• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.1
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• pp.33-39
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• 2007

LonWorks over IP (LonWorks/IP) virtual device network (VDN) is an integrated form of LonWorks device network and IP data network. LonWorks/IP VDN can offer ubiquitous access to the information on the factory floor and make it possible for the predictive and preventive maintenance on the factory floor. Timely response is inevitable for predictive and preventive maintenance on the factory floor under the real-time distributed control. The network induced uncertain time delay deteriorates the performance and stability of the real-time distributed control system on LonWorks/IP virtual device network. Therefore, in order to guarantee the stability and to improve the performance of the networked distributed control system the time-varying uncertain time delay needs to be compensated for. In this paper, under the real-time distributed control on LonWorks/IP VDN with uncertain time delay, a control scheme based on disturbance observer and ZPETC(Zero Phase Error Tracking Controller) phase lag compensator is proposed and tested through computer simulation. The result of the proposed control is compared with that of internal model controller (IMC) based on Smith predictor and disturbance observer. It is shown that the proposed control scheme is disturbance and noise tolerant and can significantly improve the stability and the tracking performance of the periodic reference. Therefore, the proposed control scheme is well suited for the distributed servo control for predictive maintenance on LonWorks/IP-based virtual device network with time-varying delay.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.3
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• pp.1-12
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• 2001

We consider the robust control problem for non-minimum phase(NMP) systems with parametric uncertainty. First, a new method that translates such an uncertain NMP system into a interval family of minimum phase(MP) transfer functions followed a time delay term in the form of Pade' approximation is presented. The controller to be proposed consists of a compensator with Smith predictor structure, so that it can compensate the time delay behaviour due to NMP plant. Therein, the main feedback controller for a family of MP plants has been designed by using quantitative feedback theory(QFT) such that satisfies the robust stability against the structured uncertainty. The stability and performance of overall system are examined through an illustrative example.

• Journal of Power Electronics
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• v.17 no.3
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• pp.821-834
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• 2017

This paper reports on a single-inductor multiple-output step-up converter with digital control. A systematic analog-to-digital-controller design is explained. The number of digital blocks in the feedback path of the proposed converter has been decreased. The simpler digital pulse-width modulation (DPWM) architecture is then utilized to reduce the power consumption. This architecture has several advantages because counters and a complex digital design are not required. An initially designed unit-delay cell is adopted recursively for the construction of coarse, intermediate, and fine delay blocks. A digital limiter is then designed to allow only useful code for the DPWM. The input voltage is 1.8 V, whereas output voltages are 2 V and 2.2 V. A co-simulation was also conducted utilizing PowerSim and Matlab/Simulink, whereby the 55 nm process was employed in the experimental results to evaluate the performance of the architecture.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.73-78
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• 2020

In this study, a novel reactive power control scheme is proposed to supply stable reactive power to the distribution line by compensating a ripple voltage of DC link. In a single-phase system, a magnitude of second harmonic is inevitably generated in the DC link voltage, and this phenomenon is further increased when the capacity of DC link capacitor decreases. Reactive power control was performed by controlling the d-axis current in the virtual synchronous reference frame, and the voltage control for maintaining the DC link voltage was implemented through the q-axis current control. The proposed method for compensating the ripple voltage was classified into three parts, which consist of the extraction unit of DC link voltage, high pass filter (HPF), and time delay unit. HPF removes an offset component of DC link voltage extracted from integral, and a time delay unit compensates the phase leading effect due to the HPF. The compensated DC voltage is used as feedback component of voltage control loop to supply stable reactive power. The performance of the proposed algorithm was verified through simulation and experiments. At DC link capacitance of 375 uF, the magnitude of ripple voltage decreased to 8 Vpp from 74 Vpp in the voltage control loop, and the total harmonic distortion of the current was improved.

