List of English Publication

@inproceedings{nokey,

title = {On Existence of Uniformly Marginally Stable Zeros of Linear Sampled-data Systems and its Application to Stable Inversion-based Control},

author = {GYUNGHOON PARK and HYUNGBO SHIM and Tomomichi Hagiwara},

url = {https://ieeexplore.ieee.org/document/10488419},

doi = {10.1109/ACCESS.2024.3384396},

issn = {2169-3536},

year  = {2024},

date = {2024-07-01},

urldate = {2024-07-01},

volume = {Early Access},

publisher = {IEEE Access},

abstract = {This paper investigates a class of sampled-data systems in which at least one of the discretetime zeros remains on the unit circle regardless of the sampling period. This type of zero is referred to as an

‘‘uniformly marginally stable’’ (UMS) zero. Utilizing this novel concept, we present necessary conditions

as well as sufficient conditions for the continuous-time plant whose sampled-data model has an UMS

zero. The significance of the symmetry regarding the zeros and the poles of the continuous-time plant is

highlighted as it plays a vital role in enforcing a discrete-time zero of the sampled-data system to be UMS,

for both discretization zeros and intrinsic zeros. We develop the theory for sampled-data systems employing

a conventional sampler and a zero-order hold together with a single-input single-output continuous-time

plant, and then observe that certain results can be extended to the generalized holds. As an application, we

establish a condition for sampled-data systems that allow for discrete-time stable inversion-based control

where the absence of such an UMS zero is crucial in the design of such control systems.},

keywords = {},

pubstate = {forthcoming},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Design of Q-filter-based Disturbance Observer for Differential Algebraic Equations and a Robust Stability Condition: Zero Relative Degree Case},

author = {Hamin Chang and Stephan Trenn},

url = {https://ieeexplore.ieee.org/abstract/document/10383698},

doi = {10.1109/CDC49753.2023.10383698},

isbn = {979-8-3503-0124-3},

year  = {2023},

date = {2023-12-15},

urldate = {2023-12-15},

booktitle = {2023 62nd IEEE Conference on Decision and Control (CDC)},

pages = {8489-8494},

publisher = {IEEE Control Systems Society},

address = {Marina Bay Sands, Singapore},

abstract = {While the disturbance observer (DOB)-based controller is widely utilized in various practical applications, there has been a lack of extension of its use to differential algebraic equations (DAEs). In this paper, we introduce several lemmas that establish necessary and/or sufficient conditions for specifying the relative degree of DAEs. Using these lemmas, we also figure out that there is a class of DAEs which can be viewed as linear systems with zero relative degree. For the class of DAEs, we propose a design of Q-filter-based DOB as well as a robust stability condition for systems controlled by the DOB through time domain analysis using singular perturbation theory. The proposed stability condition is verified by an illustrative example.},

keywords = {Differential algebraic equation, Disturbance observer, Disturbance rejection},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Conversion of Controllers to Have Integer State Matrix for Encrypted Control: Non-Minimal Order Approach},

author = {Joowon Lee and Donggil Lee and Seungbeom Lee and Junsoo Kim and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/abstract/document/10383200},

doi = {10.1109/CDC49753.2023.10383200},

isbn = {979-8-3503-0124-3},

year  = {2023},

date = {2023-12-14},

urldate = {2023-12-14},

booktitle = {2023 62nd IEEE Conference on Decision and Control (CDC)},

pages = {5091-5096},

publisher = {IEEE Control Systems Society},

address = {Marina Bay Sands, Singapore},

abstract = {To implement an encrypted dynamic controller based on homomorphic encryption that operates for an infinite time horizon, it is essential for every component of the controller's state matrix to be an integer. In this paper, we tackle the challenge of converting a pre-designed controller into a new one with an integer state matrix while preserving its control performance in the closed-loop system. This enables encrypted dynamic systems to be realized without re-encryption and approximation of control parameters, compared to the previous results. To achieve this, we propose two approaches and provide sufficient conditions on the design parameter for each. The first approach is to design the new controller as an estimator of the original closed-loop system, and the conditions on the estimator gain are derived. Our second approach is to formulate a problem of finding certain polynomials, whose solution leads to the design of the new controller. In a special case when the numerator of the plant transfer function is a constant, we provide a constructive method to obtain such solution.},

