Page 204 - Adaptive Identification and Control of Uncertain Systems with Nonsmooth Dynamics

CHAPTER 13

ESO Based Adaptive Sliding Mode

Control of Servo Systems With

Input Saturation

13.1 INTRODUCTION

For most of servo systems driven by servo motors connected with mechan-
ical components, there exist various non-smooth non-linearities including
friction, saturation, dead-zone, and saturations, etc., among which the in-
put saturation is one of the most widely encountered phenomena due to
the physical constraints on the maximum power of the driving motors. It
is well-known that the presence of saturation may lead to sluggish transient
response, oscillations, and even instability. To manage the effect of input
saturations, numerous research work have been carried out to design ap-
propriate controllers for both linear or non-linear systems [1–3]. One of
the well-recognized schemes, anti-windup [3], has been proved effective in
practice. The idea of anti-windup is to incorporate an extra compensator
into a pre-designed feedback control, which could compensate for the ef-
fect of saturation and recover the closed-loop system behavior as much as
possible when the control limits are violated. However, anti-windup has
been mainly developed for linear systems, resulting in difficulties in ex-
tending it to adaptive control for non-linear systems.
Moreover, in most available control designs for servo systems, all the
system state variables are required to be measurable, and the system model
is precisely known. To address uncertainties and achieve a high control
performance of servo systems, sliding mode control (SMC) has been widely
used due to its strong robustness. The critical chattering problem with high
frequency switching [4] in the traditional sliding mode control schemes
was further addressed by introducing a full order sliding mode controller
in [5]. In [6], an adaptive sliding mode control was also presented for the
PMSM system with bounded uncertainties, where the unknown upper and
lower bounds of uncertainties are online estimated. On the other hand,
to accommodate unknown system states and uncertainties simultaneously,
a new control framework, active disturbance rejection control (ADRC),
was proposed in [7], where all the system states and external disturbances
Adaptive Identification and Control of Uncertain Systems with Non-smooth Dynamics.
DOI: https://doi.org/10.1016/B978-0-12-813683-6.00017-9 203
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