Summary
In this article, a nondissipative equalization scheme is proposed to reduce the inconsistency of series connected lithium‐ion batteries. An improved Buck‐Boost equalization circuit is designed, in which the series connected batteries can form a circular energy loop, equalization speed is improved, and modularization is facilitated. This article use voltage and state of charge (SOC) together as equalization variables according to the characteristics of open‐circuit voltage (OCV)‐SOC curve of lithium‐ion battery. The second‐order RC equivalent circuit model and back propagation neural network are used to estimate the SOC of lithium‐ion battery. Fuzzy logic control (FLC) is used to adjust the equalization current dynamically to reduce equalization time and improve efficiency. Simulation results show that the traditional Buck‐Boost equalization circuit and the improved Buck‐Boost equalization circuit are compared, and the equalization time of the latter is reduced by 34%. Compared with mean‐difference algorithm, the equalization time of FLC is decreased by 49% and the energy efficiency is improved by 4.88% under static, charging and discharging conditions. In addition, the proposed equalization scheme reduces the maximum SOC deviation to 0.39%, effectively reducing the inconsistency of batteries.
Xanthan gum (XG) is one of the widely used biopolymers in oilfield development. It has low cost and will not pollute the environment. However, its limited temperature and salt tolerance restricts its application in high temperature and high salt reservoirs. An environmentally friendly hydrophobic associative polymer was prepared by grafting long-chain alkyl groups onto xanthan gum through an etherification reaction for enhanced oil recovery (EOR). The hydrophobically modified xanthan gum (MXG) was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Due to the hydrophobic association, MXG had excellent thickening, rheological properties, antiaging, temperature, and salt resistance properties. In the 30 g/L NaCl solutions, the viscosity of MXG (335 mPa s) was about 3 times that of XG (115.3 mPa s) at 65 °C. Whether in a high-salt solution (20 g/L NaCl) or reservoir injection water (mineralization of water is 7542 mg/L), modified xanthan gum can show good antiaging properties. The polymer flooding experiments showed that EOR of MXG is 25%, 7% higher than that of XG. The macroscopic mechanism of MXG flooding was studied. In summary, MXG has a wide range of applications in EOR.
Bidirectional DC-DC converter is potentially used for an energy charging or discharging device; however, the converter displays highly non-linear characteristics since its internal system parameter varies depending on the operation mode and the disturbance engagement. To cope with the nonlinearity, a bidirectional DC-DC converter based on time delay control (TDC) is designed and validated for lithium-ion battery application.
Control-oriented lithium-ion battery-fed bidirectional DC-DC converter model is constructed with MATLAB/Simulink. Converter PWM duty ratio control technique based on TDC is subsequently designed and assembled for lithium-ion battery operation regulation.Moreover, to validate the efficacy of the present approach, proportional-integral (PI) control is implemented and its results are compared with TDC results. The experimental implementation is performed with National Instrument (NI) LabVIEW, whose results show excellent bidirectional converter performance.
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