Nonlinear lead-lag controller design with experimental verification

This work presents a nonlinear lead-lag controller synthesis for a nonlinear unstable system. Nonlinear lead-lag controller is design based on describing function technique. Unstable system will first be stabilized by designing a stabilizing controller. System will then be excited by known sinusoidal input to generate describing function model of the stabilized closed-loop system. Linear lead-lag controller will be designed based on this describing model followed by optimization of linear lead-lag controller over various operating regime. Inverse describing function will be carried out to invert controller gains at various operating regime. Nonlinear controller will be experimentally verified and compare with linear controller.