List of English Publication

@article{KimYangShimKimSeo16,

title = {Robustness of Synchronization of Heterogeneous Agents by Strong Coupling and a Large Number of Agents},

author = {Jaeyong Kim and Jongwook Yang and Hyungbo Shim and Jung-Su Kim and Jin Heon Seo},

doi = {10.1109/TAC.2015.2498138},

year  = {2016},

date = {2016-10-01},

journal = {IEEE Transactions on Automatic Control},

volume = {61},

number = {10},

pages = {3096-3102},

abstract = {This technical note studies robustness of synchronization against heterogeneity of multi-agent systems. Here, heterogeneity also includes uncertainties and external disturbances in each agent. In order to effectively deal with the heterogeneous agents, we introduce the concept of the averaged dynamics which is the average of all agents’ dynamics, and then claim that two sources enhance the robustness of synchronized behavior against heterogeneity of agents’ dynamics. First, in spite of the heterogeneity of agents’ dynamics, we show that strong coupling among agents makes the trajectories of all agents arbitrarily close to the averaged dynamics. Second, in the averaged dynamics, the effect of variations in each agent gets smaller as the number of agents increases. Simulation results confirm the claim that a large number of agents with strong couplings have robust synchronization.},

keywords = {Blended dynamics, Heterogeneity, Multi-agent system, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{JooParkBackShim16,

title = {Embedding Internal Model in Disturbance Observer with Robust Stability},

author = {Youngjun Joo and Gyunghoon Park and Juhoon Back and Hyungbo Shim },

doi = {10.1109/TAC.2015.2503559},

year  = {2016},

date = {2016-10-01},

journal = {IEEE Transactions on Automatic Control},

volume = {61},

number = {10},

pages = {3128-3133},

abstract = {Abstract:

The disturbance observer has been widely employed in applications due to its powerful ability for disturbance rejection and robustness under plant uncertainties. However, it rejects the disturbance approximately rather than exactly since it is usually designed without considering structural properties of disturbance. In order to improve the disturbance rejection performance, we propose a design method to embed the internal model of disturbance into the disturbance observer structure. Furthermore, a systematic design procedure is proposed so that one can always design the disturbance observer to guarantee robust stability of the closed-loop system even though uncertain parameters of the plant belong to an arbitrarily large (but bounded) set.},

keywords = {Control system synthesis, Observer, Robustness},

pubstate = {published},

tppubtype = {article}

}

@article{ShimParkJooBackJo16,

title = {Yet Another Tutorial of Disturbance Observer: Robust Stabilization and Recovery of Nominal Performance},

author = {Hyungbo Shim and Gyunghoon Park and Youngjun Joo and Juhoon Back and Nam Hoon Jo},

url = {https://arxiv.org/abs/1601.02075},

doi = {10.1007/s11768-016-6006-9},

year  = {2016},

date = {2016-08-01},

journal = {Control Theory and Technology},

volume = {14},

number = {3},

pages = {237-249},

abstract = {This paper presents a tutorial-style review on the recent results about the disturbance observer (DOB) in view of robust stabilization and recovery of the nominal performance. The analysis is based on the case when the bandwidth of Q-filter is large, and it is explained in a pedagogical manner that, even in the presence of plant uncertainties and disturbances, the behavior of real uncertain plant can be made almost similar to that of disturbance-free nominal system both in the transient and in the steady-state. The conventional DOB is interpreted in a new perspective, and its restrictions and extensions are discussed.},

keywords = {Disturbance observer, Disturbance rejection, Robust transient response},

pubstate = {published},

tppubtype = {article}

}

@article{KimKimBackShimSeo16,

title = {Design of Stable Parallel Feedforward Compensator and its Application to Synchronization Problem},

author = {Hongkeun Kim and Seongjun Kim and Juhoon Back and Hyungbo Shim and Jin Heon Seo},

doi = {10.1016/j.automatica.2015.11.020},

year  = {2016},

date = {2016-02-01},

journal = {Automatica},

volume = {64},

pages = {208-216},

abstract = {This paper addresses the design problem of a stable parallel feedforward compensator V for a given SISO LTI plant P (possibly being of non-minimum phase and/or having relative degree greater than one). The objective of the problem is that their parallel interconnection P+V becomes minimum phase having relative degree one. Based on the classical results of simultaneous stabilization, a necessary and sufficient condition for solving the problem is presented as well as a design procedure for constructing such a compensator. The proposed feedforward compensator allows the control system to have the three useful features: (1) the ability that assigns the zeros of P+V to a region of complex numbers having arbitrary negative real parts, (2) infinite gain margin property of P+V controlled by a static output feedback, and (3) block diagonal structure of P+V. These features are extensively exploited in the synchronization problem of multi-agent systems to achieve arbitrary fast convergence rate and to have the synchronized trajectory independent of the initial conditions and parameters of the involved dynamic controllers.},

