Grouped Valley Switching Control to Optimize Efficiency and THD for DCM Boost PFC Converters

In discontinuous conduction mode (DCM) boost converters, the switching-node voltage oscillates after the inductor current reaches zero, leading to fluctuating power loss. To investigate this, a circulating energy model is first proposed. Accurate power loss is analyzed with consideration of oscillation damping effect, reverse conduction of power switch, and nonlinear capacitance effect. Analysis shows that the loss can be minimized when the switch is turned on at specific switching-node voltage valleys. Therefore, to minimize the power loss, a GVS control is proposed to count the valleys and turn on the switch at the optimal valley. However, dynamic changes in valleys will cause frequency hopping, resulting in degraded total harmonic distortion (THD) in input current. To address this issue, the GVS controller turns on the switch at constant valleys in a half-line cycle, while adaptively calculating the on -time with online tracked oscillation duration. For efficiency improvement, the optimal valleys are grouped and tuned based on a comprehensive power loss analysis. Experimental results validate the effectiveness of the proposed control. Compared with conventional variable on -time (VoT) controls, the proposed control improves an average efficiency of 0.4% across the entire power range under 110/220 VAC input. The THD is below 3.1% at 250W rated power.