keywords = {Controller encryption, Homomorphic encryption, Linear Systems},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Distributed Resilient Observer: Blended Dynamics Theory Meets L1-Minimization Approach},

author = {Donggil Lee and Junsoo Kim and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/abstract/document/10147254},

doi = {10.1109/LCSYS.2023.3284592},

year  = {2023},

date = {2023-12-13},

urldate = {2023-12-13},

booktitle = {2023 62nd IEEE Conference on Decision and Control (CDC)},

publisher = {IEEE Control Systems Society},

address = {Marina Bay Sands, Singapore},

organization = {IEEE},

abstract = {This letter presents a distributed resilient observer for continuous-time linear time-invariant plants that remains functional even under sensor attacks. The proposed method aims to determine the estimation outcome that matches the majority of sensor measurements, which is formulated as an ℓ1 -minimization problem considering all the observable components of each sensor measurement. A distributed observer based on the blended dynamics theory is then proposed to solve the ℓ1 -minimization problem in a distributed manner. As a result, the distributed resilient estimation is enabled for a broader class of systems compared to previous works. The design procedure is constructive with parameters obtained from a specified condition that is equivalent to the well-known null-space property.},

keywords = {distributed control, distributed observer, Networked control system},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {User-friendly Vehicle-to-Grid Optimal Scheduling Problem and Distributed Implementation for Plug-and-play Operation},

author = {Seungbeom Lee and Jinwook Heo and Soojeong Hyeon and Jiyeon Nam and Hyungbo Shim and Jinsung Kim},

doi = {10.23919/ICCAS59377.2023.10316855},

year  = {2023},

date = {2023-10-19},

urldate = {2023-10-19},

booktitle = {International Conference on Control, Automation and Systems (ICCAS 2023)},

publisher = {IEEE},

address = {Yeosu, Korea, Republic of},

abstract = {In this paper, we propose an optimization method of charging scheduling algorithm based on preference of vehicle owners. To suffice various desires for vehicle charging, we design objective function of optimization problem as weighted sum of some objective function to reflect various desires. To solve the problem without aggregating weight coefficient, distributed optimization based on dynamic average consensus method is implemented. By initialization-free property of dynamic average consensus, plug-and-play operation of electric vehicle is applicable. Finally, we simulate the proposed algorithm to enlighten the meaning of weighted sum for objective function and plug-and-play scenario.},

keywords = {Distributed optimization, Initialization-free, Plug-and-play},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Exponential Synchronization of Heterogeneous Multi-agent Systems via Linear-signum-type Diffusive Coupling: Blended Dynamics Approach},

author = {Jeong Mo Seong and Donggil Lee and Hyungbo Shim},

doi = {10.23919/ICCAS59377.2023.10316872},

year  = {2023},

date = {2023-10-18},

urldate = {2023-10-18},

booktitle = {International Conference on Control, Automation and Systems (ICCAS 2023)},

publisher = {IEEE},

address = {Yeosu, Korea, Republic of},

abstract = {This paper investigates the behavior of heterogeneous agents that interact through diffusive coupling, resulting in emergent blended dynamics that may not be observed in the dynamics of individual agents. In particular, we propose a linear-signum-type diffusive coupling to achieve exponential synchronization among heterogeneous agents. This finding offers a notable advantage over previous research, which primarily focused on linear-type diffusive coupling with remaining steady-state error in synchronization. We provide conditions of both linear and signum coupling strengths for achieving the exponential synchronization and analyze the associated convergence rate. Furthermore, simulation results validate the effectiveness of the proposed approach.},

keywords = {Blended dynamics, Exponential synchronization, Heterogeneous multi-agents},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Model Reference Gaussian Process Regression: Data-Driven Output Feedback Controller},

author = {Hyuntae Kim and Hamin Chang and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10156428},

