K.F. Kwok

The University of Hong Kong, Hong Kong, Hong Kong

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Publications (17)9.63 Total impact

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    ABSTRACT: High-intensity discharge (HID) lamps are becoming popular substitutes for halogen lamps in automotive headlamps because of the high lumen/watt ratio and the color of the light. In this paper, a ballast (integrated with a voltage multiplier circuit in the secondary winding of the dc converter transformer) with dimming control is presented. The proposed circuit not only eliminates one auxiliary winding but also reduces the voltage across the switch on the primary side and consequently permits the selection of switches with a lower rating. A brief review of the HID circuits is done and compared with the proposed circuit. Experimental results from the prototype are presented. This paper also presents different methods of dimming the automotive HID lamps based on analog and digital control and discusses the relative merits of each of the methods. The dimming control is implemented using both the methods, and experimental results are presented. It is envisaged that the dimming control will provide some flexibility to drivers in the control of HID lamps to suit the driving conditions in the modern cities that are very well lit at night. This paper investigates the merits of each method and discusses the practical issues for implementing such controls.
    IEEE Transactions on Industrial Electronics 08/2009; · 6.50 Impact Factor
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    ABSTRACT: In this work, a new performance parameter, namely power factor, introduced is used in the analysis of buck DC-DC converter operating in DCM. The power factor concept is now applied in the analysis of DC circuits. The derivation of the parameter and its application as one of the performance parameters in the analysis of the buck DC-DC converter operating in DCM and boost converter operating in discontinuous mode (DCM) has been carried out considering all the parasitic elements of the circuit. All the equations are normalized and expressed in terms of power factor so that a user can easily study the influence of the circuit elements on the performance of the converter. This will aid the designer to plot design curves for any loading conditions and choose the factor ldquoKrdquo, which is used to calculate the inductance required to operate the converter in a desired mode.
    Power Electronics Systems and Applications, 2009. PESA 2009. 3rd International Conference on; 06/2009
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    ABSTRACT: The paper examines the high power Light Emitted diode (LED) and the hear distribution of the heat sink. Beside we also study the relationship between temperature and the current on the LEDs luminous efficiency. The temperature rise to over the limit level that the luminous efficiency will decrease rapidly. The current increase will cause the nonequilibrium electron diffuse out of the potential wall and will increase the temperature, so as to decrease luminous efficiency and the LEDs life. Enhancing the heat manage of LEDs that can improve the luminous efficiency. Thermal design examines by using the thermal analysis. Finally we propose the electrical circuit to drive the LEDs in constant current power to maintain the temperature more constant of LEDs.
    Power Electronics Systems and Applications, 2009. PESA 2009. 3rd International Conference on; 06/2009
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    ABSTRACT: LED lighting is applied to clothing. It allows a flexible method to provide illumination of lighting. A family of converter topologies is proposed to give this simply method of power conversion. Analysis for the circuits in terms of output power, efficiency and general operation are provided. Two types of LED lighting clothing are developed. One is using super-bright LED embedded on the cloth. This gives active lighting instead of passive lighting. Another one is using optical fibre with grating to form lighting pattern.
    Power Electronics Systems and Applications, 2009. PESA 2009. 3rd International Conference on; 06/2009
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    ABSTRACT: In this work, a new performance parameter, namely power factor, is introduced in the analysis of DC-DC converters. The power factor, which is used frequently in AC circuits, is now applied in the analysis of DC circuits. The derivation of the parameter and its application as one of the performance parameters in the analysis of a buck DC-DC converter operating in both the continuous (CCM) and discontinuous mode (DCM) has been carried out considering all the parasitic elements of the circuit. An ideal value for the factor ldquoKrdquo is also suggested with the aid of plots for proper selection of the inductor. All the equations are normalized and expressed in terms of power factor so that a user can easily study the influence of the circuit elements on the performance of the converter. The analytical results are verified using PSPICE simulations.
    Power Engineering Conference, 2008. AUPEC '08. Australasian Universities; 01/2009
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    ABSTRACT: Based on two-dimensional (2-D) trigonometry, a new numerical method is presented to compute the nonlinear magnetic and electromagnetic torque characteristics in switched reluctance motors (SRMs). In the proposed method, the mathematical model is composed of the 2-D truncated Fourier series. The coefficients can be determined from a small amount of given magnetic or torque data acquired by experiment or finite-element (FE) analysis. The computed and experimental results demonstrate that the proposed method can be used to precisely compute the nonlinear magnetic and torque characteristics in SRMs. Hence, this paper provides a valuable approach for performance prediction, design, simulation, and control of SRMs
    IEEE Transactions on Magnetics 05/2007; · 1.42 Impact Factor
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    ABSTRACT: High-intensity discharge (HID) lighting lamp systems are widely used in applications that can provide a high light levels are desired for large areas, such as vehicle headlight, industrial and street lighting. Similar to fluorescent lighting systems, all HID lighting systems require a ballast to operate. Traditionally, magnetic ballast designs were the only choice available for HID lighting systems. Today, high-efficiency electronic HID ballasts are available that provide improved lighting quality and reduce lighting electricity use by 10 to 30 percent. The purpose of this paper is to identify requirements of the ballast interface from the perspective of the HID lamp. This study will generally brief the starting, run-up, and steady state operation of HID lamps on electronics ballasts.
