Digital DCM Detection and Mixed Conduction Mode Control for Boost PFC Converters

This paper presents a novel mixed conduction mode (MCM) digital controller with a digital signal processor (DSP)-based discontinuous conduction mode (DCM) detection technique to realize total harmonic distortion (THD) and power factor improvements in boost power factor correction (PFC) converters operating in both continuous conduction mode (CCM) and DCM during a single ac line half-cycle. By using the integrated comparators found on many DSPs, simplification and cost-reductions over existing DCM and zero-current detection methods are made possible. Additionally, performance improvements over a conventional CCM digital control technique are possible with simple software modification, and can be extended to existing boost PFC converter designs provided a compatible DSP is present. At an output power of 98 W, an experimental 650 W boost PFC converter operating in the MCM controlled by a TMS320F28035 provides a THD reduction of 40.2% and power factor improvement of 1.5% over a conventional digital controller.