530,005 research outputs found
Formal Analysis of Linear Control Systems using Theorem Proving
Control systems are an integral part of almost every engineering and physical
system and thus their accurate analysis is of utmost importance. Traditionally,
control systems are analyzed using paper-and-pencil proof and computer
simulation methods, however, both of these methods cannot provide accurate
analysis due to their inherent limitations. Model checking has been widely used
to analyze control systems but the continuous nature of their environment and
physical components cannot be truly captured by a state-transition system in
this technique. To overcome these limitations, we propose to use
higher-order-logic theorem proving for analyzing linear control systems based
on a formalized theory of the Laplace transform method. For this purpose, we
have formalized the foundations of linear control system analysis in
higher-order logic so that a linear control system can be readily modeled and
analyzed. The paper presents a new formalization of the Laplace transform and
the formal verification of its properties that are frequently used in the
transfer function based analysis to judge the frequency response, gain margin
and phase margin, and stability of a linear control system. We also formalize
the active realizations of various controllers, like
Proportional-Integral-Derivative (PID), Proportional-Integral (PI),
Proportional-Derivative (PD), and various active and passive compensators, like
lead, lag and lag-lead. For illustration, we present a formal analysis of an
unmanned free-swimming submersible vehicle using the HOL Light theorem prover.Comment: International Conference on Formal Engineering Method
Synthesis of Minimal Error Control Software
Software implementations of controllers for physical systems are at the core
of many embedded systems. The design of controllers uses the theory of
dynamical systems to construct a mathematical control law that ensures that the
controlled system has certain properties, such as asymptotic convergence to an
equilibrium point, while optimizing some performance criteria. However, owing
to quantization errors arising from the use of fixed-point arithmetic, the
implementation of this control law can only guarantee practical stability:
under the actions of the implementation, the trajectories of the controlled
system converge to a bounded set around the equilibrium point, and the size of
the bounded set is proportional to the error in the implementation. The problem
of verifying whether a controller implementation achieves practical stability
for a given bounded set has been studied before. In this paper, we change the
emphasis from verification to automatic synthesis. Using synthesis, the need
for formal verification can be considerably reduced thereby reducing the design
time as well as design cost of embedded control software.
We give a methodology and a tool to synthesize embedded control software that
is Pareto optimal w.r.t. both performance criteria and practical stability
regions. Our technique is a combination of static analysis to estimate
quantization errors for specific controller implementations and stochastic
local search over the space of possible controllers using particle swarm
optimization. The effectiveness of our technique is illustrated using examples
of various standard control systems: in most examples, we achieve controllers
with close LQR-LQG performance but with implementation errors, hence regions of
practical stability, several times as small.Comment: 18 pages, 2 figure
Analysis of control system stability under algorithmic uncertainty
Stability of control systems is one of the central subjects in control theory. The classical asymptotic stability theorem states that the norm of the residual between the state trajectory and the equilibrium is zero in limit. Unfortunately, it does not in general allow computing a concrete rate of convergence particularly due to algorithmic uncertainty which is related to numerical imperfections of floating-point arithmetic. This work proposes to revisit the asymptotic stability theory with the aim of computation of convergence rates using constructive analysis which is a mathematical tool that realizes equivalence between certain theorems and computation algorithms. Consequently, it also offers a framework which allows controlling numerical imperfections in a coherent and formal way. The overall goal of the current study also matches with the trend of introducing formal verification tools into the control theory. Besides existing approaches, constructive analysis, suggested within this work, can also be considered for formal verification of control systems. A computational example is provided that demonstrates extraction of a convergence certificate for example dynamical systems
On the Safety of Connected Cruise Control: Analysis and Synthesis with Control Barrier Functions
Connected automated vehicles have shown great potential to improve the
efficiency of transportation systems in terms of passenger comfort, fuel
economy, stability of driving behavior and mitigation of traffic congestions.
Yet, to deploy these vehicles and leverage their benefits, the underlying
algorithms must ensure their safe operation. In this paper, we address the
safety of connected cruise control strategies for longitudinal car following
using control barrier function (CBF) theory. In particular, we consider various
safety measures such as minimum distance, time headway and time to conflict,
and provide a formal analysis of these measures through the lens of CBFs.
Additionally, motivated by how stability charts facilitate stable controller
design, we derive safety charts for existing connected cruise controllers to
identify safe choices of controller parameters. Finally, we combine the
analysis of safety measures and the corresponding stability charts to
synthesize safety-critical connected cruise controllers using CBFs. We verify
our theoretical results by numerical simulations.Comment: Accepted to the 62nd IEEE Conference on Decision and Control. 6
pages, 5 figure
A graphical environment to express the semantics of control systems
We present the concept of a unified graphical environment for expressing the
semantics of control systems. The graphical control system design environment
in Simulink already allows engineers to insert a variety of assertions aimed
the verification and validation of the control software. We propose extensions
to a Simulink-like environment's annotation capabilities to include formal
control system stability, performance properties and their proofs. We provide a
conceptual description of a tool, that takes in a Simulink-like diagram of the
control system as the input, and generates a graphically annotated control
system diagram as the output. The annotations can either be inserted by the
user or generated automatically by a third party control analysis software such
as IQC or -tool. We finally describe how the graphical
representation of the system and its properties can be translated to annotated
programs in a programming language used in verification and validation such as
Lustre or C
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