  The main objective of tracking control is to steer the tracking error, that
is the difference between the reference and the output, to zero while the
plant's operation limits are satisfied. This requires that some assumptions on
the evolution of the future values of the reference must be taken into account.
Typically a simple evolution of the reference is considered, such as step,
ramp, or parabolic reference signals. It is important to notice that the
tracking problem considers possible variations in the reference to be tracked,
such as steps or slope variations of the ramps. Then the tracking control
problem is inherently uncertain, since the reference may differ from what is
expected. If the value of the reference is changed, then there is no guarantee
that the feasibility and stability properties of the resulting control law
hold. This report presents the MPC for tracking (MPCT) approach, which ensures
recursive feasibility and asymptotic stability of the setpoint when the value
of the reference is changed.
