Digital Hybrid Current Mode Control with Asymmetric Slope Compensation for Three-Level Flying Capacitor Buck Converter

Abstract

Due to high effective frequency and reduced voltage stress on the switching devices, the three level flying capacitor (3LFC) buck converter has potential to provide better efficiency and higher power density as compared to the traditional buck converter. However, the control implementation is challenging as a result of flying capacitor instability issue. In this paper, the digital hybrid current mode (HCM) control method which combines the average and peak current mode control techniques is modified and implemented to 3LFC buck converter. Flying capacitor voltage balancing is achieved by adjusting the slope compensation of the two switching pairs asymmetrically. The proposed asymmetric slope compensation technique for digital HCM control method is verified in simulations and experimentally with an ARM-based mixed-signal microcontroller on a 40 V input 13 V / 6 A output prototype.