Derivation of DCM/CCM Boundary and Ideal Duty-Ratio Feedforward for Three-level Boost Rectifier

This paper analyzes CCM/DCM operations of three-level boost (TLB) converter and derives ideal duty-ratios for feedforward control in power factor correction (PFC) applications. The analyses are conducted for two different TLB operation modes characterized by input voltage range. Since duty-ratio feedforward is a widely used technique to improve PFC transient responses and mitigate the burden of feedback control, accurate duty-ratio computations for all possible operation modes and conduction modes are necessary. By comparing the derived duty-ratios for CCM and DCM regions, current conduction modes of TLB can be detected in real-time and proper duty-ratio feedforward with minimum duty-ratio selection can be provided. The experimental results by a 500 W prototype of TLB PFC rectifier are provided in order to verify the effectiveness of the derivations and feedforward technique.