• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.475-478
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• 1999

In this paper, we propose the robust performance design of multivariable systems within the framework of Quantitative Feedback Theory(QFT) using ICD. The ICD(Individual Channel Design) is a multivariable control method based on the classical frequence response. It is considered to apply feedforward controller for compensating the effect of interconnection between channels. Performance of the proposed method are demonstrated by simulations in appling gas turbine model.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.8
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• pp.649-654
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• 2002

The essential philosophy of the QFT(Quantitative Feedback Theory) is that a suitable controller can be found by loop shaping a nominal loop transfer function such that the frequency response of this function does not violate the QFT bounds. The loop shaping synthesis involves the identification of a structure and its specialization by means of the parameter optimization. This paper presents an optimization algorithm to estimate the controller parameters from the frequency transfer function synthesis using the TLS(Total Least Squares) in the QFT loop shaping procedure. The proposed method identifies the parameter vector of the robust controller from an overdetermined linear system developed from rearranging the two dimensional system matrices and output vectors obtained from the QFT bounds. The feasibility of the suggested algorithm is illustrated with an example.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.3
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• pp.88-97
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• 2013

This paper presents a robust air-to-fuel ratio (AFR) control algorithm for managing exhaust gas recirculation (EGR) systems. In order to handle production tolerance, deterioration and parameter-varying characteristics of the EGR system, quantitative feedback theory (QFT) is applied for designing the robust AFR control algorithm. A plant model of EGR system is approximated by the first order transfer function plus time-delay (FOPTD) model. EGR valve position and AFR of exhaust gas are used as input/output variables of the plant model. Through engine experiments, parameter uncertainty of the plant model is identified in a fixed engine operating point. Requirement specifications of robust stability and reference tracking performance are defined and these are fulfilled by the following steps: during loop shaping process, a PID controller is designed by using a nominal loop transmission function represented on Nichols chart. Then, the frequency response of closed-loop transfer function is used for designing a prefilter. It is validated that the proposed QFT-based AFR control algorithm successfully satisfy the requirements through experiments of various engine operating points.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.562-568
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• 1998

During the past three decades, several techniques have been suggested for robust performance design of multivariable systems within the framework of Quantitative Feedback Theory. They are all characterized and limited by the use of loop transmission inversion. A new approach within framework is described which leads to a design tehnique without loop transmission inversion. Complete sequential design algorithms are derived for performance specifications in terms of plant input disturbance, sensitivity, complimentary sensitivity and control effort.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.199-199
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• 2000

Most of linear time-varying(LTV) systems except special cases have no general solution for the dynamic equations. Thus, it is difficult to design time-varying controllers in analytic ways, and other control design approaches such as robust control have been applied to control design for uncertain LTI systems which are the approximation of LTV systems have been generally used instead. A robust control method such as quantitative feedback theory(QFT) has an advantage of guaranteeing the stability and the performance specification against plant parameter uncertainties in frozen time sense. However, if these methods are applied to the approximated linear time-invariant(LTI) plants which have large uncertainty, the designed control will be constructed in complicated forms and usually not suitable for fast dynamic performance. In this paper, as a method to enhance the fast dynamic performance, the approximated uncertainty of time-varying parameters are reduced by the proposed QFT parameter-scheduling control design based on radial basis function (RBF) networks for LTV systems with bounded time-varying parameters.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.259-264
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• 1997

본 논문에서는 Westinghouse(WH)사에서 공급한 고리 3, 4호기의 증기발생기 모델에 강인제어 기법의 하나인 QFT(Quantitative Feedback Theory)를 적용하여 플랜트에 존재하는 불확실성이나 외란에 대해 강인성을 보장하는 제어기를 설계하였다. 증기발생기의 주파수응답 한계조건은 MATLAB QFT Toolbox를 이용하였으며, loop shaping에 의한 전달함수 식별을 위해서 근사화 기법을 적용하였다. 그리고 5∼20[%]의 저출력구간에서 모의실험을 하여 본 논문의 유용성을 보였다.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.7
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• pp.371-380
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• 2003

In this paper, a new design method of H$H_\infty$-Qn PSS using genetic algorithm(GA) is proposed to efficiently damp low frequency oscillations despite the uncertainties and various disturbances of power systems. The selection method of evaluation function is proposed for selecting the robust PSS parameters. All QFT boundaries are satisfied automatically and H$H_\infty$-norm is minimized simultaneously without trial and error procedure. The eigenvalues and the damping ratio of dominant oscillation mode are investigated to evaluate performance of designed controller for one machine infinite bus system. A disturbance attenuation performance is investigated through singular value bode diagram of the system. Dynamic characteristics are considered to verify robustness of the proposed PSS by means of nonlinear simulations under various disturbances for various operating conditions. The results show that the proposed PSS is more robust than conventional PSS.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1176-1178
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• 1996

QFT(Quantitative feedback theory) is a design method to synthesize robust controller, satisfying some design specifications. Loop shaping is regarded as one of the important steps in QFT design. In this paper, we present to apply the approximation algorithm for loop shaping to PID tuning. An example is used to illustrate its feasibility.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2005-2007
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• 2003

QFT이론은 플랜트의 변동을 고려하여 주파수영역에서 설계하는 제어기법으로 파라미터의 변화 및 외란에 강인한 제어기 설계에 적합한 방법이다. 비행 제어시스템은 다중 입력과 다중 출력을 갖는 시스템으로 내부 하중의 변화 등의 내부적인 파라미터의 변동이나 돌풍 등의 외란에 강인한 제어기의 설계를 요구받는다. 이러한 비행제어시스템에 MIMO QFT 설계방법을 적용하여 제어기를 설계하였는데, 강인한 제어기의 설계방법인 QFT에는 GA를 이용한 자동 loop-shaping 방법이 사용되었다.

• Transactions on Control, Automation and Systems Engineering
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• v.1 no.2
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• pp.94-98
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• 1999

Optical scanning systems use glavanometers to point the laser beam to the desired position on the workpiece. The angular speed of a galvanometer is typically controlled using Proportional+Integral+Derivative(PID) control algorithms. However, natural variations in the dynamics of different galvanometers due to manufacturing, aging, and environmental factors(i.e., process uncertainty) impose a hard limit on the bandwidth of the galvanometer control system. In general, the control bandwidth translates directly into efficiency of the system response. Since the optical scanning system must have rapid response, the higher control bandwidth is required. Auto-tuning PID algorithms have been accepted in this area since they could overcome some of the problems related to process uncertainty. However, when the galvanometer is attached to a larger mechanical system, the combined dynamics often exhibit resonances. It is well understood that PId algorithms may not have the capacity to increase the control bandwidth in the face of such resonances. This paper compares the achieable performance and robustness of a galvanometer control system using a PID controller tuned by the Ziegler-Nichols method and a controller designed by the Quantitative Feedback Theory(QFT) method. The results clearly indicate that-in contrast to PID designs-QFT can deliver a single, fixed controller which will supply high bandwidth design even when the dynamics is uncertain and includes mechanical resonances.