Seok-Kwon Jeong

CONTROLLER DESIGN AND ANALYSIS FOR AUTOMATIC STEERING OF PASSENGER CARS

Abstract This paper deals with a lateral controller design for active 2WS vehicles in ITS applications. First, the vehicle dynamics for typical lateral maneuvers are rigorously described by Newtons formulation. Next, based on a linear perturbed model, a robust controller via μ (mu)-synthesis is designed. Due to the characteristics of D–K iteration, the resulting high-order controller has to be reduced for implementation. Then the frequency- and time-domain responses of the robust controller are extensively evaluated through numerical simulations. Further, we present performance comparisons between full-order controller and reduced-order controller. Finally, the automated steering control presented here is shown to be robust to the prescribed levels of uncertainty for highway maneuvers.

Optimum Controller Design of a Water Cooler for Machine Tools Based on the State Space Model

ABSTRACT:Typical temperature control methods of a cooler for machine tools are hot-gas bypass and compressor variable speed control. The hot-gas bypass system has been widely used to control the cooler temperature in many general industrial fields. On the contrary, the compressor variable speed control is focused on special fields such as aerospace and high precision machine tools which need high precision control. The variable speed control system usually has two control variables such as target temperature and superheat. In other words, the variable speed control sys-tem is basically multi-input multi-output(MIMO) system. In spite of MIMO system, the proportional integral derivative(PID) feedback control methodology that based on single-input single-output (SISO) system is generally used for designing the variable speed control system. Therefore, it is inevitable to describe transfer functions for dynamic behaviors of every controlled variables and decide the PID gains with tremendous iteration process. Moreover, the designed PID gains do not provide optimum system performances. To solve these problems, high performance controller design method based on a state space model is suggested in this paper. An optimum controller is designed to minimize both control errors and energy inputs. This method was more simple to describe dynamic behaviors and easier to design the cooler controller which is MIMO system.Keywords:Water cooler(수냉각기), Optimum control(최적제어), State space model(상태공간 모델), Compressor variable speed control(압축기 가변속 제어), Multi-input multi- output system(다입력 다출력 시스템), State variable(상태변수)

Comparison of System Performances of Hot-gas Bypass and Compressor Variable Speed Control of Water Coolers for Machine Tools

Recently, the needs of system performances such as working speed and processing accuracy in machine tools have been increased. Especially, the speed increment generates harmful heat at both moving part of the machine tools and handicrafts. The heat is a main drawback to progress accuracy of the processing. Hence, a cooler system to control temperature is inevitable for the machine tools. In general, two representative control schemes, hot-gas bypass and variable speed control of a compressor, have been adopted in the water cooler system. In this paper, comparisons of system performances according to the control schemes in a cooler for machine tools were conducted in detail. Each proportional-integral feedback controller for the two different control systems is designed. The system performances, especially the temperature control accuracy and coefficient of performance which is a criterion of energy saving, were mainly analyzed through various experiments using 1RT water cooler system with different two types of control scheme. These evaluations will provide useful information to choose suitable water cooler system for the engineers who design controllers of the cooler system for machine tools.

Precise Temperature Control of Oil Coolers with Hot-gas Bypass Manner for Machine Tools Based on PI and Feedforward Control

ABSTRACT:Recently, the performances of speed and accuracy are enhanced in machine tools. The high speed of the machine tools usually causes harmful thermal displacements on the objects. To reduce the thermal displacements, machine tools generally adopt oil coolers with precise temperature control function. This study aims at precise control of oil outlet temperature in the oil coolers with hot-gas bypass manner based on PI control logic. The control system was designed for obtaining steady state error within ±0.1℃ and maximum overshoot with 0.8% even though abrupt disturbances are added to the system. We showed that the PI gains could be easily decided by numerical simulations using practical transfer function which got experiments. Also, transient characteristics could be improved significantly by reflecting the inlet temperature of an evaporator to the output of a controller feedforwardly considering periodic abrupt disturbances. Through some experiments, excellent control performances were established by the suggested control.Keywords:Hot-gas bypass(핫가스 바이패스), Oil cooler(오일쿨러), Electronic expansion valve(전자팽창밸브), PI control(PI 제어), Feedforward control(피드포워드 제어)

