Dongkun Han

The Chinese University of Hong Kong | CUHK · Department of Mechanical and Automation Engineering

Estimating the domain of attraction (DA) of an equilibrium point is a long-standing yet still challenging issue in nonlinear system analysis. The method using the sublevel set of Lyapunov functions is proven to be efficient, but sometimes conservative compared to the estimate via invariant sets. This paper studies the estimation problem of the DA f...

While a number of efficient methods have been proposed for approximating backward reachable sets, no synthesis method via backward reachable sets has been developed for estimating and enlarging the region of attraction (RA). This paper shows how to use backward reachable sets to enlarge the estimate of the RA of linear discrete-time systems, by usi...

This paper investigates robust consensus for a class of uncertain multi-agent dynamical systems. Specifically, it is supposed that the system is described by a weighted adjacency matrix whose entries are polynomial functions of an uncertain vector constrained in a semi-algebraic set. For this uncertain topology, we provide necessary and sufficient...

Finite-time motion planning with collision avoidance is a challenging issue in multi-agent systems. This paper proposes a novel distributed controller based on a new Lyapunov barrier function which guarantees finite-time stability for multi-agent systems without collisions. First, the problem of finite-time motion planning of multi-agent systems is...

Safety guarantee is essential in many engineering implementations. Reinforcement learning provides a useful way to strengthen safety. However, reinforcement learning algorithms cannot completely guarantee safety over realistic operations. To address this issue, this work adopts control barrier functions over reinforcement learning, and proposes a c...

Estimating the region of attraction for partially unknown nonlinear systems is a challenging issue. In this paper, we propose a tractable method to generate an estimated region of attraction with probability bounds, by searching an optimal polynomial barrier function. Techniques of Chebyshev interpolants, Gaussian processes and sum-of-squares progr...

Recent advances in learning techniques have enabled the modelling of unknown dynamical systems directly from data. However, in many contexts, these learning-based methods are short of safety guarantee and strict stability verification. To address this issue, this paper first approximates the partially unknown nonlinear systems by using a learned st...

Estimating the region of attraction for partially unknown nonlinear systems is a challenging issue. In this paper, we propose a tractable method to generate an estimated region of attraction with probability bounds, by searching an optimal polynomial barrier function. Chebyshev interpolants, Gaussian processes and sum-of-squares programmings are us...

Transient stability analysis is a traditional yet significant topic in power systems. The switching control schemes of the HVDC converter station after fault bring new challenges to the direct method of transient stability analysis in AC/DC power systems. To apply the direct method to investigate the transient stability of power systems accommodati...

An essential problem in the coordination of multiple agents is formation control. Significant challenges to the theoretical design may arise when the multi-agent system is subject to uncertainty. This paper considers the robust multitask formation control problem for multiple agents whose communication and measurements are disturbed by uncertain pa...

Motivated by the need to simultaneously guarantee safety and stability of safety-critical dynamical systems, we construct permissive barrier certificates in this paper that explicitly maximize the region where the system can be stabilized without violating safety constraints. An optimization strategy is developed to search for the maximum volume ba...

We consider the multi-task coordination problem for multi-agent systems under the following objectives: 1. collision avoidance; 2. connectivity maintenance; 3. convergence to desired destinations. The paper focuses on the safety guaranteed region of multi-task coordination (SG-RMTC), i.e., the set of initial states from which all trajectories conve...

Estimating the Domain of Attraction (DA) of non-polynomial systems is a challenging problem. Taylor expansion is widely adopted for transforming a nonlinear analytic function into a polynomial function, but the performance of Taylor expansion is not always satisfactory. This paper provides solvable ways for estimating the DA via Chebyshev approxima...

This paper presents a robust distributed coordination protocol that achieves generation of collision-free trajectories for multiple unicycle agents in the presence of stochastic uncertainties. We build upon our earlier work on semi-cooperative coordination and we redesign the coordination controllers so that the agents counteract a class of state (...

Formation control is a key problem in the coordination of multiple agents. It arises new challenges to traditional formation control strategy when the communication among agents is affected by uncertainties. This paper considers the robust multi-task formation control problem of multiple non-point agents whose communications are disturbed by uncert...

The goal of this study was to develop a new processing method for coal tar modification. Coal tar was extracted by binary mixed solvents which consist of toluene and n-heptane. Purified tar and coal tar pitch were obtained in the process. The results indicate that the ash content of coal tar is decreased from 1.89% to 0.03%, TI content is reduced f...

We propose and implement an algorithm based on reachability analysis to estimate the region of attraction (ROA) of an equilibrium point for nonlinear systems. The stability region is obtained via the computation of forward reachable sets. We compare our results with well-established techniques in this area. In particular, we consider the optimizati...