keywords = {Multi-agent system, Non-minimum phase, Parallel feedforward compensator, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{JeonAumShimEun16,

title = {Resilient State Estimation for Control Systems Using Multiple Observers and Median Operation},

author = {Heegyun Jeon and Sungmin Aum and Hyungbo Shim and Yongsoon Eun},

doi = {10.1155/2016/3750264},

year  = {2016},

date = {2016-01-01},

journal = {Mathematical Problems in Engineering},

volume = {2016},

abstract = {This paper addresses the problem of state estimation for linear dynamic systems that is resilient against malicious attacks on sensors. By “resiliency” we mean the capability of correctly estimating the state despite external attacks. We propose a state estimation with a bank of observers combined through median operations and show that the proposed method is resilient in the sense that estimated states asymptotically converge to the true state despite attacks on sensors. In addition, the effect of sensor noise and process disturbance is also considered. For bounded sensor noise and process disturbance, the proposed method eliminates the effect of attack and achieves state estimation error within a bound proportional to those of sensor noise and disturbance. While existing methods are computationally heavy because online solution of nonconvex optimization is needed, the proposed approach is computationally efficient by using median operation in the place of the optimization. It should be pointed out that the proposed method requires the system states being observable with every sensor, which is not a necessary condition for the existing methods. From resilient system design point of view, however, this fact may not be critical because sensors can be chosen for resiliency in the design stage. The gained computational efficiency helps real-time implementation in practice.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ShimLiberzon16,

title = {Nonlinear Observers Robust to Measurement Disturbances in an ISS Sense},

author = {Hyungbo Shim and Daniel Liberzon},

doi = {10.1109/TAC.2015.2423911},

year  = {2016},

date = {2016-01-01},

journal = {IEEE Transactions on Automatic Control},

volume = {61},

number = {1},

pages = {48-91},

abstract = {This paper formulates and studies the concept of quasi-Disturbance-to-Error Stability (qDES) which characterizes robustness of a nonlinear observer to an output measurement disturbance. In essence, an observer is qDES if its error dynamics are input-to-state stable (ISS) with respect to the disturbance as long as the plant's input and state remain bounded. We develop Lyapunov-based sufficient conditions for checking the qDES property for both full-order and reduced-order observers. We use these conditions to show that several well-known observer designs yield qDES observers, while some others do not. Our results also enable the design of novel qDES observers, as we demonstrate with examples. When combined with a state feedback law robust to state estimation errors in the ISS sense, a qDES observer can be used to achieve output feedback control design with robustness to measurement disturbances. As an application of this idea, we treat a problem of stabilization by quantized output feedback.},

keywords = {Control system synthesis, Lyapunov method},

pubstate = {published},

tppubtype = {article}

}

@article{LiberzonShim15,

title = {An Asymptotic Ratio Characterization of Input-to-State Stability},

author = {Daniel Liberzon and Hyungbo Shim},

doi = {10.1109/TAC.2015.2422482},

year  = {2015},

date = {2015-12-01},

journal = {IEEE Transactions on Automatic Control},

volume = {60},

number = {12},

pages = {3401-3404},

abstract = {For continuous-time nonlinear systems with inputs, we introduce the notion of an asymptotic ratio input-to-state stability (ISS) Lyapunov function. The derivative of such a function along solutions is upper-bounded by the difference of two terms whose ratio is asymptotically smaller than 1 for large states. This asymptotic ratio condition is sometimes more convenient to check than standard ISS Lyapunov function conditions. We show that the existence of an asymptotic ratio ISS Lyapunov function is equivalent to ISS. A related notion of ISS with nonuniform convergence rate is also explored.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{OhKimShim15,

title = {Observer-based Feedback Controller Design for Robust Tracking  of Discrete-time Polytopic Uncertain LTI Systems},

