Robust control design for a parallel resonant converter using μ-synthesis

Because of their reduced switching loss, DC-to-DC resonant converters have been widely used in the design of small size and light weight power supplies. The steady state and dynamic behaviors of the conventional series and parallel resonant converters have been thoroughly analyzed, as well as the small signal models around given nominal operating points that have been obtained. These models have been used in the past to design controllers to keep the output voltage constant in the presence of input perturbations. However, these controllers did not take into account components and load variations, which could lead to instability problems. Furthermore, the prediction of frequency range for stability was done in a posteriori, either experimentally or by a trial-and-error approach. In this paper, the authors use μ-synthesis to design a robust controller for the second-order conventional parallel resonant converter. In addition to robust stability under different load conditions, the design objectives also include rejection of disturbances at the converter input while keeping the control input and settling time within values compatible with practical implementation