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 power 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 power converter dynamics. At first, a suitable linear power 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