author = {Sangrok Oh and Jung-Su Kim and Hyungbo Shim},

doi = {10.5370/JEET.2015.10.6.2427},

year  = {2015},

date = {2015-11-01},

journal = {Journal of Electrical Engineering and Technology},

volume = {10},

number = {6},

pages = {2427-2433},

abstract = { This paper presents an observer–based robust controller for constant reference tracking of linear time invariant systems with polytopic model uncertainties. To this end, this paper not only designs a robust integral controller gain but also suggests how to determine the robust observer gain and the observer model used in the observer. Since the observer model selection is not obvious due to the polytopic uncertainties, particular attention needs to be paid to that. This paper computes the robust controller and observer gains first. Then, the observer model is selected in a way that the whole closedloop is stable and LMIs are used in the middle of choosing the gains and observer model. Simulation examples show that the proposed observer-based feedback control successfully achieves robust reference tracking. },

keywords = {Tracking},

pubstate = {published},

tppubtype = {article}

}

@article{HaParkShim15,

title = {Enhanced Performance of Disturbance Observer by Embedding a Filter and Its Application to Hard Disk Drive},

author = {Jongsoo Ha and Gyunghoon Park and Hyungbo Shim},

url = {http://www.dbpia.co.kr/Journal/ArticleDetail/NODE06513742},

year  = {2015},

date = {2015-09-01},

journal = {제어로봇시스템학회 논문지},

volume = {21},

number = {9},

pages = {811-817},

abstract = {In this paper, we present a new control structure which is obtained by adding an appropriately designed filter to a conventional disturbance observer. The proposed controlled system preserves advantages of a system with the conventional disturbance observer; disturbance rejection and nominal performance recovery. In particular, by embedding the filter, the disturbance rejection performance is enhanced compared with that of the classical disturbance observer-based controlled system. Moreover, we suggest a condition for the robust internal stability of the considered system in this paper. Simulation results regarding an effect of relatively high-frequency disturbance on hard disk drive are also presented.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{KoSongImKimJangShimCho15,

title = {Bioinspired Piezoresistive Acceleration Sensor Using Artificial Filiform Sensillum Structure},

author = {Hyoungho Ko and Haryong Song and Seunghyun Im and Hyunho Kim and Byungmoon Jang and Hyungbo Shim and Dong-il “Dan” Cho},

doi = {10.18494/SAM.2015.1082},

year  = {2015},

date = {2015-08-01},

journal = {Sensors and Materials},

volume = {27},

number = {6},

pages = {437-445},

abstract = {Hairlike structures can be found in many living things, and are considered to be the fundamental sensing structure, especially for insects. In this paper, we present a bioinspired hairlike acceleration sensor using an artificial filiform sensillum structure. The hairlike acceleration sensor is fabricated using a rigid metal rod attached to a thin piezoresistive membrane. When external acceleration is applied to the rod, the torque generates the rotational angle, thus resulting in the deflection of the membrane. The noise equivalent input acceleration resolution, the input acceleration range, and the sensitivity of the fabricated sensor are 86 mg, ±5 g, and 0.576 mV/g, respectively.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{KimHim15,

title = {Linear Systems with Hyperbolic Zero Dynamics Admit Output Regulator Rejecting Unknown Number of Unknown Sinusoids},

author = {Hyungjong Kim and Hyungbo Shim},

doi = {10.1049/iet-cta.2014.0692},

year  = {2015},

date = {2015-06-01},

journal = {IET Control Theory and Applications },

volume = {9},

number = {6},

pages = {1472-1480},

abstract = {This study presents an off-the-shelf error feedback controller that can completely rejects the sinusoidal disturbances whose magnitudes, phases, bias, frequencies and even the number of frequencies are all unknown. A closed-form solution is given under the assumptions that the plant has no uncertainty and has hyperbolic zero dynamics (i.e. there is no zero on the imaginary axis of the complex plane), and that the number of unknown frequencies has upper bound which is known. A non-minimum phase plant can be dealt with. The proposed controller is tested by a simulation, which verifies its effectiveness.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{SonKimChoiShim15,

title = {Robust Cascade Control of Electric Motor Drives Using Dual Reduced-Order PI Observer},

