<p>A resonance suppression strategy for bidirectional LLC resonant converters is proposed in this paper to address the non-monotonic voltage gain problem inherent in conventional phase-shift modulation (PSM). The mechanism of parasitic resonance between the transformer magnetizing inductance and the parasitic capacitance of synchronous rectifiers (SRs) is mathematically investigated through time-domain analysis. The analysis reveals that this resonance distorts the voltage gain curve during the freewheeling interval, leading to control instability. To resolve this, the proposed topology utilizes a secondary-side auxiliary bidirectional switch. By actively clamping the secondary voltage to zero exclusively during the resonance period, the proposed control strategy effectively eliminates parasitic oscillation and restores a monotonic voltage gain curve across the entire phase-shift range. Experimental results verify that the proposed method ensures stable constant voltage control under light-load conditions and achieves higher efficiency than the conventional PSM operation.</p>