List of English Publication

@inproceedings{nokey,

title = {Determination of Bandwidth of Q-Filter in Disturbance Observers to Guarantee Transient and Steady State Performance Under Measurement Noise},

author = {Gaeun Kim and Hyungbo Shim},

doi = {10.23919/ICCAS66577.2025.11301287},

year  = {2025},

date = {2025-11-06},

urldate = {2025-11-06},

publisher = {2025 25th International Conference on Control, Automation and Systems (ICCAS)},

address = {Songdo Convensia, Incheon, Korea},

organization = {Institute of Control, Robotics and Systems},

abstract = {Q-filter-based disturbance observer (DOB) is one of the most widely used robust controller due to its design simplicity. Such simplicity arises from that reducing τ, which is the time constant of low pass filters, not only ensures robust stability but also enhances nominal performance recovery—ability to recover the trajectory of nominal closed-loop system. However, in contrast to noise-free setup, excessively small τ can rather damage the nominal performance recovery under measurement noise. That is, minimizing τ is no longer immediately guaranteeing nominal performance recovery. Motivated by this observation, this paper concentrates on determination of τ to guarantee transient and steady state performance. This analysis uses Lyapunov method utilizing the coordinate transformation inspired by the analysis based on singular perturbation theory. As a result, we present an affordable noise level and open interval for τ that guarantees both the required performances. The analysis can also lead to theoretical demonstration on that excessively reducing τ gives assurance to achieve target performance only for noise-free case.},

keywords = {Disturbance observer, Noise measurement, Singular perturbation},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{nokey,

title = {Actuator Position Estimation for Electro-Hydraulic Ride Height Control System Using EKF and a Reduced-Order Model Obtained via Singular Perturbation},

author = {Sangwon Lee and Hyungbo Shim},

doi = {10.23919/ICCAS66577.2025.11301191},

year  = {2025},

date = {2025-11-05},

urldate = {2025-11-05},

publisher = {2025 25th International Conference on Control, Automation and Systems (ICCAS)},

address = {Songdo Convensia, Incheon, Korea},

organization = {Institute of Control, Robotics and Systems},

abstract = {Ride height control systems adjust the distance between a vehicle's chassis and the road surface to improve ride comfort, aerodynamics, and underbody protection. Among various types, electro-hydraulic systems use hydraulic actuators to lift or lower the vehicle body. In such systems, ride height is usually measured by sensors mounted on the vehicle body. However, these sensors do not directly measure the actuator's internal position. As a result, the controller may continue commanding motion even after the actuator reaches its stroke limit. This can lead to noise generation, mechanical wear, and reduced ride quality. To solve this problem, we propose a model-based method to estimate the internal position of a single-acting actuator using only measurable signals. First, a full-order model of the system is developed, including the motor, pump, valves, and actuator dynamics. Then, a reduced-order model is derived using singular perturbation to simplify the computation. An extended Kalman filter is designed based on this reduced model. Simulation results are validated against experimental data obtained from vehicle-level tests. The proposed method shows accurate and robust performance under various operating conditions and sensor noise, making it suitable for practical ride height control systems.},

keywords = {Estimation theory, Extended Kalman Filter, Reduced order system, Singular perturbation},

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{LeeShim19b,

title = {Behavior of a network of heterogeneous Li´enard systems under strong output coupling},

author = {Jin Gyu Lee and Hyungbo Shim},

doi = {https://doi.org/10.1016/j.ifacol.2019.11.788},

year  = {2019},

date = {2019-09-04},

booktitle = {Proc. of 8th IFAC Symposium on Mechatronic Systems & 11th IFAC Symposium on Nonlinear Control Systems},

journal = {Proc. of 2016 IEEE 55th Conference on Decision and Control},

volume = {52},

number = {16},

pages = {256-261},

publisher = {IFAC},

address = {Vienna, Austria},

abstract = {In this paper, to participate in the understanding of a biological system, we analyze the synchronous and oscillatory behavior of coupled Liénard systems. In particular, we will consider a network of heterogeneous Liénard systems under output diffusive coupling to take into account two fundamental characteristics of a biological system. The key idea in this work is to emphasize the role of a network, which introduces an emergent behavior that each individual element approximately follows, hence making elements approximately synchronize. The intuition comes from a series of developments recently made in the name of ‘blended dynamics,’ and thus, the common philosophy of ‘blended dynamics’ approach enables us to illustrate a biological phenomenon that collective behavior is preserved even when there are some malfunctioning elements.},

keywords = {Approximate synchronization, Blended dynamics, Heterogeneous multi-agents, Internal model principle, Lienard system, Oscillations, Singular perturbation, Strong coupling},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{YunShimChang17,

title = {Singular Perturbation for Sampled-Data Systems With Fast Subsystems},

author = {Hyeonjun Yun and Hyungbo Shim and H. J. Chang

},

doi = {10.1016/j.ifacol.2017.08.1255},

year  = {2017},

date = {2017-07-12},

booktitle = {Proc. of the 20th World Congress},

pages = {8475-8480},

address = {Toulouse, France},

organization = {IFAC},

abstract = {We present a sampled-data version of the well-known Tikhonov’s theorem on singular perturbation theory. In particular, we claim that the nonlinear sampled-data systems with fast subsystems can be treated as a singularly perturbed system in a discrete-time sense. In this case, we show that the sampling period can be considered as a singular perturbation parameter. Following the nomenclature of the singular perturbation theory, we define the degenerate (DG) system and the boundary-layer (BL) system and obtain the solution of the sampled-data system as an approximation of the solutions of the lower-order subsystems. Finally, a simple example, sampled-data implementation of disturbance observer, is included to validate the theory.},

keywords = {Singular perturbation},

pubstate = {published},

tppubtype = {inproceedings}

}