Design of a robust voltage controller for a buck-boost converter using mu-synthesis

This paper proposes the structured singular value (mu) approach to the problem of designing an output voltage regulator for a Buck-Boost converter with current-mode control. This approach allows a quantitative description of the effects of reactive components’ tolerances and operating point variations, which strongly affect the converter dynamics. At first, a suitable linear converter model is derived, whose parameter variations are described in terms of perturbations of the linear fractional transformation (LFT) class. Then, mu-analysis is used to evaluate the robustness of a conventional PI voltage regulator with respect to the modeled perturbations. Finally, the approximate mu-synthesis procedure known as D-K iteration is used to design a robustly performing regulator. Simulation results are presented, describing the small and large signal behavior of a reduced order approximation of the mu-synthesized controller.