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RISS 인기검색어
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- 저자 : Chi K. Tse (검색결과 4 건)
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K. H. Loo,Y. M. Lai,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Most commercial white LEDs are made from blue LEDs coated with YAG phosphor. They generally produce emission spectra that shift in opposite directions under the influences of current amplitude and junction temperature changes. By using a commercial white LED sample, LUXEON K2, the effects of current amplitude and junction temperature on the chromaticity shift of white LEDs over dimming, during which both parameters are known to assert their influences simultaneously, are studied experimentally. The impact of driving/dimming by dc current is discussed through a graphical analysis and verified by experimental measurement. Due to the counteracting influences of current amplitude and junction temperature changes, driving/dimming white LEDs by dc current offers a more superior chromaticity stability compared to PWM. By means of selection of a heat sink’s thermal resistance estimated from an analytical equation derived in this paper, it is found that the overall chromaticity shift of white LEDs over dimming can be minimized at low cost.
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Variable Bi-Level Phase-Shifted Driving Method for High-Power RGB LED Lamps
S. K. Ng,K. H. Loo,Y. M. Lai,K. T. Mok,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Based on the recently proposed bi-level driving method, this paper presents an extended version of the existing method, which is aimed at maximizing the luminous output of high-power LED lamps by piecewise-linear tracing of their luminous output curves under AM (amplitude modulation) driving. The proposed driving method divides the luminous output curve of an AM-driven LED into a multiple sections, where each section is approximated by a straight line with two predefined end-points acting as the lower and upper current levels as used in the existing bi-level driving method. The intermediate current and luminosity values lying between the upper and lower current levels are obtained by duty cycle mixing of the two current levels. The joined multiple sections has enabled a near-maximum luminous output to be extracted from the LED while a linear dimming is realized within each section. The proposed driving method is verified by implementation in a single-driver RGB color LED lighting system with the red, green, and blue LED driven in a time-sequential manner (or shifted in phase). Experimental results show that a significant gain in luminous efficacy, hence energy saving, is achieved compared to the commonly used pulse-width modulation (PWM) driving.
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K. H. Loo,G. R. Zhu,Y. M. Lai,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Direct methanol fuel cells (DMFC) have been widely researched for applications in portable electronics due to their use of liquid fuel for easy storage and transportation compared to gaseous hydrogen. However, DMFC’s performance is strongly affected by methanol crossover that significantly degrades the fuel conversion efficiency at low output power, and is characterized by an increasing efficiency at increasing output power. The maximum efficiency point (MEP) is inherently difficult to track due to the commonly unknown methanol crossover rate, but since it is typically located very close to the maximum power point (MPP), an alternative tracking approach based on the MPP is proposed. In this paper, a fuel-cell-oriented MPP tracking (MPPT) algorithm based on resistance matching is developed, implemented, and tested in the context of a DMFC/supercapacitor hybrid power system. To account for the generally slow fuel cell dynamics, the DMFC is constantly tracked at the MPP while any surplus or deficit power is absorbed or delivered by the supercapacitor bank. The detailed formulation of the algorithm and the power flow design and realization are also discussed.
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Community-based Informed Agents Selection for Flocking with a Virtual Leader
Nuwan Ganganath,Chi-Tsun Cheng,Xiaofan Wang,Chi K. Tse 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.1
It has been studied that a few informed individuals in a group of interacting dynamic agents can influencethe majority to follow the position and velocity of a virtual leader. Previously it has been shown that a cluster-basedselection of informed agents can drive more agents to follow the virtual leader compared to a random selection. However, a practical question is: How many informed agents to select? In order to address this, here we proposea novel method for selecting informed agents based on community structures in the initial spatial distribution ofagents. The number of informed agents are decided based on the strongest community structure. We test andanalyze the performance of the proposed method against random and cluster-based selections of informed agentsusing extensive computer simulations. Results of our study show that community-based selection can be usefulin deciding an optimum number of informed agents such that a majority of the group can achieve their commonobjective.
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