J Control Theory Appl 2008 6 (1) 45–52
DOI 10.1007/s11768-008-7188-6
State feedback stabilization of cascaded nonlinear
systems with discontinuous connection
Maiko HIRANO
1
, Tielong SHEN
1
, Kazuhisa ITO
2
, Katutoshi TAMURA
1
(1.Department of Mechanical Engineering, Sophia University, Tokyo 102-8554 Japan;
2.Department of Mechanical Engineering, Tottori University, Tottori 680-8552, Japan)
Abstract: In practical engineering, many phenomena are described as a discontinuous function of a state variable,
and the discontinuity is usually the main reason for the degradation of the control performance. For example, in the set-
point control problem of mechanical systems, the static friction (described by a sgn function of velocity of the contacting
faces) causes undesired positioning error. In this paper, we will investigate the stabilization problem for a class of nonlinear
systems that consist of two subsystems with cascaded connection. We will show the basic idea with a special case first, and
then the result will be extended to more general cases. Some interesting numerical examples will be given to demonstrate
the effectiveness of the proposed design approach.
Keywords: Cascaded connection; Discontinuous systems; Filippov solution
1 Introduction
In practical engineering, the cascaded connection of two
subsystems is a typical structure in control systems. The
normal form of a smooth nonlinear affine system is de-
scribed by a nonlinear subsystem connected with an inte-
grator chain in cascaded connection [1]. For example, in
the application of motion control, the controlled mechanical
plant is driven by active forces which are usually provided
by electric or hydraulic actuators, and the latter is forced by
the control signal, which is the design control input.
Indeed, the control design for cascaded nonlinear systems
is an old topic in control theory, and Lyapunov framework-
based design approaches to the feedback stabilizing con-
troller have been well established by many researchers (for
example, [2∼6] and their references). It has been shown
by [2] that if the driving subsystem is linear and stabiliz-
able, and the unforced driven subsystem is asymptotically
stable, the cascaded system may be stabilized by state feed-
back control under the condition that the connecting func-
tion is spanned by the output of the driving subsystem. This
result is established based on the fact that if we can find a
Lyapunov function for the unforced subsystem and a stor-
age function for the linear driving subsystem, then the sum
of the functions will play the role of Lyapunov function for
the cascaded system. As shown in [6, 7], this result can be
extended to the case in which the driving subsystem is non-
linear but strictly passive. On the other hand, under the con-
dition that the driven system is input-to-state stable with re-
spect to the driving signal, an alternative design approach
has been provided where additional cross term is required
in the sum. An approach has been presented by [8] for con-
structing the cross term such that the sum plays the role of
Lyapunov function. However, all previous works targeted
the systems that are described by differential equations with
smooth functions.
In this paper, we focus our attention on a class of cas-
caded nonlinear systems with discontinuous connection. As
is well-known, the dynamics of the nonlinear systems with
discontinuity is described by differential equations with dis-
continuous right-hand side, and a feasible way to analyze
the behavior of the solution is the Filippov-framework. We
will target a class of nonlinear systems that consist of two
smooth subsystems with discontinuous connection. We will
show that if the driven system is in the weakly minimum
phase with relative degree one and the driving system is pas-
sive, then we can find a state feedback control such that the
closed loop system is globally stable and the state converges
ultimately to any given small closed set. Finally, three nu-
merical examples will be shown to demonstrate the effects
of the proposed controllers.
2 Motivation and problem formulation
Consider the nonlinear systems described as follows:
⎧
⎪
⎨
⎪
⎩
˙x = f
1
(x)+c(x, sgn(φ(x)),y),
˙
ξ = f
2
(ξ)+g(ξ)u,
y = h(ξ),
(1)
where f
i
(·)(i =1, 2), g(·) and c(·, ·, ·) are nonlinear smooth
functions with appropriate dimensions according to the di-
Received 10 September 2007.