Analysis and experimentation of nonlinear adaptive controllers for the series resonant converter

It is the purpose of this paper to explore the problem of regulating the output voltage of a de-to-de series resonant converter (SRC), These converters have highly nonlinear dynamics fed by a bipolar square signal generator whose commuting frequency is the only accessible control variable in the control architecture that we study, Therefore, we are confronted with the problem of controlling a nonlinear switched system by means of a modulating frequency signal, Two more complications that make this problem more challenging are that the full state is typically not available for measurement, and that the output load, usually represented by a resistance, is unknown. We show here that-for constant control input-SRC's have a unique globally attractive periodic orbit, which motivates us to consider a first harmonic approximation of the system, We then prove that this reduced model consists of a known static nonlinearity in cascade with a first order system with unknown parameters, for which adaptive output feedback solutions can be derived. We propose two different schemes, first a passivity-based controller which, as usual in these schemes, achieves asymptotically the inversion of the nonlinearity, We prove that, under some practically reasonable considerations, this control law reduces to the dissipative controller recently proposed hg Stankovic et al, The second scheme directly inverts the static nonlinearity and applies standard adaptive techniques to the resulting linear system, The three controllers are implemented in an experimental setup and the results are presented as a comparative study.