• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.3
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• pp.29-38
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• 1998

This ppaer suggests a congestion control scheme for CL(ConnectionLess) overlay network using the feedback loops getween CL werver, between CL servers, and the header translation table of CL server. The CL overlay network for CBDS(Connectionless Broadband Data Service) defined by ITU0T(International Telecommunication Union-Telecommunication) consists of CL servers which route frames and links which connect between CL user and CL server or between CL servers. In this CL overlay network, two kinds of congestions, link congestion and CL server congestion, may occur. We suggest a scheme that can solve the congestion using ABR(Available Bit Rate) feedback control loop, the traffic control mechanism. This scheme is the link-by-link method suing the ABR feedback control loops between CL user and CL server or between CL servers, and the header translation table of CL server. As CL servers are always endpoints of ABR connections, the congestion staturs of the CL server can be informed to the traffic sources using RM(Resource Management) cell of the ABR feedback loops. Also CL server knows the trafffic sources making congestion by inspecting the source address field of CLNAP-PDUs(ConnectionLess Network Access Protocol - Protocol Data Units). Therefore this scheme can be implemeted easily using only both ABR feedback control loop of ATM layer and the congestion state table using the header translation table of CL server because it does not require separate feedback links for congestion control of CL servers.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.618-628
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• 2016

Active power filter (APF) has been proved as a flexible solution for compensating the harmonic distortion caused by nonlinear loads in power distribution power systems. Digital repetitive control can achieve zero steady-state error tracking of any periodic signal while the sampling points within one repetitive cycle must be a known integer. However, the compensation performance of the APF would be degradation when the grid frequency varies. In this paper, an improved repetitive control scheme with frequency adaptive capability is presented to track any periodic signal with variable grid frequency, where the variable delay items caused by time-varying grid frequency are approximated with Pade approximants. Additionally, the stability criterion of proposed repetitive control scheme is given. A three-phase shunt APF experimental platform with proposed repetitive control scheme is built in our laboratory. Simulation and experimental results demonstrate the effectiveness of the proposed repetitive control scheme.

• ETRI Journal
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• v.31 no.2
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• pp.182-192
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• 2009

Rain attenuation and intercell interference are two crucial factors in the performance of broadband wireless access networks such as local multipoint distribution systems (LMDS) operating at frequencies above 20 GHz. Power control can enhance the performance of downlink CDMA-based LMDS systems by reducing intercell interference under clear sky conditions; however, it may damage system performance under rainy conditions. To ensure robust operation under both clear sky and rainy conditions, we propose a novel power-control scheme which applies an adaptive neuro-fuzzy inference system (ANFIS) for downlink CDMA-based LMDS systems. In the proposed system, the rain rate and the number of users are two inputs of the fuzzy inference system, and output is defined as channel quality, which is applied in the power control scheme to adjust the power control region. Moreover, ITU-R P.530 is employed to estimate the rain attenuation. The influence of the rain rate and the number of users on the distance-based power control (DBPC) scheme is included in the simulation model as the training database. Simulation results indicate that the proposed scheme improves the throughput of the DBPC scheme.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1982-1985
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• 2003

Future cellular networks will mainly be driven by, high quality channels, high band with utilization, low power consumption and efficient network management. For a given channel allocation, the capacity and quality of communication of cellular radio systems using CDMA(Code Division Multiple Access) can be increased by using a transmitter power control scheme to combat the near-far problem. Centralized power control schemes or distributed ones to maximize the minimum signal-to-interference in each user of CDMA wireless network have been investigated. This paper has proposed a distributed power control algorithm, which employs an adaptive search scheme, in order to solve quickly the linear systems of equations for power update in CDMA cellular radio systems. The simulation results show that the proposed scheme has faster convergence rate than the typical bang-bang type of distributed power control algorithm, which has been much used as a reference algorithm in IS-95A and W-CDMA communication network.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.1042-1046
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• 1993

