Hyuk-Jun Chang

Design and Development of a Functional Safety Compliant Electric Power Steering System

ISO 26262 is an international standard for the functional safety of electric and electronic systems in vehicles, and this standard has become a major issue in the automotive industry. In this paper, a functional safety compliant electronic control unit (ECU) for an electric power steering (EPS) system and a demonstration purposed EPS system are developed, and a software and hardware structure for a safety critical system is presented. EPS is the most recently introduced power steering technology for vehicles, and it can improve driver’s convenience and fuel efficiency. In conformity with the design process specified in ISO 26262, the Automotive Safety Integrity Level (ASIL) of an EPS system is evaluated, and hardware and software are designed based on an asymmetric dual processing unit architecture and an external watchdog. The developed EPS system effectively demonstrates the fault detection and diagnostic functions of a functional safety compliant ECU as well as the basic EPS functions.

Evaluation of the basic reproduction number of MERS-CoV during the 2015 outbreak in South Korea

In 2015 an outbreak of Middle East Respiratory Syndrome (MERS) has occurred in South Korea, which has been known to be the second biggest outbreak of MERS so far. In this paper we study an estimation of the basic reproduction number of the coronavirus (CoV) of MERS based on the reported data from the MERS spread in South Korea. To this end we employ a mathematical model described by a set of ordinary differential equations, i.e. the well-known susceptible-infected-removed (SIR) model. First we fit the model to the epidemic curve data obtained from the outbreak. Then we can identify the model parameters and also the basic reproduction number. Note that there had been no control intervention during the early stage of the MERS outbreak in South Korea, which can be considered as the best condition for the estimation study of intrinsic epidemic parameters of MERS, such as basic reproduction number.

Estimation of basic reproduction number of the Middle East respiratory syndrome coronavirus (MERS-CoV) during the outbreak in South Korea, 2015

BackgroundIn South Korea, an outbreak of Middle East respiratory syndrome (MERS) occurred in 2015. It was the second largest MERS outbreak. As a result of the outbreak in South Korea, 186 infections were reported, and 36 patients died. At least 16,693 people were isolated with suspicious symptoms. This paper estimates the basic reproduction number of the MERS coronavirus (CoV), using data on the spread of MERS in South Korea.MethodsThe basic reproduction number of an epidemic is defined as the average number of secondary cases that an infected subject produces over its infectious period in a susceptible and uninfected population. To estimate the basic reproduction number of the MERS-CoV, we employ data from the 2015 South Korea MERS outbreak and the susceptible-infected-removed (SIR) model, a mathematical model that uses a set of ordinary differential equations (ODEs).ResultsWe fit the model to the epidemic data of the South Korea outbreak minimizing the sum of the squared errors to identify model parameters. Also we derive the basic reproductive number as the terms of the parameters of the SIR model. Then we determine the basic reproduction number of the MERS-CoV in South Korea in 2015 as 8.0977. It is worth comparing with the basic reproductive number of the 2014 Ebola outbreak in West Africa including Guinea, Sierra Leone, and Liberia, which had values of 1.5–2.5.ConclusionsThere was no intervention to control the infection in the early phase of the outbreak, thus the data used here provide the best conditions to evaluate the epidemic characteristics of MERS, such as the basic reproduction number. An evaluation of basic reproduction number using epidemic data could be problematic if there are stochastic fluctuations in the early phase of the outbreak, or if the report is not accurate and there is bias in the data. Such problems are not relevant to this study because the data used here were precisely reported and verified by Korea Hospital Association.

Analysis of the HIV eradication phenomenon at the early stage of infection with an extracellular deterministic model.

We investigate the phenomenon of HIV eradication at the early stage of the infection and evaluate the chance of the eradication with a mathematical model. We employ an extracellular deterministic model of the HIV infection dynamics and modify the model to include the pharmacokinetics and pharmacodynamics of antiretroviral HIV drugs. In addition we consider clinical experiments for the prevention of HIV infection using pre-exposure chemoprophylaxis treatment. Exploiting the mathematical model we implement the experiment numerically. The study in this paper is supported by the clinical results and provides a theoretical explanation for the results. The result suggests that the protocol of the experiment eradicates the virus in HIV infected patients.

