Windup prevention in systems with input and output constraints

The prevention of windup due to a saturation of the input signal can be regarded as a solved problem. The results concerning the prevention of windup in the presence of output constraints are not so numerous and they only solve special aspects. Lately a new solution to the prevention of windup in the presence of output saturation has been presented. It uses a two degrees of freedom control structure to obtain a robust tracking of persistent reference signals and a robust rejection of persistent disturbances also in the case of sensor saturation. The amplitudes of the control signals generated by the new scheme can, however, become quite large so that it is of interest to investigate the prevention of windup in the simultaneous presence of input and output saturations. The results presented here must be regarded as a first engineering approach to the prevention of windup in the joint presence of input and output saturation, because rigorous mathematical proofs for the stability of the new scheme are not available to date. An example demonstrates the application of the new approach and the results achievable.