Young Chol Kim

Direct Digital Control of Single-Phase AC/DC PWM Converter System

This paper presents a new technique for directly designing a linear digital controller for a single-phase pulse width modulation (PWM) converter systems, based on closed-loop identification. The design procedure consists of three steps. First, obtain a digital current controller for the inner loop system by using the error space approach, so that the power factor of the supply is close to one. The outer loop is composed of a voltage controller, a current control loop including a current controller, a PWM converter, and a capacitor. Then, all the components, except the voltage controller, are identified by a discrete-time equivalent linear model, using the closed-loop output error (CLOE) method. Based on this equivalent model, a proper digital voltage controller is then directly designed. It is shown through PSim simulations and experimental results that the proposed method is useful for the practical design of PWM converter controllers.

Fixed, low-order controller design with time response specifications using non-convex optimization

In this paper, we present a new algorithm for designing a fixed, low-order controller with time response specifications for a linear time invariant (LTI) plant. For the two-parameter feedback configuration, the problem of finding a fixed or low-order controller to meet the desired time response specifications is reduced to the least square estimation (LSE) in the sense of partial model matching (PMM), which results in a quadratic cost function. The closed-loop stability condition imposed on controller parameters is formulated by polynomial function constraints associated with the cost function. When the cascade feedback structure is considered, the zeros of the controller may be a big obstacle to designing a good time response controller. This problem can also be formulated using polynomial constraints. Consequently, it is shown that the total problem here can be formulated as a global optimization problem with a quadratic objective function and polynomial function constraints in controller parameter space. We show that the software GloptiPoly [1] can be used as a simple algorithm to solve this problem. Finally, several illustrative examples are given.

The Complete Set of PID Controllers with Guaranteed Gain and Phase Margins

The problem of determining the entire set of PID controllers that stabilize a linear time invariant(LTI) plant has been recently solved in [1], [2]. In this paper, we extend these results to the problem of obtaining the complete set of PID parameters that attains prescribed gain and phase margins. An example is given for illustration.

Automatic guidance control of an articulated all-wheel-steered vehicle

This paper presents automatic guidance control of a single-articulated all-wheel-steered vehicle being developed by the Korea Railroad Research Institute. The vehicle has an independent drive motor on each wheel except for the front axle. The guidance controller is designed so that the vehicle follows the given reference path within permissible lateral deviations. We use a three-input/three-output linearised model derived from the nonlinear dynamic model of the vehicle. For the purpose of simplifying the controller and making it tunable, we consider a decentralised control configuration. We first design a second-order decoupling compensator for the two-input/two-output system that is strongly coupled and then design a first-order controller for each decoupled feedback loop by using the characteristic ratio assignment method. The simulation results for the nonlinear dynamic model indicate that the proposed control configuration successfully achieves the design objectives.

Portable digital esophageal stethoscope system

Heart sound occurs when the heart contracts and expands. It provides information on myocardial contractility and blood vessels, which is not obtainable from ECG. For this reason, stethoscopy of heart sound in anesthesiology is a very crucial means for acquiring cardiac information and preventing intraoperative medical accidents, and it requires a system for precise objective measurement and analysis of heart sound and murmur. Thus, this study purposed to develop portable digital esophageal stethoscope (PDES) that can objectify and quantify heart sound and murmur. In this study, we designed PDES for precise measurement and analysis of heart sound and murmur data. Heart sound information obtained by inserting the sensor of the PDES into the patients esophagus can be transmitted to a terminal or a PC and displayed on the screen The amplitude and waveform of heart sound are displayed using self-developed software Heart Sound 1.0. The results of experiment with the developed PDES showed that data on the amplitude and waveform of heart sound and murmur were produced stably in real-time. In addition, when heart sound was heard using a headphone, the sound was clear without external murmur. The PDES developed in this study, which complements the disadvantages of traditional esophageal stethoscope while preserving its advantages, could not only examine heart sound and murmur using an esophageal catheter but also display the amplitude and waveform of heart sound and murmur and measure the patients body temperature. Accordingly, the developed PDES is expected to be useful in the continuous stethoscopy of heart sound during operation and to contribute to research on heart sound by providing heart sound data.

