The paper presents an approach for achieving sec-the system is not abrupt and chattering is avoided. The control ond order sliding mode in continuous-time systems. The existing is so structured that finite reaching time is guaranteed. methods of second order sliding mode control are based on relayThe terminology "second order sliding mode" comes from control in the derivative of the input. Such a control, though the fact that using this technique, both the sliding function o continuous, is not smooth in close proximity of the sliding surface. and it that sl conuous funct i nbt The proposed control algorithm achieves second order sliding and its derivative & are continuous functions of time and both mode by using a smooth control signal which avoids the use of would become equivalently equal to zero after a finite amount a relay in the control. of time i.e., or C1. This is in contrast with the traditional or first order sliding mode control where &r is discontinuous. The aforementioned control strategy, though it guarantees I. INTRODUCTION smoothness in the system and avoids chattering, does not proSliding mode control[.], [2] is a control technique in which duce a control that is smooth (or continuously differentiable) * due to the discontinuity in it. Thus, the control u C C°. the closed loop system is rendered some desirable properties In theiscpaper,iwep o aTsimpe control aot to by confining the system to a pre-specified sub-manifold of the achieve seprosldn . mo e control syesithout state space by application of an appropriate control.Traditionally, sliding mode control methods have been de-the use of a relay in the control. Further, the proposed signed for systems of relative degree of one. Most of these algorithm guarantees a continuously differentiable or smooth control techniques are relay based techniques in which the control. The algorithm is illustrated for systems with relative degree of one or two with respect to the sliding function control switches between two structures based on the sign i.e, systems wherein u appears in the expression of & and of the sliding function[3], [4]. This type of control structure ' e' causes a serious problem during practical implementation. In practice, the actuators cannot switch at an infinite frequency along the sliding surface, as demanded by the theory of the relay based sliding mode control algorithms. This leads to Consider the n-th order system high frequency finite amplitude oscillations of the system f=() + g()u(1) representative point and the control signal, around the sliding surface. This phenomenon, termed as chattering, is undesirable g( ) > 0, Vx as it may excite unmodeled dynamics in the system and may and the sliding function o(X() with or being a continuously also lead to fatigue and actuator failure. differentiable function of x such that the sliding surface or = 0Many researchers have worked on a solution to this problem. constitutes a stable sub-manifold of the state space.
A boundary layer based technique[5], [6], [7] was initiallyThe aim is to d...