W.L. Chan

The University of Hong Kong, Hong Kong, Hong Kong

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Publications (137)159.58 Total impact

  • K.M. Tsang · W.L. Chan
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    ABSTRACT: This paper presents a novel high power single switch DC/DC converter with galvanic isolation for photovoltaic (PV) systems. The converter input current and output voltage can both be regulated independently based on the operation of a single switch. The output voltage can be controlled based on the duty ratio of the electronic switch and is no longer determined by the turn ration of the isolation transformer. With the proposed configuration and switching action, the average magnetic flux within the transformer core over one switching cycle is zero and hence a full switching cycle can be used for high power transfer. A fast current controller is also developed for the proposed converter such that maximum power point tracking (MPPT) algorithm based on PV panel output current can be developed. Moreover, MPPT based on a triangular reference input current is implemented. Experimental results are included to demonstrate the effectiveness of the proposed converter and control scheme.
    No preview · Article · Sep 2015 · Solar Energy
  • K. M. Tsang · W. L. Chan
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    ABSTRACT: Partial shading on photovoltaic (PV) arrays causes multiple peaks on the output power-voltage characteristic curve and local searching technique such as perturb and observe (P&O) method could easily fail in searching for the global maximum. Moreover, existing global searching techniques are still not very satisfactory in terms of speed and implementation complexity. In this paper, a fast global maximum power point (MPPT) tracking method which is using current sweeping for photovoltaic arrays under partial shading conditions is proposed. Unlike conventional approach, the proposed method is current based rather than voltage based. The initial maximum power point will be derived based on a current sweeping test and the maximum power point can be enhanced by a finer local search. The speed of the global search is mainly governed by the apparent time constant of the PV array and the generation of a fast current sweeping test. The fast current sweeping test can easily be realized by a DC/DC boost converter with a very fast current control loop. Experimental results are included to demonstrate the effectiveness of the proposed global searching scheme.
    No preview · Article · Mar 2015 · Energy Conversion and Management
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: Ocean wave energy is very promising. However, existing systems are using rectifying circuits to convert variable voltage and variable frequency output of electric generator into DC voltage and then use grid-tied inverter to connect to the power grid. Such arrangement will not only reduce the overall efficient but also increase the cost of the system. A direct AC–AC converter is a desirable solution. In this paper, a six-switch AC–AC converter has been proposed as a single phase grid-connected interface. New switching scheme has been derived for the converter such that the virtual input AC–DC conversion and the output DC–AC conversion can be decoupled. State-space averaging model and pulse width modulation scheme have been derived for the converter. As the input and the output operations can be decoupled, two independent controllers have been designed to handle the input AC–DC regulation and the output DC–AC regulation. The proposed scheme demands for two separate duty ratios and novel switching scheme has been derived to realize the combined duty ratios in one switching cycle. Power regulation, harmonics elimination and power factor correction control algorithms have also been derived for the converter when it is connected to the supply grid. Experimental results of a small scale model are included to demonstrate the effectiveness of the proposed switching and control schemes.
    No preview · Article · Mar 2015 · Energy Conversion and Management
  • Kai Ming Tsang · W.-L. Chan
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    ABSTRACT: A novel design of a power grid interface using a coupled inductor filter with a frequency notching characteristic is presented in this paper. Traditional grid-tie power converters are connected to the supply grid via an L filter, an LC filter or an LCL filter, respectively, to reduce the harmonics caused by the switching. The efficiency of the grid interface can be improved by reducing the switching frequency and the size of the filtering inductor. To reduce the size of the filtering inductor and retaining the similar attenuation characteristics for the switching ripples, a coupled inductor filter is used to replace the conventional filter. To illustrate the capability of the proposed approach, the design of a coupled inductor notch filter to attenuate the switching ripples is provided. A simple controller has also been derived for the grid interface to act as an active power filter such that a power factor correction and a harmonics reduction can both be achieved. The proposed coupled inductor filter could be applied to any applications requiring a power grid interface. The experimental results are included to demonstrate the effectiveness of the proposed filter.
    No preview · Article · Jul 2014 · IET Power Electronics
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    ABSTRACT: The dependence of stochastic resonance in the feed-forward-loop neuronal network motifs on the noise and time delay are studied in this paper. By computational modeling, Izhikevich neuron model with the chemical coupling is used to build the triple-neuron feed-forward-loop motifs with all possible motif types. Numerical results show that the correlation between the periodic subthreshold signal's frequency and the dynamical response of the network motifs is resonantly dependent on the intensity of additive spatiotemporal noise. Interestingly, the excitatory intermediate neuron could induce intermittent stochastic resonance, whereas the inhibitory one weakens its influence on the intermittent mode. More importantly, it is found that the increasing delays can induce the intermittent appearance of regions of stochastic resonance. Based on the effects of the time delay on the stochastic resonance, the reasons and conditions of such intermittent resonance phenomenon are analyzed.
