• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.2
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• pp.133-138
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• 2024

Lithium-ion batteries are used in many fields due to their high energy density, fast charging conditions, and long cycle life. However, overcharging, over-discharging, physical damage, and use of lithium-ion batteries at high temperatures can reduce battery life and cause damage to people due to fire or explosion due to damage to the protection circuit. In order to reduce the risk of these batteries and improve battery performance, the characteristics of the charging and discharging process must be analyzed and understood. Therefore, in this paper, we analyze the charging and discharging characteristics of lithium-ion batteries using a battery charger and discharger and simulator to reduce the risk of loss of life due to overcharge and overdischarge, as well as casualties from fire and explosion due to damage to the protection circuit.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1438-1440
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• 1998

In this work, simultaneous measur of space charge and conduction current was c out in LDPE with air gap by Pulsed-Electro-Aco Method. Also, effect of long time charging at con electric field on the formation of space charge conduction was investigated. From the experim results. we knew that the homo space charge formed near the dielectric surfaces and moving the bulk of dielectric as the electric field elevated. This was related with the deep traps b carriers and de trapping by Poole-field lowering conduction current was coincident with the Pool emission. From the long time charging experimen obtained the results that the negative space was moving into the dielectric bulk as the cha continued and the positive space charge accumulated at upper surface of LDPE.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.347-352
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• 1971

The variations of the positive and negative electrode potentials, and of internal pressure were measured during the charge of the sealed type Ni-Cd cell. Both polarization characteristics of a paste type Cd-electrode as a gas diffusion electrode in 30% KOH solution and the effects of active carbon electrode as an oxygen consuming auxiliary electrode of the Ni-Cd cell on the charging characteristics of the cell were studied. Peak voltage at the end of charge of the cell is ascribed to the peak at the negative electrode potential, which is due to the concentration polarization by the lack of $Cd^{++}$ ion and oxygen concentration. And the recovery of the negative electrode potential is resulted from depolarization by the increasing diffusion limiting current density with the increasing oxygen pressure. The active carbon electrode was effective as an oxygen consuming auxiliary electrode. The internal pressure of the cell could be maintained below 200mmHg even at one hour rate charge and overcharge by the use of active carbon electrode as an auxiliary electrode.

• Journal of Power Electronics
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• v.11 no.4
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• pp.490-498
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• 2011

This paper presents a novel analysis, design, and implementation of a battery charging three-phase high frequency semi-controlled power converter feasible for plug-in hybrid electric vehicles. The main advantages of the proposed topology include high efficiency; due to lower power losses and reduced number of switching elements, high output power density realization, and reduced passive component ratings proportionally to the frequency. Additional advantages also include grid economic utilization by insuring unity power factor operation under different possible conditions and robustness since short-circuit through a leg is not possible. A high but acceptable total harmonic distortion of the generator currents is introduced in the proposed topology which can be viewed as a minor disadvantage when compared to traditional boost rectifiers. A hysteresis control algorithm is proposed to achieve lower current harmonic distortion for the rectifier operation. The rectifier topology concept, the principle of operation, and control scheme are presented. Additionally, a dc-dc converter is also employed in the rectifier-battery connection. Test results on 50-kHz power converter system are presented and discussed to confirm the effectiveness of the proposed topology for PHEV applications.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.2
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• pp.176-181
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• 2016

Recent years, supercapacitors have been attracting a growing attention as an efficient energy storage, due to their long-lifetime, device reliability, simple device structure and operation mechanism and, most importantly, high power density. Along with the increasing interest in flexible/stretchable electronics, the supercapacitors with compatible mechanical properties have been also required. A eutectic gallium-indium (EGaIn) liquid metal could be a strong candidate as a soft electrode material of the supercapacitors because of its insulating surface oxide layer for electric double layer formation. Here, we report the electrochemical study on the charging/reaction process at the interface of EGaIn liquid metal and electrolyte. Numerical fitting of the charging current curves provides the capacitance of EGaIn/insulating layer/electrolyte (${\sim}38F/m^2$). This value is two orders of magnitude higher than a capacitance of a general metal electrode/electrolyte interface.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.5
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• pp.514-525
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• 2023

