• 대한전기학회논문지:전력기술부문A
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• 제48권6호
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• pp.773-780
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• 1999

A digital tracking controller is proposed for micro electrostatic actuator with input nonlinearity, where disturbance observer is utilized in cooperation with inverse function. Generally the disturbance observer is announced to be robust to modeling uncertainty, and external disturbance. But, when the nonlinearity exists in the systems, the disturbance observer may not directly be applied to that system, because the nonlinearity may destabilize the overall system. Therefore, first, we linearize the nonlinear input characteristics of micro electrostatic actuator by the use of inverse function. Secondly, we apply disturbance observer to approximately linearized system for eliminating the residuals of nonlinearity and the modeling uncertainty. Then, we get the good properties of the disturbance rejection as well as the robustness due to the own nature of disturbance observer. In this case, we propose a sufficient condition for the robust stability of overall systems. Furthermore, we discuss the problem that may be exposed when disturbance observer is applied to the internally stable system with saturation, and analyze two methods to overcome input saturation problem in the sense of internal stability. Simulations have been carried out to show the effectiveness of the proposed controller.

• 대한기계학회논문집
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• 제17권5호
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• pp.1123-1131
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• 1993

본 논문에서는 비행체의 사이드슬립(sideslip)의 변화를 최소로 하면서 롤(roll) 및 요(yaw) 운동을 제어하는 것을 제어목표로 하여, 입출력 갯수가 같은 정방(square)시스템과 입출력 갯수가 다른 비정방(nonsquare)시스템에 대하여 LQG/LTR 및 비례 재어기를 각각 설계하여 그 성능을 비교분석한다.

• Journal of Power Electronics
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• 제18권4호
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• pp.1075-1085
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• 2018

To deal with the operation performance degradation of permanent magnet synchronous machine (PMSM) drives with uncertainties and unmodeled dynamics, this paper presents a finite-time nonlinear disturbance observer (FTNDO) based discretized integral sliding mode (DISM) composite control scheme. Based on the reaching-law approach, a DISM speed controller featuring a superior dynamic quality and global robustness against disturbances is constructed. This controller can avoid the reaching phase and overlarge control action. In addition, a sliding mode differentiator based FTNDO is devised and extended to the discrete-time domain for disturbance estimation. The attractive features of the FTNDO are that it can provide a finite-time converging estimation and alleviate the chattering effect in conventional sliding mode observers, while retaining robustness to parameter variations. By feeding the estimate forward to the pre-stage DISM controller, both disturbances and chattering can be significantly suppressed. Moreover, considering the estimation error of a FTNDO caused by discrete sampling, a stability analysis of the composite controller is discussed. Experimental results validate the superiority of the presented scheme.

• 한국생산제조학회지
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• 제20권5호
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• pp.589-597
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• 2011

In this paper, optimal tuning of a cross-coupled controller linked with the feedforward controller and the disturbance observer is studied to improve contouring and tracking accuracy as well as robustness against disturbance. Previously developed integrated design and optimal tuning methods are applied for developing the robust tuning method. Strict mathematical modeling of the multivariable system is formulated as a state-space equation. Identification processes of the servomechanism are conducted for mechanical servo models. An optimal tuning problem to minimize both the contour error and settling time is formulated as a nonlinear constrained optimization problem including the relevant controller parameters of the servo control system. Constraints such as relative stability, robust stability and overshoot, etc. are considered for the optimization. To verify the effectiveness of the proposed optimal tuning procedure, linear and circular motion experiments are performed on the xy-table. Experimental results confirm the control performance and robustness despite the variation of parameters of the mechanical subsystems.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.2087-2092
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• 2005

Using disturbance observer (DOB) is effective in enhancing the performance of dynamic system in the presence of disturbances. Recently the definition of disturbance has been expanded to modeling uncertainty including parameter variation, internal disturbance. Various structures of DOB have been proposed to improve sensitivity of system for better disturbance rejection performance. However in the case of improvement of sensitivity function, it tends to bring poor transient response due to cross-coupling and phase lag. Furthermore it could be very sensitive to measurement noise due to increased peak of complementary sensitivity function. In this paper, a dual disturbance observer (Dual-DOB) is proposed to reduce the effect of such cross-coupling. It is possible for us to improve the sensitivity function with additional external DOB with hardly affecting complementary sensitivity function. Thus it is able to have robustness against measurement noise. Since we are able to design DOBs of internal and external loop independently, we could prevent transient response quality from degrading while improving the sensitivity function. The proposed Dual-DOB is applied to a commercial optical disk drive tracking servo system. The experimental result shows that the Dual-DOB is an effective method in rejecting the disturbance as well as improving the tracking performance.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.425-428
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• 1998

This paper proposes a new fuzzy controller using variable structure control theory. In this paper, after the time-varying fuzzy sliding surface is designed, the fuzzy rules are defined based on the variable structure control theory. This design method makes the fuzzy controller design more structured and can guarantee the stability and robustness of the fuzzy controller and overcome the shortcoming of the variable structure system. Through computer simulation and experiment of nonlinear inverted pendulum system, this thesis demonstrate that system has the robustness against disturbance and modelling error, and the tracking performance of it is improved.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1996년도 창립기념 전력전자학술발표회 논문집
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• pp.5-12
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• 1996

In this paper, we design a Continuous Variable Structure Controller which can control robot manipulators to follow the desired planned trajectory with accuracy and robustness, and improve continuity and robustness of variable structure control, based on disturbance observer. We also analyze the stability the proposed algorithm and then verify the usefulness and performance through simulation stuies.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.474-477
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• 1995

In this paper, the nonlinear model of axial electro-magnetic suspension(EMS) system is presented. The characteristic of attracyion force is analyzed by FEM. Some simulation is given to compare the sliding mode control based on the input-output linearization with the classical linear control using Taylor approximation. Real result of regulating control, transient response comparison, and robustness control with disturbance using the sliding mode method is presented.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.182-184
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• 1987

When a .epsilon.$_{1}$-modification is applied to a plant with unmodeled dynamics and bounded output disturbance, the output error seems to be relatively large. A .epsilon.$_{1}$-modification with the same switching action as in the switching a modification is proposed to reduce the output proposed adaptive control scheme is to a second-oder plant and it can be asserted that the control objective is satisfied.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.127-130
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• 1991

A magnetic levitation system with hybrid magnets, which is composed of permanent magnets and electromagnets, consumes less power than the conventional attraction type system. A parallel complementary controller on the lift controller is proposed to reduce the sensitivity for parameter variation and force disturbance. Simulation and experiment show that the lift system has robustness to force disturbance.