Identification for Nonlinear Feedback Limit-Cycle Systems Using Harmonic Balance Methods

This paper proposes a method for identifying inherently closed-loop systems with nonlinear feedback by using an identification technique for Hammerstein systems, when only one measurement variable is available in the loop. The method is based on harmonic balance and representing the linear transfer function and the nonlinearity by basis functions. It is also shown that a multiplicative periodic reference signal enhances the identifiability of the system by adding sinusoids with interweaving frequencies to the original unforced case