Analysis of explicit model predictive control for path-following control

In this paper, explicit Model Predictive Control(MPC) is employed for automated lane-keeping systems. MPC has been regarded as the key to handle such constrained systems. However, the massive computational complexity of MPC, which employs online optimization, has been a major drawback that limits the range of its target application to relatively small and/or slow problems. Explicit MPC can reduce this computational burden using a multi-parametric quadratic programming technique(mp-QP). The control objective is to derive an optimal front steering wheel angle at each sampling time so that autonomous vehicles travel along desired paths, including straight, circular, and clothoid parts, at high entry speeds. In terms of the design of the proposed controller, a method of choosing weighting matrices in an optimization problem and the range of horizons for path-following control are described through simulations. For the verification of the proposed controller, simulation results obtained using other control methods such as MPC, Linear-Quadratic Regulator(LQR), and driver model are employed, and CarSim, which reflects the features of a vehicle more realistically than MATLAB/Simulink, is used for reliable demonstration.

Extended root-locus technique applied to pole-placement for PI controller design

The root-locus method is often employed when a controller that can find its gains is designed. Usually the method is used to determine only one design parameter. However most controllers for industrial applications have more than one controller gain: for example proportional-integral-derivative (PID) controllers have three controller gains, P, I, and D. As the root-locus technique cannot complete the designs of controllers with more than one gain, designing controller with more than one parameter requires an extension of the conventional root-locus technique. This paper proposes an extended root-locus method for controllers with two parameters. Matlab is used as a computation tool to demonstrate the effectiveness of the proposed method through the solution of numerical examples. We demonstrate the determination of two controller gain parameters based on this extension of the root-locus method, which can be applied to controller design problems with multiple parameters.

State-space analysis of discrete-time disturbance observer for sampled-data control systems

We present a state-space analysis of discrete-time disturbance observer (DOB) for a class of sampled-data control systems. Unlike the continuous-time case, it is well-known that sampling process may yield non-minimum phase zeros (called sampling zeros). Motivated by the truncated Taylor series (TTS) model which well describes the behavior of sampling zeros in the state-space, we present a condition for robust stability of the uncertain sampled-data control system with the discrete-time DOB. In particular, using the discrete-time singular perturbation theory, we show that the uncertain plant with disturbance behaves like a disturbance-free nominal model with the help of the discrete-time DOB.

An evaluation of the emergence of drug resistant virus for HIV/AIDS drug treatments

HIV/AIDS drug treatment, such as highly active anti-retroviral therapy (HAART), often fails due to the emergence of drug resistant species. In this paper we investigate a new estimation method for the possibility of emergence of drug resistant mutation. To the best knowledge of the author this work is the first study to try to describe quantitatively the possibility of drug resistance emergence for HIV/AIDS drug treatments. In simulation studies we compare HIV/AIDS treatment methods, such as structured treatment interruption (STI) and improved gradual dosage reduction (iGDR), based on the proposed analysis. From the analysis we can explain why STI treatment often fails and also can show that iGDR is desirable rather than STI particularly in terms of the decrease of the possibility of emergence of drug resistant virus.

A preliminary result on frequency-shaped model predictive control

This paper introduces frequency-shaped model predictive control (FSMPC) by considering the cost function in the frequency domain, which applies for discrete-time linear systems. Borrowing from the idea of using Parsevals theorem in the technique of the frequency-shaped LQR, we show that FSMPC can be formulated as a standard form of MPC. The terminal cost of the proposed FSMPC is chosen such that, when there are no state/input constraints, the optimal cost of FSMPC becomes the same as that of the frequency-shaped LQR, from which two benefits are obtained. That is, the closed-loop stability is straightforwardly achieved, and the performance of frequency-shaped LQR is inherited while state/input constraints are taken into account. A few examples are included to illustrate the effectiveness of the proposed FSMPC.

Design of Autonomous Cruise Controller with Linear Time Varying Model

Cruise control is a technology for automatically maintaining a steady speed of vehicle as set by the driver via controlling throttle valve and brake of vehicle. In this paper we investigate cruise controller design method with consideration for distance to vehicle ahead. We employ linear time varying (LTV) model to describe longitudinal vehicle dynamic motion. With this LTV system we approximately model the nonlinear dynamics of vehicle speed by frequent update of the system parameters. In addition we reformulate the LTV system by transforming distance to leading vehicle into variation of system parameters of the model. Note that in conventional control problem formulation this distance is considered as disturbance which should be rejected. Consequently a controller can be designed by pole placement at each instance of parameter update, based on the linear model with the present system parameters. The validity of this design method is examined by simulation study.