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An E-capless AC-DC CRM Flyback LED Driver with Variable On-time Control
Kai Yao,Xiaopeng Bi,Siwen Yang 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2
LED is a promising new generation of green lighting with the advantages of high efficiency, good optical performance, long lifetime and environmental friendliness. A pulsating current can be used to drive LEDs. However, current with a high peak-to-average ratio is unfavorable for LEDs. A novel control scheme for the ac-dc critical conduction mode (CRM) flyback LED driver is proposed in this paper. By using the input voltage, output voltage and average output current to control the turn-on time of the switch, the peak-to-average ratio of the output current can be reduced. The operation principle is analyzed and an implementation circuit is put forward. Experimental results show the effectiveness of the proposed scheme.
An E-capless AC-DC CRM Flyback LED Driver with Variable On-time Control
Yao, Kai,Bi, Xiaopeng,Yang, Siwen The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2
LED is a promising new generation of green lighting with the advantages of high efficiency, good optical performance, long lifetime and environmental friendliness. A pulsating current can be used to drive LEDs. However, current with a high peak-to-average ratio is unfavorable for LEDs. A novel control scheme for the ac-dc critical conduction mode (CRM) flyback LED driver is proposed in this paper. By using the input voltage, output voltage and average output current to control the turn-on time of the switch, the peak-to-average ratio of the output current can be reduced. The operation principle is analyzed and an implementation circuit is put forward. Experimental results show the effectiveness of the proposed scheme.
Creep Failure and Damage Mechanism of Inconel 718 Alloy at 800–900 °C
Kai Chen,Jianxin Dong,Zhihao Yao 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
The creep behavior and damage mechanisms of 718 alloys were investigated at 800–900 °C in air. The fracturemorphology and microstructure evolution were observed by optical, scanning and transmission electron microscope. Besides,the creep damage tolerance (λ) and creep strain evolution curve were also calculated. The results showed that the creep curvesof 718 alloys at 800 or 850 °C consisted of primary and tertiary stages, while the steady-state region became apparent at900 °C. The apparent creep activation energy of 718 alloy was in the range from 446.3 to 491.8 kJ/mol. The alloy presentedductile fracture at 800 °C due to the nucleation, growth and linkage of creep voids. However, the failure of alloys at 850 or900 °C presented necking to a point due to the microstructure degradation. Further investigations showed the softening ofmaterials and the loss of mechanical performance could be mainly attributed to the coarsening or decrease of strengtheningprecipitates. Above 850 °C, it was found that γ′ phases would dissolve into matrix and stress promoted the re-dissolution ofγ′ phases or led to the break of δ phases. Moreover, the creep strain evolution curves indicated that 718 alloys kept a relativestable state at 800–900 °C when the strain fraction was below 1.
Stability Analysis of Discrete-Time Piecewise-Linear Systems: A Generating Function Approach
Kai Liu,Jianghai Hu,Yu Yao,Baoqing Yang,Xin Huo 제어·로봇·시스템학회 2014 International Journal of Control, Automation, and Vol.12 No.5
This paper studies the exponential stability of a class of discrete-time piecewise-linear systems (DPLS). Some basic properties of the proposed DPLS are established, which enables the generating function approach to be used for the system stability analysis. By introducing the generating functions of DPLS and showing their properties, a sufficient and necessary condition for the exponential stability of DPLS is derived. Furthermore, the maximum exponential growth rate of system trajectories can be obtained exactly by computing the radii of convergence of the generating functions. The algorithm for computing the generating functions is developed and two examples are given to demonstrate the proposed approach.
Exponential Stability Analysis of Planar Piecewise-Linear Systems: An Integral Function Approach
Kai Liu,Yu Yao,Baoqing Yang,Venkataramanan Balakrishnan,Yang Guo 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.2
This paper studies the exponential stability of continuous-time planar piecewise-linear systems (PPLS). By introducing a novel conception of integral function of PPLS and showing its properties, a sufficient and necessary condition for the exponential stability is derived. Furthermore, the exponential growth rate of system trajectories can be obtained accurately by computing the convergence radius of integral function. The algorithm for computing the integral function is developed and two examples are given to demonstrate the proposed approach.
