Abstract-The paper presents the design of sliding modeThe purpose of this paper is to show that sliding mode control for the higher order system via reduced order model. control design can also be done via reduced order model. It It has been shown that a sliding mode control designed for the will be also shown that if a sliding mode control is designed reduced order model gives similar performance for the higher .. r order system. The method has been illustrated by numerical from the reduced order model and lf appled to the higher examples.order system by aggregation, it results in sliding mode motion for the high order system. Index Terms-Sliding mode control, order reduction, con-The brief outline of this paper is as follows: In Section troller simplification II, a brief review on discrete-time sliding mode control is presented. The main result of this paper is included in Section III followed by the illustrative example and simulation results in Section IV. Conclusions are drawn in Section V advantage of the sliding mode control over the other control C strategies is that when the system is confined to the sliding x(k + 1) = TX(k) + FTU(k)(1) manifold, popularly termed as the sliding surface, the system y(k) = Cx(k) is robust, insensitive to parameter uncertainties and external disturbance. The advent of digital computers and samplers in Let, the system be transformed into normal form through a control implementation has broadened the study of discrete-transformation N(k) Tx(k), with the dynamics time systems and the design of control systems in discrete-time. Recently a few researchers have worked on discrete-timesliding mode controller design [4], [5]. In discrete-time sliding mode control, the control input is A. Switching Plane Design calculated once in every sampling interval and is held constant during this period. Due to the finite sampling frequency, it Consider a sliding surface of the form xT = 0 with the may happen in discrete-time sliding mode that the system state sliding function parameter be of form trajectory is unable to move along the sliding surface. It maymove about the sliding surface, thus giving quasi siding mode motion. Regardless of other advantages, the sliding mode The procedure for sliding surface design [8] can be described controller for any system has a complexity proportional to the as follows. number of states in the system. Hence, for a high order system, The system in Eqn. (2) in normal form, when restricted on the sliding mode controller design is also more complicated. the sliding surface CT= 0, would obey the relationship Model order reduction and the reduced order modeling have received considerable attention in the literature in the last thirty years. However a very few research papers are available which where, z2(k) constitutes the last m states of Nk).deal with the controller design via reduced order model [6], Thus, the dynamics of -1 can be represented as [7].