirculation bubble (RB), standing vortex (SV), and traveling vortices (TV) depending on the Reynolds number and geometrical conditions. The variation of flow pattern is closely related to the spectral characteristics of steady state, periodic state, and quasi-periodic state. Based on these flow patterns and unsteady features, the transition scenario is proposed with increasing the plate angle. The flow is evolved from the steady state to the periodic and quasi-periodic state, and the frequency-locking phenomenon is observed for specific Reynolds numbers at a certain range of plate angle. In addition, the heat transfer enhancement is discussed with flow patterns and unsteady characteristics. The Nusselt numbers continuously increases from the steady state of RB to the periodic state of SV, while their variations are discontinuous when the periodic state of SV is changed into the quasi-periodic state of TV. The flow analyses show that these discontinuities are related to the supercritical Hopf bifurcation and the additional appearances of fundamental frequency. Also, the frequency-locking state before the development of quasi-periodic state with multiple frequencies brings about a jump increase of heat transfer. The disturbed flows by the inclined plates exhibit the logarithmic variation and Nusselt number correlation similar to the transition flow.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oscillatory flows are characterized by three vortical structures. </LI> <LI> The discontinuous variation of <I>Nu</I> is strongly related to the quasi-periodic state. </LI> <LI> The frequency-locking phenomenon depends on the flow development with multiple frequencies. </LI> <LI> The disturbed flows exhibit Nusselt number correlations similar to the transition flow. </LI> </UL> </P>
Spindle Spinel CoFeCoO4 Microparticles/rGO as an Oxygen Reduction and Oxygen Evolution Catalyst
Bowen Wang,Nian Tao,Junchen Liu,Hao Wang,Yinxiao Du,Hujiang Yang,Yonggang Wang,Kai Huang,Ru Zhang,Ming Lei 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.4
The representative spinel-type materials AB2O4 (both A and B are transition metals) electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been investigated and significant improvements have been achieved in the activity and durability for ORR and OER in the alkaline solution. But CoFeCoO4 was not explored widely like ZnCo2O4 (or NiCo2O4) as the ORR electrocatalyst for its relatively complicated atomic site occupation. CoFeCoO4 has a typical cubic spinel structure with Co2+ in the tetrahedron and Co3+ and Fe3+ in the octahedron. A mixture of Co3+ and Fe3+ in the B site makes the oxide have a wider overlap between transition metal 3d orbit and O 2p orbit, which can lead to an effective charge transfer in the rate-determining steps of ORR process and then enhance the ORR activity. The high electronic conductivity and specific surface area of rGO can accelerate charger transfer and provide more catalytic sites, which would contribute to a faster ORR process. In this work, the porous spindle CoFeCoO4 microparticles which were synthesized by hydrothermal technology, were assembled on the rGO surface to obtain the CoFeCoO4/rGO composite, which exhibited enhanced ORR activity and catalytic stability comparable to that of Pt/C. On the other hand, the OER catalytic activity of the prepared samples was also studied to explore the potential of CoFeCoO4/rGO as a bifunctional oxygen catalyst.