Optimal PID design for voltage mode control of DC-DC buck converters

This paper presents an LQR-based output-feedback integral control design 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 state-feedback LQR design is then designed, following which the derivative term in the control design is approximated using a high-gain observer (HGO). Even without an integrator, i.e., PD control, the voltage error can be practically stabilized, while asymptotic stability is achieved with integral (i.e. PID) control. 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 a traditional PID design (based on desired gain-crossover frequency and phase-margin) that is implemented in analog hardware. 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.