Liwei An

Prof. Liwei An

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Academic Career Length

10Years (2017-Present)

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

Representative Publications

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12 January 2018 in IEEE Transactions on Cybernetics
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Journal Article
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LALiwei An
Liwei An
Guanghong YangGuanghong Yang
Guanghong Yang
Cyber-physical systems (CPSs) are naturally highly interconnected and complexly nonlinear. This paper investigates the problem of decentralized adaptive output feedback control for CPSs subject to intermittent denial-of-service (DoS) attacks. The considered CPSs are modeled as a class of nonlinear uncertain strict-feedback interconnected systems. When a DoS attack is active, all the state variables become unavailable and standard backstepping cannot be applied. To overcome this difficulty, a switching-type adaptive state estimator is constructed. Based on an improved average dwell time method incorporated by frequency and duration properties of DoS attacks, convex design conditions of controller parameters are derived in term of solving a set of linear matrix inequalities. The proposed controller guarantees that all closed-loop signals remain bounded, while the error signals converge to a small neighborhood of the origin. As an illustrative example, the proposed control scheme is applied to a power network system.
26 October 2017 in IEEE Transactions on Automatic Control
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LALiwei An
Liwei An
Guanghong YangGuanghong Yang
Guanghong Yang
This paper investigates the problem of secure state estimation for cyber-physical systems modeled by continuous or discrete-time linear systems when some sensors are corrupted by an attacker. A novel state observer is proposed with adaptive switching mechanism. Attack tolerance principle is established based on adaptively truncating the injection channels of attacks. To implement it, a switching function matrix is introduced into the observer design. Driven by a well-defined performance index, the switching function matrix automatically reaches and remains in the desired entry mode and turns off the input channels of attacks. Based on the equivalence between $s$-strong detectability of the observation error system and $2s$-sparse detectability of the original system, the observation error system is proven to be asymptotically stable even under the cyber attacks. Compared with the existing complex static batch optimization algorithms, the proposed adaptive observer can be derived only by offline solving a set of simple linear matrix inequalities. Simulation examples are given to illustrate the estimation performance and the computational efficiency of the proposed method.
3 July 2023 in IEEE Transactions on Automatic Control
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LALiwei An
Liwei An
Guanghong YangGuanghong Yang
Guanghong Yang
CDChao Deng
Chao Deng
CWChangyun Wen
Changyun Wen
Reference governors are add-on control schemes which enforce state constraints on pre-stabilized systems by modifying, whenever necessary, the reference. This paper studies the design schemes of reference governors for collisions-free leader-following coordination (CF-LFC) of nonlinear multi-agent systems under unreliable communications. The “unreliability” is characterized as irregular topology switchings (e.g., due to communication failures, adversarial attacks, or other agents' blockages), which will often cause large transient coordination errors and further result in interagent collisions. To address it, an event-triggered reference governor is proposed which dominates agents to perform the leader-following task if the tracking error meets the closed-loop system performance requirement, and otherwise the agents will temporarily “forget” the task and focus on avoiding collisions. By constructing heterogeneous Lyapunov functions, it is shown that the reference governor can achieve the CF-LFC despite the presence of topology switchings. Also, for a special class of nonlinear systems with strict-feedback form, a non-event-triggered reference governor is further proposed by reconstructing the controller with a high-order integrator of barrier function as the control gain to adaptively adjust the transient tracking errors.
7 December 2021 in IEEE Transactions on Automatic Control
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LALiwei An
Liwei An
Guanghong YangGuanghong Yang
Guanghong Yang
This paper studies the problem of distributed optimal coordination (DOC) for heterogeneous linear multi-agent systems. Compared with the existing results where the structure constraints on local gradients or system matrices are required, the considered DOC framework is sufficiently general in the sense that no extra assumption is required except for the convexity/differentiability of local objective functions and the controllability/observability of linear systems. A necessary and sufficient condition for the existence of the solution to the DOC problem is proposed in terms of the relationship between the objective function and so-called convergence-reachable set of linear systems. Under this fundamental condition, the original DOC problem is transformed into the one with additive equality constraint, without loss of the optimality, which generates a trackable solution for agent dynamics. By using a new state transformation technique, it is proved that the proposed DOC algorithm guarantees the global asymptotical convergence by utilizing only local interaction. Simulation results on the motion coordination illustrate the proposed algorithm.
11 May 2021 in IEEE Transactions on Automatic Control
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LALiwei An
Liwei An
Guanghong YangGuanghong Yang
Guanghong Yang
Multiagent distributed optimal coordination (DOC) involves the motion conflicts of a large numbers of physical systems, which lead to significant safety challenges in terms of collision avoidance. This article studies the problem of secure DOC for multiple uncertain Euler–Lagrangian (EL) systems. The objective is to steer each EL agent to achieve the optimization task while avoiding collisions with other agents. The main challenge focuses on the co-design of optimal coordination strategy and collision avoidance mechanism. The safety barrier certificates in the closed form of path integrals are constructed, which generate provably collisions-free behaviors. With convex optimization and adaptive nonlinear control, a fully distributed protocol is proposed. Based on Lyapunov method and boundedness analysis for the barrier functions, it is proved that the protocol simultaneously guarantees the global convergence and collision avoidance of the EL systems in the presence of parametric uncertainties .
4 June 2024 in IEEE Transactions on Automatic Control
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LALiwei An
Liwei An
Guanghong YangGuanghong Yang
Guanghong Yang
This article studies the problem of collision/obstacle avoidance in the distributed cooperative output regulation of nonlinear multiagent systems (MASs). First, a nonlinear distributed command governor equipped by two dynamical barrier functions is constructed to generate safe command signals. Then, a filtering-based distributed command tracking control scheme is proposed. It is shown that the MAS adaptively reconfigures its formation shape in a distributed way when entering into the barrier function's coverage to avoid collisions, and quickly recovers the desired formation shape along with the reference trajectory after being away from the barrier function's coverage. Simulation results are given to illustrate the effectiveness of the proposed scheme.