273 Dipti D. Bhawarkar, A.A. Godbole, A. A. Apte International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 6, Issue 7 July 2017 Uncertainty and Disturbance Estimator Based Sliding Mode Control of 2 nd Order System Dipti D. Bhawarkar, Post graduate student Department of Electrical Engineering All India Shri Shivaji Memorial society College of Engineering Pune A.A. Godbole, Professor Department of Electrical Engineering All India Shri Shivaji Memorial society College of Engineering Pune A.A. Apte Assistant Professor Department of Electrical Engineering All India Shri Shivaji Memorial society College of Engineering Pune ABSTRACT This work deals with the issue of control of an uncertain system by using uncertainty and disturbance estimator (UDE). A typical second order system is considered for illustration. The results may be extended to a real life application. UDE is used to estimate the uncertainty and the control law ensures robust performance. The proposed technique is validated through simulation in MATLAB. The effectiveness of UDE based control is shown for different types of disturbances. Keywords Uncertainty and disturbance estimator (UDE), Robust control, Disturbance estimation. I. INTRODUCTION In most of the practical systems uncertainties are always present. Uncertainty includes unmodeled dynamics and external disturbances. Disturbance signals and dynamic perturbations are two varieties of uncertainties. Input and output disturbance, sensor noise and actuator noise, etc are included in disturbance signals. A mathematical model of any real system is always just an approximation of the real physical system. The difference between actual and mathematical model includes unmodeled dynamics (usually high-frequency), neglected nonlinearities in the modeling, effects of reduced-order models, and system parameter variations due to environmental changes. The stability and performance of a control system may adversely be affected due to these uncertainties. With growing inerest in high-precision control, utilization of disturbance rejection technique is generally required in the controller design. During the past decades, Time delay control (TDC) [3] is used for system with unknown dynamics. It is based on the assumption that a continuous signal remains unchanged during a small enough period, the past observation of uncertainties and disturbances is used to modify the control action directly. But it has some limitations such as, presence of oscillations in control system and due to delay system becomes unstable. To overcome this issue recently an uncertainty and disturbance estimator (UDE)-based control method was proposed in [1]. It has good capability of uncertainty and disturbance rejection and reference tracking. UDE is considered as replacement of time delay control (TDC). UDE-based control method is based on assumption that a continuous signal can be approximated when it passes through an appropriate filter. Notable feature of UDE is that it is not affected by modelling inaccuracies and does not require apriori knowledge of disturbances, except the information about the bandwidth, during the design process (but needed for the analysis of stability). Disturbances can be external disturbances or internal parameter variations. UDE based control law can effectively tackle all such uncertainties. UDE technique is successfully applied to diverse system like non- affine nonlinear system [4], robust input-output linearization [5], robot manipulator [7], voltage control of DC-DC power converter [8], robust control of electric motor drive [9], control of Unmanned Aerial vehicles