Control Architecture for LLC Resonant Converters With High Input Disturbance Rejection Capability Using Output Diode Current

The controller design for the LLC resonant dc-dc converter is challenging due to the large number of poles whose locations vary with operating conditions. A controller's ability to reject input disturbance is required to reduce the input filter size, increase power density, and improve reliability. This article presents a control architecture utilizing the output diode current measurement that reduces the control-to-output transfer function for an LLC resonant converter to first order and provides a high degree of input voltage disturbance rejection with a marginal increase in implementation complexity. The increased disturbance rejection allows the reduction of the bulky dc-link capacitance at the output of the PFC in electric vehicle battery charging application. A small-signal model for the proposed control variable is derived, and loop analysis using a Bode plot highlights the advantages of the proposed method. Simulation results verify the proposed architecture's high disturbance rejection capabilities. The proposed control architecture is evaluated using a 1-kW front-end power factor correction (PFC) rectifier followed by an LLC resonant converter with an intermediate dc-link voltage of 400 V. The proposed approach achieves a 4.5x reduction in the energy storage requirement in the intermediate dc-link compared to direct frequency control without sacrificing output voltage ripple and efficiency of the LLC stage and total harmonic distortion at the input of the PFC stage.