Optimal Triple-Phase-Shift Modulation Strategy for Wide-Gain High-Efficiency Bidirectional CLLC Converter

The CLLC converter has gained significant attention in bidirectional isolated applications. However, traditional pulse frequency modulation (PFM) not only has a limited voltage regulation range but also introduces significant EMI interference, while single-phase shift (SPS) and dual-phase shift (DPS) modulation strategies can accurately regulate voltage but result in high circulating currents and difficulties in achieving zero-voltage switching (ZVS). To address these issues, a comprehensive optimal triple-phase shift (TPS) modulation strategy is proposed for the entire operating range. Where an accurate TPS mathematical model for the CLLC converter is established, and based on this model, the optimal path for the minimum current root mean square (rms) that meets the ZVS condition across the entire voltage gain range is identified. This optimal modulation strategy not only reduces the rms value of the resonant current but also extends the voltage regulation range, as validated on an 800-W experimental prototype.