Design of Sampled-Data Control Systems with One Memoryless, Time-Invariant Nonlinearity using QFT Technique

In this paper, we examine the controller design for sampled-data systems containing one memoryless, time-invariant nonlinearity within the plant. The linear part of the plant is subjected to large parameter variations. By using Kochenburger´s describing function analysis for the nonlinear part, modified templates of the plant at a set of selected frequency points can be constructed on the Nichols chart. The quantitative feedback theory (QFT) is then used to design the robust controllers. Two examples with saturation and backlash types of nonlinearity are given to demonstrate the effectiveness of this approach.