• Journal of Power Electronics
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• v.15 no.4
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• pp.1006-1017
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• 2015

This paper presents a finite control set model predictive control (FCS-MPC) strategy for the AC/DC matrix converter used in grid-connected battery energy storage system (BESS). First, to control the grid current properly, the DC current is also included in the cost function because of input and output direct coupling. The DC current reference is generated based on the dynamic relationship of the two currents, so the grid current gains improved transient state performance. Furthermore, the steady state error is reduced by adding a closed-loop. Second, a Luenberger observer is adopted to detect the AC input voltage instead of sensors, so the cost is reduced and the reliability can be enhanced. Third, a switching state pre-selection method that only needs to evaluate half of the active switching states is presented, with the advantages of shorter calculation time, no high dv/dt at the DC terminal, and less switching loss. The robustness under grid voltage distortion and parameter sensibility are discussed as well. Simulation and experimental results confirm the good performance of the proposed scheme for battery charging and discharging control.

• Journal of Power System Engineering
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• v.21 no.4
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• pp.5-17
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• 2017

This study focuses on the application of the PEM Fuel Cell(PEMFC) hybrid system, which includes a regenerative braking system with supercapacitor(SC) and battery. The purpose of this study is to evaluate the characteristics of regenerative energy and to propose solutions to increase regenerative energy via vehicle simulation. To achieve this target, we set the rated motor speed to 3,000/2,500/2,000 rpm. Because the flywheel is directly connected to the motor, the generator activates regenerative braking by using the rotational momentum of the flywheel when the flywheel reaches the set speed after the motor stops. We could then measure the characteristics of regenerative braking of voltage, current, power, energy change, etc. Meanwhile, we calculate the storage efficiency of the SC or the battery. Our results show that the SC stores 18% of the regenerative energy, while battery stores 15% of the energy. Since the regenerative energy decreases with the decrease of the motor rotating speed that 5,027 J and 2,915 J are restored at 3,000 and 2,500 rpm, respectively. The experimental results also prove that regenerative braking energy is able to be obtained if and only if the speed of flywheel is over 2,500 PRM, and the efficiency of the system can be further improved.

• Journal of Energy Engineering
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• v.20 no.2
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• pp.77-83
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• 2011

It is requested to improve negative electrode of Ni-Zn battery for industrial application. Ni-Zn battery has main problems not to commercialize because of short life cycle, heavy gassing and fast electrolyte vaporization so far. It has been studied on 8 cells performances under promoting electric, additional materials and binders changed. With these materials($Ca(OH)_2$, $Bi_2O_3$), negative electrolyte can be manufactured equal and tight as well as low gassing. Furthermore, to supply EG-EP#12(gravity 1.26), keeping stable electrolyte gravity in battery, the life cycle of Ni-Zn battery is extremely improved 200~300% than initial performance.

• Journal of IKEEE
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• v.23 no.2
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• pp.667-674
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• 2019

The recent incidents of Nuclear Power Plant(NPP) gave rise to a total power outage caused by the loss of the functions of the off-site and the emergency power supply. Currently, emergency power supply of NPP have been taken into account by Li-ion batteries instead of existing lead-acid batteries. In order to judge the applicability of the cylindrical Li-ion battery, it is necessary to analysis the results of various electrical tests. This paper investigates the basic electrical characteristics test of three types of cylindrical batteries in order to select the most suitable battery and estimate state of battery through equivalent circuit model and propose method to solve the problem.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.11
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• pp.1588-1593
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• 2014

The scott transformer changes three-phase power to two single-phase power. However, this method causes unbalance and fluctuation of voltage by the change of electric railload. Recently, the AC railway system based on $3{\Phi}/1{\Phi}$ back-to-back (BTB) voltage source converter (VSC) has been proposed to solve these problems. Meanwhile, battery energy storage system (BESS) is used to compensate voltage instantaneously in power system. In this paper, BESS application to the AC railway system based on $3{\Phi}/1{\Phi}$ BTB VSC is suggested to compensate voltage instantaneously. The application effect is shown through simulation using MATLAB/SIMULINK.

