NASA Aircraft Controls Research, 1983

The workshop consisted of 24 technical presentations on various aspects of aircraft controls, ranging from the theoretical development of control laws to the evaluation of new controls technology in flight test vehicles. A special report on the status of foreign aircraft technology and a panel session with seven representatives from organizations which use aircraft controls technology were also included. The controls research needs and opportunities for the future as well as the role envisioned for NASA in that research were addressed. Input from the panel and response to the workshop presentations will be used by NASA in developing future programs

Decentralized and Fault-Tolerant Control of Power Systems with High Levels of Renewables

Inter-area oscillations have been identified as a major problem faced by most power systems and stability of these oscillations are of vital concern due to the potential for equipment damage and resulting restrictions on available transmission capacity. In recent years, wide-area measurement systems (WAMSs) have been deployed that allow inter-area modes to be observed and identified.Power grids consist of interconnections of many subsystems which may interact with their neighbors and include several sensors and actuator arrays. Modern grids are spatially distributed and centralized strategies are computationally expensive and might be impractical in terms of hardware limitations such as communication speed. Hence, decentralized control strategies are more desirable.Recently, the use of HVDC links, FACTS devices and renewable sources for damping of inter-area oscillations have been discussed in the literature. However, very few such systems have been deployed in practice partly due to the high level of robustness and reliability requirements for any closed loop power system controls. For instance, weather dependent sources such as distributed winds have the ability to provide services only within a narrow range and might not always be available due to weather, maintenance or communication failures.Given this background, the motivation of this work is to ensure power grid resiliency and improve overall grid reliability. The first consideration is the design of optimal decentralized controllers where decisions are based on a subset of total information. The second consideration is to design controllers that incorporate actuator limitations to guarantee the stability and performance of the system. The third consideration is to build robust controllers to ensure resiliency to different actuator failures and availabilities. The fourth consideration is to design distributed, fault-tolerant and cooperative controllers to address above issues at the same time. Finally, stability problem of these controllers with intermittent information transmission is investigated.To validate the feasibility and demonstrate the design principles, a set of comprehensive case studies are conducted based on different power system models including 39-bus New England system and modified Western Electricity Coordinating Council (WECC) system with different operating points, renewable penetration and failures

Development of a Converter-Based Testing Platform and Battery Energy Storage System (BESS) Emulator for Microgrid Controller Function Evaluation

The microgrid has attracted increasing research attention in the last two decades. Due to the development of renewable energy resources and power electronics technologies, the future microgrid will trend to be smarter and more complicated. The microgrid controller performs a critical role in the microgrid operation, which will also become more and more sophisticated to support the future microgrid. Before final field deployment and test, the evaluation and testing of the controller is an indispensable step in the controller development, which requires a proper testing platform. However, existing simulation-based platforms have issues with potential numerical oscillation and may require huge computation resources for complex microgrid controllers. Meanwhile, field test-based controller evaluation is limited to the test conditions. Existing digital simulation-based platforms and field test-based platforms have limitations for microgrid controller testing. To provide a practical and flexible controller evaluation, a converter-based microgrid hardware testbed is designed and implemented considering the actual microgrid architecture and topology information. Compared with the digital simulation-based platforms, the developed microgrid testing platform can provide a more practical testing environment. Compared to the direct field test, the developed platform is more flexible to emulate different microgrids. As one of the key components, a converter-based battery energy storage system (BESS) emulator is proposed to complete the developed testing platform based on the testing requirements of microgrid controller functions. Meanwhile, the microgrid controller testing under different microgrid conditions is also considered. Two controllers for the microgrid with dynamic boundaries are tested to demonstrate the capability of the developed platform as well as the BESS emulator. Different testing cases are designed and tested to evaluate the controller performance under different microgrid conditions

Networked Control System: Overview and Research Trends

Abstract-Networked control systems (NCSs) have been one of the main research focuses in academia as well as in industry for many decades and have become a multidisciplinary area. With these growing research trends, it is important to consolidate the latest knowledge and information to keep up with the research needs. In this paper, the NCS and its different forms are introduced and discussed. The beginning of this paper discusses the history and evolution of NCSs. The next part of this paper focuses on different fields and research arenas such as networking technology, network delay, network resource allocation, scheduling, network security in real-time NCSs, integration of components on a network, fault tolerance, etc. A brief literature survey and possible future direction concerning each topic is included

Propulsion Controls, 1979

The state of the art of multivariable engine control is examined in order to determine future needs and problem areas and to establish the appropriate roles of government, industries, and universities in addressing these problems