    Full-text · Article · Apr 2014 · Communications in Nonlinear Science and Numerical Simulation
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    ABSTRACT: A combined method composing of the unscented Kalman filter (UKF) and the synchronization-based method is proposed for estimating electrophysiological variables and parameters of a thalamocortical (TC) neuron model, which is commonly used for studying Parkinson's disease for its relay role of connecting the basal ganglia and the cortex. In this work, we take into account the condition when only the time series of action potential with heavy noise are available. Numerical results demonstrate that not only this method can estimate model parameters from the extracted time series of action potential successfully but also the effect of its estimation is much better than the only use of the UKF or synchronization-based method, with a higher accuracy and a better robustness against noise, especially under the severe noise conditions. Considering the rather important role of TC neuron in the normal and pathological brain functions, the exploration of the method to estimate the critical parameters could have important implications for the study of its nonlinear dynamics and further treatment of Parkinson's disease.
    Full-text · Article · Mar 2014 · Chaos (Woodbury, N.Y.)
  • K. M. Tsang · W. L. Chan
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    ABSTRACT: A novel reference signal generator is combined with a multi-level inverter to form a rapid islanding detection scheme for grid-interactive PV system. The reference signal generator can easily be synchronized with the utility grid signal and produced a fixed magnitude and very low total harmonic distortion (THD) sinusoidal signal which is in phase with the utility grid signal. Unlike conventional phase-locked loop (PLL) circuitry, the reference signal generator can also provide a fixed magnitude sinusoidal signal even if the utility grid is disconnected and automatically re-synchronous with the grid rapidly. Consequently, seamless transfer between grid-connected and stand-alone modes could easily be achieved if anti-islanding protection is not required. If a saturation element is applied to the raw reference signal followed by the synthesis of the truncated signal using a multi-level inverter, the distinct flat-top feature of the synthesized signal can quickly and easily be identified if the network is in islanding mode at the point of common coupling. Experimental results are included to demonstrate the effectiveness of the proposed detection scheme. Crown Copyright
    No preview · Article · Jan 2014 · Energy Conversion and Management
  • K. M. Tsang · W. L. Chan · X. Tang
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    ABSTRACT: This paper presents a systematic way of designing control scheme for a grid-connected photovoltaic (PV) inverter featuring rapid maximum power point tracking (MPPT) and grid current shaping without using any phase-locked loop (PLL) circuitry. A simple integral controller has been designed for the tracking of the maximum power point of a PV array based on the extremum seeking control method to provide a reference PV output current for the grid interface. For the grid-connected inverter, two current loop controllers have been designed. One of the current loop controllers is designed to shape the inverter output current while the other current control loop is to follow the reference received from the maximum power point tracking algorithm and to provide a reference inverter output current for the PV inverter without largely disturbing the maximum power point of the PV array. Four power switches are used to achieve three output levels and MPPT. Moreover, it is unnecessary to use any energy storage such as rechargeable battery. Experimental results are included to demonstrate the effectiveness of the tracking and control scheme.
    No preview · Article · Nov 2013 · Solar Energy
  • Xin Tang · K. M. Tsang · W. L. Chan
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    ABSTRACT: This study develops a new control strategy for an expandable grid-connected photovoltaic (PV) system. The proposed system performs dual functions of a PV generation and an active power filter, or either one. To this end, the grid current, instead of output current of the converter, is shaped to be a sinusoidal current in phase (or opposite phase) with the grid voltage. Furthermore, its reference current is generated in multiplying the voltage loop controller output by the grid voltage waveform, and therefore non-active components analysis for harmonics elimination and reactive power compensation in the conventional design is not necessary. As a result, the algorithm is simple and easy to implement, and only one sensor for current detection plus two voltage sensors are required. Experimental results verified the effectiveness of the proposed method.
    No preview · Article · Oct 2013 · Solar Energy
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: Orthogonal least squares estimation algorithm is applied for the identification of unknown relationship between the drain current, the voltage across the drain and source of a fully on metal–oxide semiconductor field-effect transistor (MOSFET) under different temperatures. Very low loss current sensing can be derived based on the fitted model, the sensed temperature and voltage across the drain and source of the MOSFET. The model can easily be denormalized to cater for MOSFETs of the same model so that it is not necessary to test individual MOSFET in power converters. The proposed method could be useful for testing power converters during the manufacturing process. It could also be embedded into the controller to implement current control or over-current protection for power converters. Experiments and procedures to carry out the model fitting are presented.
