Analysis and design of a sliding-mode strategy for start-up control and voltage regulation in a buck converter

This study presents the analysis and design of a sliding-mode control of a buck converter operating in continuous conduction mode that minimises the energy during start-up and provides output voltage regulation in front of input voltage perturbations and load disturbances. A linear combination of inductor current and capacitor voltage errors with respect to their corresponding equilibrium values is analysed as a switching surface. A linear matrix inequalities (LMI)-based analysis to obtain optimum coefficients of the linear combination reveals that the best compromise between inrush current and output response rapidity is the current control given by the switching surface S(x) = i_L-I_E, where I_E is the current coordinate of the equilibrium point. This surface is proposed for start-up and for rejecting input voltage perturbations, because it is demonstrated that the current control is inherently insensitive to input voltage variations. Output voltage regulation in front of load perturbations or input voltage variations is achieved once the converter is in a steady state by modifying S(x) with the insertion of a PI-correcting network. The resulting controller is implemented analogically and employs two switching surfaces, that is, one surface for start-up and another one for output voltage regulation. The theoretical predictions are verified by means of simulation and experimental results.