• Journal of Electrochemical Science and Technology
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• v.10 no.1
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• pp.1-13
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• 2019

Na-ion batteries are being considered as promising cost-effective energy storage devices for the future compared to Li-ion batteries owing to the crustal abundance of Na-ion. However, the large radius of the Na ion result in sluggish electrode kinetics that leads to poor electrochemical performance, which prohibits the use of these batteries in real time application. Therefore, identification and optimization of the anode, cathode, and electrolyte are essential for achieving high-performance Na-ion batteries. In this context, the current review discusses the suitable high-voltage cathode materials for Na-ion batteries. According to a recent research survey, sodium vanadium fluorophosphate (NVPF) compounds have been emphasized for use as a high-voltage Na-ion cathode material. Among the fluorophosphate groups, $Na_3V_2(PO_4)_2F_3$ exhibited the high theoretical capacity ($128mAh\;g^{-1}$) and working voltage (~3.9 V vs. $Na/Na^+$) compared to the other fluorophosphates and $Na_3V_2(PO_4)_3$. Here, we have also highlighted the classification of Fluorophosphates, NVPF composite with carbonaceous materials, the appropriate synthesis methods and how these methods can enhance the electrochemical performance. Finally, the recent developments in NVPF for the application in energy storage devices and its outlook are summarized.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.291-298
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• 2019

We describe the improvement of insulation performance and the prevention of electrolyte leakage in a single cell in order to prevent the fuming phenomenon caused by leakage of electrolyte in a lithium secondary battery in a submerged weapon (torpedo) operated in Korea. A torpedo using lithium secondary battery as a main power source (propulsion battery) can induce the heat and fuming phenomenon, which makes it inconvenient for naval equipment operation in Korea. In the simulation test, the electrolyte of some battery cells leaked in the battery pack unit, leading to a short circuit between the main power circuit and the terminal tab of the high voltage part. We analyzed the characteristics and mechanism of the lithium secondary battery during this heat generation and fuming phenomenon. In order to prevent leakage of the electrolyte in the lithium secondary battery, the design was improved via fundamental (terminal tap enhancement) and complementary (insulation block selection and installation) measures. Comparison of the performance test before and after the improvement showed that the tensile strength of the tap terminal was improved about 2 times and the withstand voltage characteristic was improved. The application of quality improvement measures resulted in no fuming even after more than 3 years of field operation. This result is expected to improve the operation and storage stability of the torpedo propulsion cell.

• Journal of Korea Society of Industrial Information Systems
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• v.18 no.5
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• pp.73-80
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• 2013

Recently, Li-ion battery is regarded as a potential energy storage device in the lime light and it can supply power to the satellite very effectively during eclipse. Because it has better features as high voltage range, large capacity and small volume than any other battery. Generally, multi cells are connected in series to use Li-ion batteries in satellite application. Since the internal resistance of cells is different each other, voltage in some cells can be overcharged or undercharged, so capacity of the cell is reduced and the life of whole battery pack is decreased. Therefore, a voltage balancing circuit with Fly-back converter is proposed and the voltage equalization of each cell is verified the prototype in this paper.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1127-1139
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• 2018

A reduced particle-unscented Kalman filter estimation method, along with a splice-equivalent circuit model, is proposed for the state-of-charge estimation of an aeronautical lithium-ion battery pack. The linearization treatment is not required in this method and only a few sigma data points are used, which reduce the computational requirement of state-of-charge estimation. This method also improves the estimation covariance properties by introducing the equilibrium parameter state of balance for the aeronautical lithium-ion battery pack. In addition, the estimation performance is validated by the experimental results. The proposed state-of-charge estimation method exhibits a root-mean-square error value of 1.42% and a mean error value of 4.96%. This method is insensitive to the parameter variation of the splice-equivalent circuit model, and thus, it plays an important role in the popularization and application of the aeronautical lithium-ion battery pack.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.4
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• pp.347-352
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• 2013

Four types of electrolyte were tested for the application as an electrolyte in the Zn-Br redox flow battery. Electrolyte was consist of $ZnBr_2$ (electrolyte number 1), $ZnBr_2+KCl$ (electrolyte number 2), $ZnBr_2+KCl+NH_4Br$ (electrolyte number 3) and $ZnBr_2+KCl+EMPBr(C_7H_{16}BF_4N)$ (electrolyte number 4). The each electrolyte property was measured by CV (cyclic voltammetry) method. The different between the potential of anodic and cathodic maximum current density in a CV experiment (${\Delta}E_P$) was 0.89V, 0.89V, 1.06V and 0.61V for the electrolyte number 1, 2, 3 and 4, respectively. The electrolyte involved KCl increased conductivity which was appeared by anodic and cathodic maximum current density in a CV experiment. It was estimated that the electrolyte of number 3 ($ZnBr_2+KCl+NH_4Br$) and number 4 ($ZnBr_2+KCl+EMPBr$) could be suitable as an electrolyte in the Zn-Br redox flow battery with non-appeared bubble, non-Br formation and high anodic-cathodic maximum current density.