    No preview · Article · Jul 2013 · Measurement
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: This paper presents a novel approach for tracking the maximum power point of photovoltaic (PV) systems so as to extract maximum available power from PV modules. Unlike conventional methods, a very fast tracking response with virtually no steady state oscillations is able to obtain in tracking the maximum power point. To apply the proposed method, firstly, output voltages, output currents under different conditions and temperatures of a PV module are collected for the fitting of environmental invariant nonlinear model for the PV system. Orthogonal least squares estimation algorithm coupled with the forward searching algorithm is applied to sort through all possible candidate terms resulted from the expansion of a polynomial model and to come up with a parsimonious model for the PV system. It is not necessary to test all PV modules as the resultant model is valid for other modules. The power delivered by the PV system can be derived from the fitted model and the maximum power point for the PV system at any working conditions can be obtained from the fitted model. Consequently, rapid maximum power point tracking could be achieved. Experimental results are included to demonstrate the effectiveness of the fitted model in maximum power point tracking.
    No preview · Article · Jun 2013 · Energy Conversion and Management
  • K. M. Tsang · W. L. Chan · Xin Tang
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    ABSTRACT: A novel design of a multi-level shunt active power filter using a modular cascade H-bridge is presented in this article. The proposed approach enables a modular approach in the design of a multi-level active power filter. As an illustration, a five-level H-bridge active power filter with a novel switching strategy has been implemented. The design is able to reduce the voltage stress across the filter inductor and to reduce the average switching frequency. Proportional plus integral controllers have been implemented for the current control loop, overall voltage control loop, and voltage balancing loop. A feedforward controller has also been added to the current control loop to improve the current tracking. By delaying the firing time of one of the H-bridges, five levels can be realized from a cascade H-bridge active power filter. The proposed switching strategy and the realization of the five-level switching scheme are presented. Experimental results are included to demonstrate the effectiveness of the proposed filter scheme.
    No preview · Article · Apr 2013 · Electric Power Components and Systems
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: In many photovoltaic systems, rechargeable batteries are required to even out irregularities in solar irradiation. However, the health conditions of the batteries are crucial for the reliability of the overall system. In this paper, the equivalent DC resistances of Lithium ion battery cells of various health conditions during charging under different temperatures have been collected and the relationships between equivalent DC resistance, health condition and working temperature have been identified. The equivalent DC resistance can easily be obtained during the charging period of a battery by switching off the charging current periodically for a very short duration of time. A simple and effective battery charger with state of health (SOH) detection for Lithium ion battery cell has been developed based on the identified equivalent DC resistance. Experimental results are included to demonstrate the effectiveness of the proposed SOH determination scheme.
    No preview · Article · Jan 2013 · Energy Conversion and Management
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: This paper presents a systematic way of designing control scheme for a grid-connected photovoltaic (PV) inverter featuring maximum power point tracking (MPPT) and grid current shaping. Unlike conventional design, only four power switches are required to achieve three output levels and it is not necessary to use any phase-locked-loop circuitry. For the proposed scheme, a simple integral controller has been designed for the tracking of the maximum power point of a PV array based on an improved extremum seeking control method. For the grid-connected inverter, a current loop controller and a voltage loop controller have been designed. The current loop controller is designed to shape the inverter output current while the voltage loop controller can maintain the capacitor voltage at a certain level and provide a reference inverter output current for the PV inverter without affecting the maximum power point of the PV array. Experimental results are included to demonstrate the effectiveness of the tracking and control scheme.
    No preview · Article · Jan 2013 · Energy Conversion and Management
  • Xin Tang · K. M. Tsang · W. L. Chan
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    ABSTRACT: This paper presented an expandable grid-connected power quality compensator with distribution generation interface for three-phase three-wire system. The proposed system not only can control the active power flow, but also mitigate load unbalance, harmonics, and manage reactive power. The power quality compensator can simultaneously perform the two functions of power control station and active power filter or either one. To make the system more flexible, the grid current, instead of output current of the converter, is shaped to be a sinusoidal current in phase with the grid voltage. The reference currents are generated by multiplying the voltage loop controller output by the corresponding grid voltage waveforms. Consequently, harmonic analysis or dq transformation, as required in the conventional design, is not necessary. In this manner, controlling the dc voltage level is equivalent to performing an active power balance for the whole system. As a result, no additional hardware and interface are required. Experimental results verified the effectiveness of the proposed method.
