Distributed Implementation of Minimax Adaptive Controller
For Finite Set of Linear Systems
Venkatraman Renganathan, Anders Rantzer, and Olle Kjellqvist
Abstract— This paper deals with a distributed implemen-
tation of minimax adaptive control algorithm for networked
dynamical systems modeled by a finite set of linear models. To
hedge against the uncertainty arising out of finite number of
possible dynamics in each node in the network, it collects only
the historical data of its neighboring nodes to decide its control
action along its edges. This makes our proposed distributed ap-
proach scalable. Numerical simulations demonstrate that once
each node has sufficiently estimated the uncertain parameters,
the distributed minimax adaptive controller behaves like the
optimal distributed H-infinity controller in hindsight.
I. INTRODUCTION
Control of large-scale and complex systems is often
performed in a distributed manner [1] as it is practically
difficult for every agent in the network to have access to the
global information about the overall networked system while
deciding its control actions. On the other hand, designing
optimal distributed control laws when the networked system
dynamics are uncertain still remains an open problem. This
naturally calls for a learning-based controller to be employed
in such uncertain settings and it was shown in [2] that an
adaptive controller can learn the true system dynamics online
through sufficient parameter estimation and then control
the system. Multiple model-based adaptive control problems
have been extensively studied in the control literature [3]–[8].
The minimax problem of handling adversarial disturbance
and the uncertain parameters leading to an unknown linear
system was introduced in [9]. It was specialized to scalar
systems with unknown sign for input matrix in [10], to
finite sets of linear systems in [11]. However, designing
optimal distributed control laws that address the uncertainty
prevailing over true model of the networked system out of
the finite set of linear models still remains an open problem.
Minimax adaptive control problems are challenging
mainly due to the exploration and exploitation trade-off
that inevitably comes with the learning and controlling
procedure. Aiming for a distributed implementation on top
of it complicates things further. However, there are certain
classes of systems for which scalable implementation of
distributed minimax adaptive control is possible, such as the
the one with linear time-invariant discrete time systems with
symmetric and Schur state matrix. Such system models are
common in irrigation networks. For instance, the authors in
This project has received funding from the European Research Coun-
cil (ERC) under the European Union’s Horizon 2020 research and in-
novation program under grant agreement No 834142 (Scalable Con-
trol). The authors are with the Department of Automatic Control LTH,
Lund University, Sweden. (e-mail: (venkatraman.renganathan,anders.rantzer,
olle.kjellqvist)@control.lth.se).
[12] computed a closed-form expression for a decentralised
H∞optimal controller with diagonal gain matrix for network
systems with acyclic graphs. Similarly, the authors in [13]
computed a closed-form expression for the distributed H∞
optimal state feedback law for systems with symmetric
and Schur state matrix, where the total networked system
comprised of subsystems with local dynamics, that share
only control inputs and each control input affecting only two
subsystems.
Contributions: We extend the problem setting in [13]
by considering finite number of possible local dynamics in
each node and control action along each edge. Our main
contributions in this paper are as follows:
1) We develop scalable and distributed implementation of
minimax adaptive control for networked systems where
each node in the network is required to maintain the
history of just its own neighboring nodes to hedge
against the uncertainty in its local system dynamics.
2) We demonstrate the effectiveness of our proposed
approach using a buffer network based numerical ex-
ample to advocate the use of scalable and distributed
minimax adaptive control law for finite set of linear
systems.
Following a short summary of notations, this paper is orga-
nized as follows: In §II, the main problem formulation of
distributed minimax adaptive controller and its distributed
implementation is presented. The effectiveness of the pro-
posed algorithm is then demonstrated in §III. Finally, the
paper is closed in §IV along with a summary of results and
directions for future research.
NOTATIONS
The cardinality of the set Ais denoted by |A|. The set of
real numbers, integers and the natural numbers are denoted
by R,Z,Nrespectively. The subset of real numbers greater
than a given constant say a∈Rand between two constants
a, b ∈Nwith a<bare denoted by R>a and [a:b]
respectively. A vector of size nwith all values being one
is denoted by 1n. For a matrix A∈Rn×n, we denote its
transpose and its trace by A>and Tr(A)respectively. We
denote by Snthe set of symmetric matrices in Rn×nand
the set of positive (semi)definite matrices as Sn
++(Sn
+). A
symmetric matrix P∈Snis said to be positive definite
(positive semi-definite) if for every vector x∈Rn\{0},
we have x>P x > 0 (x>P x ≥0) and is denoted by
P0(P0) . An identity matrix in dimension nis
denoted by In. Given x∈Rn, A ∈Rn×n, B ∈Rn×n,
the notations |x|2
Aand kBk2
Amean x>Ax and Tr B>AB
arXiv:2210.00081v1 [eess.SY] 30 Sep 2022