Robust Hysteresis Control for Full-Bridge LLC Resonant Converters Using an Isolated Measurement Scheme

Inhalt:
The LLC resonant converter is the preferred topology for many application areas. Outstanding efficiency and power density can be achieved with such an LLC topology, yet it suffers from its poor dynamic behavior when switching frequency control is used. In this paper, a hysteresis control technique is proposed that generates the gate signals based on an isolated current sensor installed in the resonant tank. Unlike switching frequency control, the proposed hysteresis control is robust against parameter deviations of the resonant tank, which lie within a realistic range of 10%. Simulation and experimental results of a cascaded current-mode control show a settling time of 0.3 ms with no overshoot. Practical issues and how they were managed are described in detail.