Robust controller design for a parallel resonant converter using mu-synthesis

DC-to-dc resonant converters have been the object of much attention lately, These converters have the potential to provide high-performance conversion without some of the problems associated with classical pulse-width modulation (PWM)-based converters, thus allowing for smaller, lighter power supplies, However, in order to achieve this, a suitable control circuit, capable of maintaining the desired output voltage under different operating conditions, is required, In the past, small signal models obtained around the nominal operating points were used 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 either load or components variations, and thus could lead to instability in the face of component or load changes, Moreover, the 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 mu-synthesis to design a robust controller for a conventional parallel resonant converter, In addition to guaranteeing stability for a wide range of load conditions, the proposed controller rejects disturbances at the converter input while keeping the control input and the settling time within values compatible with a practical implementation, These results are validated by means of detailed nonlinear circuit simulations obtained using P-spice.