An Accurate and Simplified Time-domain Model Based Feedforward Control for LLC Converter

This brief proposes an online feedforward control strategy based on an accurate and simplified time-domain model to enhance the dynamic performance of LLC resonant converters. By expanding inverse trigonometric functions from precise time-domain transcendental equations into monotonic polynomials and optimizing the order in which the variables are solved, the simplified equations can be solved quickly and iteratively while much more accurate than current advanced simplified model. Meanwhile, a modified PI control strategy featuring desaturation capability is utilized. The PI compensated frequency becomes nonzero only after a delay of certain switching cycles following output reference voltage transitions, thereby preventing integral saturation during transients while ensuring steady-state error compensation. Experiments are carried out under typical operation conditions including output, input and load transients to validate the proposed strategy. The results demonstrate that the settling time is 10x faster than the state-of-the-art methods (e.g., 33.17 ms vs. 328.0 ms for NP transitions, 54.88 ms vs. 584.5 ms for PO-NP transitions) and dramatically increased model accuracy (4.78% error vs. 22.37% error).