• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.3
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• pp.206-211
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• 2004

In phase controlled rectifier, it's been known that a fast response is achieved by predictive current control without any overshoot. The frequent sampling period is essential to improve the firing accuracy in conventional predict current control. However, improving the firing accuracy if difficult to reduce the period of sampling efficiently because current sampling and predictive current control is carried out in every period and the ON-OFF current control is performed by comparing two different one. To improve the firing accuracy at the predictive current control, the calculated firing angle is loaded into the high-accuracy hardware timer. So the calculation of exact crossing point between the predictive and actual current is the most important. In this paper, the flow chart for proposed firing angle calculation algorithm is obtained for the fastest current control performance in transient state. The performance of proposed algorithm is verified through simulations and experiments.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.4
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• pp.261-268
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• 1989

A novel current controlled PWM voltage source type converter and control strategy is proposed that is able to draw nearly sinusoidal current at unity power factor from three phase power lines. Current error vector control scheme is used which has two operating states : low harmonic current content state and quick current response state. The state is changed according to the current error to optimize the steady state and transient state performances. To regulate the dc oupput voltage, the magnitude of the reference current is determined by a controller dc voltage error. The ac input power factor can be controlled with unity, and even leading or lagging by adjusting the relative position of the reference current with respect to the supply voltage.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.289-294
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• 2012

In recent years, understanding the dynamics of DC distribution system has become critically important due mainly to the increasing needs for the interconnection of DC distributed generators and the (DC-based) electric vehicle (EV) charging systems. In this paper, the characteristics of the DC grid system connected to the compact proton exchange membrane fuel cell (PEMFC) has been studied. In particular, the voltage and current transient phenomena were measured by varying the load of the DC grid system. Also, the voltage and current ripple were measured at the different load conditions. Our experimental results clearly manifested that the study contributes to the establishment of fundamental method to characterize the small DC grid system including distributed generation.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.7
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• pp.421-428
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• 2003

After the cable is installed, many geometric factors, such as bowing types of the cable and the length difference of the cable between each minor section will cause the impedance unbalance between cables. The impedance unbalance will increase or decrease the sheath circulating currents, which are critical to human safety and sustaining the capabilities of electric power. Accordingly, in this paper, a new method is also proposed to reduce the sheath circulating currents and an reduction equipment according to the theory of the new method is developed. The reduction equipment is tested when the cable is on service. The test results show that it can reduce the sheath circulating currents by up to 97.8［%］. This confirms the validation of the new method and the reduction equipment, and assures the safe operation of the transmission cables. In order to illustrate the safe operation of the cable with new current reduction equipment at transient state due to lightning and single line-to-ground fault, extensive simulations have been made. Then the protection scheme of sheath circulating currents reduction equipment is proposed by adopting the new device of RDP(Reduction Device Protector).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.10
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• pp.793-797
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• 2010

The basic performance of the ground system is evaluated as the ground resistance by applying low frequency current below 1 kHz. However, characteristics of the ground system should be analyzed by high frequency current up to 1 MHz since transient currents having a few hundred kHz component flow during a line-to-ground fault and/or a lightning strike. This paper deals with the design and fabrication of a wideband ground impedance meter (WGIM) which measures the impedance of ground systems in ranges from 65 Hz to 1.28 MHz. Also, a noise elimination algorithm using a digital bandpass filter is proposed. The maximum error of the WGIM is 4.91% in the measurement frequency range.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.414-418
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• 2012

In recent years, understanding the dynamics of DC distribution system has become critically important due mainly to the increasing needs for the interconnection of DC distributed generators and the (DC-based) electric vehicle (EV) charging systems. In this paper, the characteristics of the DC grid system connected to the compact proton exchange membrane fuel cell (PEMFC) has been studied. In particular, the voltage and current transient phenomena were measured by varying the load of the DC grid system. Also, the voltage and current ripple were measured at the different load conditions. Our experimental results clearly manifested that the study contributes to the establishment of fundamental method to characterize the small DC grid system including distributed generation.

