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- 저자 : Weidong Zheng (검색결과 5 건)
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Miao Shui,Weidong Zheng,Jie Shu,Qingchun Wang,Shan Gao,Dan Xu,Liangliang Cheng,Lin Feng,Yuanlong Ren 한국물리학회 2013 Current Applied Physics Vol.13 No.3
Lithium-ion battery cathode material Li1þxV3O8 is synthesized by a citric acid/tartaric acid assisted sol egel method and sintered at 350 C, 450 C and 550 C for 3 h for the formation of Li1þxV3O8 phase. The synthesized samples were fully characterized by FTIR, TG/DTA, XRD, SEM, EIS and chargeedischarge tests. Li1þxV3O8 material synthesized by tartaric acid assisted route and sintered at 450 C for 3 h shows best electro-chemical performance. It shows a high initial capacity of 249 mAh g1 and still reserves a discharge capacity of 260 mAh g1 after 50 cycles. Moreover, in the case of tartaric assisted products, no capacity decadence is observed in 50 cycles. XRD together with TG/DTA measurements reveal that compared with citric acid assisted products, the adoption of tartaric acid as chelating agent effectively lowers the crystallization temperature of amorphous Li1þxV3O8. Therefore, precursors obtained by tartaric acid route calcinated at 450 C for 3 h exhibit lower crystallinity and smaller grain size, which contributes to the better electrochemical performance of the cathode electrodes. From EIS measurements, the bulk resistance is reduced, which favors the intercalation and de-intercalation of lithium ions while cycling.
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Time-domain simulations of transient response in LiFePO4 cathode lithium ion batteries
Xiaoping Xu,Miao Shui,Weidong Zheng,Jie Shu,Lei Hui,Linxia Xu,Liangliang Cheng,Lin Feng,Yuanlong Ren 한국물리학회 2014 Current Applied Physics Vol.14 No.5
The time domain transients of batteries comprised of LiFePO4 cathode material exhibit large nonlinearity with the increasing discharging rates. Hence, the calculated overpotential transients match the experimental determined well only when the discharging current is low enough. The results of electrochemical impedance spectra at different OCV level indicate that the change of the parameters of equivalent circuit or even the circuit architecture are probably responsible for the large discrepancy between the predicted and the measured transient profiles. By taking the change of equivalent circuit model at high discharging current into consideration, we successfully simulate the time domain transients of polarization within the entire discharging current range. Also with the help of circuit analysis, the contribution of the ohmic resistance, charge transfer impedance and solid-state diffusion impedance to total polarization has been differentiated as a function of discharging time.
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Min Hong,Huanhai Xin,Weidong Liu,Qian Xu,Taiying Zheng,Deqiang Gan 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.2
The introduction of renewable energy sources into the AC grid can change and weaken the strength of the grid, which will in turn affect the stability and robustness of the doubly-fed induction generator (DFIG) wind farm. When integrated with weak grids, the DFIG wind turbine with vector power control often suffers from poor performance and robustness, while the DFIG wind turbine with synchronized control provides better stability. This paper investigates the critical short circuit ratios of DFIG wind turbine with vector power control and synchronized control, to analyze the stability boundary of the DFIG wind turbine. Frequency domain methods based on sensitivity and complementary sensitivity of transfer matrix are used to investigate the stability boundary conditions. The critical capacity of DFIG wind farm with conventional vector power control at a certain point of common coupling (PCC) is obtained and is further increased by employing synchronized control properly. The stability boundary is validated by electromagnetic transient simulation of an offshore wind farm connected to a real regional grid.
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Hong, Min,Xin, Huanhai,Liu, Weidong,Xu, Qian,Zheng, Taiying,Gan, Deqiang The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.2
The introduction of renewable energy sources into the AC grid can change and weaken the strength of the grid, which will in turn affect the stability and robustness of the doubly-fed induction generator (DFIG) wind farm. When integrated with weak grids, the DFIG wind turbine with vector power control often suffers from poor performance and robustness, while the DFIG wind turbine with synchronized control provides better stability. This paper investigates the critical short circuit ratios of DFIG wind turbine with vector power control and synchronized control, to analyze the stability boundary of the DFIG wind turbine. Frequency domain methods based on sensitivity and complementary sensitivity of transfer matrix are used to investigate the stability boundary conditions. The critical capacity of DFIG wind farm with conventional vector power control at a certain point of common coupling (PCC) is obtained and is further increased by employing synchronized control properly. The stability boundary is validated by electromagnetic transient simulation of an offshore wind farm connected to a real regional grid.
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Chao Chen,Shu Chen,Miao Shui,Xiaoping Xu,Weidong Zheng,Lin Feng,Jie Shu,Yuanlong Ren 한국물리학회 2015 Current Applied Physics Vol.15 No.2
Cathode material 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 is successfully synthesized by citrate acid assisted sol -gel method and shows pretty good electro-chemical performance. To elucidate the electro-chemical reactions and charge carrier transportation kinetics in the charge-discharge process, series of electrochemical impedance spectra for the first and the second charge process are measured on multiple given state of charges. The rapid augmentation of resistance to electronic conduction and ionic conduction within the voltage range 4.45-4.6 V where the removal of Li2O from Li2MnO3 component takes place gives us more evidence about the complicated “structurally integrated” feature of this material. The relatively large span of the arc responsible for electronic conduction and the extremely large Mn3+ related charge transfer resistance at the beginning of the second charging indicate that after one complete charge-discharge cycle, Li2MnO3 and LiNi0.5Mn0.5O2 domains still reserve its original structure and will keep its structure for the followed cycles.
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