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Weichao Zhang,Xiangwu Yan 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.3
In converter-based AC microgrids, the frequency-droop is widely applied. As a considerable share of installed capacity is replaced by renewable generation, the virtual synchronous machine (VSM) algorithm is presented to address stability issues caused by low-inertia converter interfaces. Recently, droop control loops are also modifed to improve stability. The VSM and the frequency-droop are both derived from the property imitation of synchronous generators (SGs) while researched independently. In this paper, by simplifcations in the steady state, the expression of the inertia emulation of the VSM algorithm based on the second-order SG model is linearized as a frst-order ordinary diferential equation. In frequency-droop loops, as the instantaneous power components are commonly passed through a low-pass flter for disturbance rejection, the system function of the droop control can also be transformed into a frst-order ordinary diferential equation, which is equivalent to that of the VSM under certain conditions. In terms of the inertia constant, the swing equation is normalized under per unit representation. By the same simplifcation in the VSM linearization, the equivalence between the linearized VSM and the SG is also demonstrated. Therefore, the equivalence among SGs, the VSM, and the frequency-droop are summarized, which provides insights for coordinative control of power converters integrated into current SG dominating power systems. For a specifc synchronous generator, the equivalence conditions are verifed by simulation.
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Surendran, Subramani,Shanmugapriya, Sathyanarayanan,Zhu, Pei,Yan, Chaoyi,Vignesh, Ramasamy Hari,Lee, Yun Sung,Zhang, Xiangwu,Selvan, Ramakrishnan Kalai Elsevier 2019 ELECTROCHIMICA ACTA Vol.296 No.-
<P><B>Abstract</B></P> <P>In this work, a facile single-step hydrothermal technique is used to prepare a spherically concomitant foamy NiCoP as positrode for supercapatteries. Similarly, the nitrogen-doped carbon nanofibers are prepared by simple electrospinning technique to use as negatrode. The prepared materials are raptly examined through primary studies for both energy conversion and storage applications. Fascinatingly, NiCoP electrode encourages oxygen evolution reaction, and the carbon nanofiber electrode emboldens hydrogen evolution reaction with the minimum overpotential of 257 mV and 160 mV, respectively. In addition, a supercapattery is designed and operated at a full voltage window of 1.6 V using the fusion of carbon nanofiber as the negatrode and the cutting-edge NiCoP as the positrode, which presents a superior energy (56 Wh kg<SUP>−1</SUP>) and an improved power density (5333 W kg<SUP>−1</SUP>) with a long cyclic stability (5000 cycles). Finally, the fabricated supercapattery device is used to power the constructed hybrid water electrolyser that requisites a low cell voltage of 1.71 V to afford a current density of 10 mA cm<SUP>−2</SUP>. Overall, the prepared electrodes reveal its superiority of handling the multifunctional challenges for both water electrolyzer and supercapatteries.</P>
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Selvan, Ramakrishnan Kalai,Zhu, Pei,Yan, Chaoi,Zhu, Jiadeng,Dirican, Mahmut,Shanmugavani, A.,Lee, Yun Sung,Zhang, Xiangwu Elsevier 2018 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.513 No.-
<P><B>Abstract</B></P> <P>Biomass-derived porous carbon has been considered as a promising sulfur host material for lithium-sulfur batteries because of its high conductive nature and large porosity. The present study explored biomass-derived porous carbon as polysulfide reservoir to modify the surface of glass fiber (GF) separator. Two different carbons were prepared from Oak Tree fruit shells by carbonization with and without KOH activation. The KOH activated porous carbon (AC) provides a much higher surface area (796 m<SUP>2</SUP> g<SUP>−1</SUP>) than pyrolized carbon (PC) (334 m<SUP>2</SUP> g<SUP>−1</SUP>). The <I>R</I> factor value, calculated from the X-ray diffraction pattern, revealed that the activated porous carbon contains more single-layer sheets with a lower degree of graphitization. Raman spectra also confirmed the presence of sp<SUP>3</SUP>-hybridized carbon in the activated carbon structure. The COH functional group was identified through X-ray photoelectron spectroscopy for the polysulfide capture. Simple and straightforward coating of biomass-derived porous carbon onto the GF separator led to an improved electrochemical performance in Li-S cells. The Li-S cell assembled with porous carbon modified GF separator (ACGF) demonstrated an initial capacity of 1324 mAh g<SUP>−1</SUP> at 0.2 C, which was 875 mAh g<SUP>−1</SUP> for uncoated GF separator (calculated based on the 2nd cycle). Charge transfer resistance (R<SUB>ct</SUB>) values further confirmed the high ionic conductivity nature of porous carbon modified separators. Overall, the biomass-derived activated porous carbon can be considered as a promising alternative material for the polysulfide inhibition in Li–S batteries.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Robust Unit Commitment with Virtual Synchronous Renewables
Zhang Wei-Chao,Sheng Wanxing,Duan Qing,Sha Guanglin,Zhang Yao,Huang Hanyan,Yan Xiangwu 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.6
With the increasing penetration of renewable energy sources and the consequent displacement of synchronous generators, the frequency stability of power systems deteriorates since RESs cannot participate in active power and frequency control. By emulating the outer characteristics of SGs and deloading a controllable margin, RESs can also keep headroom and provide frequency responses. This paper focuses on incorporating virtual synchronous renewables into the unit commitment to optimize the joint scheduling of energy production and spinning reserves. First, based on the interval representation of renewable uncertainty, the renewable output is decomposed into the stochastic and dispatchable portions. The dispatchable portion, defi ned as VSRs, can keep deterministic regulation headroom and participate in power balance regulation. Second, a robust security-constrained unit commitment model is proposed to achieve optimal scheduling in face of multiple uncertainties. The fl exibility of the pumped-storage hydro station is also considered. Third, the solution strategies which linearize the nonlinear terms in the objective function and constraints are introduced. Finally, the correctness and eff ectiveness of the robust unit commitment model are tested and verifi ed in the modifi ed 39-bus system.
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