author = {Young Ik Son and In Hyuk Kim and Dae Sik Choi and Hyungbo Shim},

doi = {10.1109/TIE.2014.2374571},

year  = {2015},

date = {2015-06-01},

journal = {IEEE Transactions on Industrial Electronics},

volume = {62},

number = {6},

pages = {3672-3682},

abstract = {Gyunghoon Park and Daniel Liberzon and This paper addresses the problem of preserving the nominal performance of a conventional cascade controller for electric motor drives in the presence of parameter uncertainties and external disturbances. Practical reduced-order proportional-integral (PI) observers are incorporated with predesigned PI controllers in order to enhance the robust performance of current and speed controllers. A unified analysis based on the singular perturbation theory is  presented to confirm the desired approximation of the augmented system with the PI observers to the nominal closed-loop system. The validity of the proposed dual observer-based control scheme is tested via computer simulations and experiments using a dc motor system. Both results verify that the proposed controller can be used effectively to recover the nominal performance of the conventional cascade scheme for electric motor drives.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{LeeShim15,

title = {Robust Estimation Algorithm for Switching Signal and State of Discrete-time Switched Linear Systems},

author = {Chanhwa Lee and Hyungbo Shim},

url = {http://www.dbpia.co.kr/Journal/ArticleDetail/NODE06339260},

year  = {2015},

date = {2015-05-01},

journal = {전자공학회논문지},

volume = {52},

number = {5},

pages = {214-221},

abstract = {In this paper, we present robust estimation and detection algorithms for discrete-time switched linear systems whose output measurements are corrupted by noises. First, a mode estimation algorithm is proposed based on the minimum distance criterion. Then, state variables are also observed under the active mode estimate. Second, a detection algorithm is constructed to detect the mode switching of the switched system. With the boundedness of measurement noise, the proposed estimation algorithm returns the exact active mode and approximate state information of the switched system. In addition, the detection algorithm can detect the switching time within a pre-determined time interval after the actual switching occurred.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{TanwaniShimLiberzon15,

title = {Comments on “Observability of Switched Linear Systems: Characterization and Observer Design”},

author = {Aneel Tanwani and Hyungbo Shim and Daniel Liberzon},

doi = {10.1109/TAC.2015.2422483},

year  = {2015},

date = {2015-04-30},

journal = {IEEE Transactions on Automatic Control},

volume = {60},

number = {12},

pages = {3396-3400},

abstract = {This note points out certain limitations of our results from the paper mentioned in the title, and provides a modified approach to overcome these limitations. Specifically, the observer design addressed in the aforementioned paper is, in general, only applicable to switched linear systems with invertible state reset maps and this note presents a modified algorithm for state estimation that can also handle non-invertible state reset maps. In the process, we also identify some equalities from that paper which may not hold in general for arbitrary state reset maps.},

keywords = {Linear system},

pubstate = {published},

tppubtype = {article}

}

@article{VengertsevKimSeoShim15,

title = {Consensus of Output-coupled High-order Linear Multi-agent Systems Under Deterministic and Markovian Switching Networks},

author = {Dmitry Vengertsev and Hongkeun Kim and Jin Heon Seo and Hyungbo Shim},

doi = {10.1080/00207721.2013.835884},

year  = {2015},

date = {2015-04-01},

journal = {International Journal of Systems Science},

volume = {46},

number = {10},

pages = {1790-1799},

abstract = {Consensus problem for high-order multi-agent systems is considered under deterministic and Markovian switching topologies. Only relative output information of agents is assumed to be available through the networks. First, a necessary and sufficient condition for achieving a consensus under a fixed communication network is presented. Based on this result and the stability of switched systems, a high-order multi-agent system with the proposed low-gain controller is shown to reach a consensus under deterministic switching network if the total time when the network is disconnected is, in some senses, smaller than the total time of the network being connected. Furthermore, the conditions sufficient for a high-order multi-agent system to reach an almost sure and mean-square consensus, under Markovian switching networks, are presented. Finally, illustrative examples are given to demonstrate the results.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{BackShim14,

title = {Reduced-order Implementation of Disturbance Observers for Robust Tracking of Nonlinear Systems},

author = {Juhoon Back and Hyungbo Shim},

doi = {10.1049/iet-cta.2013.1036},

year  = {2014},

date = {2014-11-20},

journal = {IET Control Theory and Applications},

volume = {8},

number = {17},

pages = {1940-1948},

abstract = {The disturbance-observer-based control (DOBC) is a well-known robust control scheme and recently its non-linear version has been developed. Observing that two components (so-called Q-filters) in the conventional DOBC structure have the same transfer function, the authors propose a reduced-order DOBC for uncertain non-linear systems. It is shown that the proposed controller also guarantees the same robust transient response as those developed before. Numerical simulations using a magnetic levitation system are included to illustrate the detailed design procedure and validate the performance of the proposed controller.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ChoYangSeo14,

