A Comparative Study of Three PFM/PWM Hybrid Modulated Control Strategies for Single‐Stage Soft‐Switching AC–DC Converter

ABSTRACT Single‐stage interleaved Boost‐LLC AC‐DC converters offer advantages such as high power capability, low cost, and reduced input current ripple. However, they typically encounter high bus voltages under universal input conditions when operating with pulse frequency modulation (PFM). To address this issue, three hybrid PFM/pulse width modulation (PWM) control strategies are proposed: output voltage feedback (Strategy I), bus voltage proportional feedforward (Strategy II), and dual‐loop feedback control (Strategy III). Corresponding optimal parameter designs are also conducted based on the principle of power balance. With the aforementioned control strategies and their optimized designs implemented, the bus voltage is effectively maintained within a reasonable range throughout the full input voltage range. Meanwhile, soft switching of the primary switches and secondary rectifier diodes is achieved. Experimental validation on a 300‐W prototype (85–265 V input, 48 V/6.25 A output) demonstrates that the proposed solutions achieve a bus voltage below 550 V, power factor (PF) above 0.98, and peak efficiency exceeding 92.8%. Furthermore, the performance differences among the three strategies are discussed and analyzed in detail.