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

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.10 no.5
• /
• pp.101-107
• /
• 1996

This paper proposed the voltage compensation analysis method in distribution system by EMTP. SVC (Static Var Compensator) of the thyristor controlled reactor type is used for compensation system. EMTP(E1ectr-o Magnetic Transient Program) model of SVC is proposed to analysis the voltage improvement characteristics at the high voltage system bus. It is composed with three parts ; rms detector, voltage regulator and gate pulse generator. The control signal of TCR is determined by rms value which was measured in system. As the result of EMTP simulation, all of the SVC characteristics like TCR current, firing pulse and bus voltage is very reliable. This method could be used to analysis the planning and the operation of compensation system in the large scale factory.

• Proceedings of the KIPE Conference
• /
• 1998.10a
• /
• pp.153-158
• /
• 1998

In this paper, a prototype of the auxiliary resonant commutated snubber circuit(ARCS) with a high frequency transformer power regeneration loop is described for voltage source type sinewave inverter system. This is a new soft switching topology developed for three phase voltage source soft-switching inverter, active power filter and reactive power compensator has significant advantage of current rating reduction for auxiliary active switching devices. In addition, this paper presents a novel prototype of voltage-source soft switching space vector-modulated inverter with ARCS mentioned above, which is more suitable and acceptable for high-power utility interactive power conditioning, along with a digital control scheme. The steady-state operating analysis of ARCS has the remarkable features and the practical design procedure of this resonant snubber are illustrated on the basis of computer simulation analysis. The operating performance evaluations in the steady-state of this three phase voltage source soft switching inverter are discussed and compared with the three phase voltage source hard switching inverter.

• Journal of the Institute of Convergence Signal Processing
• /
• v.13 no.4
• /
• pp.233-237
• /
• 2012

In this paper, We propose a control system which compensate a output of a main Neual Network using a RTDNN(Recurrent Time Delayed Neural Network) with a FLC(Fuzzy Logic Controller)After a learn of main neural network, it can occur a Over shoot or Under shoot from a disturbance or a load variations. In order to adjust above case, we used the fuzzy compensator to get an expected results. And the weight of main neural network can be changed with the result of learning a inverse model neural network of plant, so a expected dynamic characteristics of plant can be got. We can confirm good response characteristics of proposed neural network controller by the results of simulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.11 no.2
• /
• pp.166-176
• /
• 2000

In this paper, the LEO system signal degradation is mainly due to fading and doppler shift, so that the analysis of the signal degradation and compensation techniques are very important. This paper propose a Kalman filter based two step Automatic Frequency Control(AFC) to combat large and time variant frequency offset in low earth orbit satellite communication systems. The proposed Kalman AFC method estimates a frequency offset in two steps, I. e., coarse and fine estimations, extending the frequency acquisition range to even for than the symbol rate. Furthermore, it can track well a time variation of frequency offset. It is shown that the proposed compensator is able to compensate for doppler shift more than several KHz.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.52 no.4
• /
• pp.189-197
• /
• 2003

The problem of designing a parallel feedforward compensator (PFC) is considered for a class of non-square linear systems such that the closed-loop system is strictly passive. If a given square system has (vector) relative degree one and is weakly minimum phase, the system can be rendered passive by a state feedback. However, when the system states are not always measurable and the given output is considered, passivation (i.e. rendering passive) of a non-minimum phase system or a system with high relative degree cannot be achieved by any other methodologies except by using a PFC. To passivate a non-square system we first determine a squaring gain matrix and design a PFC such that the composite system has relative degree one and is minimum phase. Then the system is rendered strictly passvie by a static output feedback law. Necessary and sufficient conditions for the existence of the PFC and the squaring gain matrix are given by the static output feedback formulation, which enables to utilize linear matrix inequality (LMI). As an application of the scheme, an alternative way of replacing the role of velocity measurements is provided for the PD-control law of a convey-crane system.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.5
• /
• pp.760-768
• /
• 2016

Recently, as one of the policies for carbon free operation method of independent power system replacing diesel generator with renewable energy such as wind power and photovoltaic(PV) system has been presented. Therefore, this paper proposes an operation algorithm and modeling of independent power system by considering CVCF(constant voltage constant frequency) ESS(energy storage system) for constant frequency and voltage, LC(load control) ESS for demand and supply balancing and SVC(static var compensator) for reactive power compensation. From the simulation results based on the various operation scenario, it is confirmed that proposed operation algorithm and modeling may contribute stable operation and carbon free in independent power system.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.2
• /
• pp.550-558
• /
• 2018

This paper presents the current limit strategy of voltage controller of delta-connected H-bridge static synchronous compensator (STATCOM) under an unbalanced voltage fault event. When phase to ground fault happens, the feasibility to heighten the magnitude of sagging phase voltage is considered by using symmetric transformation method in delta-structure STATCOM. And the efficiency to cover the maximum physical current limit of switching device is considered by using vector analysis method that calculate the zero sequence current for balancing the cluster energy in delta connected H-bridge STATCOM. The result is simple and obvious. Only positive sequence current has to be used to support the unbalanced voltage sag. Although the relationship between combination of the negative sequence voltage with current and zero sequence current is nonlinear, the more negative sequence current is supplying, the larger zero sequence current is required. From the full-model STATCOM system simulation, zero sequence current demand is identified according to a ratio of positive and negative sequence compensating current. When only positive sequence current support voltage sag, the least zero sequence current is needed.

• Journal of Power Electronics
• /
• v.16 no.3
• /
• pp.849-860
• /
• 2016

The high-switching-frequency operation of power converters can achieve high power density through size reduction of passive components, such as capacitors, inductors, and transformers. However, a small-output capacitor that has small capacitance and low effective series resistance changes the small-signal model of the converter power stage. Such a capacitor can make the converter unstable by increasing the crossover frequency in the transfer function of the small-signal model. In this paper, the design and implementation of a high-frequency LLC resonant converter are presented to verify the power density enhancement achieved by decreasing the size of passive components. The effect of small output capacitance is analyzed for stability by using a proper small-signal model of the LLC resonant converter. Finally, proper design methods of a feedback compensator are proposed to obtain a sufficient phase margin in the Bode plot of the loop gain of the converter for stable operation at 500 kHz switching frequency. A theoretical approach using MATLAB, a simulation approach using PSIM, and experimental results are presented to show the validity of the proposed analysis and design methods with 100 and 500 kHz prototype converters.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.20 no.4
• /
• pp.321-329
• /
• 2015

The static synchronous compensator (STATCOM) of cascaded H-bridge configuration accompanying multiple separate DC sides is inherently subject to the problem of uneven DC voltages. These DC voltages in one leg can be controlled by adjusting the AC-side output voltage of each cell inverter, which is proportional to the active power. However, when the phase current is extremely small, large AC-side voltage is required to generate the active power to balance the cell voltages. In this study, an alternative zero-sequence current injection method is proposed, which facilitates effective cell balancing controllers at no load, and has no effect on the power grid because the injected zero sequence current only flows within the STATCOM delta circuit. The performance of the proposed method is verified through simulation and experiments.