Modelling and Design of a Droop-Based Cascaded Controller for LLC Resonant Converter

This paper proposes a digital cascaded control strategy for integrating an LLC resonant converter into a DC Microgrid. The designed control scheme is particularly suitable for battery storage applications in discharging mode. The outer loop of the cascaded controller is a droop controller which provides the reference current according to the DC grid voltage. The inner loop regulates the current according to the reference by pulse frequency modulation (PFM). A seventh-order state-space model based on first harmonic approximation (FHA) and extended describing function (EDF) was built to assist the controller design. The proposed control scheme is validated for both buck and boost operation mode in the PLECS simulation environment.