This paper describes a control scheme for a robot manipulator system which uses visual information to position and orientate the end-effector. In this scheme, the position and orientation of the target workpiece with respect to the base frame of the robot are assumed to be unknown, but the desired relative position and orientation of the end-effector to the target workpiece are given in advance. The control scheme directly integrates visual data into the servoing process without subdividing the process into determination of the position and orientation of the workpiece and inverse kinematics calculation. A neural network system is used for determining the change in joint angles required in order to achieve the desired position and orientation. The proposed system can be control the robot so that it approach the desired position and orientation from arbitrary initial ones. Simulation for the robot manipulator with six degrees of freedom will be done. The validity and the effectiveness of the proposed control scheme will be verified by computer simulations.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.519-519
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• 2000

Since the dynamics of the slave manipulator with high reduction ratio joints is likely to be much slower than that of the master manipulator, the control input the slave manipulator is so frequently saturated. This paper proposes a bilateral teleoperation control scheme for 2-DOF manipulators with high reduction ratio joints, which can effectively compensate the control input saturation. In the proposed scheme, the controllers of the slave manipulator are designed with an anti-windup feature and forces caused by the saturation are reflected to the operator holding the operating handle of the master manipulator. When the control input of the slave manipulator is saturated, the master manipulator moves slowly file to tile reflected forces. In this way, the position tracking performance of the slave manipulator with high reduction ratio joints can be enhanced regardless of saturation. The proposed scheme is shown to give excellent position tracking performance through a series of experiments.

• 제어로봇시스템학회:학술대회논문집
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• 1998.10a
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• pp.519-524
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• 1998

This paper presents a robust control scheme of free-joint manipulators to overcome actuator failures and uncertain-ties in Cartesian space where tasks are planned. The control scheme has the adaptation law for the upper bound on the norm of uncertainties through the Lyapunov function approach. To solve the dynamic singularity problem in the controller, the singular and nonsingular regions are investigated based on a computer simulation. Then a singularity-free Cartesian trajectory planning is achieved in order to guarantee the availability of the control scheme. To illustrate the validity of the proposed control scheme, simulation results for a three-link planar robot arm with a free joint are shown.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.8
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• pp.632-639
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• 2003

This paper proposes a simple compensation scheme for the time delay caused by measurement, calculation and selection of voltage vector in Direct Torque Control (DTC) of an induction motor. In general scheme, it is difficult to know the exact delay time, furthermore the delay time can be varied by program routines for calculation and processing of measured data. In this proposed scheme, by applying voltage vector at the beginning of next sampling period, a fixed delay time is achieved and its compensation becomes much simpler. Furthermore, with the simple compensation algorithm, an improved performance can be achieved by shortening sampling period. Experimental results prove the feasibility of the proposed scheme in induction motor control.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1223-1231
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• 2018

The direct torque control (DTC) scheme features a simple structure thanks to stator flux-oriented control. It has the advantage of robustness against motor parameters variation since only the stator resistance is involved in the control scheme. On the other hand, the disadvantage of DTC is large torque ripple. To reduce the torque ripple, many studies on DTC-space vector modulation (DTC-SVM) schemes, which modulate the duty ratio with a fixed switching cycle, have been proposed. However, there is the difficulty in obtaining the duty ratio for DTC-SVM. Hence, this paper proposes a new duty ratio selection and stator flux calculation methods for reducing torque ripple. Simulations and experiments were carried out to determine the validity of the proposed method. The proposed scheme has simplified the duty ratio command and achieved the same control performance as the conventional duty ratio modulation method without using the information of motor parameters.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.242-250
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• 1999

This paper presents an estimation scheme of the external torque applied on the motor by using measured motor input current when the IPM(Interior Permanent Magnet) rotor type BLDC motor operates with constant speed. In general, the BLDC motor is controlled by vector control method. If it could be operated at over critical speed, the control scheme must be modified to flux-weakening control method. The external torque applied on the motor using flux-weakening control method could not be calculated by conventional torque equation because the demagnetizing current Id exists in the motor input current. In this paper, the commonly used flux-weakening control method is studied and the modified torque estimation scheme is suggested. The estimation scheme has been verified by the simulations and experimental results.