• 전기의세계
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• v.30 no.11
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• pp.717-727
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• 1981

The phase-locked loop technique developed in the 1930's has many advantages when applied to speed control. The speed control and analysis of a three phase induction motor using the PLL are described in this paper. In this system, the phase frequency detector (PFD) compares the actual motor speed from the pulses received from a shaft encoder and desired speed, and the difference adjusts the frequency of the inverter that feeds the motor, and excellent speed regulation in the order of 0.035(%) has been-obtained. A linear continuous model of the drive is developed and system response is analysed using conventional root locus techniques. Various compensating filters and feedback signals are considered and the need for addition of derivative feedback is shown. A sampled data model is used to study the effects of discrete PFD output. Stability limitson speed are predicted. A drive was implimented and experimental results are presented to verify theoretical predictions.

• Journal of Power Electronics
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• v.4 no.2
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• pp.65-76
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• 2004

In this paper, the steady-state analysis of the three-phase self-excited induction generator (SEIG) driven by a variable-speed prime mover (VSPM) such as a wind turbine is presented. The steady-state torque-speed characteristics of the VSPM are considered with the three-phase SEIG equivalent circuit for evaluating the operating performances due to the inductive load variations. Furthermore, a PI closed-loop feedback voltage regulation scheme based on the static VAR compensator (SVC) for the three-phase SEIG driven by the VSPM is designed and considered for the wind power generation conditioner. The simulation and experimental results prove the practical effectiveness of the additional SVC with the PI controller-based feedback loop in terms of fast response and high performances.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.978-980
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• 2000

Sensorless PMSM is much studied for the industrial applications and home appliances because, a mechanical sensor reduces reliability and increases cost. Two types of instantaneous torque controls are basically used for high performance variable-speed a.c. drive : vector control and direct torque control. This paper investigates speed sensorless control of PMSM using direct torque control. The switching of inverter is determined from SVPWM realizing the command voltage which is obtained by flux error and measured current without d-q transformation. The rotor speed is estimated through adaptive observer with feedback loop. The simulation and experimental results indicate good performances.

• Journal of Power Electronics
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• v.13 no.3
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• pp.369-380
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• 2013

Direct torque control based on space vector modulation (SVM-DTC) protects the DTC transient merits. Furthermore, it creates better quality steady-state performance in a wide speed range. The modified method of DTC using SVM improves the electrical magnitudes of asynchronous machines, such as minimizing the stator current distortions, the stator flux with electromagnetic torque without ripple, the fast response of the rotor speed, and the constant switching frequency. In this paper, the proposed method is based on two new control strategies for direct torque control with space vector modulation. First, fuzzy logic control is used instead of the PI torque and a PI flux controller to minimizing the torque error and to achieve a constant switching frequency. The voltages in the direct and quadratic reference frame ($V_d$, $V_q$) are achieved by fuzzy logic control. In this scheme, the switching capability of the inverter is fully utilized, which improves the system performance. Second, the close loop of stator flux estimation based on the voltage model and a low pass filter is used to counteract the drawbacks in the open loop of the stator flux such as the problems saturation and dc drift. The response of this new control strategy is compared with DTC-SVM. The experimental and simulation results demonstrate that the proposed control topology outperforms the conventional DTC-SVM in terms of system robustness and eliminating the bad outcome of dc-offset.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.852-855
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• 1996

A variable structure controller is developed for an AC servo motor used in CNC milling machines. The designed controller is implemented as an outer loop controller to a factory designed motor-servopack system. The robustness parameter is tuned for a fast response when the speed tracking error is large, while it is tuned for small oscillations when the speed tracking error is small. The designed controller is installed on a CNC machine using a PC. Cutting experiments show improved performance over the factory-designed controller.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.342-347
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• 1995

Loop shaping $H_{\infty}$control with normalized coprime factorization was applied to a servo-motor driven high-speed powitioning system. The high-gain controller was designed to attenuate the postion errors caused byfriction effects and extermal disturbances. The non-existence of limit cycle was analyzed, though there is actuator saturation. The designed $H_{\infty}$control system was experimently tested in a rotary index table. Results showed its effectiveness to improve postion accuracy with out any compensation scheme for friction, and robustness to model perturbation and external disturbances.ces.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.8
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• pp.996-1003
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• 1999

This paper propose a position-speed controller with an estimator which can estimate states and disturbance. The overall control system consists of two parts: the position-speed controller and an estimator. The Kalman filter applied as state-feedback controller is an optimal state estimator applied to a dynamic system that involves random perturbations and gives a linear, unbiased and minimum error variance recursive algorithm to optimally estimate the unknown state. Therefore, we consider the error problem about the servo system modeling and the measurement noise as a stochastic system and implement a optimal state observer, and enhance the estimate performance of position and speed using that. Using two-degree-of freedom(TDOF) conception, we design the command input response and the closed loop characteristics independently. The servo system is to improve the closed loop characteristics without affecting the command imput response. The characteristics of the closed loop system is improved by suppressing disturbance torque effectively with the disturbance observer using a inverse-transfer matrix. Therefore, the performance of overall position-speed controller is enhanced. Finally, the performance of the proposed controller is exemplified by some simulations and by applying the real servo system.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2099-2105
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• 2017

In a power system that has a high wind penetration, the output power fluctuation of a large-scale wind turbine generator (WTG) caused by the varying wind speed increases the maximum frequency deviation, which is an important metric to assess the quality of electricity, because of the reduced system inertia. This paper proposes a stable power-smoothing scheme of a doubly-fed induction generator (DFIG) that can suppress the maximum frequency deviation, particularly for a power system with a high wind penetration. To do this, the proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while guaranteeing the stable operation of a DFIG, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WTG under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.696-698
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• 1997

The marine diesel engine have been widely applied with a mechanical hydraulic governor to control the ship speed for long time. But it was recently very difficult for the mechanical hydraulic governor to control the speed of engine under the condition of low speed and low load because of jiggling by rough fluctuation of rotating torque and hunting by dead time of diesel engine. In order to analyze the speed control system the transfer function was converted from z to w transformation. The author proposed velocity control system with feedback loop by PID controller in order to stabilize for unstable area. The influence of dead time was discussed by Nichols chart and unit step response curve. It was confirmed through computer simulation that the performance improvement of a mechanical hydraulic governor can be obtained by PID controller.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.6
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• pp.71-81
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• 2000

This paper describers a look ahead algorithm of PC-NC(personal computer numerical control). The algorithm is based on acceleration/deceleration before interpolation which doesn\`t include a command error and determines a feedrate value at the end point of each block(or start point of each block). The algorithm is represented as following; 1) calculating two maximum arrival feedrates(F$_1$,F$_2$) by an acceleration value, a command feedrate, and the distance of a NC block, 2) getting a tangent feedrate (F$_3$) of the adjacent blocks, 3) choosing a minimum value among these three feedrates, and 4) setting the value to a feedrate of a start point of the next block(or a end point of the previous block). The proposed look ahead algorithm was implemented and tested by using a commercial TROS(real time operation system) on the MS-Windows NT 4.0 in a PC platform. For interfacing to a machine, a counter board, a DAC board and a DIO board were used. The result of the algorithm increased a machining precision and a machining speed in many short blocks.