Suboptimal design of intentionally nonlinear controllers

A method of designing nonlinear controls for stationary plants is presented in the paper. The objective of the design is to produce soft-saturation-type constraints on certain state variables, such as velocity or acceleration. This is accomplished by formulating the problem as an optimization of a nonquadratic performance index. A sequence of suboptimal controls is then obtained. Although this sequence converges to the exact optimum solution, the procedure is stopped when the complexity of the resulting non-linear controller exceeds the design considerations of cost, size, and/or reliability. Experimental results of an actual design clearly indicate the desired velocity saturation effects.