• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• v.12B no.1
• /
• pp.37-43
• /
• 2002

This paper proposes a new zero-current switching (ZCS) pulse-width modulation (PWM) switch cell that has no additional conduction loss of the main switch. In this cell, the main switch and the auxiliary switch turn on and turn off under zero current condition. The diodes commutate softly and the reverse recovery problems are alleviated. The conduction loss and the current stress of the main switch are minimized, since the resonating current for the soft switching does not flow through the main switch. Based on the proposed ZCS PWM switch cell, a new family of dc to dc PWM converters is derived. The new family of ZCS PWM converters is suitable for the high power applications employing IGBTs. Among the new family of dc to dc PWM converters, a boost converter was taken as an example and has been analyzed. Design guidelines with a design example are described and verified by experimental results from the 2.5㎾ prototype boost converter operating at 40KHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.961-964
• /
• 2003

This paper presents the temperature annealing effect on the dark current of the InGaAs waveguide photodiodes, which are developed for high-speed optical receivers. The interesting experimental phenomena were observed that the dark current is significantly decreased and the breakdown voltage is slightly increased after annealing at $250^{\circ}C$ whereas the dark current and the breakdown voltage are almost constant after annealing at $200^{\circ}C$. Based on the experimental results, the long-term annealing is more effective for the dark current improvement than the conventional curing process.

• Journal of Electrochemical Science and Technology
• /
• v.11 no.4
• /
• pp.379-383
• /
• 2020

The novel voltammetry using a semi-circular potential wave for quasi-reversible charge transfer system on electrode is theoretically investigated. Compared with conventional voltammetry based on linear sweep such as linear sweep voltammetry (LSV), semi-circular potential sweep voltammetry (SCV) may decrease the charging current outside the center of potential range and increase the faradaic current at the midpoint due to variable scan rate. In this paper, we investigate the system based on macroelectrode where simple 1 dimensional (1 D) diffusion system is valid with various charge transfer rate constant (k₀). In order to observe the amplification at midpoint, voltammetric response with different midpoint ranging from -200 mV to 200 mV are studied. SCVs shows both the shift of peak potential and the amplification of peak current for quasi-reversible electrode reaction while only higher peak current is observed for reversible reaction. Moreover, the higher current at midpoint enable the amplification of current at low overpotential region which may assist the determination of onset potential as a figure-of-merit in electrocatalyst.

• Transactions on Electrical and Electronic Materials
• /
• v.7 no.2
• /
• pp.87-89
• /
• 2006

We investigated the current limiting characteristics of flux-lock type superconducting fault current limiter(SFCL) according to inductance variation of coil 2. The flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil through an iron core, and the secondary coil is connected to the superconducting element in series. The operation of the flux-lock type SFCL can be divided into the subtractive and the additive polarity winding operations according to the winding directions between the coil 1 and coil 2. The current limiting characteristics in two winding directions were dependent of on the ratio of the number of turns of coil I and coil 2. The fault current increased when the number of turns of coil 2 increased in the subtractive polarity winding. On the contrary, the fault current decreased under the same conditions in case of the additive polarity winding.

• Journal of Welding and Joining
• /
• v.16 no.4
• /
• pp.63-72
• /
• 1998

In this study, the effects of the current pulsing conditions, on the spatter generation rate during the $CO_2$ gas metal arc welding (GMAW) were investigated. Normally using the inverter type power supply, of which the welding current waveform was regulated to reduce the spatter generation rate, but in this study pulsing was imposed on the welding current. Observation of the metal transfer phenomena during the pulsed current GMAS indicated that the droplet transfer from the electrode via the short circuit transfer and the repelling transfer mode could be minimized by selecting optimum combinations of pulsing parameters, which include base and peak current, base and pak duration. It was also demonstrated in this study that proper combinations of the pulsing parameters led to reduce generation of spatters during GMAW shielded by $CO_2$ gas.

• Proceedings of the Korea Society for Industrial Systems Conference
• /
• 1997.11a
• /
• pp.451-462
• /
• 1997

A 2-dimensional numerical analysis is presented for thermal-electron heat conduction effects upon the electron transport and the drain current-voltage characteristics of submicron GaAs MESFETs, based on the use of a nonstationary hydrodynamic transport model. It is shown that for submicron GaAs MESFETs, electron heat conduction effects are significant on their internal electronic properties and also drain current-voltage characteristics. Due to electron heat conduction effects, the electron energy is greatly one-djmensionalized over the entire device region. Also, the drain current decreases continuously with increasing thermal conductivity in the saturation region of large drain voltages above 1 V. However, the opposite trend is observed in the linear region of small drain voltages below 1 V. Accordingly, for a large thermal conductivity, negative differential resistance drain current characteristics are observed with a pronounced peak of current at the drain voltage of 1 V. On the contrary, for zero thermal conductivity, a Gunn oscillation characteristic is observed at drain voltages above 2 V under a zero gate bias condition.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2003.02a
• /
• pp.36-39
• /
• 2003

HTS (High Temperature Superconducting) cable termination current lead has been designed based on simplified boundary conditions such as fixed temperature at both end and sdiabatic/convection in the side wall. However, in the real situation the current lead is enclosed with insulators and exposed to insulation oil and L$N_2$. Therefore it is necessary to consider them for the proper current lead design. In this paper, several important design parameters were chosen and their effect on the temperature distribution and heat loads on the current lead has been investigated. It was found that current lead has to be 2 stage to reach the minimum temperature requirement of insulation oil and insulator is required to reduce the cooling capacity of cryogenic system.

• Corrosion Science and Technology
• /
• v.4 no.1
• /
• pp.1-7
• /
• 2005

An alternating current (AC) corrosion on buried pipeline has been studied using coupon and ER probe. Coupons and ER probes were applied to the sites from high value of AC voltage to low value based on the survey of AC voltages on buried gas transmission pipeline over the country. Parameters such as AC current density of coupon, AC voltage, cathodic protection potential, soil resistivity and frequency were monitored continually. Corrosion induced by AC was observed even under cathodically protected condition that met cathodic protection criterion (; below -850 mV vs. CSE). Corrosion rate was affected mainly not by AC voltage but by both of frequency and AC current density. An experimental corrosion rate relation could be obtained according to effective AC current density, in which AC corrosion rate increased linearly with effective AC current density, and its slope was 0.619 in coupon method and 0.885 in ER probes.

• Proceedings of the KIPE Conference
• /
• 2005.07a
• /
• pp.575-577
• /
• 2005

This paper proposes the SRM drive system based on DC-link current, from which the phase currents can be estimated in accuracy and also they can be used in driving SRM instead of the three-phase currents. In additional, the detecting circuit for DC-link current is also proposed for increasing the resolution and decreasing the off-set. Comparing to the general drive system based on the phase current, it is verified through the experiment that the proposed SRM drive system has the good performance in steady-state responses of the speed control. Using the DC-link current, all of the 3-phase currents can be easily estimated in driving the SRM.

• Proceedings of the IEEK Conference
• /
• 2001.06e
• /
• pp.123-126
• /
• 2001

This study presents the simulation of the traction return current based on 2${\times}$25kV power supply system in order to determine the impedance bond intensity of impulse type track circuit on the Kyoungbo electrification line. The results of simulation enables us to measure the precise intensity of catenary current, returning to the substation through KTX (Korean Train Express) operated by 2${\times}$25kV power supply system with common earth network. In the wake of establishing 2${\times}$25kV and common earth network used in Korea for the first time, in particular, it is possible to determine the impedance bond intensity of impulse type track circuit, which is applicable to the Kyoungbo electrification line by specifying the relations among the traction return current, earth current, and catenary current.