• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.3
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• pp.138-142
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• 2014

In general, the voltage stability of induction generator is lower than synchronous generator. However, induction generator has many advantages rather than a synchronous generator in terms of price and maintenance. So Induction generator is used little by little in small hydroelectric power station rather than 1000kW recently. Squirrel cage induction generator generates a high inrush current at the grid-connection. This high inrush current causes a voltage drop on the grid. In order to increase the penetration of the induction generator, it is necessary to present a method of reducing inrush current. In this study, we suggested that it is possible to present a reactor startup method, by applying the parameter to reduce the voltage drop.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.2
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• pp.62-68
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• 2013

The dynamic voltage restorer (DVR) is an effective protection device for wind turbine generators based on doubly-fed induction generator (DFIG) that is operated under unbalanced voltage dip conditions. The compensating voltages of the DVR depend on the voltage dips and on the influence of the zero sequence component. The zero sequence component results in high insulation costs and asymmetry in terminal voltages. This paper proposes the use of a proportional-resonant controller in stationary reference frames for controlling zero sequence components in the DVR to protect the DFIG during unbalanced voltage dips. To enhance the proposed control method, a comparison is carried out between two cases: with and without using the control of a zero sequence component. Simulation results are presented to verify the effectiveness of the proposed control method by using the Psim simulation program.

• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.65-72
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• 2009

The new method is proposed to improve high speed detection of grid voltage phase and magnitude during a voltage dip due to a grid faults. Usually, A LPF(Low Pass Filter) is used in the feedback loop of PLL (Phase Locked Loop) system because the measured grid voltage contains harmonic distortions and sensor noises. so, a new design method of the loop gain of the PI -type controller in the PLL system is proposed with the consideration of the dynamics of the LPF. As a result, a better transient response can be obtained with the proposed design method. The LPF frequency and PI controller gain are designed in coordination according to the steady state and dynamic performance requirement. This paper shows the feasibility and the usefulness of the proposed methods through the computer simulation and the lab-scale experiments.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.2
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• pp.55-60
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• 2014

In general, A synchronous generator is higher than the voltage stability of the induction generator. However, induction generator has many advantages rather than a synchronous generator in terms of price and maintenance. So, coverage rate of the induction generator is gradually increasing in small hydroelectric power station rather than 1000kW recently. In order to increase the penetration of induction generator, pre-analysis of the operation of the generator is needed. In this study, we analyzed for the problems that occur when synchronous generator and induction generator of 1500kW is connected to the distribution system.

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.113-117
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• 2001

Specific capacitance and charge-discharge rate of EDLC using activated carbon electrode were affected by the compositions of electrolytes, the conditions of charge-discharge and physical properties of activated carbon materials. The activated carbon electrode was prepared by dip coating method. Charge-discharge test and electrochemical experiments were carried out for various kinds of organic electrolytes. Effects of charge and discharge current density on the specific capacitance were studied. Characteristics of leakage current, self-discharge and time-voltage curves in optimum conditions of organic electrolytes were compared with conventional $1M-Et_4NBF_4/PC$ electrolyte. The EDLC using MSP-20(specific surface area: $2000m^2/g$) electrode and $1M-LiPF_6/PC-DEC(1:1)$ was exhibited th highest specific capacitance of 130F/g and low polarization resistances. The EDLC using MSP-20 electrode at $1M-LiPF_6/PC-DEC(1:1)$ was small leak current of 0.0004A for 15min, long voltage retention of 0.8V after 100h and linear time-voltage curves with small IR-drop.