Modeling and verification of reconfigurable discrete event control systems

Most modern technological systems rely on complicated control technologies, computer technologies, and networked communication technologies. Their dynamic behavior is intricate due to the concurrence and conflict of various signals. Such complex systems are studied as discrete event control systems (DECSs), while the detailed continuous variable processes are abstracted. Dynamic reconfigurable systems are the trend of all future technological systems, such as flight control systems, vehicle electronic systems, and manufacturing systems. In order to meet control requirements continuously, such a dynamic reconfigurable system is able to actively adjust its configuration at runtime by modifying ist components, connections among components and data, while changes are detected in the internal/external execution environment. Model based design methodologies attract wide attention since they can detect system defect earlier, increase system reliability, and decrease time and cost on system development. An accurate, compact, and easy formal model to be analyzed is the first step of model based design methods. Formal verification is an expected effective method to completely check if a designed system meets all requirements and to improve the system design scheme. Considering the potential benefits of Timed Net Condition/Event Systems (TNCESs) in modeling and analyzing reconfigurable systems, this dissertation deals with formal modeling and verification of reconfigurable discrete event control systems (RDECSs) based on them.Die meisten modernen technologischen Systeme benötigen aufwändige Steuerungs-, Rechner- und Kommunikationstechnologien. Aufgrund von Nebenläufigkeit und Konflikten ergibt sich ein kompliziertes dynamisches Verhalten. Derartige komplexe Systeme werden dadurch untersucht, dass man sie als ereignisdiskrete Steuerungssysteme (Discrete Event Control Systems, DECSs) betrachtet und dabei die detaillierten unterlagerten kontinuierlichen Prozesse abstrahiert. Um die Anforderungen an die Steuerung durchgängig erfüllen zu können adaptieren sich dynamische rekonfigurierbare Systeme zur Laufzeit durch Modifikation ihrer Komponenten, deren Verbindungen untereinander und der gespeicherten Daten, sobald Änderungen in der internen oder externen Umgebung festgestellt werden. Beispiele für dynamische Rekonfigurierbare Systeme finden sich in der Luftfahrt, im Automobilbereich aber auch in Fertigungssystemen. Modellbasierte Entwicklungsmethoden erfreuen sich zunehmender Beliebtheit, da sie es erlauben Fehler früher im Entwicklungsprozess aufzudecken und damit zu höherer Systemverfügbarkeit bei verkürzter Entwicklungszeit führen. Ein formales Modell des Systems bildet hierbei den ersten wichtigen Schritt. Durch formale Verifikation kann dieses Modell effektiv und vollständig überprüft und ggf. verbessert werden. Eine geeignete Modellform hierfür sind Timed Net Condition/Event Systems (TNCESs). Die vorliegende Dissertation befasst sich mit der Anwendung von TNCES zur Modellierung und Verifikation rekonfigurierbarer ereignisdiskreter Steuerungssysteme (RDECSs)

Investigation of Novel Displacement-Controlled Hydraulic Architectures for Railway Construction and Maintenance Machines

This dissertation aims at showing how to transform hydraulic systems of railway multi-actuator machinery characterized by inefficient state-of-the-art systems into the 21st Century. Designing machines that are highly efficient, productive, reliable, and cost affordable represents the target of this research. In this regard, migrating from valve-controlled architectures to displacement-controlled layouts is the proper answer. Displacement-controlled systems remove the losses generated by flow throttling typical of conventional circuits, allow an easy implementation of energy recovery (e.g. during regenerative braking), and create the possibility for the use of hybrid systems capable of maximizing the downsizing of the combustion engine. One portion of the dissertation focuses on efficient propulsion systems suitable for railway construction and maintenance machines. Two non-hybrid architectures are first proposed, i.e. a novel layout grounded on two independent hydrostatic transmissions (HSTs) and two secondary controlled hydraulic motors (SCHMs) connected in parallel. Three suitable control strategies are developed according to the specific requirements for railway machines and dedicated controllers are implemented. Detailed analyses are conducted via high-fidelity virtual simulations involving accurate modeling of the rail/wheel interface. The performance of the propulsion systems is proven by acceptable velocity tracking, accurate stopping position, achieving regenerative braking, and the expected behavior of the slip coefficients on both axles. Energy efficiency is the main emphasis during representative working cycles, which shows that the independent HSTs are more efficient. They consume 6.6% less energy than the SCHMs working with variable-pressure and 12.8% less energy than the SCHMs controlled with constant-pressure. Additionally, two alternative hybrid propulsion systems are proposed and investigated. These architectures enable a 35% reduction of the baseline machine’s rated engine power without modifying the working hydraulics. Concerning the working hydraulics, the focus is to extend displacement-controlled technology to specific functions on railway construction and maintenance machines. Two specific examples of complete hydraulic circuits for the next generation tamper-liners are proposed. In particular, an innovative approach used to drive displacement-controlled dual function squeeze actuators is presented, implemented, and experimentally validated. This approach combines two functions into a unique actuator, namely squeezing the ballast and vibrating the tamping tools of the work-heads. This results in many advantages, such as variable amplitude and variable frequency of the tamping tools’ vibration, improved reliability of the tamping process, and energy efficient actuation. A motion of the squeeze actuator characterized by a vibration up to 45 Hz, i.e. the frequency used in state-of-the-art systems, is experimentally confirmed. In conclusion, this dissertation demonstrates that displacement-controlled actuation represents the correct solution for next-generation railway construction and maintenance machines