title = {Reduced-order Dynamic Observer Error Linearisation: A Natural Extension of Observer Error Linearisation},

author = {Hansung Cho and Jongwook Yang and Jin Heon Seo},

doi = {10.1080/00207179.2014.906071},

year  = {2014},

date = {2014-11-01},

journal = {International Journal of Control},

volume = {87},

number = {11},

pages = {2223-2238},

abstract = {This paper introduces the concept of reduced-order dynamic observer error linearisation (RDOEL) for multi-output systems, which is the problem of transforming a nonlinear system into a nonlinear observer canonical form with the aid of auxiliary dynamics. The proposed RDOEL framework is not only a modified version of dynamic observer error linearisation (DOEL) but also a natural extension of observer error linearisation (OEL). We provide three necessary conditions for the RDOEL problem, and then derive a necessary and sufficient condition described in terms of Lie algebras of vector fields. Furthermore, from the result, we also give a geometric necessary and sufficient condition for the OEL problem, which has not yet been completely established in the case where a diffeomorphism on the output of general form is considered.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{KimBackPark14,

title = {Design of Q-filters for Disturbance Observers via BMI Approach},

author = {Jung-Su Kim and Juhoon Back and Gyunghoon Park

},

doi = {10.1109/ICCAS.2014.6987741},

year  = {2014},

date = {2014-10-22},

journal = {Proc. of 2014 14th  International Conference on Control, Automation and Systems (ICCAS)},

pages = {1197-1200},

abstract = {The type-k disturbance observer, also known as high order disturbance observer, is a robust output feedback controller which can reject polynomial-in-time disturbances exactly and at the same time unmodeled disturbances approximately. To ensure the robust stability of the closed-loop system, the key component of the controller called Q-filter should be designed appropriately. In this paper, we formulate the design problem in terms of a set of bilinear matrix inequalities so that the coefficients of Q-filters are chosen simultaneously. The solution from the proposed method can be less conservative compared to the recursive design procedure developed recently.},

keywords = {Robustness},

pubstate = {published},

tppubtype = {article}

}

@article{OhKimShim14,

title = {Robust Stabilization of Uncertain LTI Systems via Observer Model Selection},

author = {Sangrok Oh and Jung-Su Kim and Hyungbo Shim},

url = {https://www.dbpia.co.kr/Journal/ArticleDetail/NODE02450486},

year  = {2014},

date = {2014-08-01},

journal = {제어로봇시스템학회 논문지},

volume = {20},

number = {8},

pages = {822-827},

abstract = {This paper presents a robust observer?based output feedback control for stabilization of linear time invariant systems with polytopic uncertainties. To this end, this paper not only finds a robust observer gain but also suggests how to determine the model used in the observer, which is not obvious due to model uncertainties in the conventional observer design method. The robust observer gain and the observer model are selected in a way that the whole closed-loop is stable by solving LMIs and BMIs (Linear Matrix Inequalities and Bilinear Matrix Inequalities). A simulation example shows that the proposed robust observer-based output feedback control successfully leads to closed-loop stability.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{JoJooShim14,

title = {A study of Disturbance Observers with Unknown Relative Degree of the Plant},

author = {Nam Hoon Jo and Youngjun Joo and Hyungbo Shim},

doi = {10.1016/j.automatica.2014.04.015},

year  = {2014},

date = {2014-06-01},

journal = {Automatica},

volume = {50},

number = {6},

pages = {1730-1734},

abstract = {Robust stability of the disturbance observer (DOB) control system is studied when the relative degree of the plant is not the same as that of the nominal model. The study reveals that the closed-loop system can easily become unstable with sufficiently fast Q-filter when the relative degree of the plant is not known. In a few cases of unknown relative degree, however, robust stability can be obtained, and we present a design guideline of the nominal model, as well as the Q-filter, for that purpose. Moreover, a universal design of DOB is given for a plant whose relative degree is uncertain but less than or equal to four.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ShimTanwani14,

title = {Hybrid-type Observer Design Based on a Sufficient Condition for Observability in Switched Nonlinear Systems},

