Hak Keung Lam

Dr. Hak Keung Lam

Department of Engineering, King’s College London, London WC2R 2LS, UK

Research Focus & Metrics

Academic Career Length

26Years (2001-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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6 February 2003 in IEEE Transactions on Neural Networks
Verified
Journal Article
Closed access
FLFrank H.F. Leung
Frank H.F. Leung
Hak Keung LamHak Keung Lam
Hak Keung Lam
Steve LingSteve Ling
Steve Ling
PTP.K.S. Tam
P.K.S. Tam
This paper presents the tuning of the structure and parameters of a neural network using an improved genetic algorithm (GA). It is also shown that the improved GA performs better than the standard GA based on some benchmark test functions. A neural network with switches introduced to its links is proposed. By doing this, the proposed neural network can learn both the input-output relationships of an application and the network structure using the improved GA. The number of hidden nodes is chosen manually by increasing it from a small number until the learning performance in terms of fitness value is good enough. Application examples on sunspot forecasting and associative memory are given to show the merits of the improved GA and the proposed neural network.

7 February 2022 in IEEE Transactions on Fuzzy Systems
Verified
Journal Article
Closed access
YPYingnan Pan
Yingnan Pan
YWYanmin Wu
Yanmin Wu
Hak Keung LamHak Keung Lam
Hak Keung Lam
This article studies the issue of resilient event-triggered (RET)-based security controller design for nonlinear networked control systems (NCSs) described by interval type-2 (IT2) fuzzy models subject to nonperiodic denial of service (DoS) attacks. Under the nonperiodic DoS attacks, the state error caused by the packets loss phenomenon is transformed into an uncertain variable in the designed event-triggered condition. Then, an RET strategy based on the uncertain event-triggered variable is firstly proposed for the nonlinear NCSs. The existing results that utilized the hybrid triggered scheme have the defect of complex control structure, and most of the security compensation methods for handling the impacts caused by DoS attacks need to transmit some compensation data when the DoS attacks disappear, which may lead to large performance loss of the systems. Different from these existing results, the proposed RET strategy can transmit the necessary packets to the controller under nonperiodic DoS attacks to reduce the performance loss of the systems and a new security controller subject to the RET scheme and mismatched membership functions is designed to simplify the network control structure under DoS attacks. Finally, some simulation results are utilized to testify the advantages of the presented approach.

1 January 2018 in IEEE Transactions on Fuzzy Systems
Verified
Journal Article
Closed access
Hao ShenHao Shen
Hao Shen
FLFeng Li
Feng Li
Huaicheng YanHuaicheng Yan
Huaicheng Yan
Hamid Reza KarimiHamid Reza Karimi
Hamid Reza Karimi
Hak Keung LamHak Keung Lam
Hak Keung Lam
This paper investigates the finite-time event-triggered $\mathcal{H}_\infty$ control problem for Takagi-Sugeno Markov jump fuzzy systems. Because of the sampling behaviors and the effect of network environment, the premise variables considered in this paper are subject to asynchronous constraints. The aim of this work is to synthesize a controller via an event-triggered communication scheme such that not only the resulting closed-loop system is finite-time bounded and satisfies a prescribed $\mathcal{H}_\infty$ performance level, but also the communication burden is reduced. Firstly, a sufficient condition is established for the finite-time bounded $\mathcal{H}_\infty$ performance analysis of the closed-loop fuzzy system with fully considering the asynchronous premises. Then, based on the derived condition, the method of the desired controller design is presented. Two illustrative examples are finally presented to demonstrate the practicability and efficacy of the proposed method.

24 November 2015 in IEEE Transactions on Automatic Control
Verified
Journal Article
Closed access
HLHongyi Li
Hongyi Li
YGYabin Gao
Yabin Gao
PSPeng Shi
Peng Shi
Hak Keung LamHak Keung Lam
Hak Keung Lam
In this technical note, a new fault detection design scheme is proposed for interval type-2 (IT2) Takagi-Sugeno (T-S) fuzzy systems with sensor fault based on a novel fuzzy observer. The parameter uncertainties can be captured by the membership functions of the IT2 fuzzy model. The premise variables of the plant are perfectly shared by the fuzzy observer. A stochastic process between the plant and the observer is considered in the system. A fault sensitive performance is established, and then sufficient conditions are obtained for determining the fuzzy observer gains. Finally, simulation results are provided to verify the effectiveness of the presented scheme.

20 March 2013 in IEEE Transactions on Industrial Electronics
Verified
Journal Article
Closed access
Hak Keung LamHak Keung Lam
Hak Keung Lam
HLHongyi Li
Hongyi Li
CDChristian Deters
Christian Deters
Emanuele Lindo SeccoEmanuele Lindo Secco
Emanuele Lindo Secco
HWHelge A. Wurdemann
Helge A. Wurdemann
KAKaspar Althoefer
Kaspar Althoefer
This paper focuses on designing interval type-2 (IT2) control for nonlinear systems subject to parameter uncertainties. To facilitate the stability analysis and control synthesis, an IT2 Takagi-Sugeno (T-S) fuzzy model is employed to represent the dynamics of nonlinear systems of which the parameter uncertainties are captured by IT2 membership functions characterized by the lower and upper membership functions. A novel IT2 fuzzy controller is proposed to perform the control process, where the membership functions and number of rules can be freely chosen and different from those of the IT2 T-S fuzzy model. Consequently, the IT2 fuzzy-model-based (FMB) control system is with imperfectly matched membership functions, which hinders the stability analysis. To relax the stability analysis for this class of IT2 FMB control systems, the information of footprint of uncertainties and the lower and upper membership functions are taken into account for the stability analysis. Based on the Lyapunov stability theory, some stability conditions in terms of linear matrix inequalities are obtained to determine the system stability and achieve the control design. Finally, simulation and experimental examples are provided to demonstrate the effectiveness and the merit of the proposed approach.

4 April 2016 in IEEE Transactions on Cybernetics
Verified
Journal Article
Closed access
HLHongyi Li
Hongyi Li
ZCZiran Chen
Ziran Chen
LWLigang Wu
Ligang Wu
Hak Keung LamHak Keung Lam
Hak Keung Lam
HDHaiping Du
Haiping Du
This paper investigates the problem of fault detection for nonlinear discrete-time networked systems under an event-triggered scheme. A polynomial fuzzy fault detection filter is designed to generate a residual signal and detect faults in the system. A novel polynomial event-triggered scheme is proposed to determine the transmission of the signal. A fault detection filter is designed to guarantee that the residual system is asymptotically stable and satisfies the desired performance. Polynomial approximated membership functions obtained by Taylor series are employed for filtering analysis. Furthermore, sufficient conditions are represented in terms of sum of squares (SOSs) and can be solved by SOS tools in MATLAB environment. A numerical example is provided to demonstrate the effectiveness of the proposed results.