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Na, Gyujin,Jo, Nam Hoon,Eun, Yongsoon Elsevier 2019 Journal of the Franklin Institute Vol.356 No.7
<P><B>Abstract</B></P> <P>Augmenting feedback control systems with disturbance observer (DOB) is a widely used technique in system design to compensate for the effect of exogenous disturbances as well as plant model uncertainties. In practice, actuator saturation should be taken into account in the design of control systems with DOB. In such cases, we have observed performance degradation due to zero mean measurement noise in the form of tracking loss. This phenomenon has never been reported in DOB literature. This paper reports the phenomenon, analyzes the conditions under which the tracking loss occurs, and also presents design guidelines to avoid the tracking loss. Experimental verification is also provided using a BLDC motor drive testbed.</P>
Actuator Fault Detection for Unmanned Ground Vehicles using Unknown Input Observers
Gyujin Na,Yongsoon Eun 제어로봇시스템학회 2021 제어로봇시스템학회 국제학술대회 논문집 Vol.2021 No.10
This paper proposes an actuator fault detection method for four wheel unmanned ground vehicle (UGV) dynamics. The detection method is based on unknown input observers. Technical novelty of current work compared to similar work in the literature is that wheel frictions are directly taken into account in the dynamics of UGV, and unknown input observers are developed accordingly. The vehicle dynamics is represented into linear parameter varying system and an actuator fault detection method is derived using unknown input observers for linear parameter varying (LPV) systems. The effectiveness of proposed method is evaluated under various operation scenarios of the UGV.
A Probing Signal-based Replay Attack Detection Method Avoiding Control Performance Degradation
Gyujin Na,Yongsoon Eun 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.11
This paper proposes a probing signal-based replay attack detection method that avoids control performance degradation. Employing probing signals in actuators to detect replay attacks is a well-known and effective strategy: the replay attack replaces the sensor reading with stored sensor data, and thus, no response to the probing signal is present at the sensor. Applying the probing signal, however, introduces a perturbation to the actual system output, which is either regulated to a reference value or controlled to track a desired trajectory. Therefore, the probing signal enables attack detection but simultaneously yields control performance degradation. Clearly, a trade-off exists upon determining the probing signal: a larger amplitude increases the detection probability, especially in the presence of measurement noise, but degrades the control performance; a smaller amplitude of probing signal affects the control performance less but lowers the attack detectability. To address this problem, a disturbance observer (DOB) approach is proposed in this work, where the effect of the probing signal is compensated at the output and the anomaly is detected by looking at the output of the DOB instead of the system. In this way, probing is still effective for replay attack detection, but the regulation and/or tracking performance of the system is compromised much less. An optimization of DOB parameters is presented to satisfy specifications for both attack detection probability and control performance. Simulation results on vehicle platooning and experiment results using unmanned ground vehicle system are presented that validate the efficacy of the proposed method.
Active Probing Signal-Based Attack Detection Method for Autonomous Vehicular Systems
Gyujin Na,Yongsoon Eun 제어로봇시스템학회 2020 제어로봇시스템학회 국제학술대회 논문집 Vol.2020 No.10
This paper addresses an active probing signal-based attack detection method for autonomous vehicular systems. Employing active probing signals for attack detection may become a common method for detecting replay attacks performed using prerecorded sensor data. Conventional replay attack detection methods usually operate by injecting active probing signals into the control inputs and simultaneously checking whether the effect appears on the output signals. When active probing signals are used in vehicular systems, they may change the vehicle acceleration and steering angle. The tracking performance can degrade; inspired by this issue, we develop an attack detection method employing disturbance observers. The attack detection method compensates for the effect of active probing signals and detects malicious attacks, including replay attacks. To validate the effectiveness of the proposed method, several simulations are carried out.
Attack Resilient State Estimation by Sensor Output Coding
Gyujin Na,Jaegeun Park,Yongsoon Eun 제어로봇시스템학회 2019 제어로봇시스템학회 국제학술대회 논문집 Vol.2019 No.10
Designing control systems with a level of resilience against malicious attack has become an important problem because a number of attack incidents recently occurred resulted in significant damages. Resilient state estimation refers to a method of correctly estimating plant states in spite of attacks on sensors. The underlying principle for the majority of existing resilient state estimation methods is to take advantage of redundancies in sensing. More specifically, in order to tolerate (i.e., correctly estimate the plant states) attacks on up to q sensors, the plant must satisfy 2q-redundant observability. In this work, we propose a sensor output coding based resilient state estimation that tolerates the same level of attacks but requires the plant to satisfy a relaxed condition of q-redundant observability. The coding based mechanism identifies the attacked sensors and invokes a state estimator that uses only intact sensors. This enables a correct state estimation even if more than half the sensors are corrupted, which is not possible in most existing works. To demonstrate the effectiveness of the proposed method, simulation results are presented.
Seyeong Cheon,Gyujin Na,Yongsoon Eun 제어로봇시스템학회 2020 제어로봇시스템학회 국제학술대회 논문집 Vol.2020 No.10
Disturbance Observer (DOB) is a well known tool for control systems capable of compensating model uncertainty and rejecting exogenous disturbances. It has been reported previously that zero mean measurement noise may induce tracking error in DOB based control systems with a saturation nonlinearity due to saturating actuators. In this work, DOB based control systems with two saturation constraints are considered and the effect of measurement noise is investigated. Such system architecture arises from Robust Transient DOB (RTDOB) which intentionally bounds amplitude of disturbance compensation in order to avoid peaking phenomenon that can possibly worsen transient response of the closed loop system. Systems using RTDOB have two saturation constraints, one that naturally arises from saturating actuator, and the other artificially inserted to limit the amplitude of disturbance compensation. We show that zero mean measurement noise may induce tracking error in RTDOB based systems as well, analyze the amplitude of the error with systems parameters, and discuss its severity compared to that of a regular DOB based system. The accuracy of proposed analysis is demonstrated through simulations.
2 스풀 혼합흐름 배기방식 터보팬 엔진 성능해석 모델링
이승헌(Seungheon Lee),이형진(Hyoung Jin Lee),김상조(Sangjo Kim),나규진(Gyujin Na),김중회(Jung Hoe Kim) 한국추진공학회 2023 한국추진공학회지 Vol.27 No.1
n this study, performance analysis modeling of two spool mixed flow type turbofan engine according to steady-state and transient is performed. The target engine is selected as F100-PW-229 from Pratt & Whitney, and main engine components including fan, high pressure compressors, combustion, high pressure turbines, low pressure turbines, mixer, convergent-divergent nozzle are modeled. The cooling effect of turbine through secondary flow path are considered in engine simulation model. We develop in-house Matlab/Simulink-based engine performance analysis program capable of analyzing internal engine state and compare it with GASTURB which is generally used as a commercial engine analysis program.