Design of A2DOF controller for LLC current-resonant DC-DC converters with delay time

When a pulse frequency and a load resistance of LLC current-resonant converters are changed, the static and dynamic characteristics are varied greatly. This is the prime reason why controlling LLC converters is difficult. In particular, the influence of delay time isn´t negligible at sudden load change. In this paper, an A2DOF (Approximate 2-Degree-Of Freedom) controller with considering the input delay time is proposed to suppress the output voltage variation at the load sudden change and improve the settleing time of output voltage in dynamic load response. Experimental studies using a micro-processor for the controller demonstrate that this type of digital controller is effective to suppress the variation and influences of input delay time.