doi = {10.23919/ACC55779.2023.10156428},

isbn = {979-8-3503-2806-6},

year  = {2023},

date = {2023-05-31},

urldate = {2023-05-31},

booktitle = {2023 American Control Conference (ACC)},

pages = {955-960},

publisher = {IEEE},

address = {San Diego, CA, USA},

abstract = {Data-driven controls using Gaussian process regression have recently gained much attention. In such approaches, system identification by Gaussian process regression is mostly followed by model-based controller designs. However, the outcomes of Gaussian process regression are often too complicated to apply conventional control designs, which makes the numerical design such as model predictive control employed in many cases. To overcome the restriction, our idea is to perform Gaussian process regression to the inverse of the plant with the same input/output data for the conventional regression. With the inverse, one can design a model reference controller without resorting to numerical control methods. This paper considers single-input single-output (SISO) discrete-time nonlinear systems of minimum phase with relative degree one. It is highlighted that the model reference Gaussian process regression controller is designed directly from pre-collected input/output data without system identification.},

keywords = {Data-driven control, Gaussian process, MR-GPR},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokeyt,

title = {Data-Driven Inverse of Linear Systems and Application to Disturbance Observer},

author = {Yongsoon Eun and Jaeho Lee and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10156256},

doi = {10.23919/ACC55779.2023.10156256},

isbn = {979-8-3503-2806-6},

year  = {2023},

date = {2023-05-31},

booktitle = {2023 American Control Conference (ACC)},

pages = {2806-2811},

publisher = {IEEE},

address = {San Diego, CA, USA},

abstract = {This work develops a data-based construction of inverse dynamics for LTI systems. Specifically, the problem addressed here is to find an input sequence from the corresponding output sequence based on pre-collected input and output data. The problem can be considered as a reverse of the recent use of the behavioral approach, in which the output sequence is obtained for a given input sequence by solving an equation formed by pre-collected data. The condition under which the problem gives a solution is investigated and turns out to be L-delay invertibility of the plant and a certain degree of persistent excitation of the data input. The result is applied to form a data-driven disturbance observer. The plant dynamics augmented by the data-driven disturbance observer exhibits disturbance rejection without the model knowledge of the plant.},

keywords = {Data-driven control, Disturbance observer, Disturbance rejection, Linear Systems},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{none,

title = {Stability of linear systems with slow and fast time variation and switching},

author = {Hyungbo Shim and Daniel Liberzon},

url = {https://ieeexplore.ieee.org/document/9992853},

doi = {10.1109/CDC51059.2022.9992853},

isbn = {978-1-6654-3659-5},

year  = {2022},

date = {2022-12-06},

urldate = {2022-12-06},

booktitle = {Proc. of 2022 IEEE 61st Conference on Decision and Control (CDC)},

pages = {674-678},

publisher = {IEEE},

address = {Cancun, Mexico},

abstract = {We establish exponential stability for a class of linear systems with slow and fast time variation and switching. We use the averaging method to approximate the original system by the average system which only exhibits slow time variation and switching. We then apply a stability criterion recently developed for such systems to prove stability of the average system and, consequently, of the original system.

 },

keywords = {Stability of linear systems, Switched systems, Time-varying systems},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Open-loop contraction design},

author = {Jin Gyu Lee and Thiago B. Burghi and Rodolphe Sepulchre},

doi = {10.1109/CDC51059.2022.9992765},

isbn = {978-1-6654-3659-5},

year  = {2022},

date = {2022-12-06},

urldate = {2022-12-06},

booktitle = {Proc. of 2022 IEEE 61st Conference on Decision and Control (CDC)},

publisher = {IEEE},

address = {Cancun, Mexico},

abstract = {Given a non-contracting trajectory of a nonlinear

system, we consider the question of designing an input perturbation that makes the perturbed trajectory contracting. This

paper stresses the analogy of this question with the classical

question of feedback stabilization. In particular, it is shown that

the existence of an output variable that ensures contraction of

the inverse system facilitates the design of a contracting input

perturbation. We illustrate the relevance of this question in

parameter estimation.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Initialization-free Algorithm for Discrete-time Dynamic Average Consensus and Its Application to Distributed Optimization},

author = {Jiyeon Nam and Jinwook Heo and Jeongwoo Kim and Hyungbo Shim and Jae Sung Bang and Jinsung Kim},

