Optimal Tuning of Resonant- and Repetitive-Based Controller for Single-Phase Buck–Boost Inverter With Unfolding Circuit

A Buck–boost inverter with unfolding circuit in a grid-connected mode has numerous advantages but suffers from nonlinear nature and zero-crossing spike, which are difficult to eliminate; it, therefore, requires an accurate control approach. This article presents an optimal tuning approach of the digital control system based on a proportional resonant and repetitive controller along with proper pulsewidth modulation block. Optimal performance consists in the minimal steady-state error and fast transient response keeping the system in the stable domain in a wide range of operation. It is achieved by a derived set of coefficients of the controller for different operation points. To tune the system, an appropriate transfer function of the plant is developed in the z-domain, taking into account nonlinearity of the system and digital delay. In advance, we present a detailed study of various discretization methods for best coincidence with the simulation and experimental results. Simulation and experimental results confirmed theoretical statements. The proposed approach allows double improvement of the total harmonic distortion of the grid current in most of the operating points.