State-trajectory control of LLC converter implemented by microcontroller

This paper investigates how to integrate state-trajectory control functions of LLC resonant converter within a commercial low-cost microcontroller, including Simplified Optimal Trajectory Control (SOTC) for load transient, burst mode and soft start up. Simplified calculation process is proposed for SOTC to minimize digital delay. Guideline to select a proper microcontroller is presented to limit calculation delay and ADC delay within 1 switching cycle to ensure good transient performance. Optimized transient processes are proposed to eliminate large oscillation between burst mode and normal operation. Soft start-up is implemented with sensing the output voltage only. The whole control system structure is proposed to integrate all these control functions and for the first time all these control functions are integrated in one low-cost MCU. The results are demonstrated on a 130kHz 300W 380V/12V halfbridge LLC resonant converter with MCU TMS320F2808.