url = {https://ieeexplore.ieee.org/abstract/document/10003797?casa_token=DuxZUEtvKl0AAAAA:NZLDmrslBnSuOUXJQEDoFIKpq7S_j8tpp1_m-NkuQr1uVTaA1zu7O6qXQoTxi_makBT6rgsLRQ},

doi = {https://doi.org/10.23919/ICCAS55662.2022.10003797},

isbn = {978-89-93215-24-3},

year  = {2022},

date = {2022-11-28},

urldate = {2022-11-28},

booktitle = {Proc. of 22th International Conference on Control, Automation and Systems (ICCAS)},

pages = {424-429},

publisher = {IEEE},

address = {Busan, Korea},

abstract = {In this paper, we address the problem of dynamic average consensus in a discrete-time setting. The objective of dynamic average consensus problem is for each state of agent to track the average of reference input signals of each agent in a distributed manner. Without initialization process, the proposed algorithm renders the state of each agent converge practically to the average of time-varying reference signals with any given bound. It is a simple time-domain algorithm based on two-time scale. Finally, by applying our algorithm to an distributed optimization problem, we provide two simulation results that converge correctly when the initial conditions are perturbed and that converge within certain amount of small error when numerical errors are injected every time step.},

keywords = {Dynamic average consensus, Initialization-free, Multi-agent system},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Funnel control by induced contraction},

author = {Jin Gyu Lee and Thiago B. Burghi},

doi = {10.1016/j.ifacol.2022.11.060},

year  = {2022},

date = {2022-09-12},

urldate = {2022-09-12},

booktitle = {Proceedings of the 25th International Symposium on Mathematical Theory of Networks and Systems},

volume = {55},

issue = {30},

pages = {248},

publisher = {IFAC-PapersOnLine},

address = {Bayreuth, Germany},

abstract = {This note explores a property of the internal dynamics that is essential for the

functioning of classical funnel control. We relax the property of internal dynamics boundedinput bounded-output (BIBO) stability by concentrating on a narrower class of output reference

trajectories. Our ideas have a connection with the recently introduced concept of induced

contraction, which is motivated by the phenomenon of noise-induced synchronization in neuronal

oscillators. We remark that, contrary to previous works, we only have to modify the class of

admissible output reference trajectories to handle non-minimum phase systems. We also propose

a way (specific to nonlinear systems) to choose an output reference trajectory (possibly under

output constraints) for classical funnel control to work for a certain class of unknown systems.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Method for Running Dynamic Systems Over Encrypted Data for Infinite Time Horizon without Bootstrapping and Re-Encryption},

author = {Junsoo Kim and Hyungbo Shim and Henrik Sandberg and Karl H. Johansson},

url = {https://ieeexplore.ieee.org/abstract/document/9682828},

doi = {10.1109/CDC45484.2021.9682828},

isbn = {978-1-6654-3659-5},

year  = {2021},

date = {2021-12-13},

urldate = {2021-12-13},

booktitle = {Proc. of 2021 IEEE 60th Conference on Decision and Control},

pages = {5614-5619},

publisher = {IEEE},

address = {Austin, Texas, USA},

abstract = {In this paper, we propose a method for dynamic systems to operate over homomorphically encrypted data for an infinite time horizon, where we do not make use of reset, re-encryption, or bootstrapping for the encrypted messages. The given system is first decomposed into the stable part and the anti-stable part. Then, the stable part is approximated to have finite impulse response, and by a novel conversion scheme, the eigenvalues of the state matrix of the anti-stable part are approximated to algebraic integers. This allows that the given system can be implemented to operate for an infinite time horizon using only addition and multiplication over encrypted data, without re-encrypting any portion of data. The performance error caused by the approximation and quantization can be made arbitrarily small, with appropriate choice of parameters.},

keywords = {Controller encryption, Homomorphic encryption},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Lyapunov Functions for Singularly Perturbed Hybrid Systems with Frequent Jump Dynamics},

author = {Aneel Tawani and Hyungbo Shim},

url = {https://css.paperplaza.net/conferences/conferences/CDC21/program/CDC21_ContentListWeb_4.html},

