Multirate output feedback sliding mode control of permanent magnet stepper motor using flatness property

The paper presents a method for output feedback sliding mode control for permanent magnet (PM) stepper motor which is known to be a differentially flat system. Discretization of continuous time model of the stepper motor has been carried out and linearizing outputs are selected. Discrete state variables and control inputs are obtained in terms of linearizing outputs and their higher order differences. Linearized equations for the system are thus obtained and auxiliary control is designed using reaching law approach. Then the actual control is obtained in terms of flat output and state variables. It has been shown that this can be expressed in terms of the flat output samples only. The control when applied to nonlinear system will give the same result as that of the state feedback case.