• Journal of Power Electronics
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• v.11 no.4
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• pp.533-541
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• 2011

The redundant operation of a parallel AC to DC converter via a serial communication bus is presented. The proposed system consists of three isolated CUK power factor correction modules. The controller for each converter is a dsPIC30F6010 microcontroller while a RS485 communication bus and the clock signal are used for synchronizing the data communication. The control strategy of the redundant operation relies on the communication of information among each of the modules, which communicate via a RS485 serial bus. This information is received from the communication checks of the converter module connected to the system to share the load current. Performance evaluations were conducted through experimentation on a three-module parallel-connected prototype, with a 578W load and a -48V dc output voltage. The proposed system has achieved the following: the current sharing is quite good, both the transient response and the steady state. The converter modules can perform the current sharing immediately, when a fault is found in another converter module. In addition, the transient response occurs in the system, and the output voltages are at their minimum overshoot and undershoot. Finally, the proposed system has a relatively simple implementation for the redundant operation.

• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.8-13
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• 1998

This work presents the way how to evaluate the degree of reversibility of the discharging process undergone by the nickel hydroxide film cathodically deposited on pure nickel as a positive electrode for electrochemical capacitor using the combined cyclic voltammetry and potential drop method, supplemented by galvanostatic discharge and open-circuit potential transient methods. The time interval necessary just to establish the current reversal of anodic to cathodic direction from the moment just after applying the potential inversion of anodic to cathodic direction, was obtained on cyclic voltammogram. The cathodic charge density passed upon dropping the applied potential, was calculated on potentiostatic current density-time curve. Both the time interval and the cathodic charge density in magnitude can be regarded as being measures of the degree of reversibility of the discharging process undergone by the positive active material for supercapacitor, i.e. , the longer the time interval is, the lower is the degree of reversibility and the greater the cathodic charge density is, the higher is the degree of reversibility. From the applied potential dependences of the time interval and cathodic charge density, discharge at $0.42 V_{SCE}$ was determined to be the most reversible.

• 전기의세계
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• v.25 no.1
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• pp.95-100
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• 1976

The main purpose of this paper is to study on the transient current due to the change of environmental temperature under no external field in the arrangement of M$_{1}$(metal)-P(polyver)-M$_{2}$(metal). The specimer of polymeric insulator sandwiched by two metal electrodes composes a parallel-plate condenser represented by Maxwell-model. The behaviors of short circuit current flowing in M-P-M arrangement are very complex and the analysis of its conduction mechanism appears to be much complicated. In this paper we can suggest that a contact potential difference as an energetic state exists in the thin film specimen both sides of which are contacted by two different metals having different cook functions. Futhermore the contact potential difference appears to be constant through the course of temperature change, however, the dielectric constant and caparitance of the specimen must be temperature dependent. Accordingly the charge difference induced on both sides of electrodes may be a cause for the shory circuited transient current flowing through the external circuit. It is also suggestive that the results of the observation must be considered in cases of insulation design of electrical machines and D.C. cable for high voltage use.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.5
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• pp.291-296
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• 2000

Recently large size color TV and computer monitor are very popular and a lot techniques are being developed to get a high quality picture on the screen through reducing the convergence error among the red, green and blue beams and achieving a high focusing. One of the techniques is considering the mutual effects of the components of the Brown tube. The magnetic deflection yoke, especially, stands immediately next to the electron gun and generates the leakage magnetic fields at the electron gun which affects the trajectories of the electron beams inside the gun. Hence a shield cup made of thin conducting plate is located at the end of electron gun in order to shield the leakage flux from the deflection yoke. Since the red, green and blue beams are placed unsymmetrically the shielding effects of the shield cup on the beams are not same and eddy current controller, made of thin conducting plate, is auxiliary placed inside the shield cup. In this paper a transient magnetic field analysis algorithm is developed using boundary element method, and applied to the analysis of the shielding effects of the eddy current controller of shield cup in an electron gun.