doi = {10.1109/CDC45484.2021.9682912},

year  = {2021},

date = {2021-12-13},

urldate = {2021-12-01},

booktitle = {Proc. of 2021 IEEE 60th Conference on Decision and Control},

pages = {5382-5387},

publisher = {IEEE},

address = {Austin, Texas, USA},

abstract = {This article considers the stability analysis for a class of hybrid systems with the focus being on the frequently occurring jump dynamics. The system class is modelled as a singularly perturbed hybrid system where the singular perturbation parameter governs the frequency of jumps. Consequently, this results in a quasi steady-state system modeled by a differential equation without any jumps, and the boundary-layer system described by purely discrete dynamics. By imposing appropriate assumptions on the quasi steady-state system and the boundary-layer system, we derive results showing practical convergence to a compact attractor when the jumps occur frequently often. Our system class is motivated by the control design problem in a network of second-order continuous-time coupled oscillators, where each agent communicates the information about its position to the neighbors at discrete times. As a corollary to our main result, we show that if the information exchange between the agents and their neighbors is frequent enough, then the oscillators achieve practical consensus.},

keywords = {Hybrid system, Lyapunov function, Singular perturbation},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{KimShimHan20,

title = {Design Procedure for Dynamic Controllers based on LWE-based Homomorphic Encryption to Operate for Infinite Time Horizon},

author = {Junsoo Kim and Hyungbo Shim and Kyoohyung Han},

doi = {https://doi.org/10.1109/CDC42340.2020.9304509},

isbn = {978-1-7281-7447-1},

year  = {2020},

date = {2020-12-18},

urldate = {2020-12-18},

booktitle = {Proc. of 2020 IEEE 59th Conference on Decision and Control},

pages = {5463-5468},

publisher = {IEEE},

address = {Jeju, Korea},

abstract = {The design of encrypted controllers, which perform control operation directly over encrypted signals via homomorphic cryptosystems, should consider both security of the control data and performance of the controller. Considering the use of Learning With Errors (LWE) based cryptosystem, in this paper, we present a design procedure for encrypted linear dynamic controllers. Providing a guideline for choosing the parameters of the cryptosystem as well as quantization, the procedure guarantees both the desired level of security and performance. Receiving the encrypted signals of the plant input as well as the output, the proposed controller is able to perform the dynamic operation over encrypted data for infinite time horizon, without the use of decryption or reset of the state. Thanks to additively and multiplicatively homomorphic property of the LWE-based cryptosystem, information of both control signals and gain matrices is protected by encryption.},

keywords = {Controller encryption, Homomorphic encryption},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{LeeKimShim20b,

title = {Distributed Aggregation Over Homomorphically Encrypted Data under Switching Networks},

author = {Donggil Lee and Junsoo Kim and Hyungbo Shim},

doi = {https://doi.org/10.1109/CDC42340.2020.9304350},

isbn = {978-1-7281-7447-1},

year  = {2020},

date = {2020-12-18},

urldate = {2020-12-18},

booktitle = {Proc. of 2020 IEEE 59th Conference on Decision and Control},

pages = {5495-5500},

publisher = {IEEE},

address = {Jeju, Korea},

abstract = {This paper presents a distributed algorithm for additive aggregation over encrypted data. Our algorithm allows networked systems to compute the sum of all individual data without revealing each node's private contribution. To conceal the private data, the local computations on each node and the communications with neighbor nodes are conducted by utilizing the additively homomorphic cryptosystem. As a consequence, the leader node which has the secret key of the cryptosystem recovers the correct outcome after decryption in a finite time. Moreover, the leader cannot learn the private data of the other nodes. Furthermore, the proposed algorithm can operate on encrypted data for an infinite time horizon even when the network varies intermittently with time.},

keywords = {Distributed aggregation, Homomorphic encryption},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{CheonKimKimLeeShim20,

title = {Authenticated Computation of Control Signal from Dynamic Controllers},

author = {Jung Hee Cheon and Dongwoo Kim and Junsoo Kim and Seungbeom Lee and Hyungbo Shim},

