Research on Hybrid Control Strategy for High-Voltage High-Power LLC Resonant Converters

This study addresses the development requirements of high-voltage power modules by proposing an inverter-type DC power supply design based on an LLC resonant converter, employing a hybrid control strategy combining frequency modulation (PFM) and phase-shift modulation (PSM) to optimize dynamic response and steady-state performance. Initially, a small-signal model of the LLC resonant converter was established in MathCAD using the extended describing function method. This model derives the transfer functions between switching frequency-output voltage and phase-shift duty cycle-output voltage, followed by the design of a two-pole two-zero (2P2Z) compensator through amplitude-frequency characteristic analysis to ensure control loop stability. A simulation model was constructed in MATLAB/Simulink to validate the effectiveness of the proposed control strategy. The simulation results demonstrate: Full soft-switching operation of power switches (ZVS turn-on and ZCS turn-off), significantly reducing switching losses; Fast dynamic response with output voltage capable of rapid rise within 100 μs. High steady-state accuracy, maintaining output voltage ripple below 1%, meeting stringent requirements for high-voltage power supplies. This research provides a viable control solution for the optimized design of high-voltage, high-power supplies, combining fast dynamic regulation with high-efficiency characteristics.