Fast Supplementary Voltage Control Strategy to Mitigate Catastrophic Trip-off Risk of Wind Turbines

Yin Lifu,Liu Yongcheng,Wang Zhuxiu,Xu Ang,Li Zhengtian,Lin Xiangning,Feng Zhongnan,Zhuo Yixin 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.6

There exists such a risk that Magnetic Control Reactor (MCR) type Static Var Compensator (SVC), which is widely used in wind farms, still outputs excessive reactive power after fault removal in the wind farm due to the slow regulating speed of MCR, leading to catastrophic trip-off problem of wind turbine. For the purpose of overcoming the shortage of MCR-type SVC on regulating speed and eff ectively controlling the transient over-voltage level of wind farm due to fault removal, an novel fast supplementary voltage control strategy for MCR-type SVC based on decision tree algorithm is proposed. The over-voltage level and trip-off risk of each wind turbine after fault removal is predicted by the proposed dynamic voltage security decision tree system. According to the predictions, appropriate capacitor banks are shed to lower the risk of wind turbine trip-off due to overvoltage, resulting from reactive power over-compensation. It can be proven with case studies that the proposed strategy is capable of reducing the risk of over-voltage in wind farms, accompanied by the excellent computational effi ciency.

Robust Fractional-order PID Tuning Method for a Plant with an Uncertain Parameter

Xu Li,Lifu Gao 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.3

The robust design of fractional-order proportional-integral-differential (FOPID) controllers for controlled plants with uncertainty is a popular research topic. The well-studied “flat phase”condition is effective for the gain variation but not for variations in other parameters. This paper addresses the problem of tuning a robust FOPID controller for a plant with a known structure and an uncertain parameter (a coefficient or order in the plant transfer function). The method is based on preserving the phase margin of the open-loop system when the plant parametervaries around the nominal value. First, the partial derivatives of the gain crossover frequency with respect to the plant parameters are calculated. Then, the partial derivatives of the phase margin with respect to the plant parameters are obtained as the robust performance indexes. In addition, the equations needed to compute FOPID parameters that meet the specifications in the frequency domain are obtained and used as nonlinear constraints. Finally, the FOPID parameters can be obtained by optimizing the robust performance indexes under these constraints. Simulation experiments are carried out on examples with different types of uncertain parameters to verify the effectiveness of the tuning method. The results show that the requirements are fulfilled and that the system with the proposed FOPID controller is stable and robust to variations in the uncertain parameters. Comparisons clearly show that the controllers designed by the proposed method provide relatively robust performance.

A Simple Frequency-domain Tuning Method of Fractional-order PID Controllers for Fractional-order Delay Systems

Xu Li,Lifu Gao 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.7

The fractional-order proportional-integral-derivative (FOPID) controller is an improvement over the traditional PID controller. However, most existing methods of FOPID controller design are complex and not suitable for practical application. This paper presents a simple and efficient design method of FOPID controllers for fractional-order controlled plants with time delays. The method is based on four frequency-domain specifications—namely, gain crossover frequency, phase margin, phase crossover frequency and gain margin. The implicit nonlinear equations related to the controller parameters are formulated using these specifications. To simplify the mathematical calculation, the explicit equations of the controller parameters are analytically derived. Then, the FOPID controller parameters can be adjusted in a graphical manner. Two fractional-order plus time-delay plants are considered as simulation examples. The results show that the design requirements are successfully met and superior control performance is obtained via the proposed tuning method.

Fuzzy Fractional Order Sliding Mode Control for Automatic Clutch of Vehicle AMT

Yingchun Long,Lifu Li 보안공학연구지원센터 2015 International Journal of Smart Home Vol.9 No.2

The automatic clutch driving system of vehicle automated manual transmission (AMT) is a typical nonlinear system. A fast and accurate position control is difficult to achieve because of the nonlinearity of the load changes caused by the clutch diaphragm spring, the cushion spring, and other nonlinear components and because of the uncertainty of the load changes caused by the cushion spring deformation in the clutch engagement process at varying temperatures on the friction surface. In this paper, based on the theory of fractional calculus and traditional sliding mode control, the method of fuzzy fractional order sliding mode control (FFOSMC) is proposed for clutch control. By selecting the fractional order sliding surface, the laws of control are designed; and self-tuning of the switch gain is realized with the fuzzy controller. Theoretical analysis and numerical simulation revealed that compared with the traditional fuzzy integer order sliding mode controller, FFOSMC achieves better dynamic performance in position control and better robustness against load disturbance and other uncertain factors.