A Controller Design for Precision Laser-Beam Positioning System

This article presents a decentralized control strategy for a two-axis precision laser-beam positioning system (PLPS). The PLPS is composed of two integrated subsystems: the telescope system equipped with a FSM platform and the beam alignment system. The strategy included actual data acquisition, system analysis and modeling, digital controller design, and experimental evaluations. The controller had a sensitivity margin of less than −10 dB at 20 Hz on each axis, and maintained the stability of PLPS. The system had moderate robustness, tracked the command signals and output responses without steady-state errors.

Direct digital control of PWM converter using closed-loop identification

This paper presents a new technique of designing a direct digital controller for a single-phase pulse width modulation (PWM) converter system, based on closed-loop identification. It is difficult to analytically design a controller due to the double loop structure of the PWM converter control system. The design procedure consists of three steps. First, obtain a current controller for the inner loop system by using the error space approach, which is a powerful method for robust tracking control design. The outer loop is composed of a voltage controller, a current control loop including the current controller, a PWM converter, and a capacitor. Then, all the components, except the voltage controller, are identified by a discrete-time equivalent linear method, using the closed-loop output error (CLOE) method. Based on the equivalent model, a proper digital voltage controller is then directly designed. It is shown through PSim simulations and experimental results that the proposed method is useful for the practical design of PWM converter controllers.

Three-Dimensional Dynamic Model of Full Vehicle

A three-dimensional dynamic model for simulating various motions of full vehicle is presented. The model has 16 independent degrees of freedom (DOF) consisting of three kinds of components; a vehicle body of 6 DOF, 4 independent suspensions equipped at every corner of the body, and 4 tire models linked with each suspension. The dynamic equations are represented in six coordinate frames such as world fixed coordinate, vehicle fixed coordinate, and four wheel fixed coordinate frames. Then these lead to the approximated prediction model of vehicle posture. Both lateral and longitudinal dynamics can be computed simultaneously under the conditions of which various inputs including steering command, driving torque, gravity, rolling resistance of tire, aerodynamic resistance, etc. are considered. It is shown through simulations that the proposed 3D model can be useful for precise design and performance analysis of any full vehicle control systems.

The Entire Set of First Order Controllers Guaranteed Stability and Gain/Phase Margins for a LTI Plant with Time Delay

The problem of determining the entire set (say S0) of the first order controllers (FOC) that stabilize a linear time invariant (LTI) plant with delay free has been recently solved. In this paper, we extend this solution to the case of LTI plant with time delay. The main result shows that all the stabilizing FOC for a given LTI plant including time delay are represented in a linear transformation of S0 at every fixed frequency. It is also shown that the whole set of FOC satisfying the given gain and/or phase margins for the plant is determined by the slightly modified linear transformation of S0 at every fixed frequency. Examples are given for illustration

Issues in Linear Feedback Control Design with Notch Filters

In this note, we describe some design issues that should be carefully considered when one designs a linear feedback controller which includes a notch filter. Notch filters are generally used to compensate the effects of resonant modes that may result in large magnitude peaks in the frequency domain. It is common that practical engineers prefer to add such a notch filter after having previously designed a feedback controller in the absence of the filter. Apparently the resulting performance does not seem to be different from when a feedback controller is designed for a plant that has been previously compensated by a notch filter. In order to compare the performance of both approaches, a low-order controller design method that uses partial model matching ideas has been applied to a linear time invariant (LTI) model. The results suggest that frequency domain characteristics such as the sensitivity function and stability margins will tend to be similar for both approaches. On the other hand, when notch filter compensation is used before designing a feedback controller there is a tendency to achieving much better time responses.