Automatica 59 (2015) 164–170
Contents lists available at ScienceDirect
Automatica
journal homepage: www.elsevier.com/locate/automatica
Brief paper
State-space H
∞
controller design for descriptor systems
✩
Masaki Inoue
a
, Teruyo Wada
b,1
, Masao Ikeda
c
, Eiho Uezato
d
a
Department of Applied Physics and Physico-Informatics, Keio University, Yokohama, Kanagawa 223-8522, Japan
b
Department of Mechanical Engineering, Osaka University, Suita, Osaka 565-0871, Japan
c
Headquarters, Osaka University, Suita, Osaka 565-0871, Japan
d
Department of Mechanical Systems Engineering, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
a r t i c l e i n f o
Article history:
Received 28 November 2013
Received in revised form
22 January 2015
Accepted 2 June 2015
Available online 24 June 2015
Keywords:
Descriptor systems
State-space controllers
Linear matrix inequalities
H
∞
control
Dynamic output feedback
a b s t r a c t
This paper proposes a new linear matrix inequality (LMI) method to design state-space H
∞
controllers
for linear time-invariant descriptor systems. Unlike preceding studies, where descriptor-type controllers
are first computed and then numerically transformed to state-space controllers, the proposed method
carries out the transformation analytically in the parameter domain. We derive a necessary and
sufficient LMI condition for the existence of a state-space controller with the same dynamic order of the
descriptor system to be controlled, which makes the closed-loop system regular, impulse-free, stable,
and guarantees the H
∞
norm bound imposed on the closed-loop transfer function. Furthermore, we
present parameterization of all such state-space controllers by variables satisfying the LMI condition and
an arbitrary nonsingular matrix. The LMIs utilized in this paper are strict ones, that is, those containing
no equality, while LMIs with equality constraints have been extensively used in the analysis and design
for descriptor systems. The strict LMIs play key roles in deriving the results of this paper.
© 2015 Elsevier Ltd. All rights reserved.
1. Introduction
This paper considers H
∞
control of general linear time-
invariant descriptor systems including irregular or impulsive ones.
There have been a number of preceding studies using linear matrix
inequalities (LMIs), which deal with descriptor-type controllers
of the same size as the systems to be controlled. Necessary and
sufficient conditions have been proposed for the existence of such
H
∞
controllers, and coefficients of controllers are given by the
solutions of LMIs (see, e.g., Masubuchi, Kamitane, Ohara, & Suda,
1997, Rehm & Allgöwer, 2001, Uezato & Ikeda, 1999 and Xu & Lam,
2006). Theoretically, these results are satisfactory.
✩
This work was partially supported by the Grant-in-Aid for JSPS (the Japan
Society for the Promotion of Science) Fellows, No. 22 · 631 and the Grant-in-Aid
for Scientific Research (C), No.24560548 from JSPS. The material in this paper was
not presented at any conference. This paper was recommended for publication in
revised form by Associate Editor Harry L. Trentelman under the direction of Editor
Richard Middleton.
E-mail addresses: minoue@appi.keio.ac.jp (M. Inoue),
wada@mech.eng.osaka-u.ac.jp (T. Wada), ikeda@mech.eng.osaka-u.ac.jp
(M. Ikeda), uezato@mibai.tec.u-ryukyu.ac.jp (E. Uezato).
1
Tel.: +81 6 6879 4084; fax: +81 6 6879 4878.
However, it is not easy to compute the control inputs from the
measured outputs by descriptor-type controllers, because we do
not have an efficient way of solving descriptor-type equations, that
is, differential equations under algebraic constraints. Therefore, we
usually transform the descriptor-type controllers to input–output
equivalent state-space controllers or transfer functions. The
transformations are carried out in the numerical domain. This idea
would be fine in practical control.
In this paper, we take a different approach, the original idea
of which the authors adopted in deriving state-space stabilizing
controllers for descriptor systems (Inoue, Wada, Ikeda, & Uezato,
2012). We obtain state-space controllers for a descriptor system
without computing descriptor-type controllers numerically. The
state-space controllers are realized by treating descriptor-type
controllers in the parameter domain, where the coefficients of the
descriptor-type controllers are expressed by variables satisfying
LMIs, which describe a necessary and sufficient condition for the
existence of a descriptor-type H
∞
controller, and arbitrary param-
eters. We analytically transform the descriptor-type controllers to
input–output equivalent state-space controllers whose dimension
is the same as the dynamic order (the rank of the coefficient matrix
for the time-derivative of the descriptor variable) of the descriptor-
type controller under a necessary and sufficient condition for the
equivalent transformation. In this way, we can derive all parame-
terized state-space H
∞
controllers for a given system, which make
http://dx.doi.org/10.1016/j.automatica.2015.06.021
0005-1098/© 2015 Elsevier Ltd. All rights reserved.