List of English Publication

@article{nokey,

title = { Robust Stability Condition and Simplified Design of Filter-embedded Disturbance Observer},

author = {Hamin Chang and Donghyeon Song and Chanhwa Lee and Hyungbo Shim},

url = {https://link.springer.com/article/10.1007/s12555-024-0503-2},

doi = {10.1007/s12555-024-0503-2},

issn = { 1598-6446},

year  = {2024},

date = {2024-12-09},

urldate = {2024-12-09},

journal = {International Journal of Control, Automation, and Systems},

volume = {22},

pages = {3584-3594},

publisher = {International Journal of Control, Automation and Systems},

abstract = {Embedding a filter is one of the simplest ways to enhance the disturbance attenuation performance of

feedback control systems. In this paper, we introduce the filter-embedded disturbance observer (FDOB) and present

a rigorous stability analysis of the FDOB. The proposed robust stability condition for the closed-loop system with

the FDOB shows that if the filter to be embedded is stable and has zero relative degree with unity high-frequency

gain, then the FDOB can be designed by simply adding the filter to a well-designed conventional disturbance

observer (DOB) that guarantees closed-loop robust stability, and by adjusting the time constant of the Q-filter of the

conventional DOB. It is also highlighted that the FDOB can be implemented by integrating the filter into the Q-filter

of the conventional DOB, maintaining the add-on structure of the conventional DOB. In addition, it is shown that

internal models of disturbances can be directly embedded into the filter of FDOB, which does not affect the design

of the Q-filter. Simulation results on a motor control system are provided to validate the theoretical results.

},

keywords = {Disturbance observer},

pubstate = {published},

tppubtype = {article}

}

@article{Na2020,

title = {Disturbance observer approach for fuel-efficient heavy-duty vehicle platooning},

author = {Gyujin Na and Gyunghoon Park and Valerio Turri and Karl H. Johansson and Hyungbo Shim and Yongsoon Eun},

doi = {https://doi.org/10.1080/00423114.2019.1704803},

issn = {0042-3114},

year  = {2020},

date = {2020-05-01},

journal = {Vehicle System Dynamics},

volume = {58},

number = {5},

pages = {748-767},

abstract = {Heavy-duty vehicle platooning has received much attention as a method to reduce fuel consumption by keeping inter-vehicle distance short. When a platoon follows a fuel-optimal velocity profile calculated using preview road slope information, significant improvement in the fuel economy occurs. To calculate the optimal velocity in the existing method, however, platoon should acquire expensive road slope data in advance. As an alternative, we propose a road slope estimation method, which enables platoon to calculate the optimal velocity profile without the usage of actual road slope data. Other major challenges in platoon operation include overcoming the effect of the vehicle model uncertainties and external disturbances for ensuring the control performance. The most significant part of the disturbances arises from slopes along a route. Existing method for reducing the effect of the slope employs a feed-forward type compensation in the control loop by combining the vehicle position acquired from GPS and the slope database. However, this method exhibits limitations: the mass of the vehicles in the platoon is uncertain which lowers the accuracy of the feed-forward compensation, and the platoon requires the pre-acquired slope database. To overcome these limitations, we propose an alternative method employing disturbance observer. Simulations of various scenarios are conducted to show the efficacy of the proposed method using the actual road slope data of a Swedish highway.},

keywords = {Disturbance observer, Heavy-duty vehicle platoon, Road slope estimation, Robust control},

pubstate = {published},

tppubtype = {article}

}

@article{ParkShim18,

title = {Guaranteeing Almost Fault-free Tracking Performance from Transient to Steady-state: a Disturbance Observer Approach},

author = {Gyunghoon Park and Hyungbo Shim},

doi = {10.1007/s11432-017-9435-3},

year  = {2018},

date = {2018-07-01},

journal = {Science China Information Sciences},

volume = {61},

number = {7},

abstract = {** Invited Paper for the Special Issue on Advances in Disturbance/Unvertainty Estimation and Attenuation Technique With Applications **



In this paper, we propose an output-feedback fault-tolerant controller (FTC) for a class of uncertain multi-input single-output systems under float and lock-in-place actuator faults. Of particular interest is to recover a fault-free tracking performance of a (pre-defined) nominal closed-loop system, during the entire time period including the transients due to abrupt actuator faults. As a key component, a high-gain disturbance observer (DOB) is employed to rapidly compensate the lumped disturbance, a compressed expression of all the effect of actuator faults (as well as model uncertainty and disturbance) on the system. To implement this high-gain approach, a fixed control allocation (CA) law is presented in order to keep an extended system with a virtual scalar input to remain of minimum phase under any patterns of faults. It is shown via the singular perturbation theory that the proposed FTC, consisting of the high-gain DOB and the CA law, resolves the problem in an approximate but arbitrarily accurate sense. Simulation results with the linearized lateral model of Boeing 747 are performed to verify the validity of the proposed FTC scheme.},

keywords = {Disturbance observer, Fault-tolerant},

pubstate = {published},

tppubtype = {article}

}

@article{KimChoiKimShinShimKim17,

title = {Robust Control of an Equipment-added Multirotor Using Disturbance Observer},

author = {Suseong Kim and Seungwon Choi and Hyeonggeun Kim and Jongho Shin and Hyungbo Shim and H. Jin Kim},

