Modeling and controller design of a bidirectional resonant converter battery charger

In this manuscript, an optimized and detailed controller design methodology is proposed for a bidirectional CLLLC-type resonant converter for battery charging application. While this topology of resonant converters offers a number of advantages, including soft-switching in all switches, and very high power-stage efficiency, the dynamic characteristics of this converter change significantly as the battery charges or discharges which imposes difficulty in closed loop controller design. High-Q resonant peaking in the open-loop bode-plots of this converter is main cause of system instability. In this paper, a controller design methodology is proposed that will guarantee a stable operation during the entire operating frequency range in both battery charging mode (BCM) and regeneration mode (RM). To validate the proposed controller design methodology, the output current and voltage loop controllers are designed for a 3.5 kW converter. The step response showed a stable system thus validating the proposed controller design methodology.