• Journal of Power Electronics
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• v.16 no.6
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• pp.2359-2367
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• 2016

Inductive power transfer (IPT) systems have become increasingly popular in recharging electric vehicle (EV) batteries. This paper presents an investigation of a series parallel/series (SP/S) resonant compensation network based IPT system for EVs with further optimized circular pads (CPs). After the further optimization, the magnetic coupling coefficient and power transfer capacity of the CPs are significantly improved. In this system, based on a series compensation network on the secondary side, the constant output voltage, utilizing a simple yet effective control method (fixed-frequency control), is realized for the receiving terminal at a settled relative position under different load conditions. In addition, with a SP compensation network on the primary side, zero voltage switching (ZVS) of the inverter is universally achieved. Simulations and experiments have been implemented to validate the favorable applicability of the modified optimization of CPs and the proposed SP/S IPT system.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.3
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• pp.139-146
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• 2019

As the number of electric vehicles (EVs) in Jejudo Island increases, the secondary use of EV batteries is becoming increasingly mandatory not only in reducing greenhouse gas emissions but also in promoting resource conservation. For the secondary use of EV batteries, their capacity and performance at the end of automotive service should be evaluated properly. In this study, the battery state information from the on-board diagnostics or OBD2 port was acquired in real time while driving three distinct routes in Jejudo Island, and then the battery operating characteristics were assessed with the driving routes. The route with higher altitude led to higher current output, i.e., higher C-rate, which would reportedly deteriorate state of health (SOH) faster. In addition, the SOH obtained from the battery management system (BMS) of a 2017 Kia Soul EV with a mileage of 55,000 km was 100.2%, which was unexpectedly high. This finding was confirmed by the SOH estimation based on the ratio of the current integral to the change in state of charge. The SOH larger than 100% can be attributed to the rated capacity that was lower than the nominal capacity in EV application. Therefore, considering the driving environment and understanding the SOH estimation process will be beneficial and necessary in evaluating the capacity and performance of retired batteries for post-vehicle applications.

• Progress in Superconductivity and Cryogenics
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• v.16 no.3
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• pp.21-25
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• 2014

As wireless power transfer (WPT) technology using strongly coupled electromagnetic resonators is a recently explored technique to realize the large power delivery and storage without any cable or wire, this technique is required for diffusion of electric vehicles (EVs) since it makes possible a convenient charging system. Typically, since the normal conducting coils are used as a transmitting coil in the CPT system, there is limited to deliver the large power promptly in the contactless EV charging system. From this reason, we proposed the combination CPT technology with HTS transmitting antenna, it is called as, superconducting contactless power transfer for EV (SUWPT4EV) system. As the HTS coil has an enough current density, it can deliver a mass amount of electric energy in spite of a small scale antenna. The SUCPT4EV system has been expected as a noble option to improve the transfer efficiency of large electric power. Such a system consists of two resonator coils; HTS transmitting antenna (Tx) coil and normal conducting receiver (Rx) coil. Especially, the impedance matching for each resonator is a sensitive and plays an important role to improve transfer efficiency as well as delivery distance. In this study, we examined the improvement of transmission efficiency and properties for HTS and copper antennas, respectively, within 45 cm distance. Thus, we obtained improved transfer efficiency with HTS antenna over 15% compared with copper antenna. In addition, we achieved effective impedance matching conditions between HTS antenna and copper receiver at radio frequency (RF) power of 370 kHz.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1664-1673
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• 2016

Lithium rechargeable cells are used in many industrial applications, because they have high energy density and high power density. For an effective use of these lithium cells, it is essential to build a reliable battery management system (BMS). Therefore, the state of charge (SOC) estimation is one of the most important techniques used in the BMS. An appropriate modeling of the battery characteristics and an accurate algorithm to correct the modeling errors in accordance with the simplified model are required for practical SOC estimation. In order to implement these issues, this approach presents the comparative analysis of the SOC estimation performance using equivalent electrical circuit modeling (EECM) and noise suppression technique (NST) in three representative $LiCoO_2/LiFePO_4/LiNiMnCoO_2$ cells extensively applied in electric vehicles (EVs), hybrid electric vehicles (HEVs) and energy storage system (ESS) applications. Depending on the difference between some EECMs according to the number of RC-ladders and NST, the SOC estimation performances based on the extended Kalman filter (EKF) algorithm are compared. Additionally, in order to increase the accuracy of the EECM of the $LiFePO_4$ cell, a minor loop trajectory for proper OCV parameterization is applied to the SOC estimation for the comparison of the performances among the compared to SOC estimation performance.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.143-151
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• 2018