    No preview · Article · Jun 2012 · IEEE Transactions on Energy Conversion
  • Y.-Y. Chen · J. Wang · K.-M. Tsang · W.-L. Chan · X.-L. Wei · B. Deng
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    ABSTRACT: The ghostburster model exhibits periodic spiking, chaotic bursting and periodic bursting responding to different depolarized currents. The transition between periodic spiking and chaotic bursting is caused by the saddle- node bifurcation of limit cycles. The transition of neuronal dynamics near the saddle-node bifurcation point of limit cycles was realized by a washout filter-aid feedback approach, and the intrinsic mechanisms of these transitions were analyzed through decomposing the system to a fast subsystem and a slow one. The detailed mechanisms of the washout filter on the full dynamical model were given based on the analysis of the fast and the slow subsystem. It was found that the dendritic spike failure was connected to the 'ghost' of the saddle-node bifurcation of fixed points and the critical point at which the fast subsystem went through a transition from a period-one limit cycle to a period-two limit cycle. Washout filter could change the bifurcation point of local maxima in dendritic potential, and thus change the firing patterns.
    No preview · Article · May 2012 · Tianjin Daxue Xuebao (Ziran Kexue yu Gongcheng Jishu Ban)/Journal of Tianjin University Science and Technology
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    ABSTRACT: In this paper, a robust control system combining backstepping and sliding mode control techniques is used to realize the synchronization of two gap junction coupled chaotic FitzHugh–Nagumo (FHN) neurons in the external electrical stimulation. A backstepping sliding mode approach is applied firstly to compensate the uncertainty which occur in the control system. However, the bound of uncertainty is necessary in the design of the backstepping sliding mode controller. To relax the requirement for the bound of uncertainty, an adaptive backstepping sliding mode controller with a simple adaptive law to adapt the uncertainty in real time is designed. The adaptive backstepping sliding mode control system is robust for time-varying external disturbances. The simulation results demonstrate the effectiveness of the control scheme.Highlights► A backstepping sliding mode controller is firstly used to synchronize two coupled chaotic FHN neurons. ► Then, an adaptive law is derived to adapt the uncertainty of control system in real time. ► The adaptive backstepping sliding mode controller is robust for external disturbance. ► The simulation results demonstrate the effectiveness of the control scheme.
    Full-text · Article · Mar 2012 · Communications in Nonlinear Science and Numerical Simulation
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: A novel design of multilevel DC–AC inverter using only single renewable energy source is presented in this paper. The proposed approach enables multilevel output to be realised by a few cascaded H-bridges and a single energy source. As an illustration, a 27-level inverter has been implemented based on three cascaded H-bridges with a single energy source and two capacitors. Using the proposed novel switching strategy, 27 levels can be realized and the two virtual energy sources can be well regulated. Experimental results are included to demonstrate the effectiveness of the proposed inverter.
    No preview · Article · Jan 2012 · Energy Conversion and Management
  • K. M. Tsang · W. L. Chan
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    ABSTRACT: A fast acting regenerative dc electronic load based on the single-ended primary inductor converter (SEPIC) converter has been implemented. A simple multiloop feedback control system has been design for the SEPIC converter to realize the main function of electronic load. Instead of discharging via resistive load, the output of the converter is connected to rechargeable batteries such that discharged energy can be saved for future use. Circuit implementation of the proposed scheme is presented and experimental results are included to demonstrate the effectiveness of the proposed design.
    No preview · Article · Jan 2012 · IEEE Transactions on Power Electronics
  • K.M. Tsang · W.L. Chan
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    ABSTRACT: A novel controller based on the decoupling of single-ended primary inductor converter (SEPIC) state-space averaging model to four simple first-order systems is proposed. Instead of designing a single controller for a fourth-order SEPIC converter, four PI controllers are designed for the four decoupled systems. Combining the four PI controllers with the four decoupled systems forms a multi-loop feedback control system which is able to work at a wider operating condition. Circuit implementation of the proposed controller is presented and experimental results are included to demonstrate the effectiveness of the proposed design scheme.
    No preview · Article · Oct 2011 · IET Power Electronics

Publication Stats

1k Citations
159.58 Total Impact Points

Institutions

  • 1999-2015
    • The University of Hong Kong
      • Department of Electrical and Electronic Engineering
      Hong Kong, Hong Kong
  • 1993-2014
    • The Hong Kong Polytechnic University
      • Department of Electrical Engineering
      Hong Kong, Hong Kong
  • 2011
    • Tianjin University
      • School of Electrical Engineering and Automation
      Tianjin, Tianjin Shi, China
  • 2005
    • Changsha University of Science and Technology
      Ch’ang-sha-shih, Hunan, China
  • 2003
    • Harbin Engineering University
      Charbin, Heilongjiang Sheng, China
    • Beijing University of Aeronautics and Astronautics (Beihang University)
      Peping, Beijing, China
  • 1997
    • City University London
      Londinium, England, United Kingdom
  • 1991-1997
    • City University of Hong Kong
      Chiu-lung, Kowloon City, Hong Kong