A digital closed-loop control strategy for maintaining the 180° phase shift of an interleaved BCM boost converter for PFC applications

Abstract

This paper focuses on the design and implementation of a digital closed-loop control scheme to maintain the 180° phase shift of an interleaved Boundary-Conduction-Mode (BCM) boost converter. The closed-loop control scheme operates by differentially modulating the on-time of each phase to adjust the phase-shift. Zero-Current-Detection (ZCD) circuits control the turn-on instant for the MOSFET of each boost converter. The ZCD circuit is designed so that the MOSFET of each phase turns on after the energy stored in the output capacitance of the MOSFET has discharged back into the boost converter's input capacitor, resulting in reduced converter power losses. This is known as valley switching. The main advantage of using a closed-loop control scheme is that the ZCD circuitry always controls the turn-off instance of the MOSFET for each phase of the boost converter. Therefore BCM operation and valley switching is always ensured, and neither phase of the converter can enter Continuous-Conduction Mode (CCM), which can lead to high inductor currents and damage the converter. A digital control scheme was implemented using a TMS320F28069 microcontroller and experimental results are demonstrated on a 600 W prototype interleaved BCM converter.