REDUCTION OF AMPLITUDE DEPENDENT GAIN VARIATIONS IN CONTROL OF NON-LINEAR WIENER TYPE SYSTEMS

Amplitude dependent gain variations of the static non-linear block of a Wiener type system is a major source of instability when feedback control is applied. A linearizing feedback can be applied to reduce these variations, using the static non-linearity of an identified Wiener model. The remaining amplitude dependent loop errors are analysed in the paper. A result that quantifies the remaining relative differential loop gain error with a simple formula is given. It is explained why small prediction errors of a model identified in open loop can also be a good indication of small remaining amplitude dependent closed loop gain errors. To illustrate the discussion, linearizing feedback is applied to a highly non-linear pH-control loop.