Abstract: This paper proposes a frequency feedforward control method based on simplified time-domain analysis of LLC resonant converters to address the unsatisfactory dynamic response of traditional linear controllers. By simplifying the time-domain equations of LLC converters under three operating conditions - under resonance, over resonance near the resonance point, and over resonance far from the resonance point - we develop three simplified time-domain iterative algorithms that enable real-time calculation of the ideal switching frequency in digital controllers. These calculated frequencies are then fed forward to linear controllers, significantly improving the dynamic response of LLC converters. The proposed simplified time-domain algorithm can also compute working waveforms including voltage gain, resonant current, and resonant voltage in real time. Simulation results demonstrate that the algorithm's calculated working waveforms and voltage gain curves closely match those obtained from detailed time-domain analysis, confirming the algorithm's accuracy. An experimental prototype validates the dynamic response improvement achieved by the proposed feedforward control. Experimental results indicate that this feedforward control effectively optimizes performance across various LLC converter dynamic processes while imposing a relatively low computational burden on digital controllers.