Showing papers by "Nicholas Kottenstette published in 2010"

Feedback Thermal Control for Real-time Systems

Abstract: Thermal control is crucial to real-time systems as excessive processor temperature can cause system failure or unacceptable performance degradation due to hardware throttling. Real-time systems face significant challenges in thermal management as they must avoid processor overheating while still delivering desired real-time performance. Furthermore, many real-time systems must handle a broad range of uncertainties in system and environmental conditions. To address these challenges, this paper presents Thermal Control under Utilization Bound (TCUB), a novel thermal control algorithm specifically designed for real-time systems. TCUB employs a nested feedback loop that dynamically controls both processor temperature and CPU utilization through task rate adaptation. Rigorously modeled and designed based on control theory, TCUB can maintain both desired processor temperature and CPU utilization, thereby avoiding processor overheating and maintaining desired soft real-time performance. A salient feature of TCUB lies on its capability to handle a broad range of uncertainties in terms of processor power consumption, task execution times, ambient temperature, and unexpected thermal faults. The robustness of TCUB makes it particularly suitable for real-time embedded systems that must operate in highly unpredictable environments. The advantages of TCUB are demonstrated through extensive simulations under a broad range of system and environmental uncertainties.

Relationships between positive real, passive dissipative, & positive systems

Abstract: This paper shows how: i) (strongly) positive real; ii) (asymptotically stable) dissipative (strictly-input) passive; and iii) (Lm 2 -stable strictly) positive; continuous time system definitions are equivalent for linear time invariant (LTI) systems. In parallel this paper shows how: i) (strictly) positive real; ii) (asymptotically stable) dissipative (strictly-input) passive; and iii) (lm 2 -stable strictly) positive; discrete time system definitions are equivalent for LTI systems. A frequency test is derived to determine if a single input single output LTI system is strictly output passive. Finally, the necessary conditions to synthesize a system which is both passive and stable but neither strictly-input passive nor strictly-output passive are presented.

Automated synthesis of Time-Triggered Architecture-based TrueTime models for platform effects simulation and analysis

Abstract: The TrueTime toolbox simulates real-time control systems, including platform-specific details like process scheduling, task execution and network communications. Analysis using these models provides insight into platform-induced timing effects, such as jitter and delay. For safety-critical applications, the Time-Triggered Architecture (TTA) has been shown to provide the necessary services to create robust, fault-tolerant control systems. Communication induced timing effects still need to be simulated and analyzed even for TTA-compliant models. The process of adapting time-invariant control system models, through the inclusion of platform specifics, into TTA-based TrueTime models requires significant manual effort and detailed knowledge of the desired platform's execution semantics. In this paper, we present an extension of the Embedded Systems Modeling Language (ESMoL) tool chain that automatically synthesizes TTA-based TrueTime models. In our tools, timeinvariant Simulink models are imported into the ESMoL modeling environment where they are annotated with details of the desired deployment platforms. A constraint-based offline scheduler then generates the static TTA execution schedules. Finally, we synthesize new TrueTime models that encapsulate all of the TTA execution semantics. Using this approach it is possible to rapidly prototype, evaluate, and modify controller designs and their hardware platforms to better understand deployment induced performance and timing effects.

A passivity-based approach to deployment in multi-agent networks

Abstract: Surveillance and convoy tracking applications often require groups of networked agents for redundancy and better coverage. An important goal upon deployment is to establish a formation around a target. Although there exist distributed algorithms using only local communication that achieve this goal, they typically ignore destabilizing effects resulting from implementation uncertainties, such as network delays and data loss. This paper resolves these issues by introducing a discrete-time distributed design framework that uses a compositional, passivity-based approach to ensure lm 2 -stability regardless of overlay network topology, in the presence of network delays and data loss. For the restricted case of a uniform node degree in the overlay network topology, the paper shows that asymptotic formation establishment is achieved. Finally, simulations of velocity-limited unmanned air vehicles (UAVs) are presented that demonstrate the robustness of the network architecture to network delays and data loss. This paper will appear in the Proceedings of ICINCO 2010 Seventh International Conference on Informatics in Control, Automation and Robotics, Funchal, Madeira Portugal. http://www.icinco.org/

Discrete-time IDA-passivity based control of coupled tank processes subject to actuator saturation

Abstract: Interconnection damping assignment passivity based control (IDA-PBC) is an emerging control design method which allows an engineer to systematically design an advanced controller for complex non-linear systems. As a result specific gain ranges can be determined which can prevent an operator (adversary) from accidentally (maliciously) setting control gains which could potentially destabilize the system. However in order to generate the controller the engineer will have to resort to using symbolic numerical solvers in order to complete the design. This can be both a cumbersome and error-prone task which can be automated. We present initial results of a tool which simplifies IDA-PBC. In addition many fluid control problems posses tight operating regions in which pumps degrade over time. As a result actuator saturation may occur for given set-point profiles which will lead to integrator wind-up and more oscillatory behavior. We provide a non-linear anti-windup control-law which greatly improves system resilience to such degradation. Finally we demonstrate that IDA-PBC works reasonably well for moderately large sampling times by simply applying the bilinear transform to approximate any additional (non-linear) integral control terms.

Online stability validation using sector analysis

Abstract: Our previous work has explored the use of compositional stabilization techniques for embedded flight control software[9] based on passivity properties of controller components and systems. Zames[21] presented a compositional behavior-bounding technique for evaluating stability of nonlinear systems based on real intervals representing cones (sectors) that bound possible component behaviors. Many innovations in control theory have developed from his insights. We present a novel use of his sector bound theory to validate the stability of embedded control implementations online. The sector analysis can be implemented as a computationally efficient check of stability for different parts of a control design. The advantage of the online application of this technique is that it takes into account software platform effects that impact stability, such as time delays, quantization, and data integrity.We present a brief overview of the sector concept, our compatible control design approach, application of the technique to model-based embedded control software design, an example of its use to find design defects, and insights that may be drawn from our investigation so far. In the present work we only consider software (discrete-time) control of nonlinear continuous-time systems without switching.