A generalized control scheme for automatic resonant frequency tracking

Abstract

This paper presents a generalized control scheme for automatic resonant frequency tracking (ARFT) in resonant converters. This technique monitors either phase or gain relationship of a state variable pair in the resonant tank to detect frequency drift. Considering an arbitrary n-element tank, the plant model is derived for a realistic frequency ramp caused by slowly varying ambient conditions. A generic procedure is presented not only to choose the most appropriate variable pairs for phase and gain comparison individually but also to make the final choice (phase/gain) of the ARFT approach. This method is applied to a parallel LLC converter to conclusively decide the most accurate ARFT strategy and the corresponding variable pair. Experimental results for steady-state and transient operations are showcased to validate the accuracy of the proposed scheme.