energies Article Full-Bridge Active-Clamp Forward-Flyback Converter with an Integrated Transformer for High-Performance and Low Cost Low-Voltage DC Converter of Vehicle Applications Jaeil Baek 1 and Han-Shin Youn 2,* 1 Department of Electrical Engineering, Princeton University, Princeton, NJ 08540, USA; [email protected] 2 Department of Electrical Engineering, Incheon National University, 119, Academy-ro, Yeonsu-gu, Incheon 406840, Korea * Correspondence: [email protected] Received: 14 January 2020; Accepted: 12 February 2020; Published: 16 February 2020 Abstract: This paper presents a full-bridge active-clamp forward-flyback (FBACFF) converter with an integrated transformer sharing a single primary winding. Compared to the conventional active-clamp-forward (ACF) converter, the proposed converter has low voltage stress on the primary switches due to its full-bridge active-clamp structure, which can leverage high performance Silicon- metal–oxide–semiconductor field-effect transistor (Si-MOSFET) of low voltage rating and low channel resistance. Integrating forward and flyback operations allows the proposed converter to have much lower primary root mean square (RMS) current than the conventional phase-shifted-full-bridge (PSFB) converter, while covering wide input/output voltage range with duty ratio over 0.5. The proposed integrated transformer reduces the transformer conduction loss and simplify the secondary structure of the proposed converter. As a result, the proposed converter has several advantages: (1) high heavy load efficiency, (2) wide input voltage range operation, (3) high power density with the integrated transformer, and (4) low cost. The proposed converter is a very promising candidate for applications with wide input voltage range and high power, such as the low-voltage DC (LDC) converter for eco-friendly vehicles. Keywords: active-clamp converter; DC-DC converter; eco-friendly vehicle; forward-flyback converter; high efficiency; high power density; integrated transformer; low-voltage DC converter; soft-switching 1. Introduction Nowadays, eco-friendly vehicles such as hybrid electric vehicle and electric vehicle have been researched and developed to satisfy the strengthened CO2 emission regulations as well as to increase fuel economy [1–3]. A lot of power conversion systems have been studied for eco-friendly vehicles. These power conversion systems require not only a high efficiency to improve the fuel economy but also a high power density because those are installed in the engine and trunk rooms of eco-friendly vehicles. Moreover, the price of eco-friendly vehicles is much higher than that of the traditional vehicles due to additional power conversion systems, i.e., drive motor, inverter, converters, and battery. Therefore, reducing the production cost is also one of the most important design considerations for eco-friendly vehicles. Furthermore, the power consumption caused by electronic devices of vehicles has been rapidly increased due to the remarkable improvement of information technology and development of electronic system such as advanced driver assistance system (ADAS), motor drive steering system (MDPS), traction control system (TCS), information devices, etc. [4]. Energies 2020, 13, 863; doi:10.3390/en13040863 www.mdpi.com/journal/energies Energies 2019, 12, x FOR PEER REVIEW 2 of 17 Energies 2020, 13, 863 2 of 17 Energies 2019, 12, x FOR PEER REVIEW 2 of 17 To supply power to electronic devices of vehicles, a LDC converter that charges low voltage (LV) battery (e.g., 13.6 V) with the energy stored in high voltage (HV) battery (e.g. 300 V) is commonly ToTo supply supply power power to to electronic electronic devices devices of of vehicles vehicles,, a a LDC LDC converter converter that that charges charges low low voltage voltage (LV) (LV) used in eco-friendly vehicles. The LV battery is usually controlled to maintain its nominal voltage. batterybattery (e.g., 13.613.6 V)V) withwith the the energy energy stored stored in in high high voltage voltage (HV) (HV) battery battery (e.g., (e.g. 300 300 V) is V) commonly is commonly used Namely, the LDC converter should be designed to cover wide input voltage range of the HV battery. usedin eco-friendly in eco-friendly vehicles. vehicles. The LV The battery LV battery is usually is usually controlled controlled to maintain to maintain its nominal its nominal voltage. voltage. Namely, Due to the increased power consumption of high-performance electronic devices (ADAS, MDPS, and Namely,the LDC the converter LDC converter should be should designed be designed to cover wide to cover input wide voltage input range voltage of the range HV of battery. the HV Due battery. to the so on) in vehicles, the discharging current of the LV battery has been increased. 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