• Journal of ILASS-Korea
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• v.24 no.4
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• pp.163-170
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• 2019

In this study, feedback logic using dual O₂ sensor values were developed to increase the purification capability of a three-way catalyst (TWC) in a compressed natural gas (CNG) engine. A heavy-duty inline 6-cylinder engine was used and the CNG was supplied to the engine through a mixer. This study consists of two main parts, namely, the proportional integral (PI) control with a front O₂ sensor and the feedback control with dual O₂ sensors. In the PI control experiment, effects of various parameters, such as P gain, I gain, and lean delay, on the TWC capability were identified. Based on the results of the PI control experiment, the feedback logic using dual O₂ sensor values were developed. In both cases, the nitrogen oxides (NO_X) emissions were nearly zero. However, the carbon monoxide (CO) emissions were reduced significant in the feedback logic with dual O₂ sensors than in the PI control with the front O₂ sensor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.264-270
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• 2011

This paper reports a filtered velocity feedback (FVF) controller, which is an alternative to direct velocity feedback (DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated The effects of the design parameters (cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function (OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased The control performance is finally estimated for the clamped beam. More than 10dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.940-950
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• 2011

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems at high frequencies due to non-collocated sensor/actuator configuration with the DVFB can be alleviated by the proposed FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The dynamics of a clamped plate under forces and moments and the FVF controllers are formulated. The stability of the control system and performance are investigated with the open loop transfer function(OLTF). It is found that the FVF controller has a higher gain margin than the corresponding DVFB controller owing to the rapid roll-off behavior at high frequencies. Although the gain margin cannot be fully utilized because of the enhancement at the high frequencies, the vibration at the modes lower than the tuning frequency is well controlled. This performance of the FVF controller is shown to be improved from that of the DVFB controller. It is, however, noted that the stability around the tuning frequency is very sensitive so that the enhancement in vibration level should be followed. The reduction performance at low frequencies using the FVF controller should be compromised with the enhancement in the vibration at high frequencies while designing the controller.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.4
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• pp.189-197
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• 2003

The problem of designing a parallel feedforward compensator (PFC) is considered for a class of non-square linear systems such that the closed-loop system is strictly passive. If a given square system has (vector) relative degree one and is weakly minimum phase, the system can be rendered passive by a state feedback. However, when the system states are not always measurable and the given output is considered, passivation (i.e. rendering passive) of a non-minimum phase system or a system with high relative degree cannot be achieved by any other methodologies except by using a PFC. To passivate a non-square system we first determine a squaring gain matrix and design a PFC such that the composite system has relative degree one and is minimum phase. Then the system is rendered strictly passvie by a static output feedback law. Necessary and sufficient conditions for the existence of the PFC and the squaring gain matrix are given by the static output feedback formulation, which enables to utilize linear matrix inequality (LMI). As an application of the scheme, an alternative way of replacing the role of velocity measurements is provided for the PD-control law of a convey-crane system.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.6
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• pp.641-646
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• 2014

In this paper, we propose a controller for a ball and beam system which reduces the measurement error effect under AC and DC noise. The ball and beam system measures data through a sensor. If sensor noise is included in a controller via the feedback channel, the signal is distorted and the entire system cannot work normally. Therefore, some appropriate action for the measurement error effect is essential in the controller design. Our controller is equipped with a gain-scaling factor and a compensator to reduce the effect of measurement error in the feedback signal. Effectively, our proposed controller can reduce the AC and DC noise of a feedback sensor. We analyze the proposed controller by Laplace transform technique and illustrate the improved control performance via an experiment for a ball and beam system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.720-725
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• 2015

This paper describes the design of a wideband cascode amplifier using a feedback network and microwave small-signal transistors. The adopted cascode structure enables the miller effect to be lessened, cutoff frequency to increase, and reduction of gain in the mid-band to be mitigated. In addition, a feedback network is added to the cascode structure to improve the input matching and ripple performances over the wide operating band. The designed cascode amplifier contains a feedback network for small size and broadband amplification, whereas balanced amplifiers and distributed amplifiers have been used widely. The measurement shows $8.5dB{\pm}1.5dB$ of gain over 1000-2000MHz. The fabricated cascode amplifier has more than 8dB of gain over a 1000MHz bandwidth with a good flatness. The measured performances agree with the predicted ones even a minor shift in operating frequency is observed.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.7
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• pp.48-55
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• 1997

An adaptive output feedback controller is designed for tracking control of an n-link robot manipulator with unknown load. High-gain obwserver that is used to estimate joint velocities is designed to avoide the restriction of the allowable variation range of unknown parmeters as well as improve the state estimation error. We saturate the control inut outside a domain of interest and use an adaptive law with a parameter projection feature to guarantee boundedness of all the trajectories in the closed-loop system. Simulation resutls on a 2-link manipulator illustrate that when the speed of the high-gain observer is sufficiently high, the proposed controller recovers the performance under state feedback control.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.1
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• pp.11-18
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• 2003

We consider a single-input-single-output nonlinear system which is represented in a normal form. The model contains the uncertainty. A high-gain observer is used to estimate the states variables to reject a modeling uncertainty We design the globally bounded output feedback controller using sliding mode control to stabilize the closed-loop system. The globally bounded output feedback controller reduce the peaking in the states variables. The proposed method give a more design freedom in the design of the globally bounded controller than that of the previous work.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.596-600
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• 1992

In CLOS guidance, feedback compensation of the Coriolis acceleration is used to reduce miss distance. This paper presents the effects of the bandwidth of target and missile on the optimal Coriolis acceleration compensation. A state space formulation of CLOS guidance is used to implement CLOS guidance in feedback form. And the LQR control method is applied to find the optimal feedback gain. From the analysis of the Riccati equations of the optimal control, the following facts are observed: When the target is agile, the optimal gain is reduced, since the compensation becomes ineffective. The missile bandwidth also affects the Coriolis accleration compensation. Narrower missile requires more compensation for the Coriolis acceleration.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.231-234
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• 2002

In this paper, we propose an efficient bias circuit for hearing aid using discrete BJT. The collector feedback bias circuit, widely used for the hearing aid, has a resister for negative feedback. As the resistor affects AC and DC simultaneously, it is quite difficult to adjust amplifier gain without changing DC bias point. The previous bias circuit also has weak point to be oscillated by the positive feedback of power noise if gain of hearing aid is high. In the proposed circuit, we can reduce the two weak points of the previous circuit by adding a resistor which is ${\beta}$ times larger than collector resistor between base of BJT and power supply.