Adaptive fast terminal SMC for input nonlinearity
Journal of Advanced Computational Intelligence and Intelligent Informatics Vol.0 No.0, 200x
Abstract: This study investigates the terminal sliding
mode (TSM) control for a class of first-order
uncertain systems with dead-zone and saturation.
First, a new adaptive TSM control law was proposed
for the single-input and single-output (SISO) systems
by employing an integral fast TSM. It achieves
rejection for both system uncertainty and input
nonlinearity. The global reaching condition of the
sliding mode is guaranteed by the Lyapunov stability
theory. The new control law possesses faster
convergence than the linear sliding mode method,
and the singularity problem of TSM is avoided. Then,
the control law was extended for tracking control of a
dynamic model of spacecraft which was a multi-input
and multi-output (MIMO) system. Finally, the
simulation results confirmed the effectiveness of the
proposed control method.
Keywords: adaptive control, terminal sliding mode
control, input nonlinearity
1. INTRODUCTION
As a robust control technique, the sliding mode control
(SMC) has been developed for a wide range of linear and
nonlinear systems [1-3]. The early studies of SMC
concentrated on the linear sliding mode (LSM) which
featured asymptotical convergence. In recent years, the
terminal sliding mode (TSM) control has received much
attention. Its major advantage is the finite-time
convergence. The TSM control has been used in many
applications, such as robots [4], spacecraft [5], and
DC-DC buck converters [6-7].
It is well known that the TSM has faster convergence
than the LSM when the system states are near the origin.
However, the convergence of TSM is slower if the
system states are far away from the origin. So, fast TSM
(FTSM) was proposed to enhance its convergence by Yu
et al. in [8]. The other drawback of TSM is singularity
problem. As a negative fractional power item arises in
the derivative of TSM, it may lead to an infinite large
control signal. Due to the limitation of practical
implementations, this is hard to be accepted. Moreover,
this may deteriorate the system stability or damage the
devices. Considering this problem, Feng, Yu, and Liu et
al. contributed to propose new forms of TSM known as
nonsingular TSM (NTSM) in [9-11]. Although the
singularity is avoided, a stagnation problem of sliding
mode arises. It means that the derivative of Lyapunov
function for the sliding mode may remain zero before the
Lyapunov function converges to zero. If this occurs, the
motion of sliding mode stagnates at some nonzero points
in the reaching phase. As a result, the system trajectory
cannot converge to the origin or the reference signal, and
the control objective will not be achieved. Note that, it is
difficult to prove that this stagnation problem does not
occur in the case that the NTSM control is cooperated
with the adaptive technique. Therefore, the adaptive
technique was combined with the TSM and FTSM
controllers in [12-14]. Thus, the control singularity
problem still existed.
Most of the TSM control research focused on the
second-order systems. For higher order systems,
Mobayen and Wu et al. studied on the recursive TSM
control which was applied to non-holonomic systems
[15,16] and hypersonic flight vehicle [17,18]. Being
different from the conventional TSM control designed
for matched uncertainty, Yang et al. proposed a novel
NTSM control approach for mismatched disturbance in
[19]. The disturbance rejection was achieved by a new
sliding manifold with disturbance observer technique.
Besides the model uncertainties and disturbances, the
input nonlinearity also makes negative effects on the
system stability and control performance. In practice, the
common input nonlinearity includes dead-zone,
saturation, and sector nonlinearity. For the sector
nonlinearity, Hsu proposed a special LSM controller
form in [20]. With this controller form, a useful lemma
was introduced to transform the irreversible nonlinear
input function to some available control parameters.
Furthermore, dead-zone was considered in [21]. With
Hsu’s method, TSM control was developed for sector
nonlinearity by Yang and Aghababa et al. in [22-24]. For
the adaptive NTSM control in [22,23], the switching gain
was directly adjusted by adaptive technique. However, it
is difficult to prove that the stagnation problem does not
occur. So the switching gain was changed to constant
gain in the extreme case that the stagnation may occur.
In [25], Hu et al. proposed a LSM controller for
systems subjected to input saturation using Hsu’s method.
The effect of input saturation was estimated by adaptive
technique. Moreover, Chen et al. designed a TSM
controller for uncertain systems with unknown
Linjie Xin
*1
, Qinglin Wang
*1
, Yuan Li
*1
, and Jinhua She
*2
*1
School of Automation, Beijing Institute of Technology, Zhongguancun Street, Haidian District, Beijing, 100081 China
E-mail: xinlinjie08@163.com; wangql@bit.edu.cn; liyuan@bit.edu.cn ()
*2
School of Engineering, Tokyo University of Technology, 1404-1 Katakura, Hachioji, Tokyo, 192-0982 Japan
E-mail: she@stf.teu.ac.jp
Adaptive fast terminal sliding mode control for a class
of uncertain systems with input nonlinearity