Fixed Frequency Operation in Critical Conduction Mode with Voltage-Controlled Variable Inductor

This study introduces a novel voltage-controlled variable inductor (VI) that effectively fixes the switching frequency of DC-DC converters operating in the critical conduction mode (CRM). The proposed VI addresses the limitations encountered with conventional current-controlled VIs, such as complex winding structures, control challenges, and reliance on magnetic saturation. In the proposed voltage-controlled VI, the primary-side inductance of a coupled inductor is regulated by an auxiliary voltage source on the secondary side. The validity of the proposed VI is experimentally verified using a prototype CRM boost converter with an output voltage of 400 V. Experimental results demonstrate that the switching frequency remains fixed at 100 kHz, and the main converter maintains soft switching characteristics regardless of variations in output power.