Model-based Fault Diagnosis and Fault Accommodation for Space Missions : Application to the Rendezvous Phase of the MSR Mission

The work addressed in this thesis draws expertise from actions undertaken between the EuropeanSpace Agency (ESA), the industry Thales Alenia Space (TAS) and the IMS laboratory (laboratoirede l’Intégration du Matériau au Système) which develop new generations of integrated Guidance, Navigationand Control (GNC) units with fault detection and tolerance capabilities. The reference mission isthe ESA’s Mars Sample Return (MSR) mission. The presented work focuses on the terminal rendezvoussequence of the MSR mission which corresponds to the last few hundred meters until the capture. Thechaser vehicle is the MSR Orbiter, while the passive target is a diameter spherical container. The objectiveat control level is a capture achievement with an accuracy better than a few centimeter. The research workaddressed in this thesis is concerned by the development of model-based Fault Detection and Isolation(FDI) and Fault Tolerant Control (FTC) approaches that could significantly increase the operational andfunctional autonomy of the chaser during rendezvous, and more generally, of spacecraft involved in deepspace missions. Since redundancy exist in the sensors and since the reaction wheels are not used duringthe rendezvous phase, the work presented in this thesis focuses only on the thruster-based propulsionsystem. The investigated faults have been defined in accordance with ESA and TAS requirements andfollowing their experiences. The presented FDI/FTC approaches relies on hardware redundancy in sensors,control redirection and control re-allocation methods and a hierarchical FDI including signal-basedapproaches at sensor level, model-based approaches for thruster fault detection/isolation and trajectorysafety monitoring. Carefully selected performance and reliability indices together with Monte Carlo simulationcampaigns, using a high-fidelity industrial simulator, demonstrate the viability of the proposedapproaches.Les travaux de recherche traités dans cette thèse s’appuient sur l’expertise des actionsmenées entre l’Agence spatiale européenne (ESA), l’industrie Thales Alenia Space (TAS) et le laboratoirede l’Intégration du Matériau au Système (IMS) qui développent de nouvelles générations d’unités intégréesde guidage, navigation et pilotage (GNC) avec une fonction de détection des défauts et de tolérance desdéfauts. La mission de référence retenue dans cette thèse est la mission de retour d’échantillons martiens(Mars Sample Return, MSR) de l’ESA. Ce travail se concentre sur la séquence terminale du rendez-vous dela mission MSR qui correspond aux dernières centaines de mètres jusqu’à la capture. Le véhicule chasseurest l’orbiteur MSR (chasseur), alors que la cible passive est un conteneur sphérique. L’objectif au niveaude contrôle est de réaliser la capture avec une précision inférieure à quelques centimètres. Les travaux derecherche traités dans cette thèse s’intéressent au développement des approches sur base de modèle de détectionet d’isolation des défauts (FDI) et de commande tolérante aux défaillances (FTC), qui pourraientaugmenter d’une manière significative l’autonomie opérationnelle et fonctionnelle du chasseur pendant lerendez-vous et, d’une manière plus générale, d’un vaisseau spatial impliqué dans des missions située dansl’espace lointain. Dès lors que la redondance existe dans les capteurs et que les roues de réaction ne sontpas utilisées durant la phase de rendez-vous, le travail présenté dans cette thèse est orienté seulementvers les systèmes de propulsion par tuyères. Les défaillances examinées ont été définies conformément auxexigences de l’ESA et de TAS et suivant leurs expériences. Les approches FDI/FTC présentées s’appuientsur la redondance de capteurs, la redirection de contrôle et sur les méthodes de réallocation de contrôle,ainsi que le FDI hiérarchique, y compris les approches à base de signaux au niveau de capteurs, les approchesà base de modèle de détection/localisation de défauts de propulseur et la surveillance de sécuritéde trajectoire. Utilisant un simulateur industriel de haute-fidélité, les indices de performance et de fiabilitéFDI, qui ont été soigneusement choisis accompagnés des campagnes de simulation de robustesse/sensibilitéMonte Carlo, démontrent la viabilité des approches proposées