Compound Control of Sliding-Model Variable Structure and Fractional Order PIλDμ for Automatic Clutch of Vehicle AMT

Yingchun Long,Lifu Li 보안공학연구지원센터 2014 International Journal of Control and Automation Vol.7 No.5

Carbon Nanotube Paper as Anode for Flexible Lithium-Ion Battery

Xiaogang Sun,Zhenhong Liu,Neng Li,Xiaoyong Wu,Yanyan Nie,Zhipeng Pang,Lifu Yue,Hao Tang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.11

In this investigation, multiwalled carbon nanotube (MWCNT) paper consists of MWCNTs and cellulose was fabricated by traditional paper-making method. It was applied directly as negative electrode in flexible lithium ion battery to replace ordinary electrode which is combined with anode material and current collector. The electrochemical performances of the as-produced MWCNT paper (AMP) and carbonized MWCNT paper (CMP) were evaluated in this study. The morphology and structure of the MWCNT papers were observed by scanning electron microscopy (SEM). The electrochemical performance of the battery was operated by cell test and electrochemical impedance spectroscopy (EIS) measurement. The charging and discharging results indicated that the CMP behaves with higher capacity than AMP. And the EIS analysis showed that a lower charge transfer resistance can be obtained in the CMP. The excellent electrochemical performance verifies the feasibility of MWCNT papers as a promising candidate for the anode in flexible lithium ion battery.

Two new triterpenoid saponins derived from the leaves of Panax ginseng and their antiinflammatory activity

Li, Fu,Cao, Yufeng,Luo, Yanyan,Liu, Tingwu,Yan, Guilong,Chen, Liang,Ji, Lilian,Wang, Lun,Chen, Bin,Yaseen, Aftab,Khan, Ashfaq A.,Zhang, Guolin,Jiang, Yunyao,Liu, Jianxun,Wang, Gongcheng,Wang, Ming-Kui The Korean Society of Ginseng 2019 Journal of Ginseng Research Vol.43 No.4

Background: The leaves and roots of Panax ginseng are rich in ginsenosides. However, the chemical compositions of the leaves and roots of P. ginseng differ, resulting in different medicinal functions. In recent years, the aerial parts of members of the Panax genus have received great attention from natural product chemists as producers of bioactive ginsenosides. The aim of this study was the isolation and structural elucidation of novel, minor ginsenosides in the leaves of P. ginseng and evaluation of their antiinflammatory activity in vitro. Methods: Various chromatographic techniques were applied to obtain pure individual compounds, and their structures were determined by nuclear magnetic resonance and high-resolution mass spectrometry, as well as chemical methods. The antiinflammatory effect of the new compounds was evaluated on lipopolysaccharide-stimulated RAW 264.7 cells. Results and conclusions: Two novel, minor triterpenoid saponins, ginsenoside $LS_1$ (1) and 5,6-didehydroginsenoside $Rg_3$ (2), were isolated from the leaves of P. ginseng. The isolated compounds 1 and 2 were assayed for their inhibitory effect on nitric oxide production in LPS-stimulated RAW 264.7 cells, and Compound 2 showed a significant inhibitory effect with $IC_{50}$ of $37.38{\mu}M$ compared with that of NG-monomethyl-L-arginine ($IC_{50}=90.76{\mu}M$). Moreover, Compound 2 significantly decreased secretion of cytokines such as prostaglandin $E_2$ and tumor necrosis factor-${\alpha}$. In addition, Compound 2 significantly suppressed protein expression of inducible nitric oxide synthase and cyclooxygenase-2. These results suggested that Compound 2 could be used as a valuable candidate for medicinal use or functional food, and the mechanism is warranted for further exploration.