doi = {https://doi.org/10.1109/CDC42340.2020.9304150},

isbn = {978-1-7281-7447-1},

year  = {2020},

date = {2020-12-16},

urldate = {2020-12-16},

booktitle = {Proc. of 2020 IEEE 59th Conference on Decision and Control},

pages = {3249-3254},

publisher = {IEEE},

address = {Jeju, Korea},

abstract = {Significant concerns on networked control systems are modifications on the control signals caused by a compromise on the network or the controller, since it can cause a devastating behavior or even entire failure of the system. In this paper, we present a fundamental solution to this problem by proposing a new authenticated computation that checks the matrix-vector multiplications-the main arithmetic of a controller-and verifies the updates on the states of the controller. It enables the plant-side not only to check the computation of the controller with much less computational cost than that required for the computation itself, but also to detect any modifications on the control signals.},

keywords = {Secure control system, Verifiable computation},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{JangKimShim20,

title = {Lemmas on Determination of Minimum Bandwidth of Q-Filter for Robust Stability of Feedback Loop with Disturbance Observers},

author = {Hamin Chang and Hyuntae Kim and Hyungbo Shim},

doi = {https://doi.org/10.1109/CDC42340.2020.9303855},

isbn = {978-1-7281-7447-1},

year  = {2020},

date = {2020-12-14},

urldate = {2020-12-14},

booktitle = {Proc. of 2020 IEEE 59th Conference on Decision and Control},

pages = {893-898},

publisher = {IEEE},

address = {Jeju, Korea},

abstract = {As the disturbance observer (DOB)-based controller has been widely applied in practice, various aspects of the disturbance observer have been theoretically studied. In particular, robust stability of the linear closed-loop system with single-input single-output (SISO) Q-filter-based DOB has been rigorously analyzed, and finally, a necessary and sufficient condition for robust stability was obtained under the premise that the bandwidth of Q-filter is large. However, even the most recent study about the design of Q-filter-based DOB for robust stability does not offer a practical method for the determination of the Q-filter's bandwidth. In this paper, we present several lemmas regarding the determination of the bandwidth, from which a procedure is developed that can exactly compute the threshold of the bandwidth, so that robust stability (against parametric variations of the plant within a prescribed range) is lost if the bandwidth of the Q-filter becomes lower than that. The proposed procedure is implemented in a MATLAB toolbox named DO-DAT, which is now available at https://do-dat.github.io.},

keywords = {Disturbance observer},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{HyeonKimShim20,

title = {Design of Robust Feed-through Compensator via Disturbance Observer},

author = {Soojeong Hyeon and Hyuntae Kim and Hyungbo Shim},

doi = {https://doi.org/10.1109/CDC42340.2020.9303990},

isbn = {978-1-7281-7447-1},

year  = {2020},

date = {2020-12-14},

urldate = {2020-12-14},

booktitle = {Proc. of 2020 IEEE 59th Conference on Decision and Control},

pages = {916-921},

publisher = {IEEE},

address = {Jeju, Korea},

abstract = {A feed-through compensator is a dynamic system designed for a given plant, whose output is added to the output of the plant. It is typically used in order for the zeros of the combination of the plant and the compensator (seen from the new output) to have desired properties. In particular, Isidori and Marconi (2008) utilized a robust feed-through compensator for uncertain non-minimum phase nonlinear systems, which makes the combined system become of minimum phase so that the output feedback stabilization is rather easily achieved. For the design of robust feed-through compensator, they introduced the so-called auxiliary system and showed that, if the auxiliary system admits a robust output feedback stabilizer, then the robust feed-through compensator can be systematically constructed. This paper, while restricted to linear systems, presents a constructive method for designing the robust output feedback stabilizer for the auxiliary system. For this, minimum phaseness of the auxiliary system (not the plant itself) is required. In order to overcome this restriction, we also proposed a kind of nested design for which it is enough for the second auxiliary system of the auxiliary system to have minimum phaseness.},

keywords = {Disturbance observer, Robust control},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{SeongShim20,

title = {Estimation of 3-Axis Body Angular Velocity Using Accelerometers Combined With High Speed Propellers},

author = {Jeong Mo Seong and Hyungbo Shim},

url = {https://www.dbpia.co.kr/pdf/pdfView.do?nodeId=NODE10493765&mark=0&useDate=&bookmarkCnt=0&ipRange=N&accessgl=Y&language=ko_KR},

year  = {2020},

date = {2020-10-16},

booktitle = {Proc. of 20th International Conference on Control, Automation and Systems (ICCAS)},

