UBC Theses and Dissertations

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UBC Theses and Dissertations

Synchronous rectification for LLC resonant converter in battery charging application Amiri, Peyman


Everyday the number of devices with a battery inside is increasing. From smartphones to electric vehicles, batteries are widely used in different power ratings. Charging time is one of the major obstacles in widespread use of battery powered electric vehicles. Developing high power chargers is one of the key steps to achieve fast charging. Developing high power chargers requires design of compact and high efficiency converters. LLC Resonant converter is widely used in the structure of medium to high power chargers. Utilizing synchronous rectification technique, along with the converter intrinsic soft switching characteristic, has led to above 95% efficiency for LLC resonant converter. Due to presence of magnetizing inductance in the structure of resonant tank in LLC resonant converter, the secondary side currents are not completely synchronous with the primary side gate signals. This makes the control of secondary MOSFETs complicated. Although synchronous rectification for LLC resonant converter has been the focus of research for at least a decade, most of the methods developed for synchronous rectification focus on fixed output voltage applications. However, in battery charging process, the output voltage of the converter varies in a wide range. As a result, new flexible synchronous rectification methods are needed to work in different operating points during the charging process. In this research, the requirements for LLC resonant converter in battery charging application are investigated. Based on these requirements, an LLC converter with 24V rated output voltage and maximum 650W output power is designed. Next, the control requirements for LLC resonant converter in battery charging application are explained. Additionally, the settings for an analog integrated circuit from Infineon Technologies are modified to meet the requirement for battery charging application. At the end, experimental results are presented to show the effectiveness of the control settings in different operating conditions.

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