Fixed-Frequency Boundary Control of Buck Converter With Second-Order Switching Surface

This paper presents a fixed-frequency boundary control of buck converters. The method is based on integrating the concept of variable hysteresis into the boundary control technique with second-order switching surface. The switching frequency is maintained constant over a wide range of supply voltages and output loads. The method is based on using a frequency-to-voltage converter and comparing its output voltage with a reference voltage to control the width of the hysteresis in the boundary controller. It also combines the advantages of the boundary control that the converter can reach the steady state in two switching actions after large-signal disturbances. The basic operating principles, stability analysis, and design procedures will be given. The proposed control method has been successfully applied to control a 140 W, 24 V/12 V buck converter. The steady-state characteristics, including the switching frequency and output voltage ripple, at different input voltages and output loads with and without the proposed control method have been compared. The system responses under large-signal supply voltage and load disturbances will be discussed.