Nonlinear control of buck-boost AC/DC converters: output voltage regulation & power factor correction

We are considering the problem of controlling AC/DC switched power converters of the buck-boost type. The control objectives are twofold: (i) regulating the output voltage to a desired reference value, (ii) assuring a unitary power factor by enforcing the voltage and the current delivered by the electric network to be in phase. The considered problem is dealt by designing a cascade-structure nonlinear controller. The inner loop of the latter regulates the active power provided by the network; it is built-up using the backstepping design approach. The outer loop regulates the converter squared output voltage using a PI regulator; such a simple solution is made possible using adequate model transformations and loop operation mode separation. The controller thus obtained is shown to achieve the control objectives and proves to be robust with respect to load changes.