Transient Control and Soft Start-Up for 1-MHz LLC Converter With Wide Input Voltage Range Using Simplified Optimal Trajectory Control
Ahmed Nabih, Mohamed H. Ahmed, Qiang Li, Fred C. Lee
Abstract
The 48-V bus converters are widely used in telecommunications and network power architectures. A single-stage regulated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> bus converter can achieve high efficiency and high power density. This article addresses the control challenges of a regulated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> converter for 48-V bus converter applications. Simplified optimal trajectory control (SOTC) is used to control a 1-MHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> converter with an input voltage range of 40–60 V and a frequency range of 0.8–1.8 MHz. A digital implementation of two-step SOTC is proposed for the high-frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> using a low-speed microcontroller (MCU). The proposed implementation can achieve the optimum transient performance and minimize settling time. SOTC can achieve the optimum transient response for an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> operating at resonant frequency but has a limited impact at a wide gain range. As a result, a feedforward compensation is proposed, in conjunction with SOTC, to achieve optimum transient response at a wide input voltage range or wide gain range. Moreover, a soft start-up with adaptive switching frequency is proposed to achieve start-up under limited current stress over the whole input voltage range. The experimental results are demonstrated on a 1-MHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> 48-V bus converter using a 90-MHz TMS320F28069 Piccolo MCU.