Analysis of Z-Source Inverters in Wireless Power Transfer Systems and Solutions for Accidental Shoot-Through State

Wang, Tianfeng,Liu, Xin,Jin, Nan,Ma, Dianguang,Yang, Xijun,Tang, Houjun,Ali, Muhammad,Hashmi, Khurram The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Wireless power transfer (WPT) technology has been the focus of a lot of research due to its safety and convenience. The Z-source inverter (ZSI) was introduced into WPT systems to realize improved system performance. The ZSI regulates the dc-rail voltage in WPT systems without front-end converters and makes the inverter bridge immune to shoot-through states. However, when the WPT system is combined with a ZSI, the system parameters must be configured to prevent the ZSI from entering an "accidental shoot-through" (AST) state. This state can increase the THD and decrease system power and efficiency. This paper presents a mathematical analysis for the characteristics of a WPT system and a ZSI while addressing the causes of the AST state. To deal with this issue, the impact of the system parameters on the output are analyzed under two control algorithms and the primary compensation capacitance range is derived in detail. To validate the analysis, both simulations and experiments are carried out and the obtained results are presented.

Analysis of Z-Source Inverters in Wireless Power Transfer Systems and Solutions for Accidental Shoot-Through State

Tianfeng Wang,Xin Liu,Nan Jin,Dianguang Ma,Xijun Yang,Houjun Tang,Muhammad Ali,Khurram Hashmi 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Wireless power transfer (WPT) technology has been the focus of a lot of research due to its safety and convenience. The Z-source inverter (ZSI) was introduced into WPT systems to realize improved system performance. The ZSI regulates the dc-rail voltage in WPT systems without front-end converters and makes the inverter bridge immune to shoot-through states. However, when the WPT system is combined with a ZSI, the system parameters must be configured to prevent the ZSI from entering an “accidental shoot-through” (AST) state. This state can increase the THD and decrease system power and efficiency. This paper presents a mathematical analysis for the characteristics of a WPT system and a ZSI while addressing the causes of the AST state. To deal with this issue, the impact of the system parameters on the output are analyzed under two control algorithms and the primary compensation capacitance range is derived in detail. To validate the analysis, both simulations and experiments are carried out and the obtained results are presented.

Micro Convexity Elimination of Tungsten Carbide in Electrical Discharge Milling for Lens Moulds

Tianfeng Zhou,Si-Bo Wang,Xin Liu,Zhi-Qiang Liang,Xibin Wang 한국정밀공학회 2017 International Journal of Precision Engineering and Vol.18 No.12

Electrical discharge milling (ED milling) using spherical electrode is considered to fabricate tungsten carbide (WC) lens moulds for high volume and cost efficient mass production comparing with hemispherical electrode whose wear is noticeably larger. However, micro convexity with dome shape generating in the center of the mould leads to poor surface quality of moulds when using spherical electrode. Therefore, based on boundary layer theory, the forming mechanism of the micro convexity is analyzed in detail by measuring its height and profile by virtue of 3D laser scanning microscope and scanning electron microscope (SEM). The relationship between the boundary layer thickness and the discharge gap is subsequently established, which can be utilized to reduce the convexity to improve the surface quality of lens mould. Then a method to eliminate the micro convexity is proposed. In addition, experiments of different discharge gaps were carried out to confirm the boundary layer theory. Results show that the height of micro convexity can be reduced to 4 μm when the discharge gap was specified to the boundary layer thickness at certain rotational speed.

Improvement of Glass Formability in Ultrasonic Vibration Assisted Molding Process

Tianfeng Zhou,Jiaqing Xie,Jiwang Yan,Kuriyagawa Tsunemoto,Xibin Wang 한국정밀공학회 2017 International Journal of Precision Engineering and Vol.18 No.1

Micro optical elements with complex shapes are needed increasingly in optical, optoelectronic and biomedical industries. Since glass molding process is an effective approach to fabricate microstructures, and its surface quality strongly depends on the filling capacity of glass at high temperature. To improve the formability and reduce adhesion between the glass and the mold at high temperature, ultrasonic vibration is applied to improve the formability in the molding process. Fundamental experiments are carried out to test the effectiveness of ultrasonic vibration on friction force decrease and a bonding model on the glass-mold interface at elevated temperature is proposed. Finite element method (FEM) simulation and glass molding experiments are conducted to evaluate the improvements of material formability brought about by ultrasonic vibration. The results show that the ultrasonic vibration can significantly lower the friction force and increase the glass formability.

