For LLC resonant converters under load disturbances

conventional PI control often exhibits slow dynamic response

while the self-coupling PI can accelerate response but tends to introduce higher output voltage ripple. To leverage the complementary advantages of both

a dual-loop control strategy was proposed in which the self-coupling PI serves as the outer voltage loop and the conventional PI as the inner current loop. This configuration improves transient performance while maintaining low steady-state ripple. To enable accurate loop compensation design

a mathematical model of the LLC resonant converter was developed based on the cycle-by-cycle analysis method

from which the small-signal transfer function is derived. Using this model

tuning rules for the self-coupling PI controller were established

and the dual-loop controller parameters were designed through frequency-domain analysis and validated via simulation. Finally

an experimental LLC resonant converter platform was built. Experimental results demonstrate that

compared with the conventional PI-PI dual-loop control

the proposed self-coupling-PI-based strategy achieves comparable output ripple while reducing the recovery time under sudden load increase and decrease by 40% and 14%

respectively

and lowering the overshoot by 57% and 50%.