In this paper, a novel hybrid configuration combining a phase-shift full-bridge (PSFB) and a half-bridge resonant LLC converter is proposed for the On-Board Charger of Electric Vehicles (EVs). In the proposed converter, the PSFB converter shares the lagging-leg switches with half-bridge resonant converter to achieve the wide ZVS range for the switches and to improve the efficiency. The output voltage is modulated by the effective-duty-cycle of the PSFB converter. The proposed converter employs an active reset circuit composed of an active switch and a diode for the transformer which makes it possible to achieve zero circulating current and the soft switching characteristic of the primary switches and rectifier diodes regardless of the load, thereby making the converter highly efficient and eliminating the reverse recovery problem of the diodes. In addition an optimal power sharing strategy is proposed to meet the specification of the charger and to optimize the efficiency of the converter. The operation principle the proposed converter and design considerations for high efficiency are presented. A 6.6 kW prototype converter is fabricated and tested to evaluate its performance at different conditions. The peak efficiency achieved with the proposed converter is 97.7%.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.173-179
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• 2020

Electric vehicles (EVs) using lithium secondary batteries (LIBs) with excellent power and long-term cycle performance are gaining interest as the successors of internal combustion engine (ICE) vehicles. However, there are few systematic researches for fast charging to satisfy customers' needs. In this study, we compare the degradation of LIB where its composition is LiNi_0.5Co_0.2Mn_0.3/Graphite with the constant current and constant power-charging method. The charging speed was set to 1C, 2C, 3C and 4C in the constant current mode and the value of constant power was calculated based on the energy at each charging speed. Therefore, by analyzing the battery degradation based on the same charging energy but different charging method; CP charging method can slow down the battery degradation at a high rate of 3C through the voltage curve, capacity retention and DC-IR. However, when the charging rate was increased by 4C or more, the deviation between the LIBs dominated the degradation than the charging method.

• Journal of the Korean Electrochemical Society
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• v.12 no.3
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• pp.203-218
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• 2009

The development of lithium-ion battery (LIB) technologies and their application in the field of large-scale power sources, such as electric vehicles (EVs), hybrid EVs, and plug-in EVs require enhanced reliability and superior safety. The main components of LIBs should withstand to the inevitable heating of batteries during high current flow. Carbonate solvents that contribute to the dissociation of lithium salts are volatile and potentially combustible and can lead to the thermal runaway of batteries at any abuse conditions. Recently, an interest in nonflammable materials is greatly growing as a means for improving battery safety. In this review paper, novel approaches are described for designing highly safe electrolytes in detail. Non-flammability of liquid electrolytes and battery safety can be achieved by replacing flammable organic solvents with thermally resistive materials such as flame-retardants, fluorinated organic solvents, and ionic liquids.

• Resources Recycling
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• v.28 no.5
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• pp.3-18
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• 2019

Due to the increasing demand for clean energy, the consumption of lithium ion batteries (LIBs) is expected to grow steadily. Therefore, stable supply of lithium is becoming an important issue globally. Commercially, most of lithium is produced from the brine and minerals viz., spodumene, although various processes/technologies have been developed to recover lithium from other resources such as low grade ores, clays, seawaters and waste lithium ion batteries. In particular, commercialization of such recycling technologies for end-of-life LIBs being generated from various sources including mobile phones and electric vehicles(EVs), has a great potential. This review presents the commercial processes and also the emerging technologies for exploiting minerals and brines, besides that of newly developed lithium-recovery-processes for the waste LIBs. In addition, the future lithium-supply is discussed from the technical point of view. Amongst the emerging processes being developed for lithium recovery from low-grade ores, focus is mostly on the pyro-cum-hydrometallurgical based approaches, though only a few of such approaches have matured. Because of low recycling rate (<1%) of lithium globally compared to the consumption of lithium ion batteries (56% of lithium produced currently), processing of secondary resources could be foresighted as the grand opportunity. Considering the carbon economy, environment, and energy concerns, the hydrometallurgical process may potentially resolve the issue.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2247-2255
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• 2017

Because the on-board charger (OBC) is installed in electric vehicles (EVs), high power density is regarded as a key technology. Among components of the OBC, inductors occupy more than 30% of the total volume. Thus, it is important to reduce the volume and the weight of inductors while maintaining thermal stability. Discontinuous conduction mode (DCM) can satisfy these requirements; however, only a few studies have adopted the DCM operation for OBCs because of the large inductor current ripple. In this paper, a design process is proposed for application of the DCM operation to OBCs. In order to analyze the inductor losses accurately, a numerical formula for the inductor current ripple is deduced based on a detailed analysis. Two inductors are fabricated using several ferrite cores and powder cores taking into consideration the inductor size, inductor losses, and temperature rise. In order to verify the analysis and design process, experimental results are presented that show that the designed inductors satisfy the requirements of the OBCs.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.313-320
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• 2018

This study proposes a new voltage balancer with bidirectional DC-DC converter function. The proposed balancer can serve as a voltage balancer and a bidirectional DC-DC converter. Thus, the balancer can be applied to battery management systems or fast chargers in electric vehicles (EVs) charging stations while balancing bipolar DC bus voltages. The proposed system has unlimited voltage balancing range unlike the conventional voltage balancing control using a three-level DC-DC converter. A comparison of the voltage balancing range between the proposed and conventional scheme is explored to confirm this superiority. Simulation and experimental results are provided to validate the effectiveness of the proposed system.