Abstract—A higher order sliding mode control with Self-tuni-
ng Law algorithm is proposed for a class of uncertain nonlinear
systems. This problem can be viewed as the finite time stabiliza-
tion of a higher order dynamic system with unknown but
bounded system uncertainties. An adaptation tuning approach
without high frequency switching is developed based on
geometric homogeneity and sliding mode control. The stability
of proposed procedure is proven by using the Lyapunov theory
and guarantees robustness against uncertainties. The upper
bounds of uncertainties are not required to be known in advance.
An illustrative example demonstrates the advantages of the
strategy.
I. INTRODUCTION
OBUSTNESS of a control system is very important bec-
ause various uncertainties exist in practical applications.
Among various design approaches, sliding mode control
(SMC) is a robust technique to control nonlinear systems
operating under uncertainty conditions. It has been a topic of
great interest in control theory with applications wide [1-5].
The main attractive features of the SMC are: 1) the SMC is
one of the control systems with a simple structure; 2) the
sliding motion is guaranteed to be insensitive to bounded
parametric and functional uncertainties. SMC has been well
established as a general design tool for robust control.
However, it is also well known that traditional SMC
technique may have the shortcoming of chattering
phenomenon in practice [6,7]. A number of methods have
been proposed to reliably prevent chattering. One of them is
replacing the “signum” function with a boundary layer
function or an approximated signum function [8]. Although
the transient performance is still guaranteed, asymptotic
stability and finite reaching time are lost [9], and poor
steady-state tracking error may result. And others such as
observer-based solution [10].
To overcome this problem, a new approach called “higher
order sliding mode (HOSM)” has been recently proposed
[11-13]. Keeping the main advantages of the standard sliding
mode control, the chattering effect is eliminated and higher
This work was supported in part by NSFC Grant 60574055, Specialized
Research Fund for Doctoral Program of Higher Education grant
20050056037, and Tianjin Science and Technology Keystone Project grant
06YFGZGX01700
Qun Zong is with College of Electric and Automation Engineering, Tianjin
University, Tianjin 300072, China.
Zhanshan Zhao is with College of Electric and Automation Engineering,
Tianjin University, Tianjin 300072, China. (corresponding author e-mail:
zhzhsh127@163.com).
Liqian Dou is with College of Electric and Automation Engineering, Tianjin
University, Tianjin 300072, China.
order precision is provided. As a special case of HOSM
methods, many papers in the case of second order sliding
mode algorithms are proposed in[5], [14-16]. These
algorithms are characterized by a finite-time convergence.
Arbitrary-order sliding controllers for single input single
output systems (SISO) with finite time convergence have
been recently proposed in [17-19]. However, the convergence
rate cannot be arbitrarily selected. An interesting HOSM
based on integral SMC are proposed in [20]. The advantages
of this method are the robustness of the system during the
entire response. However, there are two drawbacks in this
approach: 1) Complex off-line computations are needed
before starting the control action. 2) The knowledge of the
upper bound of the system uncertainties is hard accurately
known.
The approach is modified in this paper, so that a continuous
feedback is produced combining the robustness of high-order
sliding modes and finite-time stabilization by continuous
control. The aim is to deal with unknown but bounded system
uncertainties. The upper bounds of uncertainties are not
required to be known in advance. Tracking performance is
guaranteed. System robustness, as well as stability, is proven
by using the Lyapunov theory.
The outline of this paper is as follows. Section 1 states the
problem and assumptions. In Section 2, the proposed higher
order SMC is derived. In Section 3, simulations for example
demonstrate the efficiency and the advantages of the
proposed algorithm and Section 4 concludes the paper.
II. PROBLEM
FORMULATION
Let us consider a single input single output systems (SISO)
represented by the mode
() ()
()
fx gxu
yx
σ
+
=
(1)
where
n
R∈ , uR
and ()
are the state variable, the
control input and measured smooth output function
respectively.
()
x and ()
x are uncertain smooth functions.
y
is a smooth measurable output vector. The uncertainties
on
()
x and ()
x which due to parameter variations,
unmodeled dynamics or external disturbances do not satisfy
the well-known matching condition. Assume that:
Assumption 1. The relative degree vector r of system (1)
with respect to
(,)
t
is constant and known, and the
associated zero dynamics are stable.
Higher Order Adaptive Sliding Mode Control
for a Class of SISO Systems
Qun Zong, Member IEEE, Zhanshan Zhao, Liqian Dou
Joint 48th IEEE Conference on Decision and Control and
28th Chinese Control Conference
Shanghai, P.R. China, December 16-18, 2009
FrB12.6
978-1-4244-3872-3/09/$25.00 ©2009 IEEE 7759