This study conducted numerical simulations with the purpose of analyzing the impact of variations in outlet pressure conditions under extreme temperature conditions on the fluid dynamics and performance of a check valve utilized in hydrogen refueling systems. Under the extreme temperature conditions, changes in outlet pressure conditions of the check valve were investigated to analyze velocity distributions, pressure distributions, and temperature distributions in the operational and connection regions. The analysis results indicated that changes in outlet pressure had a significant influence on the internal temperature variation of the check valve. Furthermore, due to density variations in the connection region caused by the cooling effect of excessively cooled hydrogen, a bias in the primary flow direction towards the lower part of the valve outlet was observed in the outlet area. Through a comparison of the results of the valve's inherent flow performance, represented by the flow coefficient, it was observed that when the pressure difference between the inlet and outlet was below 0.37 MPa, sufficient flow was not ensured.

• Transactions of the Korean hydrogen and new energy society
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• v.35 no.1
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• pp.83-89
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• 2024

In order to confirm the safety against vibration of high-pressure fittings for mobile hydrogen charging devices, the natural frequency was confirmed through ANSYS, and vibration data occurring during driving was applied to utilize the vehicle's operating power spectral density data specified in MIL-STD-810H regulations. Fatigue analysis and resonance were confirmed, and as a result, it was confirmed that the sum of the pure phase ratios was less than 1 for the driving history presented in the standard, and there was no risk of resonance.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.3
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• pp.161-167
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• 2018

In battery-operated systems, an isolated converter is used to interface the utility grid with the system to increase stability when charging and discharging batteries. Systems such as vehicle-to-grids (V2Gs), on-board chargers, and energy storage systems (ESSs) have recently become popular, and the roles of isolated converters have become important considerations in fabricating such devices. A fixed-frequency LLC converter, which is a type of isolated converter, presents the advantages of high efficiency and high power density by performing zero-voltage switching (ZVS) over wide frequency ranges. However, the magnetizing inductance of the LLC converter should be designed to enable ZVS in all switching devices. Therefore, in this study, the operating characteristics of the LLC circuit are analyzed, and an optimal design method for ZVS operation is established. Moreover, an 8 kW LLC high-efficiency and high-power-density resonant converter is designed and tested for ESS application. The LLC converter achieves 98% efficiency at rated power.

• Nuclear Engineering and Technology
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• v.49 no.8
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• pp.1748-1751
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• 2017

Reduced activation ferritic/martensitic (RAFM) steels are widely applied as structural materials in the nuclear industry. To investigate hydrogen's effect on RAFM steels' elastic properties and the mechanism of that effect, a procedure of first principles simulation combined with experiment was designed. Density functional theory models were established to simulate RAFM steels' elastic status before and after hydrogen's insertion. Also, experiment was designed to measure the Young's modulus of RAFM steel samples with and without hydrogen charging. Both simulation and experiment showed that the solubility of hydrogen in RAFM steels would decrease the Young's modulus. The effect of hydrogen on RAFM steels' Young's modulus was more significant in water-quenched steels than it was in tempering steels. This indicated that defects inside martensite, considered to be hydrogen traps, could decrease the cohesive energy of the matrix and lead to a decrease of the Young's modulus after hydrogen insertion.

• Bulletin of the Korean Chemical Society
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• v.30 no.4
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• pp.817-820
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• 2009

To meet the high current load requirement from the high energy density realized by metal oxide and high power density graphite, we propose a novel hybrid supercapacitor consisting of Nb2O5 and KS6 graphite in 1.0 M LiPF6-EC:DEC (1:2). This new system exhibits a sloping voltage profile from 2.7 to 3.5 V during charging and presents a high operating voltage plateau between 1.5 and 3.5 V during discharging. The cell was tested at a current density of 100 mA/g with a cut-off voltage between 3.0 and 1.0 V. This novel energy storage system delivers the highest initial discharge capacity of 55 mAh/g and exhibits a good cycle performance.