• • The HGRD-LLC converter achieves a maximum voltage gain of 8.0 with a peak efficiency of 97.2% at 960 W output power, enabling a 60–480 V output range within a narrow switching frequency band of 90–190 kHz. This eliminates the need for extreme frequency modulation that degrades efficiency in conventional LLC designs, directly benefiting battery charging systems for electric vehicles and renewable energy storage where wide voltage compliance is mandatory.
• • Five distinct operating modes yield resonant-frequency gain ratios of 1:2:4:6:8, providing discrete gain steps that cover a 8× output voltage span without sacrificing zero-voltage switching (ZVS) across the full load range. This multi-modal approach reduces switching losses by maintaining soft-switching conditions, a critical factor for thermal management in high-power-density converters.
• • The converter attains a peak efficiency of 97.2%, exceeding the 95.0–96.7% range reported for prior multi-mode LLC topologies (references [2], [12], [14], [18], [19]) by up to 2.2 percentage points. This efficiency gain translates to lower heat dissipation and higher reliability in continuous-duty renewable energy charging applications.
• • Experimental validation on a 960 W prototype confirms stable operation across the entire 60–480 V output range, with ZVS constraints satisfied under all five modes. The 8.0 maximum gain is 33% higher than the 6.0 gain of the closest prior dual-resonator topology (reference [13]), while maintaining a simpler control scheme than asymmetric resonant tank designs.