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 ou tput voltage of a de-to-de series resonant converter (SRC), These converter s have highly nonlinear dynamics fed by a bipolar square signal generator w hose commuting frequency is the only accessible control variable in the con trol architecture that we study, Therefore, we are confronted with the prob lem of controlling a nonlinear switched system by means of a modulating fre quency signal, Two more complications that make this problem more challengi ng are that the full state is typically not available for measurement, and that the output load, usually represented by a resistance, is unknown. We s how here that-for constant control input-SRC's have a unique globally attra ctive periodic orbit, which motivates us to consider a first harmonic appro ximation of the system, We then prove that this reduced model consists of a known static nonlinearity in cascade with a first order system with unknow n 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 no nlinearity, 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 nonlinear ity and applies standard adaptive techniques to the resulting linear system , The three controllers are implemented in an experimental setup and the re sults are presented as a comparative study.