Sliding Mode Control Design Based on New Approaching Criteria for Linear Lipschitz Switching Surface
Kai Zheng,Tielong Shen,Yu Yao 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
A new design method of sliding mode control (SMC) is proposed to generalize the conversional procedure which is usually based on Filippov’s approaching conditions for only smooth surface. As the fundamental result, the new approaching criteria are developed to show the sufficient conditions on the relation between the trajectories and a nonsmooth surface in state space, if the dynamics of the trajectories can be described by Filippov’s differential inclusion. According to the new approaching criteria, the approaching phase design of SMC can be relaxed, through the switching surface may be nonsmooth. Furthermore, for a class of nonlinear single-input single-output (SISO) systems, the sliding mode controller with a linear Lipschitz continuous switching surface can be systemically designed. From the viewpoint of SMC, it provides a new path to realize the different requirements of the sliding motion according to the partitioned regions.
Kai Hsia,Tien-Shiang Wang,Chin-Su Liu,Chih-Kuan Su,Chien-Chin Chen,Chang-Ching Yeh,Hsinyu Lee,Chao-Ling Yao,Tsung-Yu Tseng,Shih-Hwa Chiou,Hsu Ma,Chih-Hsun Lin,Jen-Her Lu 한국생물공학회 2023 Biotechnology and Bioprocess Engineering Vol.28 No.3
Decellularized human umbilical arteries (dHUA) is an off-the-shelf graft that can potentially serve as vascular scaffolds in tissue engineering of small-diameter vascular grafts. This research aimed to investigate that dHUA could exhibit adequate endothelialization for a long term in xenogenic transplantation. 13 dHUAs were implanted in rat abdominal aortas up to 90 days. Rats were divided into three groups in terms of survival period: Group 1, one to seven days (n = 6); Group 2, 14 to 30 days (n = 4) and Group 3, 90 days (n = 3). The explants were analyzed by histological, immunohistochemistry and magnetic resonance angiography (MRA) examination. Allograft implantation of 12 decellularized rat abdominal aortas` were processed the same way as the rat in order to make a comparison for survival rates (Group 1, n = 5; Group 2, n = 4; Group 3, n = 3). The results demonstrated that the survival rates of xenograft and allograft implantation were estimated to be 59.2% vs. 58.3% in Group 1, 50.7% vs. 58.3% in Group 2 and 3. Grafts harvested from Group 2 were showed CD31, endothelial nitric oxide synthase expression at intima, and α-smooth muscle actin, CD45, CD68 and CD168 expression at the tunica externa. A layer structure with obvious endothelialization and fiber regeneration/orientation could be inspected from the explants of Group 3. MRA demonstrated the patency of dHUA on day 30 and 90. In conclusion, more than 50% dHUA maintained patency in the xenogenic model till 90 days after surgery. A mature vessel-like functional structure with intact endothelial layer was observed then. This warrants further study in the reinforcement of decellularized vascular scaffolds.
The Technical Benefits of Future GNSS for Taiwan
Kai-Wei Chiang,Ming Yang,Meng-Lun Tsai,Yao-Yun Chang,Chi-Kuang Chu 한국항해항만학회 2006 한국항해항만학회 학술대회논문집 Vol.2 No.-
The next decade promises drastic improvements and additions to global navigation satellite systems (GNSS). Plans for GPS modernization include a civilian code measurement on the L2 frequency and a new L5 signal at 1176.45MHz. Current speculations indicate that a fully operational constellation with these improvements could be available by 2013. Simultaneously, the Galileo Joint Undertaking is in the development and validation stages of introducing a parallel GNSS called Galileo. Galileo will also transmit freely available satellite navigation signals on three frequencies and is scheduled to be fully operational as early as 2008. In other words, a dual system receiver (e.g., GPS+GALILEO) for general users can access six civil frequencies transmitted by at least fifty eights navigation satellites in space. The advent of GALILEO and the modernization of GPS raise a lot of attention to the study of the compatibility and interoperability of the two systems. A number of performance analyses have been conducted in a global scale with respect to availability, reliability, accuracy and integrity in different simulated scenarios (such as open sky and urban canyons) for the two systems individually and when integrated. Therefore, the scope of this article aims at providing the technical benefits analysis for Taiwan specifically in terms of the performance indices mentioned above in a local scale, especially in typical urban canyon scenarios. The conclusions gained by this study will be applied by the Land Survey Bureau of Taiwanese as the guideline for developing future GNSS tracking facilities and dual GNSS processing module for precise surveying applications in static and kinematic modes.