| 1. |
- Aminifar, Amir, et al.
(författare)
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Control-Quality Driven Design of Cyber-Physical Systems with Robustness Guarantees
- 2013
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Ingår i: Design, Automation & Test in Europe (DATE 2013). - : IEEE. - 1530-1591. - 9781467350716 ; , s. 1093-1098
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Konferensbidrag (refereegranskat)abstract
- Many cyber-physical systems comprise several control applications sharing communication and computation resources. The design of such systems requires special attention due to the complex timing behavior that can lead to poor control quality or even instability. The two main requirements of control applications are: (1) robustness and, in particular, stability and (2) high control quality. Although it is essential to guarantee stability and provide a certain degree of robustness even in the worst-case scenario, a design procedure which merely takes the worst-case scenario into consideration can lead to a poor expected (average-case) control quality, since the design is solely tuned to a scenario that occurs very rarely. On the other hand, considering only the expected quality of control does not necessarily provide robustness and stability in the worst-case. Therefore, both the robustness and the expected control quality should be taken into account in the design process. This paper presents an efficient and integrated approach for designing high-quality cyber-physical systems with robustness guarantees.
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| 2. |
- Aminifar, Amir, et al.
(författare)
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Designing High-Quality Embedded Control Systems with Guaranteed Stability
- 2012
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Ingår i: 33rd IEEE Real-Time Systems Symposium (RTSS 2012. - 1052-8725. - 9781467330985
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Konferensbidrag (refereegranskat)abstract
- Many embedded systems comprise several controllers sharing available resources. It is well known that such resource sharing leads to complex timing behavior that degrades the quality of control, and more importantly, can jeopardize stability in the worst-case, if not properly taken into account during design. Although stability of the control applications is absolutely essential, a design flow driven by the worst-case scenario often leads to poor control quality due to the significant amount of pessimism involved and the fact that the worst-case scenario occurs very rarely. On the other hand, designing the system merely based on control quality, determined by the expected (average-case) behavior, does not guarantee the stability of control applications in the worst-case. Therefore, both control quality and worst-case stability have to be considered during the design process, i.e., period assignment, task scheduling, and control-synthesis. In this paper, we present an integrated approach for designing high-quality embedded control systems, while guaranteeing their stability.
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| 3. |
- Aminifar, Amir, et al.
(författare)
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Stability-Aware Analysis and Design of Embedded Control Systems
- 2013
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Ingår i: Proceedings of the International Conference on Embedded Software (EMSOFT), 2013. - : IEEE conference proceedings. - 9781479914432 - 9781479914425 ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- Many embedded systems comprise several controllers sharing available resources. It is well known that such resource sharing leads to complex timing behavior that can jeopardize stability of control applications, if it is not properly taken into account in the design process, e.g., mapping and scheduling. As opposed to hard real-time systems where meeting the deadline is a critical requirement, control applications do not enforce hard deadlines. Therefore, the traditional real-time analysis approaches are not readily applicable to control applications. Rather, in the context of control applications, stability is often the main requirement to be guaranteed, and can be expressed as the amount of delay and jitter a control application can tolerate. The nominal delay and response-time jitter can be regarded as the two main factors which relate the real-time aspects of a system to control performance and stability. Therefore, it is important to analyze the impact of variations in scheduling parameters, i.e., period and priority, on the nominal delay and response-time jitter and, ultimately, on stability. Based on such an analysis, we address, in this paper, priority assignment and sensitivity analysis problems for control applications considering stability as the main requirement.
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| 4. |
- Araujo, Jose, 1985-
(författare)
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Design and Implementation of Resource-Aware Wireless Networked Control Systems
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Networked control over wireless sensor and actuator systems is of growing importancein many application domains. Energy and communication bandwidth are scarce resources in such systems. Despite that feedback control might only be needed occasionally, sensor and actuator communications are often periodic and with high frequency in today’s implementations. In this thesis, resource-constrained wireless networked control systems with an adaptive sampling period are considered. Our first contribution is a system architecture for aperiodic wireless networked control. As the underlying data transmission is performed over a shared wireless network, we identify scheduling policies and medium access controls that allow for an efficient implementation of sensor communication. We experimentally validate three proposed mechanisms and show that best performance is obtained by a hybrid scheme, combining the advantages of event- and self-triggered control as well as the possibilities provided by contention-based and contention-free medium accesscontrol. In the second contribution, we propose an event-triggered PI controller for wireless process control systems. A novel triggering mechanism which decides the transmission instants based on an estimate of the control signal is proposed. It addresses some side-effects that have been discovered in previous PI proposals, which trigger on the state of the process. Through simulations we demonstrate that the new PI controller provides setpoint tracking and disturbance rejection close to a periodic PI controller, while reducing the required network resources. The third contribution proposes a co-design of feedback controllers and wireless medium access. The co-design is formulated as a constrained optimization problem, whereby the objective function is the energy consumption of the network and the constraints are the packet loss probability and delay, which are derived from the performance requirements of the control systems. The design framework is illustrated in a numerical example.
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| 5. |
- Cervin, Anton, et al.