• 전기의세계
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• v.31 no.2
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• pp.126-131
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• 1982

Induction motors are known to cause voltage dip, oscillating torque and inrush current on the dynamic period. To compensate for these undesirable effects, the prediction of dynamic performances is required. The dynamic performances are determinated by circuit time constants. From this point of view, in this paper, the dynamic equivalent circuit included only three time-constant parameters are presented. To predict more simply dynamic performances, the new characteristics time constant parameters are analyzed, and now these parameters are described as the function of circuit time constants. This paper reviews and analyzes the use of series capacitance compensations, and the use of this analysis can make simply a prediction about oscillating conditions.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.12
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• pp.133-140
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• 2013

Cascaded H-Bridge multi-level inverters can be implemented through the series connection of single-phase modular power bridges. In recent years, multi-level inverters are becoming increasingly popular for high power applications due to its improved harmonic profile and increased power ratings. This paper presents a control method for balancing the dc-link voltage and ride-through enhancement, a modified pulse width-modulation Compensation algorithm of cascaded H-bridge multi-level inverters. During an under-voltage protection mechanism, causing the system to shut down within a few milliseconds after a power interruption in the main input sources. When a power interruption occurs finish, if the system is a large inertia restarting the load a long time is required. This paper suggests modifications in the control algorithm in order to improve the sag ride-through performance of ac inverter. The new proposed strategy recommends maintaining the DC-link voltage constant at the nominal value during a sag period, experimental results are presented.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1590-1592
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• 2000

The time to tracking breakdown of treated filled specimen is longer than untreated filled specimen. And, after the RWDT, the surface of specimen by adding untreated filler appeared heavy erosion. It was found that the addition to surface treated filler. the better tracking resistance. In the RWDT, the breakdown specimen is not affected by the dry flashover voltage. despite the fact that the surface degradation of tracking test has different state on each specimen. This suggests that wet flashover voltage play an important role in evaluating of tracking and erosion on the surface degradation in tracking test. And, the flashover voltage of specimen under wet conditions are greatly affected by the salt concentration and degree of degradation by the RWDT. Because of hydrophobicity and degree of degradation by the RWDT, the flashover voltage of treated filled specimen is higher than that of untreated filled specimen. Different types of specimen may have different hydrophobicity and their surface state under contaminated conditions may not be the same. It is assumed that this phenomenon is related to the decrease in hydrophobicity of the surface of the materials.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1265-1274
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• 2018

This paper proposes a virtual flux (VF) and positive-sequence power based control strategy to improve the performance of grid-interfaced three-phase voltage source converters against unbalanced and distorted grid conditions. By using a second-order generalized integrator (SOGI) based VF observer, the proposed strategy achieves an AC voltage sensorless and grid frequency adaptive control. Aiming to realize a balanced sinusoidal line current operation, the fundamental positive-sequence component based instantaneous power is utilized as the control variable. Moreover, the fundamental negative-sequence VF feedforward and the harmonic attenuation ability of a sequence component generator are employed to further enhance the unbalance regulation ability and the harmonic tolerance of line currents, respectively. Finally, the proposed scheme is completed by combining the foregoing two elements with a predictive direct power control (PDPC). In order to verify the feasibility and validity of the proposed SOGI-VFPDPC, the scenarios of unbalanced voltage dip, higher harmonic distortion and grid frequency deviation are investigated in simulation and experimental studies. The corresponding results demonstrate that the proposed strategy ensures a balanced sinusoidal line current operation with excellent steady-state and transient behaviors under general grid conditions.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.2
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• pp.182-190
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• 2011

This paper proposes a LVRT (Low Voltage Ride Through) control strategy which should be satisfied by grid-connected wind power system when grid faults occur. The LVRT regulation indicates rules or actions which have to be executed according to the voltage dip ratio and the fault duration. Especially the wind power system has to support the grid with specified reactive current to secure the grid stability when voltage reduction ratio is over 10%. The LVRT regulation in this paper is based on the German Grid Code and full-scale variable speed wind power conversion system is considered for LVRT control strategy. The proposed LVRT control strategy satisfies not only LVRT regulation but also makes power balance between wind turbine and power system through additional DC link voltage regulation algorithms. Because it is impossible to control grid side power when the 3-phase to ground fault occurs, the DC link voltage is controlled by a generator side inverter using the DC link voltage control strategy. Through the simulation and experiment result, the proposed LVRT control strategy is evaluated and its effectiveness is verified.