• Journal of Power Electronics
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• v.9 no.1
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• pp.74-84
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• 2009

The design and implementation of a high performance PID (Proportional Integral & Differential) style controller with zero-phase error tracking property is considered in this article. Unlike a ball screw driven system, the controller in a direct drive system should provide a high level of tracking performance while avoiding the problems due to the absence of the gear system. The stiff mechanical element in a direct drive system allows high precise positioning capability, but relatively high tracking ability with minimal position error is required. In this work, a feasible position controller named 'Unified PID controller' is presented. It will be shown that the function of the closed position loop can be designed into unity gain system in continuous time domain to provide minimal position error. The focus of this work is in two areas. First, easy gain tunable PID position controller without speed control loop is designed in order to construct feasible high performance drive system. Second, a simple but powerful zero phase error tracking strategy using the pre-designed function of the main control loop is presented for minimal tracking error in all operating conditions. Experimental results with a s-curve based position pattern commonly used in industrial field demonstrate the feasibility and effective performance of the approach.

• Journal of Mechanical Science and Technology
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• v.20 no.5
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• pp.634-642
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• 2006

The aim of this paper is to increase the performance of hysteresis compensation for Shape Memory Alloy (SMA) actuators by using inverse Preisach model in closed-loop control system. This is used to reduce hysteresis effects and improve accuracy for the displacement of SMA actuators. Firstly, hysteresis is identified by numerical Preisach model implementation. The geometrical interpretation from first order transition curves is used for hysteresis modeling. Secondly, the inverse Preisach model is formulated and incorporated in closed-loop PID control system in order to obtain desired current-to-displacement relationship with hysteresis reducing. The experimental results for hysteresis compensation by using this method are also shown in this paper.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1008-1011
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• 1996

Most control systems of power plants are using classical PID controllers for their process control. In order to get the desired control performances, the correct tuning of PID controllers is very important. Sometimes, it is necessary to retune PID controllers after the change of system operating condition and system design change, etc. Commercial auto-tuning controllers such as relay feedback controller can be used for this purpose. However, using these controllers to the safety-critical systems of nuclear power plants may be cause of unsafe operation, because they are using test signals for tuning. A new system identification auto-tuning method without using test signal has been developed in this paper. This method uses process input/output signals for system identification of unknown control process. From the model information of control process which was obtained from system identification approach, the optimal PID parameters can be calculated. The method can be used in the safety-critical systems because it is not using test signals during system modeling process.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.4
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• pp.299-305
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• 2013

The complexity and severe nonlinearity of multi-machine power systems make it difficult to design a control input for voltage regulation using modern control theory. This paper presents a model-based PID control scheme for the regulation of the bus voltage to a desired value. To this end, a fourth-order linear system is constructed using input and output data obtained using the TSAT (Transient Security Assessment Tool); the input is assumed to be applied to the grid through the STATCOM (STATic synchronous COMpensator) and the output from the grid is a bus voltage. On the basis of the model, it is identified as to which open-loop poles of the system make the response to a step input oscillatory. To reduce this oscillatory response effectively, a model-based PID control is designed in such a way that the oscillatory poles are no longer problematic in the closed loop. Simulation results show that the proposed PID control dampens the response effectively.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10a
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• pp.529-533
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• 1990

This paper treats the computational time delay issue in designing digital control systems. The computational time delay margin, within which the closed-loop stability is guaranteed, is analyzed using Rouche theorem. A PID control algorithm is proposed for compensating the computational time delay. Finally, the analyzed and the exact computational time delay margins are compared, and the performance of the proposed PID controller is shown through an illustrative example.

• Journal of Biomedical Engineering Research
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• v.20 no.2
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• pp.183-190
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• 1999

The purpose of this study was to develop a portable and convenient closed-loop contrel type electrical stimulator for patients with foot drop. This system restores walking movement as well as prevents from atrophy or necrosis of lower limb muscles and increases blood circulation in hemiplegic patients caused by traffic accident, industrial disaster or stoke. This system detects the changes of the ankle joint angle during walking, and then controls the stimulus intensity automatically to maintain the programmed level of the ankle joint angle. Also, this automatic system controls the stimulus intensity which is affected by increased electrode impedance resulting from long time use. The system detects the joint angle by an optical sensor and includes modified PID control which adjusts the stimulus intensity if the joint angle deviates from the preset value. Stimulus parameters are 30~80 volt, 40 Hz, and 0.2 ms. The system was applied to five hemiplegic patients for 42 days. Duration of stimulation was 15 min/day for the first week and then the duration was gradually increased to 30, 60, 90 and 120 min/day. The muscle force was increased up to 29.7%, muscle fatigue was decreased compared with the level before stimulation and the pattern of locomotion was improved. These results suggest that the electrical stimulator with closed-loop control type is more convenient and effective in restoration of locomotion of patients with foot drop than open-loop system.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.9
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• pp.750-754
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• 2005

This paper deals with the design problem of multivariable PID controllers guaranteeing the closed-loop system stability and a prescribed $H_\infty$ norm bound constraint. We reduce the problem to the static output feedback stabilization problem. We derive a necessary and sufficient condition f3r the existence of PID controllers and we give an explicit formula of PID controllers. We also give an existence condition of PID controllers guaranteeing a prescribed decay rate. Finally, we give an LMI-based design algorithm, together with a numerical design example.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.2
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• pp.130-137
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• 2013

In this paper, decoupled controller design for Autonomous Underwater Vehicle(AUV) and its simulated performance test results and Hardware In the Loop Simulation(HILS) results are presented. Control system design is done using the PD control scheme. Stability analysis and step response of closed loop system under uncertain parameter condition are also presented. The results of full coupled nonlinear model simulation show the well applicability of the designed controller. From the results of HILS, we can verify performance of real time processing and implemented hardware for AUV.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.5
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• pp.103-110
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• 2000

In This paper, we propose a design procedure for a SD $H_{\infty}$controller with PID performance. In developing the procedure, we use the basic idea of standard$H_{\infty}$problem, and then applied it to the SD system, which consists of the continuous plant and the discrete controller. This $H_{\infty}$controller design procedure involves the selections of weighting functions. The selections considered the relation of the closed loop specification between the $H_{\infty}$controller and PID. We illustrate this procedure in the controller design for a two-mass spring system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.4
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• pp.509-518
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• 2014

Though various techniques have been studied as a way of adjusting parameters of PID controllers, no perfect method of determining parameters is available to date. Especially the deign of PID controller for unstable processes with dead time(UPWDT) is even more difficult due to various reasons. Generally the existing design procedures for UPWDT involve deriving formulas to meet gain and phase margin specifications, or using inner loop to stabilize UPWDT before applying PID controller. In this paper, the dual-input describing function(DIDF) method is proposed, by which the performance and robustness of the closed-loop system can be improved. The method is based on moving the critical point (-1+j0) of Nyquist stability to a new position arbitrarily selected on the complex plane. This can be done by determining appropriate coefficients of the DIDF. As a result, we can easily determine parameters of PID-type controller by using existing conventional tuning methods for stable or unstable systems. Simulation results are included to show the effectiveness of the proposed method.