Optimal PI Controller Design for Refrigeration System Considering Disturbance

ABSTRACT:The proportional plus integral(PI) feedback control manner has been used in many general industrial fields such as refrigeration system because of its simple design process and favorable control performance. This paper deals with optimized PI controller design of the refrigera-tion system based on evaluation functions such as integrated absolute error(IAE). The suggested optimal PI gains can be easily calculated by a simple program and the optimal controllability satisfying the evaluation function can be assured. Furthermore, at the initial step of controller design, the suggested optimal gain is able to reflect some noise disturbances caused by an inverter which drives variable speed compressors. The validity of the suggested optimal gain is investigated by some simulations and experiments to verify its efficiency. From the results of comparing control performance between the optimal PI controller based on the evaluation function and the PI controller designed by the Matlab tuner which was known as the most popular gain tuner, the optimal PI controller showed more desirable control performance especially in transient responses.Keywords:Optimal PI controller(최적 PI 제어기), Refrigeration system(냉동시스템), Evaluation function(평가함수), Noise disturbance(노이즈 외란)

Active steering for intelligent vehicles using advanced control synthesis

This paper considers the design of an active steering controller of an intelligent vehicle for general lane change manoeuvres. First, we present a unified formulation of lateral vehicle dynamics. Next, the design method includes the 2-DOF H∞ loop-shaping control scheme for lane change manoeuvres, in the face of co-prime factorisation perturbations. Furthermore, the controller has been reduced to a reasonable order before real implementation. The resulting controller is then evaluated in both frequency- and time-domains. Finally, it is shown that the presented controller provides excellent performance over a wide range of simulated manoeuvring conditions.

Operating Number Control of Compressors Based on Cooperative Logic for a High Efficiency Centrifugal Water Chiller

This paper discusses compressors operating number control strategy using cooperative logic to cope with variable partial load for high efficiency of a centrifugal water chiller. The cooperative logic is composed of a speed-up and speed-down controller, enabling smooth operation of compressors and equivalent distribution of thermal load in each compressor. This centrifugal water chiller design can be operated with high efficiency without incurring excessive energy waste and large transient phenomena at partial load states. Simulations in MATLAB and experiments in a real chiller system were conducted and verified the high efficiency control of a centrifugal water chiller achieved by the suggested strategy.

Practical Modeling and PI Controller Design for Centrifugal Water Chillers

This paper describes the PI controller design based on a practical transfer function model for centrifugal water chillers. The rotational speed of a compressor and the opening angle of an electronic expansion valve were simultaneously regulated as manipulated variables to maintain temperature reference and to ensure high efficiency of the chiller. The COP according to the change in each variable was investigated by performing some static experiments, and it was reflected in the PI controller design to accomplish the high efficiency control. Especially, the practical transfer function model of the chiller was built based on the dynamic experimental data considering the strong inherent non-linearity and complexity of the chiller system. The validity of the designed PI controller was proven by some experimental results using the test facility and the results were also compared to the conventional evaporating pressure control results.

State Equation Modeling and the Optimum Control of a Variable-Speed Refrigeration System

Abstract This paper deals with precise analytical state equation modeling of a variable speed refrigeration system (VSRS)for optimum control in state space. The VSRS is described as multi-input and multi-output (MIMO) system, which hastwo controlled variables and two control inputs. First, the Navier-Stokes equation and mass flow rate were applied to eachcomponent of the basic refrigeration cycle to build a dynamic model. The dynamic model, represented by a differentialequation, was transformed into the state equation formula. Next, a full-order state observer was built to estimate all of thestate variables to compose an optimum control system. Then, an optimum controller was designed to minimize an evaluationfunction that has input energy and control error. Finally, simulations and experiments were conducted to verify the validityof the proposed modeling and designed optimum controller to regulate target temperature and superheat in a 1RT oil coolersystem. The results show that the proposed method, state equation modeling and optimum control, is efficient to ensure optimal control performance of the VSRS.

Precise Position Synchronous Control of Four-Axes System Based on Acceleration Control

In this paper, we deal with a precise position synchronous control of four-axes system which is working under various load disturbances. Each axis driving system is consisted of a speed controller and an acceleration controller as an inner loop instead of conventional current control scheme. The acceleration control plays an important roll to suppress load disturbances quickly. Also, each axis is coupled by a maximum position synchronous error comparison to minimize position synchronous errors according to integration of speed differency. As a result, the proposed system enables precise synchronous control with good robustness against load disturbances during transient as well as steady state. The stability and robustness of the proposed system are investigated through its frequency characteristic and numerical simulations. Finally, experimental results under load disturbances demonstrate the effectiveness of the proposed control system fur four-axes position synchronous control.