Robust control design for a conventional series resonant converter using μ-synthesis

Because of their reduced switching losses, DC-to-DC resonant converters have been used extensively in the design of smaller size and lighter weight power supplies. The steady state and dynamic behaviors of both the conventional series and parallel resonant converters have been thoroughly analyzed and small-signal models around given nominal operating points have been obtained. These models have been used in the past to design controllers that attempted to keep the output voltage constant in the presence of input perturbations. However, these controllers did not take into account neither load nor components variations, and this could lead to instability in the face of component or load changes. Moreover, prediction of the frequency range for stability was done a posteriori, either experimentally or by a trial and error approach. In this paper we use μ-synthesis to design a robust controller for a series resonant converter. In addition to robust stability the design objectives include rejection of disturbances at the converter input while keeping the control input and the settling time within values compatible with a practical implementation