A comparative study of state-space controllers with offset-free reference tracking

Steady-state control error occurs in case of unmeasured disturbances or disagreement between the model and the actual behaviour of the system because, state-space controllers do not have integral character. This problem (offset-free reference tracking) of state-space controllers has been observed in both theoretical and application areas (industrial MPC Implementation IDCOM, DMC, and QDMC IDCOM-M) for long time. The common solution is based on the model of the controlled system which is extended with the disturbance model. The article describes a simple approach to implement a system based on standard state-space controller with state vector estimation with additional parallel I-controller. Approach involving the I-controller in the process model of the controlled system is considered as another variant of predictive controller. The proposed solution with four variants of state-space controllers are demonstrated by simulation of MIMO system with three inputs and two.