(författare)
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Optimal On-line Sampling Period Assignment: Theory and Experiments
- 2011
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Ingår i: IEEE Transactions on Control Systems Technology. - 1558-0865. ; 19:4, s. 902-910
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Tidskriftsartikel (refereegranskat)abstract
- In embedded systems, the computing resources are often scarce and several control tasks may have to share the same computer. In this brief, we assume that a set of feedback controllers should be implemented on a single-CPU platform. We study the problem of optimal sampling period assignment, where the goal is to assign sampling rates to the controllers so that the overall control performance is maximized. We derive expressions relating the expected cost over a finite horizon to the sampling period, the computational delay, and the amount of noise acting on the plant. Based on this, we develop a feedback scheduler that periodically assigns new sampling periods based on estimates of the current plant states and noise intensities. Extensive experiments show that online sampling period assignment can deliver significantly better control performance than the state-of-the-art, static period assignment.
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| 6. |
- Cervin, Anton
(författare)
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Stability and Worst-Case Performance Analysis of Sampled-Data Control Systems with Input and Output Jitter
- 2012
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Ingår i: 2012 American Control Conference (ACC). - 9781457710957 ; , s. 3760-3765
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Konferensbidrag (refereegranskat)abstract
- When a feedback controller is implemented in a networked embedded system, the computations and communications induce delays and jitter, which may destabilize the control loop. The majority of previous work on analysis of control loops with time-varying delays has focused on output (actuation) jitter. In many embedded systems, input (sampling) jitter is also an issue. In this paper, we analyze the combined effect of input and output jitter on the stability and performance of linear sampled-data control systems. The analysis is performed via a loop transformation involving two time-varying uncertainties. We show how the input-output gains of the linear part of the transformed system can be computed using a fast-sampling/fast-hold approximation. At the same time, we reduce the conservativeness of a previous stability theorem for pure output jitter.
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| 7. |
- Farias, Gonzalo, et al.
(författare)
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Java Simulations of Embedded Control Systems
- 2010
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 10:9, s. 8585-8603
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a new Open Source Java library suited for the simulation of embedded control systems. The library is based on the ideas and architecture of TrueTime, a toolbox of Matlab devoted to this topic, and allows Java programmers to simulate the performance of control processes which run in a real time environment. Such simulations can improve considerably the learning and design of multitasking real-time systems. The choice of Java increases considerably the usability of our library, because many educators program already in this language. But also because the library can be easily used by Easy Java Simulations (EJS), a popular modeling and authoring tool that is increasingly used in the field of Control Education. EJS allows instructors, students, and researchers with less programming capabilities to create advanced interactive simulations in Java. The paper describes the ideas, implementation, and sample use of the new library both for pure Java programmers and for EJS users. The JTT library and some examples are online available on http://lab.dia.uned.es/jtt.
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| 8. |
- Farias, Gonzalo, et al.
(författare)
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Teaching Embedded Control Systems
- 2010
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Ingår i: International Journal of Engineering Education. - 0949-149X. ; 26:4, s. 938-949
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a novel approach to building virtual laboratories of embedded control systems using TrueTime and Easy Java Simulations. TrueTime is a freeware MATLAB/Simulink based tool commonly used to simulate embedded control systems. Easy Java Simulations is a popular authoring tool that facilitates the creation of pedagogical simulations. According to the proposed approach, authors use TrueTime to develop the simulation of an embedded control system and then move to Easy Java Simulations to link the system to a sophisticated graphical user interface that provides the visualization and user interaction of the virtual lab required for pedagogical purposes. The combination of these two tools conforms a powerful, yet simple, approach to the creation of effective pedagogic simulation of real-time control systems.
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| 9. |
- Henningsson, Toivo, et al.
(författare)
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A Simple Model for the Interference Between Event-Based Control Loops Using a Shared Medium
- 2010
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Ingår i: ; , s. 3240-3245
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Konferensbidrag (refereegranskat)abstract
- Traditionally, control loops are closed using periodic sensing and actuation. When communication resources are scarce, however, much may be gained from transmitting only when something important has happened in the loop. This paper presents a simple model of the interference between event-based control loops caused by sharing a common medium, based on the coupled dynamics of a Markov chain representing the state of the medium, and the processes modeled as integrators disturbed by white noise. The model is simple enough to derive the stationary state distribution at low computational cost using mostly standard linear time-invariant system theory (applied in the spatial dimension), while capturing important aspects of the problem. Control laws are optimized to minimize state variance using the limited communication resources. The results are compared to the less restrictive but unrealistic case of aperiodic control, and to simulations of the system without simplifications.
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| 10. |
- Pawlowski, Andrzej, et al.
(författare)
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Generalized Predictive Control With Actuator Deadband for Event-Based Approaches
- 2014
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Ingår i: IEEE Transactions on Industrial Informatics. - 1941-0050. ; 10:1, s. 523-537
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Tidskriftsartikel (refereegranskat)abstract
- This work presents an event-based control structure using the generalized predictive control (GPC) algorithm with actuator deadband. The main objective of this work is to limit the number of controlled system updates. In this approach, the controlled process is sampled with a constant sampling time and is updated in an asynchronous way that depends on the obtained control signal value. To achieve the desired control properties, a hybrid system framework is used to model the virtual actuator deadband. The deadband is modeled as system input constraints in the GPC's optimization procedure, exploring mixed integer quadratic programming (MIQP) techniques. The presented control structure considers adjustable actuator deadband as an additional tuning parameter and allows a tradeoff between control performance and the number of events/updates. This fact is very important for the lifetime of the actuators and minimizes their wear, especially for mechanical and electromechanical systems. The minimization of actuator usage can be also understood as an economical saving. Other benefits can be found in distributed control systems, where various control system agents are connected through computer networks, and where a reduction in communication is always welcome.
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