• International Journal of Control, Automation, and Systems
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• v.1 no.1
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• pp.68-75
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• 2003

This paper presents an effective trajectory planning algorithm for industrial robot manipulators. Given the end-effector trajectory in Cartesian space, together with the relevant constraints and task specifications, the proposed method is capable of planning the optimum end-effector trajectory. The proposed trajectory planning algorithm considers the joint acceleration limit, end-effector velocity limits, and trajectory allowance. A feedforward compensator is also incorporated in the proposed algorithm to counteract the delay in joint dynamics. The algorithm is carefully designed so that it can be directly adopted with the existing industrial manipulators. The proposed algorithm can be easily programmed for various tasks given the specifications and constraints. A three-dimensional test trajectory was planned with the proposed algorithm and tested with the Performer MK3s industrial manipulator. The results verified effective manipulator performance within the constraints.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.502-510
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• 1997

A disturbance rejection controller using eccentricity filtering and LQ control techniques is proposed to alleviate the effecto of major roll eccentricity in multivariable cold-rolling processes. Fundamental problems in multivariable cold-rolling processes such as process time delay inherent in exit thickness measurement and non-stationary characteristics of roll eccentricity signals can be overcome by the proposed control method. The filtered instantaneous estimate of roll eccentricity may be exploited to improve instantaneous estimate of the exit thickness variation based on roll force and roll gap measurements, and a feedforward compensator is augmented as a reference for a gaugemeter thickness estimator. LQ feedback controller is combined with eccentricity filter for the attenuation of the exit thickness variation due to the entry thickness variation. The simulation results show that the roll eccentricity disturbance is significantly eliminated and other disturbances also are attenuated.

• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.100-103
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• 2004

A systematic method for tunable dispersion compensation based on chirped fiber Bragg gratings without a center wavelength shift is proposed. The specially designed mechanical rotator can flexibly control the chirping ratio along the fiber grating and the corresponding dispersion value. The group delay can be linearly controllable since the proposed method can induce a linear strain gradient with the rotation angle change. The dispersion value could be controlled from 228.04 ㎰/nm to 1430.7 ㎰/nm with small center wavelength shift, which was less than 0.03 nm.

• International Journal of Control, Automation, and Systems
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• v.1 no.4
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• pp.474-483
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• 2003

Belt drives provide freedom to position the motor relative to the load and this phenomenon enables reduction of the robot arm inertia. It also facilitates quick response when employed in robotics. Unfortunately, the flexible dynamics deteriorates the positioning accuracy. Therefore, there exists a trade-off between the simplicity of the control strategy to reject time varying disturbance caused by flexibility of the belt and precision in performance. Resonance of the system further leads to vibrations and poor accuracy in positioning. In this paper, accurate positioning of a belt driven mechanism using a feed-forward compensator under maximum acceleration and velocity constraints is proposed. The proposed method plans the desired trajectory and modifies it to compensate delay dynamics and vibration. Being an offline method, the proposed method could be easily and effectively adopted to the existing systems without any modification of the hardware setup. The effectiveness of the proposed method was proven by experiments carried out with an actual belt driven system. The accuracy of the simulation study based on numerical methods was also verified with the analytical solutions derived.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.182-189
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• 2014

This paper proposes a decoupler design method to reduce interaction between exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT) systems in passenger car diesel engines. The EGR valve and VGT vane are respectively used to control air-to-fuel ratio (AFR) of exhaust gas and intake pressure. A plant model for EGR and VGT systems is defined by a first order transfer function plus time-delay model, and the loop interaction between these systems is analyzed using a relative normalized gain array (RNGA) method. In order to deal with the loop interaction, a design method for simplified decoupler is applied to this study. Feedback control algorithms for AFR and intake pressure are composed of a compensator using PID control method and a prefilter. The proposed decoupler is evaluated through engine experiment, and the results successfully showed that the loop interaction between EGR and VGT systems can be reduced by using the proposed decoupler. Furthermore, it presents stable performance even off from the designed operating point.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1005-1008
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• 1996

We consider the interval of a gain within which it is guaranteed that a feedback control system is stable. This paper presents the condition under which either a unity feedback control system is stable for a connected gain interval with a proportional compensator cascaded with an open loop forward transfer function. By the connected interval we mean that all the numbers between any two numbers in the connected interval belongs to the connected interval. The condition may be described by a frequency inequality in terms of the denominator and/or numerator of the closed loop transfer function. We also consider the conditions for the discrete-time control systems and the time delay continuous-time control systems. We show that this condition cannot be extended for the transfer function having complex coefficients via a counterexample.