Convert unconstrained MPC controller to zero/pole/gain form
sys = zpk(MPCobj)
The zpk function computes the zero-pole-gain form of the linear
controller ss(MPCobj) as an LTI system in zpk
form corresponding to the MPC controller when the constraints are not active. The
purpose is to use the linear equivalent control in Control System Toolbox™ software for sensitivity and other linear analysis.