Effects of relative tool sharpness on surface generation mechanism of precision turning of electroless nickelphosphorus coating

Qian Yu,Tianfeng Zhou,Yupeng He,Peng Liu,Xibin Wang,Jiwang Yan 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.7

Relative tool sharpness (RTS) is identified as the ratio of undeformed chip thickness to tool cutting edge radius. This paper studies the effects of RTS on the surface generation mechanism of precision turning of electroless nickel-phosphorus (Ni-P) coating. An Rshaped tungsten carbide (WC) tool was adopted for the face turning experiment. The cutting edge radius was 1.84 μm measured by a laser scanning confocal microscope (LSCM). The chip formation behavior, cutting forces and surface morphology were investigated under different RTS values. Results showed that the chip changes from continuous to discontinuous as RTS decreases from 0.54 to 0.27, indicating the transition of the material removal mechanism. The periodical fluctuations with small amplitudes on the machined surface are associated with the high-frequency tool-tip vibration. The low-frequency fluctuations of the cutting forces are related to the material swelling and recovery. The optimal machined surface roughness was obtained at the RTS of 0.38.

Screening potential reference genes for reverse transcription-quantitative polymerase chain reaction normalization in Atrijuglans hetaohei (Lepidoptera: Gelechioidea)

Li Feifei,Li Yan,Wang Tao,Li Tianfeng,Zhu Shuying,Pei Pei,Tang Guanghui 한국곤충학회 2020 Entomological Research Vol.50 No.6

Atrijuglans hetaohei Yang (Lepidoptera: Gelechioidea), is one of the major pests that seriously damage the walnut fruits. Although the morphology and physiology of A. hetaohei have been widely studied, suitable reference genes for normalizing target gene expression have not been identified. In this study, the expressions of eight candidate reference genes including GAPDH, β-Tubulin, TATA-binding protein (TBP), Histone, Ubiquitin-conjugating enzyme 9 (UBC9), arginine kinase (AK), 28S and elongation factor 1 alpha (EF1α) in different developmental stages and various larval tissues of A. hetaohei were determined using reverse transcription-quantitative polymerase chain reaction. Moreover, the expression stability of the selected reference genes was evaluated by ΔCt method, BestKeeper, NormFinder, geNorm and ReFinder, a comprehensive software platform. These results demonstrated that the best reference genes were GAPDH and 28S at different developmental stages of A. hetaohei; and the optimum references in various larval tissues of A. hetaohei were 28S, Histone and TBP. Our study should be useful to analyze the expression profiles of target genes and form a solid foundation for future research on the understanding of the genes’ biological functions in A. hetaohei.

Intelligent classification methods of grain kernels using computer vision analysis

Lee, Choon Young,Yan, Lei,Wang, Tianfeng,Lee, Sang Ryong,Park, Cheol Woo IOP Pub 2011 Measurement Science and Technology Vol.22 No.6

<P>In this paper, a digital image analysis method was developed to classify seven kinds of individual grain kernels (common rice, glutinous rice, rough rice, brown rice, buckwheat, common barley and glutinous barley) widely planted in Korea. A total of 2800 color images of individual grain kernels were acquired as a data set. Seven color and ten morphological features were extracted and processed by linear discriminant analysis to improve the efficiency of the identification process. The output features from linear discriminant analysis were used as input to the four-layer back-propagation network to classify different grain kernel varieties. The data set was divided into three groups: 70% for training, 20% for validation, and 10% for testing the network. The classification experimental results show that the proposed method is able to classify the grain kernel varieties efficiently.</P>

Input-output Finite-time Stability of Switched Singular Continuous-time Systems

Tian Feng,Baowei Wu,Yue-E Wang,YangQuan Chen 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.5

This paper is concerned with the problem of input-output finite-time stability (IO-FTS) for a class of switched singular continuous-time systems. First, the concept of IO-FTS is extended to switched singular systems. Then, by using the average dwell time switching approach and constructing multiple Lyapunov functions, a sufficient condition of IO-FTS for the considered system is presented in the form of linear matrix inequalities (LMIs). Furthermore, based on the derived conditions, a suitable state feedback controller is designed to stabilize the switched singular systems. Finally, an illustrative example is provided to demonstrate the effectiveness of the proposed technique.