doi = {10.1109/TCST.2017.2711602},

year  = {2018},

date = {2018-07-01},

journal = {IEEE Transactions on Control Systems Technology},

volume = {26},

number = {4},

pages = {1524-1531},

abstract = {Modifications of multirotor unmanned aerial vehicles are increasingly popular by integrating tools, sensors, or a robotic arm depending on types of applications. In these circumstances, precise motion control against model uncertainty and disturbance is essential. This brief presents an inner-loop control structure to recover the dynamics of a multirotor combined with additional objects similar to the bare multirotor using disturbance observer (DOB)-based approach. In addition, in the process of the inner-loop controller design and the associated stability proof, it is revealed that the safe operation bounds of the modified multirotor in accordance with the amount of inertia added to the multirotor. The proposed control design is validated with flight experiments using a multirotor integrated with a four-DOF robotic arm, where the multirotor is commanded to follow a desired trajectory while the robotic arm is in motion. The results show superior tracking performance of the proposed structure in comparison with backstepping control without DOB.},

keywords = {Aerodynamics, Disturbance observer, Mathematical modeling, Vehicle dynamics},

pubstate = {published},

tppubtype = {article}

}

@article{ParkShimJoo18,

title = {Recovering Nominal Tracking Performance in an Asymptotic Sense for Uncertain Linear Systems},

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

doi = {10.1137/17M1122657},

year  = {2018},

date = {2018-03-01},

journal = {SIAM Journal on Control and Optimization},

volume = {56},

number = {2},

pages = {700-722},

abstract = {In this paper, we consider the problem of recovering a (predefined) nominal output trajectory in the presence of model uncertainty and external disturbance. In particular, whereas the nominal performance recovery (NPR) has been studied in an approximate fashion in the literature, we extend the notion of the NPR in an asymptotic sense from the perspective of the internal model principle: that is, as long as the disturbance and reference signals are generated by an exogenous system, the actual output not only is kept close to the nominal trajectory as much as desired but also asymptotically converges to the nominal one as time elapses. It is shown via the singular perturbation theory that the asymptotic NPR can be achieved for uncertain minimum-phase systems under arbitrarily large (but bounded) model uncertainty. A disturbance observer (DOB) approach is employed in the controller design, with the internal model embedded into the so-called Q-filter, which is a key component of the DOB. Simulation results for mechanical positioning systems illustrate that the asymptotic NPR can enhance robust performance of control systems.},

keywords = {Disturbance observer, Internal model principle, Nominal performance recovery, 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{JonnBack12,

title = {Power Regulation of Variable Speed Wind Turbines using Pitch Control based on Disturbance Observer},

author = {Youngjun Joo and Juhoon Back},

doi = {10.5370/JEET.2012.7.2.273},

year  = {2012},

date = {2012-03-01},

journal = {Journal of Electrical Engineering and Technology},

volume = {7},

number = {2},

pages = {273-280},

abstract = {Most variable speed wind turbines have pitch control mechanisms and one of their objectives is to protect turbines when the wind speed is too high. By adjusting pitch angles of wind turbine, the inlet power and the torque developed by the turbine are regulated. In this paper, the difference between the real wind speed and its rated value is regarded as a disturbance, and a component called disturbance observer (DOB) is added to the pre-designed control loop. The additional DOB based controller estimates the disturbance and generates a compensating signal to suppress the effect of disturbance on the system. As a result, the stability and the performance of the closed loop system guaranteed by an outer-loop controller (designed for a nominal system without taking into account of disturbances) are approximately recovered in the steady state. Simulation results are presented to verify the performance of the proposed control scheme.},

keywords = {Disturbance observer, Power regulation},

pubstate = {published},

tppubtype = {article}

}

@article{JoShimSon10,

title = {Disturbance observer for non-minimum phase linear systems},

author = {Nam Hoon Jo and Hyungbo Shim and Young Ik Son},

doi = {10.1007/s12555-010-0508-x},

issn = {1598-6446},

year  = {2010},

date = {2010-10-01},

journal = {International Journal of Control, Automation and Systems},

volume = {8},

number = {5},

pages = {994-1002},

abstract = {Disturbance observer (DOB) approach has been widely employed in the industry thanks to its powerful ability to attenuate disturbances and compensate plant uncertainties. Motivated by the fact that the application of the DOB approach has been limited to minimum phase systems, we propose a new DOB configuration for non-minimum phase systems. Rigorous analysis for robust stability and performance recovery is presented in terms of a new filter Θ (s). By restricting the plant uncertainty to a multiplicative perturbation, we also present a systematic design methodology for the filter Θ(s) by virtue of the H∞ synthesis technique. An illustrative example of autopilot design is presented to show the effectiveness of the proposed method for which it is not easy to design H∞ controller to achieve some control goals. The simulation results show that the response of the perturbed system in the presence of disturbance can be recovered to the nominal system response in the absence of disturbance.},

keywords = {Disturbance observer},

pubstate = {published},

tppubtype = {article}

}

@article{ShimJo09,

title = {An Almost Necessary and Sufficient Condition for Robust Stability of Closed-loop Systems with Disturbance Observer},

author = {Hyungbo Shim and Nam Jo},

doi = {10.1016/j.automatica.2008.10.009},

issn = {0005-1098},

year  = {2009},

date = {2009-01-01},

journal = {Automatica},

volume = {45},

number = {1},

pages = {296-299},

abstract = {The disturbance observer (DOB)-based controller has been widely employed in industrial applications due to its powerful ability to reject disturbances and compensate plant uncertainties. In spite of various successful applications, no necessary and sufficient condition for robust stability of the closed loop systems with the DOB has been reported in the literature. In this paper, we present an almost necessary and sufficient condition for robust stability when the Q-filter has a sufficiently small time constant. The proposed condition indicates that robust stabilization can be achieved against arbitrarily large (but bounded) uncertain parameters, provided that an outer-loop controller stabilizes the nominal system, and uncertain plant is of minimum phase.},

keywords = {Disturbance observer},

pubstate = {published},

tppubtype = {article}

}