publisher = {IEEE},

address = {Busan, Korea},

abstract = {In this paper, we design a 3-axis body angular velocity estimator for propeller actuated aerial vehicles using two 2-axis accelerometers combined with two propellers that rotate fast. A kinematic model of the aerial vehicle is used. Simulation results verify the performance of the 3-axis body angular velocity estimator.},

keywords = {Actuator combined accelerometer, Aerial Vehicle, Gyroscope},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{LeeKim20,

title = {Synchronization of Lur'e-type Nonlinear Systems using Incremental Output-feedback Passivity with Shortage of Passivity},

author = {Seungjoon Lee and Hongkeun Kim},

url = {https://www.dbpia.co.kr/pdf/pdfView.do?nodeId=NODE10493756&mark=0&useDate=&bookmarkCnt=0&ipRange=N&accessgl=Y&language=ko_KR},

year  = {2020},

date = {2020-10-16},

booktitle = {Proc. of 20th International Conference on Control, Automation and Systems (ICCAS)},

publisher = {IEEE},

address = {Busan, Korea},

abstract = {This paper studies the synchronization problem of Lur’e-type nonlinear systems. For the analysis, the concept of incremental output-feedback passivity (iOFP) is introduced and generalized using the shortage of passivity. It is shown that Lur’e-type nonlinear system is iOFP and examples are presented. Using iOFP, a sufficient condition (which is in form of sector condition) is proposed for the Lur’e-type nonlinear systems to achieve the synchronization using static output diffusive couplings. Results are further extended to nonlinear coupling under fully connected network. Numerical simulations are given to demonstrate the proposed results.},

keywords = {Multi-agent systems, Passivity, Synchronization},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{LeeShim20,

title = {Blended dynamics approach for analysis and construction of distributed optimization algorithms},

author = {Seungjoon Lee and Hyungbo Shim},

url = {https://www.dbpia.co.kr/pdf/pdfView.do?nodeId=NODE10493601&mark=0&useDate=&bookmarkCnt=0&ipRange=N&accessgl=Y&language=ko_KR},

year  = {2020},

date = {2020-10-15},

booktitle = {Proc. of 20th International Conference on Control, Automation and Systems (ICCAS)},

publisher = {IEEE},

address = {Busan, Korea},

abstract = {In this paper, the recently proposed concept of blended dynamics of a heterogeneous multi-agent system is introduced. Although the blended dynamics is originally proposed for the analysis of heterogeneous multi-agent system, it is argued that the same approach provides a flexible framework for the analysis and construction of the distributed algorithms. The utility of the proposed approach is first illustrated by systematically constructing the distributed gradient descent algorithm from the centralized gradient descent method. The proposed approach is further extended to derive two variants of distributed algorithms utilizing the heavy-ball method. Finally, drawback of the proposed approach is identified and integral action is employed to resolve the issue.},

keywords = {Distributed optimization, Multi-agent systems},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{LeeKimShim20,

title = {Zero-Dynamics Attack on Homomorphically Encrypted Control System},

author = {Joowon Lee and Junsoo Kim and Hyungbo Shim},

doi = {https://doi.org/10.23919/ICCAS50221.2020.9268374},

isbn = {978-89-93215-20-5},

year  = {2020},

date = {2020-10-14},

urldate = {2020-10-14},

booktitle = {Proc. of 20th International Conference on Control, Automation and Systems (ICCAS)},

pages = {385-390},

publisher = {IEEE},

address = {Busan, Korea},

abstract = {Against recent cyber-attack strategies on networked control systems which commonly utilize information of control data, the notion of encrypted control system has been introduced, to protect private data in the network layer by encryption. However, even though the adversary cannot learn the information from the encrypted control signals or parameters, it is known that their values can be manipulated by the adversaries, based on homomorphic property of the cryptosystem. In this paper, we demonstrate that the injection of zero-dynamics attack is possible even for encrypted control systems. By injecting an attack signal, generated with knowledge of the plant model, directly on the encrypted controller output being transmitted to the actuator, we show that it disrupts the plant state while it is undetectable from the input and output of the controller. Simulation results are presented to demonstrate the effectiveness of the proposed attack.},