author = {Hyungbo Shim and Aneel Tanwani},

doi = {10.1002/rnc.2901 },

year  = {2014},

date = {2014-04-01},

journal = {International Journal of Robust and Nonlinear Control},

volume = {24},

number = {6},

pages = {1064-1089},

abstract = {This paper presents a sufficient condition for observability of continuous‐time switched nonlinear systems that also involve state jumps. Without the assumption of observability of individual modes, the sufficient condition is based on gathering partial information from each mode so that the state is completely recovered after several switchings. Based on the sufficient condition, a hybrid‐type observer is designed, which comprises a copy of the actual plant and an error correction scheme at discrete time instants. In order to execute the proposed design, the observable component of the state at each mode needs to be estimated without transients or ‘peaking’ (caused by high‐gain observers), and this motivates us to introduce a back‐and‐forth estimation technique. Under the assumption of persistent switching, analysis shows that the estimate thus generated converges asymptotically to the actual state of the system. Simulation results validate the utility of the proposed algorithm. Copyright © 2012 John Wiley & Sons, Ltd.},

keywords = {Large‐time observability},

pubstate = {published},

tppubtype = {article}

}

@article{KimShimJo14,

title = {Adaptive Add-on Output Regulator for Rejection of Sinusoidal Disturbances and Application to Optical Disc Drives},

author = {Hyungjong Kim and Hyungbo Shim and Nam Hoon Jo},

doi = {10.1109/TIE.2014.2304920},

year  = {2014},

date = {2014-02-10},

journal = {IEEE Transactions on Industrial Electronics},

volume = {61},

number = {10},

pages = {5490-5499},

abstract = {In this paper, we revisit an add-on output feedback controller that achieves output regulation and disturbance rejection. By add-on controller, we mean an additional controller, which runs harmonically with a preinstalled controller that has been in operation for the plant. When the disturbance attenuation performance of the preinstalled controller is not satisfactory, the add-on controller can be used to eliminate the disturbance. Some advantages of the proposed add-on controller include that it can be designed without much information about the preinstalled controller and it can be plugged in the feedback loop any time in operation without causing unnecessary transient response. In particular, we propose an adaptive add-on controller, which can eliminate sinusoidal disturbances of unknown frequencies. Both simulation and experimental results of the track-following control for optical disc drive systems confirm the effectiveness of the proposed method.},

keywords = {Adaptive control, Control system synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{LeeJoShimSon13,

title = {On the Stability of Critical Point for Positive Systems and Its Applications to Biological Systems},

author = {Joo-Won Lee and Nam Hoon Jo and Hyungbo Shim and Young Ik Son},

doi = {10.5370/JEET.2013.8.6.1530},

year  = {2013},

date = {2013-11-01},

journal = {Journal of Electrical Engineering and Technology},

volume = {8},

number = {6},

pages = {1530-1541},

abstract = {The coexistence and extinction of species are important concepts for biological systems and can be distinguished by an investigation of stability. When determining local stability of nonlinear systems, Lyapunov indirect method based on the Jacobian linearization has been widely employed due to its simplicity. Despite such popularity, it is not applicable to singular systems whose Jacobian has at least one eigenvalue that is equal to zero. In such singular cases, an appropriate Lyapunov function should be sought to determine the stability of systems, which is rather difficult and quite involved. In this paper, we seek for a simple criterion to determine stability of the equilibrium that is located at the boundary of the positive orthant, when one of eigenvalues of the Jacobian is zero. The goal of the paper is to present a generalized condition for the equilibrium to attract all trajectories that starting from initial condition in the positive orthant and near the equilibrium. Unlike the Lyapunov direct method, the proposed method requires just a simple algebraic computation for checking the stability of the critical point. Our approach is applied to various biological systems to show the effectiveness of the proposed method.},

keywords = {Center manifold, Positive system},

pubstate = {published},

tppubtype = {article}

}

@article{VengertsevKimSeoShim13,

title = {Consensus of output-coupled high-order linear multi-agent systems under deterministic and Markovian switching networks},

author = {Dmitry Vengertsev and Hongkeun Kim and Jin Heon Seo and Hyungbo Shim},

doi = {10.1080/00207721.2013.835884},

issn = {0020-7721},

year  = {2013},

date = {2013-09-20},

journal = {International Journal of Systems Science},

volume = {46},

number = {10},

pages = {1790-1799},

abstract = {Consensus problem for high-order multi-agent systems is considered under deterministic and Markovian switching topologies. Only relative output information of agents is assumed to be available through the networks. First, a necessary and sufficient condition for achieving a consensus under a fixed communication network is presented. Based on this result and the stability of switched systems, a high-order multi-agent system with the proposed low-gain controller is shown to reach a consensus under deterministic switching network if the total time when the network is disconnected is, in some senses, smaller than the total time of the network being connected. Furthermore, the conditions sufficient for a high-order multi-agent system to reach an almost sure and mean-square consensus, under Markovian switching networks, are presented. Finally, illustrative examples are given to demonstrate the results.},

