Nonlinear adaptive feedforward in a two-degrees-of-freedom controller

An adaptive feedforward steady-state gain in a two-degrees-of-freedom controller for a nonlinear SISO plant is investigated. The examination of a less complicated structure gives hints to how an update law may be constructed in the nonlinear case. Stability is shown in the simpler case for a update law based on an estimation error using projection, and simulations show that filtering may lead to improved performance. By using an adaptive feedforward function inspired by gain-scheduling techniques, a simulation example for the nonlinear structure is also shown. The conclusions are that the scheme has potential but that more research is needed for the nonlinear setup.