keywords = {Controller encryption, Cyber-physical systems, Homomorphic encryption, Zero-dynamics},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{KimFarokhiShamesShim20,

title = {Toward Nonlinear Dynamic Control over Encrypted Data for Infinite Time Horizon},

author = {Junsoo Kim and Farhad Farokhi and Iman Shames and Hyungbo Shim

},

url = {http://ifatwww.et.uni-magdeburg.de/ifac2020/media/pdfs/4453.pdf},

year  = {2020},

date = {2020-07-11},

booktitle = {Proc. of the 21th World Congress},

publisher = {IFAC},

address = {Berlin, Germany},

abstract = {Recent studies on encrypted control using homomorphic encryption allow secure operation by directly performing computations on encrypted data without decryption. Implementing dynamic controllers on encrypted data presents unique challenges due to limitations on the number of operations on an encrypted message. Hence, it may not be possible to perform the recursive operations for an infinite time horizon. In this note, we demonstrate that it is possible to run a dynamic controller over encrypted data for an infinite time horizon if the output of the controller can be represented as a function of a fixed number of previous inputs and outputs. The presented implementation requires encryption at both input and output of the plant. We identify a class of nonlinear systems that can accommodate the proposed implementation. The closed-loop performance can be guaranteed using the proposed encrypted controller by ensuring that quantization error is made arbitrarily small with appropriate choice of parameters. We show that the proposed method is amenable to linear systems (as a subset of the said nonlinear systems) with performance guarantees.},

keywords = {Controller encryption, Privacy, Secure control system},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{NamKimParkShim20,

title = {Weighted Averaged Behavior of Synchronization among Heterogeneous Agents in a Sampled-data Setting},

author = {Jiyeon Nam and Taekyoo Kim and Gyunghoon Park and Hyungbo Shim},

doi = {https://doi.org/10.23919/ACC45564.2020.9147285},

year  = {2020},

date = {2020-07-03},

booktitle = {Proc. of 2020 Annual American Control Conference (ACC)},

pages = {4405-4410},

publisher = {IEEE},

address = {Denver, CO, USA},

abstract = {In this paper, we address the problem of synchronization among heterogeneous agents in a sampled-data setting. The key observation is that the sample-and-hold process introduces additional node-wise weights on the Laplacian matrix in the discrete-time domain. We then show that in the sampled-data setting, all of the agents' states approach the state of the so-called weighted averaged dynamics, an auxiliary dynamics that represents the collective behavior of heterogeneous agents when they are synchronized. In addition, admissible ranges of the sampling period and the diffusive coupling gain are computed, with which the consensus among the agents is achieved in a practical sense.},

keywords = {Blended dynamics, Heterogeneous multi-agents, Sampled data system},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Utility of Edge-wise Funnel Coupling for Asymptotically Solving Distributed Consensus Optimization},

author = {Jin Gyu Lee and Thomas Berger and Stephan Trenn and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/abstract/document/9143983},

doi = {10.23919/ECC51009.2020.9143983},

isbn = {978-3-90714-402-2},

year  = {2020},

date = {2020-05-12},

booktitle = {Proc. of 2020 European Control Conference (ECC)},

pages = {911-916},

publisher = {IEEE},

address = {St. Petersburg, Russia},

abstract = {A new approach to distributed consensus optimization is studied in this paper. The cost function to be minimized is a sum of local cost functions which are not necessarily convex as long as their sum is convex. This benefit is obtained from a recent observation that, with a large gain in the diffusive coupling, heterogeneous multi-agent systems behave like a single dynamical system whose vector field is simply the average of all agents' vector fields. However, design of the large coupling gain requires global information such as network structure and individual agent dynamics. In this paper, we employ a nonlinear time-varying coupling of diffusive type, which we call `edge-wise funnel coupling.' This idea is borrowed from adaptive control, which enables decentralized design of distributed optimizers without knowledge of global information. Remarkably, without a common internal model, each agent achieves asymptotic consensus to the optimal solution of the global cost. We illustrate this result by a network that asymptotically finds the least-squares solution of a linear equation in a distributed manner.},

keywords = {Distributed optimization, Funnel control, Multi-agent systems},

pubstate = {published},

tppubtype = {inproceedings}

}