AAS 99-149

H_inf Controller Design with Nonlinear Actuator

Shahzad Khaligh

Raytheon Systems Company, El Segundo, CA


This paper emphasizes the application of H_inf theory to a class of nonlinear system represented by their describing functions. The model comprises two limiters and an integrator representing a saturating actuator cascaded in series with a linear plant. The proposed technique linearizes the nonlinearity applying the Sinusoidal Input Describing Function (SIDF) technique and then utilizes the H_inf theory to obtain the stabilizing controller. The describing function of the actuator appears to be a low pass filter function of both amplitude and frequency of the input signal. Further, H_inf technique is chosen because it minimizes the worst possible error during operation of the system. This technique, in general, can be used for the class of systems that satisfy the describing function technique in conjunction with the H_inf technique.