The non-aromatic hydrocarbon (NAH), fraction rich in aromatic(<360°C) and soft pitch were separated from coal tar by DMF extraction under optimal conditions: 50°C, solvent/coal tar of 1.5, with yields of 20.8%, 38.7 % and 40.5%, respectively. Compared with the components distilled directly from coal tar,aromatics content was more enriched in <360°C...

The integration of mixed-critical tasks into a platform is an increasingly important trend in the design of real-Time systems due to its efficient resource usage. With a growing variety of activation patterns considered in real-Time systems, some of them capture arbitrary activation patterns. As a consequence, the existing scheduling approaches in...

The goal of this research was to develop and optimize solvent extraction techniques for processing Baoming shale oil. The influence of extraction solvent, extraction temperature, solvent/oil mass ratio, and settling time on shale oil refining was investigated and the optimized conditions were determined. The results show that among the tested solve...

Extract oil in the Xinjiang Baoming shale oil was separated through solvent refining with furfural as the solvent. Then phenols in the extract oil were concentrated preliminarily. The fraction of ≤280℃ in the extract oil was separated as the raw materials for deeper enrichment. The enriched phenols were obtained by column chromatography and analyze...

An increasingly important issue in the area of uncertain systems is the estimation of the Robust Domain of Attraction (RDA). Though this topic is of great interest, most of attention has been paid to the RDA for uncertain polynomial systems. This paper considers the RDA for rational polynomial systems and non-polynomial systems, both with parametri...

The load-following capabilities of power plants became increasingly important in recent years as a means of ensuring a reliable operation of future power systems. In this work, we propose a generic approach, based on reachability analysis, to rigorously verify the safety of critical components that often pose limitations on the flexibility of conve...

Indonesian oil sands were separated in a multi-phase extraction system with solvent phase, water washing agent phase and oil sands. The effects of m(water)∶m(oil sands), pH of water phase, m(solvents)∶m(oil sands) and temperature on the extraction of bitumen from the oil sands were studied. The results showed that, under the optimum technological c...

Transient stability analysis is a traditional yet significant topic in power systems. In order to obtain the stability domain of the post-fault equilibrium point, the Lyapunov method is proven to be effective and efficient once a Lyapunov function has been found. The main innovation of this paper consists in the use of rational Lyapunov functions t...

Robust synchronization problem is a key issue in chaotic circuits and nonlinear systems. This paper is concerned with robust synchronization problem of polynomial nonlinear system affected by time-varying uncertainties on topology, i.e., structured uncertain parameters constrained in a bounded-rate polytope. Via partial contraction analysis, novel...

This paper investigates robust consensus for multi-agent systems with discrete-time dynamics affected by uncertainty. In particular, the paper considers multi-agent systems with single and double integrators, where the weighted adjacency matrix is a polynomial function of uncertain parameters constrained into a semialgebraic set. Firstly, necessary...

This study studies robust local synchronisation in multi-agent systems with time-varying parametric uncertainties constrained in a polytope. In contrast to the existing methods with non-convex conditions via using quadratic Lyapunov function, a new criteria is proposed based on using homogeneous polynomial Lyapunov functions where the original syst...

This brief studies local and global synchronization in multiagent systems with nonlinear dynamics with respect to equilibrium points and periodic orbits. For local synchronization, a method is proposed based on the transformation of the original system into an uncertain polytopic system and on the use of homogeneous polynomial Lyapunov functions. F...

This paper addresses robust discrete-time consensus problem of multiple agents with uncertain structure, where the network coupling weights are supposed polynomial functions of an uncertain vector constrained in a semialgebraic set. Based on the Lyapunov stability theory, a necessary and sufficient condition for robust discrete-time consensus is pr...

This paper addresses robust consensus problems among multiple agents with uncertain parameters constrained in a given set. Specifically, the network coefficients are supposed polynomial functions of an uncertain vector constrained in a set described by polynomial inequalities. First, the paper provides a necessary and sufficient condition for robus...

A novel non-mechanistic approach for voltage collapse is proposed. By incorporating the notions of ranking clustering and fuzzy weighting with rough-set clustering, a new algorism for load clustering is presented, and then the probability model of load distribution is constructed. In the basis of fuzzy regression analysis of load improving pattern,...

A reactive power optimization model is presented, which considers both static and dynamic reactive power compensation. The probability model of voltage collapse is constructed based on the load margin probability analysis using the least square algorithm. The comprehensive reactive power optimization model is proposed based on the probability analy...