Contribuições ao projeto de controladores robustos a variações paramétricas aplicados a conversores conectados à rede

Abstract

This Ph.D. thesis provides contributions to the design of robust current controllers for grid-connected converters, including: i) a time-varying model to deal with the magnetic soft saturation in the filter inductors and the possible variation of the grid impedance; ii) systematic procedures to design the gains of state feedback controllers robust against magnetic soft saturation, obtained by means of linear matrix inequalities; iii) an optimization of the performance of controllers by means of pole location robust against uncertainties in the grid impedance, taking into account a trade-off between transient performance and control effort. For the design of the robust controllers, the plant is modeled in a polytopic way, in the discrete time domain, including the delay due to the digital implementation of the controller. An arbitrary number of resonant controllers are also included to ensure tracking of sinusoidal references and rejection of harmonic disturbances from the grid voltages, for instance. In the sequence, two strategies based on linear matrix inequalities (robust pole location and H2 guaranteed cost) are used to obtain robust state feedback gains. These gains are implemented in practice in a digital signal processor, leading to real-time simulation results based on hardware-in-the-loop and also on experimental results based on a prototype which exhibit high quality transient and steady state performances. The currents injected into the grid meet the requirements of the IEEE 1547 Standard, in the case of magnetic soft saturation of the filter inductors, and also in the case of uncertain and possibly time-varying grid impedances.