Multi-step Simplified Optimal Trajectory Control (SOTC) for fast transient response of high frequency LLC converters

This paper proposes Multi-step Simplified Optimal Trajectory Control (SOTC) for the high frequency LLC converters. SOTC can improve the transient performance of the LLC converters by immediately changing the pulse width of the primary driving signal during the load transient. However, the implementation of SOTC requires high-performance digital controllers. The proposed Multi-step SOTC calculates the trajectory based on only the output voltage and the load current, and settles the resonant tank within multi steps. With the proposed Multi-step SOTC, low-cost controllers can be used to control the high frequency LLC converters with the state-trajectory control concept. The number of steps in multi-step SOTC is selected based on the speed of the controller and the switching frequency of the LLC converters. Experimental results are demonstrated on a 500kHz 1kW 400V/12V LLC converter.