3.3kW Bidirectional OBC Design with Active Clamp Flyback Converter Hyeok-Min Kwon, So-Jeong Kong, Jae-Hyuck Choi, Dae-Young Hong and Jun-Young Lee† Myongji University Electrical Engineering

3.3kW Bidirectional OBC Design with Active Clamp Flyback Converter Hyeok-Min Kwon, So-Jeong Kong, Jae-Hyuck Choi, Dae-Young Hong and Jun-Young Lee† Myongji University Electrical Engineering 

 액티브 클램프 플라이백 컨버터를 이용한 3.3kW 양방향 OBC 설계 권혁민, 공소정, 최재혁, 홍대영, 이준영† 명지대학교 전기공학과 

 ABSTRACT 

본 논문은 3.3kW급 OBC에 사용되는 DC-DC 양방향 Flyback 컨버터를 제안한다. 기존 Flyback 컨버터에서 보조 스 위치를 사용한 회로를 적용하여 변압기 누설 값에 저장된 에너 지를 재활용하여 메인 스위치 전압 스파이크를 최소화하는 방 식을 사용했고 이를 대칭구조로 적용하였다. 모든 전력반도체 소자는 SiC-MOSFET을 적용하였다. 스위칭 주파수 70kHz 조 건에서 입력전압은 400V이며 배터리 전압 100V, 250V, 330V, 450V 네 구간에서 정상 동작을 확인하였으며 정방향 최대 효 율:97.58%, 역방향 최대 효율 97.48%를 달성하였다.

ABSTRACT

This paper proposes a DC-DC bi-directional flyback converter used in a 3.3kW class OBC. In the existing flyback converter, a circuit using an auxiliary switch was applied to recycle the energy stored in the transformer leakage value to minimize the main switch voltage spike, and this was applied in a symmetrical structure. All power semiconductor devices applied SiC-MOSFETs. Under the condition of the switching frequency of 70kHz, the input voltage was 400V, and normal operation was confirmed in four sections of battery voltage 100V, 250V, 330V, and 450V, and the maximum forward efficiency: 97.58% and the maximum reverse efficiency 97.48% were achieved.

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Three-Phase Single-Stage Bidirectional CCM Soft-Switching AC–DC Converter With Minimum Switch Count-Jaeyeon Lee , Hyeonju Jeong, Tat-Thang LE , Member, IEEE, and Sewan Choi , Fellow, IEEE

Three-Phase Single-Stage Bidirectional CCM Soft-Switching AC–DC Converter With Minimum Switch Count Jaeyeon Lee , Hyeonju Jeong, Tat-Thang LE , Member, IEEE, and Sewan Choi , Fellow, IEEE 

 Abstract—In this article, a three-phase single-stage bidirectional ac–dc converter with low component count is proposed. The single-stage structure is configured by integrating a threephase ac–dc converter and a three-phase dual active bridge converter. The power factor correction and bidirectional power control are performed by adjusting the modulation index of sinusoidal pulse width modulation (SPWM) and phase-shift angle between the primary and secondary bridges. The lowfrequency components generated by SPWM are absorbed by fundamental blocking capacitors connected in series with transformer windings, resulting in true high-frequency isolation. The proposed converter can achieve soft-switching of all switching devices even in continuous conduction mode. A 110 Vac, 3 kW, 100 kHz prototype is implemented to validate the proposed concept and demonstrated 95.34% peak efficiency.

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Compact Integrated Transformer – Grid Inductor Structure for E-Capless Single-Stage EV Charger Ramadhan Muhammad Hakim, Huu-Phuc Kieu, Junyeong Park, Tat-Thang LE, Member, IEEE, Sewan Choi, Fellow, IEEE, Byeongseob Song, Hoyoung Jung, and Bokyung Yoon

Compact Integrated Transformer – Grid Inductor Structure for E-Capless Single-Stage EV Charger Ramadhan Muhammad Hakim, Huu-Phuc Kieu, Junyeong Park, Tat-Thang LE, Member, IEEE, Sewan Choi, Fellow, IEEE, Byeongseob Song, Hoyoung Jung, and Bokyung Yoon 

 Abstract—This paper proposes a planar magnetic integration technique that combines the grid inductors and transformer in the single-stage E-capless EV charger into one core. The proposed integration technique reduces the number of magnetic components; therefore, the cost, total magnetic core loss, and volume can be significantly reduced. Using the integrated structure, the overall converter power density increases up to 11.1% compared to the non-integrated one. This paper also presents a detailed analysis of the optimal PCB winding arrangement considering both AC resistance and winding stray capacitance. Due to the high DC resistance of PCB winding, Litz wire was also considered for the proposed integrated structure. The effectiveness of the proposed structure was validated by implementing it on a 3.7 kW prototype of a single-stage AC-DC converter. Results show that the prototype with the proposed integrated structure achieved higher efficiency with both PCB winding and Litz wire. Peak efficiency of 97.17% and 6.55 kW/L power density were achieved. 

