• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.2
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• pp.163-169
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• 2000

From the viewpoint of the cost effective design of power conversion systems, it is very important to fully u utilize the CillTent capacity of power devices over all circumstances. Therefore this paper deals with the l practical design of digital CillTent controller to meet the requirements of fast and overshoot free control r response over the varying control voltage bOlmds, the accompanied computational delay, and the system U W1certainties. The proposed controller consists of high gain PI control schemes using both the conditional i integrator and the modified delay compensator. The simulation and experimental results show the validity of t the proposed controller.

• International Journal of Control, Automation, and Systems
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• v.6 no.4
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• pp.495-505
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• 2008

This paper describes modeling Voltage Sourced Inverter (VSI) type Flexible AC Transmission System (FACTS) controllers and control methods for power system dynamic stability studies. The considered FACTS controllers are the Static Compensator (STATCOM), the Static Synchronous Series Compensator (SSSC), and the Unified Power Flow Controller (UPFC). In this paper, these FACTS controllers are derived in the current injection model, and it is applied to the linear and nonlinear analysis algorithm for power system dynamics studies. The parameters of the FACTS controllers are set to damp the inter-area oscillations, and the supplementary damping controllers and its control schemes are proposed to increase damping abilities of the FACTS controllers. For these works, the linear analysis for each FACTS controller with or without damping controller is executed, and the dynamic characteristics of each FACTS controller are analyzed. The results are verified by the nonlinear analysis using the time-domain simulation.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.6
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• pp.402-408
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• 2004

This paper proposes the novel V/f control method to improve the stability of a V/f controlled induction motor drive system. The conventional V/f control method used in the proposed V/f control method is a vector-based method that is slightly different from the existing conventional V/f control method. The proposed control method uses a dynamic current compensator to improve the stability of a V/f controlled induction motor drive system. This proposed method is easy to implement and completely eliminates the motor oscillation phenomenon causing the instability of a V/f controlled induction motor drive system, especially when the system is driven near the resonant frequency in steady-state with light load. Additionally, this paper analyzes theoretically the instability of a V/f controlled induction motor drive system and shows the validity of the Proposed V/f control method through simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.487-490
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• 2001

Power Quality and Reliability are becoming important issues for critical and sensitive loads. This paper describes the Line Interactive UPS with the function of Voltage Compensator that is 'Line interactive Dynamic Voltage Restorer(LIDVR). The main purpose of a LIDVR is to compensate for voltage sag(dip), outage and overvoltage. The overall system consists of three controller 1) current controller with prediction 2) voltage controller and 3) proposed variable DC LINK controller. The variable DC LINK control technique using the LIDVR protects DC LINK from overflowing the input current. The simulation results are depicted in this paper to show the effect of this proposed system.

• Journal of Power Electronics
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• v.19 no.3
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• pp.803-814
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• 2019

This paper proposes a three-phase current balancing strategy in a power transmission system employing distributed static series compensators (DSSCs). With the proposed variable quadrature voltage injection method, the DSSC emulates either an inductive or a capacitive impedance into the transmission line, and the magnitudes of the phase currents are balanced. Hence, the phase imbalances in the power transmission system are significantly reduced. As a result, the power transfer capability of the transmission lines can be improved. The operational principle of the DSSCs, the hardware structure and the control algorithm are described in detail. Finally, the theoretical analyses and the proposed strategy are experimentally verified through a scaled down transmission system with DSSC prototypes.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.258-259
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• 2012

This paper proposes a new control strategy to eliminate the harmonic components of stator current for stand-alone DFIG system feeding non-linear loads. In this method, the LSC operates as an active filter which is controlled by employing a proportional-integral and a resonant controller. And also, the stator current is used as the feedback signal for the compensator instead of the load current, so that the additional current sensor at the load side can be removed. The experiment is verified to validate the effectiveness of the proposed compensating method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.11
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• pp.2009-2014
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• 2017

A novel structure of phase locked loop (PLL) with a time constant comparator and a current compensator has been proposed. The proposed PLL uses small capacitors which are impossible for stable operation in a conventional PLL. It is small enough to be integrated into a single chip. The time constant comparator detects the loop filter output voltage variations using signals which are passed through small and large RC time constants. The signal from the large RC time constant node is the average of the loop filter output voltage. The output voltage of another node is approximately equal to the present loop filter voltage. The output of the time constant comparator controls a current compensator and charge/discharge small size loop filter capacitors. It makes the proposed PLL operate stably. It has been simulated and proved by HSPICE in a CMOS $0.18{\mu}m$ 1.8V process.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.116-128
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• 2010

Modeling of the three phase electric arc furnace and its voltage flicker mitigation are the purposes of this paper. For modeling of the electric arc furnace, at first, the arc is modeled by using current-voltage characteristic of a real arc. Then, the arc random characteristic has been taken into account by modulating the ac voltage via a band limited white noise. The electric arc furnace compensation with static VAr compensator, Thyristor Controlled Reactor combined with a Fixed Capacitor bank (TCR/FC), is discussed for closed loop control of the compensator. Instantaneous flicker sensation curves, before and after accomplishing compensation, are measured based on IEC standard. A new method for controlling TCR/FC compensator is proposed. This method is based on applying a predictive approach with closed loop control of the TCR/FC. In this method, by using the previous samples of the load reactive power, the future values of the load reactive power are predicted in order to consider the time delay in the compensator control. Also, in closed loop control, two different approaches are considered. The former is based on voltage regulation at the point of common coupling (PCC) and the later is based on enhancement of power factor at PCC. Finally, in order to show the effectiveness of the proposed methodology, the simulation results are provided.

• Journal of Power Electronics
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• v.10 no.1
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• pp.85-90
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• 2010

In this paper the effects of a Static Synchronous Series Compensator, which is constructed with a 48-pulse inverter, on the power demand from the grid are studied. Extensive simulation studies were carried out in the MATLAB simulation environment to observe the compensation achieved by the SSSC and its effects on the line voltage, line current, phase angle and real/reactive power. The designed device is simulated in a power system which is comprised of a three phase power source, a transmission line, line inductance and load. The system parameters such as line voltage, line current, reactive power Q and real power P transmissions are observed both when the SSSC is connected to and disconnected from the power system. The motivation for modeling a SSSC from a multi-pulse inverter is to enhance the voltage waveform of the device and this is observed in the total harmonic distortion (THD) analysis performed at the end of the paper. According to the results, the power flow and phase angle can be controlled successfully by the new device through voltage injection. Finally a THD analysis is performed to see the harmonics content. The effect on the quality of the line voltage and current is acceptable according to international standards.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.149-152
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• 1998

From the viewpoint of model-based current control, it is indispensable to use the accurate system parameters for the high control performance. This paper adopts the Least-Squares algorithm as a parameter estimation scheme because it has the fast convergence rate and the low sensitivity to noises. In case of the intelligent current controller with delay compensator, the simulation results show that the adopted estimation scheme can be successfully applied to PWM converters and also show the improved control performance in the estimated parameters.