keywords = {Consensus, nonlinear},

pubstate = {published},

tppubtype = {article}

}

@article{YunYangSeo13,

title = {Reduced-order Dynamic Observer Error Linearisation for Discrete-time Systems: An Extension of the Classical Observer Error Linearisation},

author = {Hyeonjun Yun and Jongwook Yang and Jin Heon Seo},

doi = {10.1049/iet-cta.2012.0253},

year  = {2013},

date = {2013-05-16},

journal = { IET Control Theory and Applications},

volume = {7},

number = {8},

pages = {1142-1151},

abstract = {This study addresses reduced-order dynamic observer error linearisation (RDOEL) for discrete-time systems, which is a modified version of dynamic observer error linearisation (DOEL). The authors define the concept of RDOEL and provide a necessary and sufficient condition for RDOEL. Moreover, the relation between RDOEL and DOEL is discussed when the auxiliary dynamics is an arbitrary linear controllable system. Using the relationship and an existing algorithm for DOEL, an algorithm for RDOEL also proposed, which offers lower-dimensional observers than DOEL. Finally, the authors illustrate the theory by applying it to the discrete-time hyperchaotic system due to Wang, which was derived from the generalised Rössler system via a first-order difference algorithm.},

keywords = {Reduced order system},

pubstate = {published},

tppubtype = {article}

}

@article{TanwaniShimLiberzon13,

title = {Observability for Switched Linear Systems: Characterization and Observer Design},

author = {Aneel Tanwani and Hyungbo Shim and Daniel Liberzon},

doi = {10.1109/TAC.2012.2224257},

year  = {2013},

date = {2013-04-01},

journal = {IEEE Transactions on Automatic Control},

volume = {58},

number = {4},

pages = {891-904},

abstract = {This paper presents a characterization of observability and an observer design method for switched linear systems with state jumps. A necessary and sufficient condition is presented for observability, globally in time, when the system evolves under predetermined mode transitions. Because this characterization depends upon the switching signal under consideration, the existence of singular switching signals is studied alongside developing a sufficient condition that guarantees uniform observability with respect to switching times. Furthermore, while taking state jumps into account, a relatively weaker characterization is given for determinability, the property that concerns with recovery of the original state at some time rather than at all times. Assuming determinability of the system, a hybrid observer is designed for the most general case to estimate the state of the system and it is shown that the estimation error decays exponentially. Since the individual modes of the switched system may not be observable, the proposed strategy for designing the observer is based upon a novel idea of accumulating the information from individual subsystems. Contrary to the usual approach, dwell-time between switchings is not necessary, but the proposed design does require persistent switching. For practical purposes, the calculations also take into account the time consumed in performing computations.},

keywords = {Linear system, Time-varying system},

pubstate = {published},

tppubtype = {article}

}

@article{KimShimBackSeo13,

title = {Consensus of Output-coupled Linear Multi-agent Systems Under Fast Switching Network: Averaging Approach},

author = {Hongkeun Kim and Hyungbo Shim and Juhoon Back and Jin Heon Seo},

doi = {10.1016/j.automatica.2012.09.025},

year  = {2013},

date = {2013-01-01},

journal = {Automatica},

volume = {49},

number = {1},

pages = {267-272},

abstract = {This study addresses the problem of consensus of multi-agent systems, consisting of a set of identical MIMO LTI systems, under a time-varying network that has a well-defined average (with uniform convergence to the average). The information delivered through the communication network is the output of each system. First, it is shown that consensus is reached asymptotically by using a group of compensators if the network switches sufficiently fast and the compensators are designed such that the multi-agent system asymptotically achieves consensus for the average of the network. Further, we find a relation between the two agreements, one obtained from considering the switching network and the other obtained from replacing the network with its average. Then, for a class of minimum phase systems, we remove the fast switching condition by redesigning the compensators. Finally, the formation stabilization of unicycle-type mobile robots is dealt with as an application of the problem, and it is demonstrated via a computer simulation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}