25,670 research outputs found
HyPLC: Hybrid Programmable Logic Controller Program Translation for Verification
Programmable Logic Controllers (PLCs) provide a prominent choice of
implementation platform for safety-critical industrial control systems. Formal
verification provides ways of establishing correctness guarantees, which can be
quite important for such safety-critical applications. But since PLC code does
not include an analytic model of the system plant, their verification is
limited to discrete properties. In this paper, we, thus, start the other way
around with hybrid programs that include continuous plant models in addition to
discrete control algorithms. Even deep correctness properties of hybrid
programs can be formally verified in the theorem prover KeYmaera X that
implements differential dynamic logic, dL, for hybrid programs. After verifying
the hybrid program, we now present an approach for translating hybrid programs
into PLC code. The new tool, HyPLC, implements this translation of discrete
control code of verified hybrid program models to PLC controller code and, vice
versa, the translation of existing PLC code into the discrete control actions
for a hybrid program given an additional input of the continuous dynamics of
the system to be verified. This approach allows for the generation of real
controller code while preserving, by compilation, the correctness of a valid
and verified hybrid program. PLCs are common cyber-physical interfaces for
safety-critical industrial control applications, and HyPLC serves as a
pragmatic tool for bridging formal verification of complex cyber-physical
systems at the algorithmic level of hybrid programs with the execution layer of
concrete PLC implementations.Comment: 13 pages, 9 figures. ICCPS 201
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
PALS-Based Analysis of an Airplane Multirate Control System in Real-Time Maude
Distributed cyber-physical systems (DCPS) are pervasive in areas such as
aeronautics and ground transportation systems, including the case of
distributed hybrid systems. DCPS design and verification is quite challenging
because of asynchronous communication, network delays, and clock skews.
Furthermore, their model checking verification typically becomes unfeasible due
to the huge state space explosion caused by the system's concurrency. The PALS
("physically asynchronous, logically synchronous") methodology has been
proposed to reduce the design and verification of a DCPS to the much simpler
task of designing and verifying its underlying synchronous version. The
original PALS methodology assumes a single logical period, but Multirate PALS
extends it to deal with multirate DCPS in which components may operate with
different logical periods. This paper shows how Multirate PALS can be applied
to formally verify a nontrivial multirate DCPS. We use Real-Time Maude to
formally specify a multirate distributed hybrid system consisting of an
airplane maneuvered by a pilot who turns the airplane according to a specified
angle through a distributed control system. Our formal analysis revealed that
the original design was ineffective in achieving a smooth turning maneuver, and
led to a redesign of the system that satisfies the desired correctness
properties. This shows that the Multirate PALS methodology is not only
effective for formal DCPS verification, but can also be used effectively in the
DCPS design process, even before properties are verified.Comment: In Proceedings FTSCS 2012, arXiv:1212.657
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