HYBRID-CONTROLLED IPOS LLC CONVERTER FOR FUEL CELL APPLICATIONS

Fuel-cell power conditioning systems require DC–DC converters to achieve high efficiency, wide-range voltage regulation, and reliable operation under significant input and load variations. To address these requirements, this paper investigates an IPOS-type secondary LLC resonant DC–DC converter and proposes a hybrid control strategy combining pulse-frequency modulation (PFM) and phase-shift modulation (PSM). In the proposed scheme, PFM is employed as the primary control method to realize wide-range voltage regulation, while a frequency-clamping with phase-shift compensation mechanism is introduced to maintain effective power control and dynamic performance when the switching frequency reaches its practical upper limit. The effectiveness of the proposed topology and control strategy is validated through MATLAB/Simulink simulations and experimental studies on a laboratory prototype. Experimental results demonstrate a peak conversion efficiency of 96.6% under rated conditions, with efficiency remaining above 96% near the rated load range. In addition, the maximum output voltage deviation between two IPOS phases is limited to 1.9% under full-load operation, and fast, stable input-current tracking is achieved under step reference changes from 20 A to 80 A without noticeable overshoot. These results confirm that the proposed converter and hybrid control strategy are well suited for high-efficiency, wide-range fuel-cell energy conversion applications.