μ-synthesis of a robust voltage controller for a buck-boost converter

This paper proposes the structured singular value (μ) 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 component 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, μ-analysis is used to evaluate the robustness of a conventional PI voltage regulator with respect to the modeled perturbations. Finally, the approximated μ-synthesis procedure known as D-K iteration is used to design a regulator ensuring robust performance. Simulated results are presented, describing the small and large signal behaviour of a reduced-order approximation of the μ-synthesised controller.