It is well known that the structural phase transitions in ferroelectri
c materials are connected with strong nonlinear properties. Therefore
a series resonance circuit consisting of a linear coil and a nonlinear
capacitor that is made of ferroelectric material can show all feature
s of nonlinear dynamical systems: period-doubling, hysteresis and dete
rministic chaotic behavior. In the chaotic region it is necessary to u
se a method of controlling chaotic systems to snitch into periodic beh
avior for fitting to a model equation. The used control method perturb
ates the system only in a very small range. The advantage of the metho
d is that one can get all needed parameters of control only by system
measurements without using any kind of model.