Index Terms—Planar cores, Electric vehicles, Battery chargers, AC-DC power converters

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High voltage insulation design of coreless, planar PCB transformers for multi-MHz power supplies Ole Christian Spro, Student Member, IEEE, Frank Mauseth, Member, IEEE---Department of Electric Power Engineering, Norwegian University of Science and Technology, Trondheim, Norway, Dimosthenis Peftitsis, Senior Member, IEEE

High voltage insulation design of coreless, planar PCB transformers for multi-MHz power supplies Ole Christian Spro, Student Member, IEEE, Frank Mauseth, Member, IEEE, Dimosthenis Peftitsis, Senior Member, IEEE,

 Abstract—This paper investigates the insulation design for printed, planar, coreless, and high-frequency transformers with high isolation-voltage. By using finite element analysis on 2D axial-symmetry, the transformer circuit parameters and electric field distribution are modelled and estimated. Several transformers are designed for an operating frequency of 6.78 MHz. The high frequency, coreless design allows for using thicker insulation material while ensuring a high transformer efficiency. The inclusion of the coupling capacitance in the design optimisation results in several design solutions with the same figure of merit, but with different footprint and isolation voltages. Moreover, high electric fields are identified around the sharp edges of the PCB windings. Finally, the electrical and isolation performance is verified experimentally. The measured electrical properties are close to the simulated values, validating the chosen model. Breakdown tests demonstrate the feasibility of isolation voltage levels up to several tens of kilovolts. The majority of breakdowns occurs at the outer edge of the PCB winding that was identified as a high-field area. Additionally, a concept for grading the electric field of PCB windings is also proposed. Based on the results, the design aspects are discussed in detail for planar, high-frequency isolation transformers with medium-voltage isolation level.

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A Study on the Explosion and Fire Risk of the Lithium Battery by Sang-BoSim Department of Fire and Disaster Prevention Engineering, The graduate School Hoseo University-Asan,Korea -리튬 배터리의 폭발 및 화재 위험성에 관한 연구-

A Study on the Explosion and Fire Risk of the Lithium Battery Sang-BoSim Department of Fire and Disaster Prevention Engineering, The graduate School Hoseo University-Asan,Korea 

 ABSTRACT

 Due to recent development of IT technology, information level of Korea is said to be the world-best. Thus mobile devices such as cell phones, notebook, and tablet PC that could be used without limitations are trending. Along the trend, high energy high density secondary batteries used as the power source for portable devices are also in the spotlight, and among them Lithium battery demand is rising. Generally a Lithium battery should be certified with KS C 8541 (Lithium secondary battery rule) in order to be on the market. However, battery accidents are growing in number and people are raising questions about the safety of the batteries.

Certified Lithium battery’s safety is guaranteed within normal state, but at abnormal states such as damage to protective circuit, the danger rises due to elimination of minimum protection. Recent studies regarding Lithium batteries only measured ignition status for flammable gas, but did not provide detailed analysis. Also, risk analysis according to battery capacity and comparative analysis between the two representative batteries, Lithium Polymer battery and Lithium Ion battery are rarely carried out. Also, research about general danger of Lithium batteries such as ignition at high temperature environment is incomplete.

This study selected five types of Li-Polymer batteries and three types of Li-Ion batteries of different capacity in order to analyze ignition and fire danger according to usage environment. The results are as following.

1. We designed an ignition circuit using IEC type spark ignition test apparatus based on KS C IEC 60079-11 standard in order to measure the explosion hazard of Lithium battery spark discharge. Through measuring the ignition limit of methane, propane, ethylene, and helium, the result showed that gas with higher danger showed more explosion to less number of battery connection. Also, batteries with not Protection Circuit Module (PCM) exploded more often during connection with battery compared with batteries that had protection circuits.

2. An experiment was conduction using a pyrostat based on UL 1642 and KS C 8541 standard in order to measure Lithium battery’s explosion danger at high temperature environment. As the result, Li-Polymer batter with pack type external material had higher risk of explosion compared to cap type Li-Ion battery. Li-Polymer battery had 160~170℃ explosion between 1970~2700 seconds, and the explosion occurred for the electrolytes seeped out from the cracked battery pack after swelling due to evaporation. On the other hand, Li-Ion battery had 176~197℃ explosion between 3000~3800 seconds caused by vaporized electrolyte increasing the pressure within the battery and protruding to the vulnerable positive (+) end.

3. Short circuit was designed in order to measure the temperature increase according to the short circuit current. For batteries with protection circuit, there was no temperature change caused by short circuit current due to current limitation. However, for batteries with no protection circuit, 30.7~35.6A of maximum short circuit current was produced. For Li-Polymer battery, the current fell until 3.9~12.7A after the maximum short circuit current, but increased again to 5.5~17.8A, showing two-step curve pattern. The maximum temperature was 125℃. For Li-Ion battery, the maximum short circuit current fell steeply to 1.3A and decreased steadily, showing a single step curve pattern. It is because the PTC thermistor embed inside limited the flowing current. The maximum temperature was 95℃.

Thus in order to minimize the danger of Lithium battery explosion, the Lithium battery connection number and discharge characteristics should be considered when used at environment with flammable gas. And swelling and explosive characteristics should be considered when using Li-Polymer and Li-Ion batteries at high temperature environment. Also, to prevent hazards caused by mistakes and abnormal statues, a dual safety device of protection circuits are recommended. 

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