    Power Electronics Systems and Applications, 2006. ICPESA '06. 2nd International Conference on; 12/2006
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    ABSTRACT: This paper is to examine different circuit topologies of HID electronic ballasts for the application in automotive systems. The paper examines the practical issues for the implementation of an HID ballast for the automotive environment. Some of the vital practical issues for successful operation of the HID lamp are discussed. Experimental waveforms from the prototype built in the laboratory, under cold and hot re-strike, are presented. The implication of the freeform optics design will also be discussed in the xenon lamp design which is integrated with the whole system
    Power Electronics Specialists Conference, 2006. PESC '06. 37th IEEE; 07/2006
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    ABSTRACT: The leakage inductance of the spiral winding transformer is examined. Two dimensional leakage field is modeled and leakage field linkage is then obtained to calculate the leakage inductance. The transformer is an air core based with a separation between the primary and secondary. The application is for contactless power conversion
    Electromagnetic Field Computation, 2006 12th Biennial IEEE Conference on; 01/2006
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    ABSTRACT: The class-E DC-DC power converter using piezoelectric transformer as the voltage stepping is examined in this paper. A generalized state-space averaging method is used for modeling. The system is simulated to examine the models. The open-loop characteristics of this converter are analyzed based on this model. In addition to simplifying this model, the singular perturbation method is used. In the end, the simulation results verify all the models. A ladder circuit is used to adding a number of piezoelectric transformer converter together which can avoid the isolation problem of the piezoelectric transformer
    PESC Record - IEEE Annual Power Electronics Specialists Conference 01/2006;
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    ABSTRACT: In this paper, a transformer with small size and relatively insensitive to distributing parameter is present. Two types of four different high-voltage pulse transformers used in the igniter circuit of HID ballast are examined. This comparison concludes that the transformer with the smallest size using R core is optimal. Experiment results are used to validate the conclusion
    Electromagnetic Field Computation, 2006 12th Biennial IEEE Conference on; 01/2006
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    ABSTRACT: Web-based method has been used in teaching engineering and many other subjects for quite some time. This paper is to discuss the Web-based teaching of power electronics using a number of new techniques. The paper also discusses the assessment of the course and survey through questionnaire in order to assess the success of the proposed method.
    Power Electronics Systems and Applications, 2004. Proceedings. 2004 First International Conference on; 12/2004
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    ABSTRACT: Piezoelectric transformer (PZT) is a device which transforms voltage by piezoelectric effect and converse piezoelectric effect of ceramic material. Compared with electromagnetic transformer, it has favorable characteristics of miniaturization, electromagnetic-noise free and the variable voltage gain with frequency and impedance. The modeling of piezoelectric transformer is the base of control and optimize. The principle of transforming voltage is presented in this paper. In addition, different modeling methods were brought into comparisons. Merits, shortcomings and the future work in modeling of PZT were given.
    Power Electronics Systems and Applications, 2004. Proceedings. 2004 First International Conference on; 12/2004
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    ABSTRACT: This paper discusses techniques used to develop an electronic book about electromagnetics. The techniques are based on problem-based learning, which is the latest method used for teaching. This method, together with engineering tools, is well suited for teaching these subjects to students in Asia. The proposed techniques allows teaching to be not limited to paper study by allowing the use of multimedia methods and computational electromagnetics. This enables the users to have a variety of means for the study of these areas. The embedded computing software and the design program also enhance the users' interest.
    IEEE Transactions on Magnetics 06/2003; · 1.42 Impact Factor
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    ABSTRACT: Calculation of the winding losses of high frequency transformer based on one-dimensional field analysis is normally inapplicable for complex winding configurations. This paper presents a matrix modeling method which can produce a generalized mechanism to solve the AC winding losses. The transformer is modeled in a matrix connected filament. This is an alternative method to the finite element and is a filament approach. Experimental results and computation results using the proposed method are found to have good agreement.
    COMPEL International Journal of Computations and Mathematics in Electrical 11/2002; 21(4):573-580. · 0.28 Impact Factor
  • K. W. E. Cheng, K. F. Kwok
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    ABSTRACT: An advanced distance learning method is introduced that is especially programmed for non-native English speakers. Many language features have been implemented to arouse undergraduate students' interests in learning. The package is also programmed to help professors to teach much easier than before.
    01/2002;
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    ABSTRACT: This paper presents the functions of a multimedia program developed under the project “Using Multi-lingual Web-based Distance Teaching Mode and Problem-based Learning Approach to Enhance Engineering Students' Learning Interest and English Standard”. The program comprises of three functions, namely Interactive Exercises, Graph Plotting and Language Translation. The last function is subdivided into web-based dictionary, essay to link, spell check and text to speech. The role and the structures of these functions are examined in this paper
    Intelligent Multimedia, Video and Speech Processing, 2001. Proceedings of 2001 International Symposium on; 02/2001