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Publications (5)11.45 Total impact

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    ABSTRACT: This paper presents a fixed-frequency boundary control of buck converters. The method is based on integrating the concept of variable hysteresis into the boundary control technique with second-order switching surface. The switching frequency is maintained constant over a wide range of supply voltages and output loads. The method is based on using a frequency-to-voltage converter and comparing its output voltage with a reference voltage to control the width of the hysteresis in the boundary controller. It also combines the advantages of the boundary control that the converter can reach the steady state in two switching actions after large-signal disturbances. The basic operating principles, stability analysis, and design procedures will be given. The proposed control method has been successfully applied to control a 140 W, 24 V/12 V buck converter. The steady-state characteristics, including the switching frequency and output voltage ripple, at different input voltages and output loads with and without the proposed control method have been compared. The system responses under large-signal supply voltage and load disturbances will be discussed.
    IEEE Transactions on Power Electronics 10/2009; · 5.73 Impact Factor
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    ABSTRACT: A fixed-frequency boundary control of buck converter will be presented in this paper. The methodology is based on integrating the concept of variable hysteresis into the previously proposed boundary control technique with second-order switching surface. The switching frequency is maintained constant by using a frequency-to-voltage converter and comparing its output with a reference voltage to control the width of the hysteresis in the boundary controller. Compared with the methods using phase-locked loops, the proposed method has a wider lock-in range. Moreover, it integrates the advantages of the boundary control that the converter can settle into the steady state in two switching actions after large-signal input or output disturbances. The basic operating principles, stability analysis and design procedures will be given. The proposed control method has been successfully applied to control a 140 W, 24 V/12 V buck converter. The large-signal dynamic responses under supply voltage and load disturbances will be given.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    C.N.-m. Ho, H.S.H. Chung, K.T.K. Au
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    ABSTRACT: This paper presents a fast dynamic control scheme for capacitor-supported single-phase dynamic voltage restorers (DVRs) for inductive loads. The scheme consists of two main control loops as inner and outer loops. The inner loop is used to dictate the gate signals for the switches in the DVR. It is based on the boundary control method with the second-order switching surface. The load voltage can ideally be reverted to the steady state in two switching actions during a supply voltage dip. The outer loop is used to generate the DVR output reference for the inner loop. It has three control modes for achieving two different functions, including the output regulation and output restoration. The first mode is for regulating the capacitor voltage on the dc side of the inverter, so that the output of the DVR is regulated at the nominal voltage. The second mode is for restoring the output with the near minimum energy injection by the DVR during a voltage dip. The third mode is in maximum voltage injection and will be activated when the capacitor voltage is reduced to a level that starts distorting the output voltage in the second mode. The mode boundaries will be derived in this paper. By studying the small-signal characteristics of the control loops, a set of design procedures will be derived. A 500 VA, 110 V, 60 Hz prototype has been built and tested with nonlinear inductive loads. The dynamic behaviors of the prototype under different voltage dip depths will be investigated.
    IEEE Transactions on Power Electronics 02/2008; · 5.73 Impact Factor
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    C.N.M. Ho, K.T.K. Au, H.S.H. Chung
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    ABSTRACT: The difference between the fast dynamics associated with the input current of power factor correctors (PFCs) and the slow dynamics associated with their output voltage is typically exploited by using multiple control loops. The overall dynamic response is generally limited by the output voltage regulation loop. Research into an analogy-based controller for PFCs is at a slow pace. This paper applies the concept of the boundary control method with a second-order switching surface for the boost type PFC, so as to achieve fast dynamic response. The method is based on predicting the state trajectory movement after a hypothesized switching action and the output can ideally be reverted to the steady state in two switching actions during the large-signal input voltage and output load disturbances. Besides, there is another control loop to compensate the error for the capacitor aging. Theoretical predictions are verified with the experimental results of a 300 W, 110 V prototype.
    Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007
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    ABSTRACT: This paper presents the digital implementation of a recently developed boundary control method with second-order switching surface for inverters. The control principle is based on estimating the state trajectory movement after a switching action, resulting in a high state trajectory velocity along the switching surface. This phenomenon accelerates the trajectory moving towards the target operating point. The mathematical derivation and generation of the gate signal and feedback signal will be given. A 320 W prototype has been built and tested. The large-signal dynamic responses of the inverter will be given.
    Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007