Voltage mode SMC of DC-DC buck converters

This paper presents an output-feedback continuous SMC with integral action for voltage regulation of a buck DC-DC converter in continuous-conduction mode (CCM). The averaged state-space model is first transformed to normal form, with the new states being the output and its derivative. A continuous state-feedback SMC with “conditional integral action”, that is active only inside the boundary layer, is designed, and the output derivative approximated using a high-gain observer (HGO). For this relative degree two system, the design we present is simply a saturated PID control with anti-windup. Even without the conditional integrator, i.e., saturated PD control, the voltage error can be practically stabilized, while asymptotic stability is achieved with integral (i.e. PID) control. Moreover, the use of the “conditional integrator” guarantees that the design retains both the transient performance as well as asymptotic error regulation of ideal SMC. A baseline LQR design is used to design the sliding surface parameters, and the design is experimentally verified using the Power Pole board designed by Hirel Systems and the University of Minessota configured as a buck converter, the dSPACE DS1104 board used for the control implementation. The controller's performance is compared against the baseline LQR PID design (without windup compensation). Simulation and experimental results show that the proposed control method results in satisfactory voltage regulation performance under widely varying input voltage variations and load changes.