Asymmetric PWM Control Scheme During Hold-Up Time for $LLC$ Resonant Converter

Abstract

To narrow down the switching-frequency-variation range of an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter, asymmetric pulsewidth modulation (APWM) of the hold-up time is proposed. During the hold-up time, the modulation method of an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is changed from frequency modulation (FM) to APWM. Since the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter achieves a higher gain with APWM than it does with FM at the same switching frequency, the switching-frequency-variation range is reduced. Therefore, an optimal design of the magnetic components is possible, resulting in a high efficiency under normal operation and a high power density. The proposed control scheme is applied to an 85-W <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter.