Determination Of Parameter Regions For Diagonal Dominance And Stability Of Mimo Systems

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2017Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 2017Endüstride karşılaşılan sistemlerin birçoğu birden fazla giriş ve çıkış değişkenine sahiptir. Bu tarz sistemler SISO sistemlerle karşılaştırıldıklarında, birçok farklı yapısal özellikleri göze çarpmaktadır. Örneğin, en genel durumda herhangi bir çıkış tüm girişlerden az veya çok etkilenir. Diğer taraftan, kontrolör türleri açısından bakıldığında ise araştırmacılar genel olarak "merkezi" ve "merkezi olmayan" olmak üzere iki farklı kontrol yapısına odaklanmışlardır. Ancak, ayarlanacak parametre sayısının azlığı, dayanıklılık ve operatör açısından kullanım kolaylığı gibi nedenlerle merkezi olmayan kontrol yapılarının uygulamalarda daha sık tercih edildiği ileri sürülebilir. Farklı giriş çıkış çiftleri arasındaki etkileşimlerin önemli boyutlara ulaştığı durumlarda ise bu tür kontrolörlerin performansı ve etkinliği genel olarak azalır. Yukarıda bahsedilen nedenlerden dolayı MIMO sistemlerde etkileşimlerin azaltılması özellikle merkezi olmayan kontrolör tasarımı açısından büyük bir önem arz etmektedir. MIMO sistemlerde etkileşimleri azaltmak amacıyla kullanılabilecek yöntemlerden bir tanesi de tam köşegenleştirme ile karşılaştırıldığında daha zayıf bir koşulun sağlanmasını gerektiren köşegen baskınlık kavramıdır. Köşegen baskın sistemlerde bir giriş değişkeni özel bir çıkış değişkeni ile diğer çıkışlara oranla çok daha fazla ilişkilidir. Bu nedenle, bu tezin en temel hedeflerinden bir tanesi MIMO sistemlerde köşegen baskınlık koşullarını sağlayan kontrolör parametre bölgelerinin belirlenmesidir. Buna ek olarak, en genel durumda köşegen baskınlık kararlılığı gerektirmediğinden çok değişkenli sistemleri kararlı kılan kontrolör parametrelerinin belirlenmesi de yine bu tez kapsamında amaçlanan temel hedeflerden bir diğeridir. Sonuç olarak, merkezi olmayan kontrolör tasarımına ön adım oluşturacak şekilde hem köşegen baskınlık hem de kararlılık koşullarının sağlandığı kontrolör parametre bölgelerinin belirlenmesi hedeflenmektedir. Literatürde köşegen baskınlık kavramının önemi özellikle Rosenbrock'un 1970'lerin başındaki çalışmalarından sonra artmıştır. Ancak süreç içerisinde araştırmacıların büyük bir çoğunluğu köşegen baskınlık ile ilgili olarak belirli bir ölçütü en iyileyen kontrolör parametre çiftlerinin belirlenmesine yönelmiştir. Bu durum ise bir sonraki tasarım adımında kısıtlamalara neden olabilmektedir. Buna ek olarak, parametre belirsizliği durumunda köşegen baskınlığın korunup korunmadığı ve/veya belirlenen parametre çiftinin köşegen baskınlık sınırlarına ne kadar yakın olduğu genel olarak detaylı bir şekilde araştırılmamıştır. Bu tez kapsamında köşegen baskınlık üzerindeki gerek ve yeter koşulların belirlenmesi hedeflendiğinden, özel olarak TITO sistemler ve köşegen yapıdaki kontrolör durumu detaylı olarak ele alınmıştır. Bu tarz sistemleri, verilen sabit bir frekans değerinde köşegen baskın kılan kontrolör parametreleri üzerindeki gerek ve yeter koşullar belirlenmiştir. Elde edilen sonuçlar sonlu sayıdaki frekans noktası için de geçerlidir ve pratik açıdan bakıldığında verilen bir frekans aralığına da genişletilebilir durumdadır. Buna ek olarak, daha iyi baskınlık oranı sağlayan parametre bölgelerinin belirlenmesine yönelik olarak orjinal köşegen baskınlık tanımına ağırlık faktörleri eklenmiş ve bu durum için gerek ve yeter koşullar belirlenmiştir. Son olarak da statik köşegen kontrolör durumunda sütun köşegen baskınlığı için kontrolör parametre bölgelerinin yapısını değiştiren kritik frekans değerleri belirlenmiştir. Elde edilen sonuçların köşegen baskınlık açısından etkinlikleri, örnek sistemler ve farklı kontrolörler üzerinden, Gershgorin Diskleri ve köşegen baskınlık çizimleri kullanılarak gösterilmiştir. MIMO sistemleri kapalı çevrimde kararlı kılan kontrolör parametrelere bölgelerinin belirlenmesi için ise Lyapunov eşitliği temelli bir yöntem ileri sürülmüştür. Bu yöntem sayesinde frekans tabanlı yöntemlerde karşılaşılan tekil frekansların hesaplanması ve/veya frekans taraması gibi adımlara olan ihtiyaç ortadan kaldırılmıştır. Temel Lyapunov yaklaşımı açısından bakıldığında LTI sistemler için Lyapunov matrisi olan P(k)'nın pozitif tanımlılığı gerek ve yeter koşuldur. Ancak, Lyapunov matrisi P(k)'nın pozitif tanımlılığı en genel durumda 2n adet parametrik eşitliğin çözümünü gerektirir. Yapılan analizle bu sayı önce n+1'e indirilmiştir. Ardından, Lyapunov matris eşitliği Kronecker çarpımları ve vektörizasyon operatörü kullanılarak standart forma indirgenmiş ve tanımlanan yeni M(k) matrisinin determinantının tartışılan sistem için bir kararlılık sınırı oluşturduğu sistem matrisi A(k), Lyapunov matrisi P(k) ve Kronecker çarpımları üzerinden tanımlanan M(k)'nin birbirleriyle olan ilişkileri üzerinden gösterilmiştir. Dolayısıyla M(k) matrisinin determinantını sıfır ve sonsuz yapan kontrolör parametrelerinin ilgili sistemin kararlılık sınırını oluşturduğu belirlenmiştir. Diğer bir deyişle, kararlılık sınırlarının belirlenmesi en fazla iki adet parametrik ifadenin çözümüne indirgenmiştir. Lyapunov formulasyonunda kullanılan P(k) ve Q matrislerinin simetrikliğinden kaynaklanan M(k) matrisinin determinantınındaki tekrarlanan özdeğerler ise eleminasyon ve duplikasyon matrisleri kullanılarak uygulanan dönüşümler yardımıyla ortadan kaldırılmıştır. Önerilen yöntemin literatürde var olan PSA gibi yöntemlerle ilişkisi ise sonlu ve sonsuz kök sınırları üzerinden gösterilmiştir. Kararlı kılan kontrolör parametre bölgelerinin belirlenmesinde Lyapunov temelli bir yaklaşım kullanıldığından öne sürülen yöntem sadece MIMO sistemlerde değil Lyapunov formülasyonunun kurulabildiği çok geniş bir sistem sınıfına ve alt problemlere de uygulanabilir durumdadır. Bu durumu gösterebilmek amacıyla ilk olarak MIMO sistemlerde kontolör entegrasyonu problemi ele alınmıştır. MIMO kontrolörlerde meydana gelebilecek olası hataları göz önünde bulundururak olası hata durumlarında dahi sistemin kararlılığını garanti etmeyi amaçlayan bu probleme bir çözüm önerisi sunulmuştur. Önerilen yöntemin etkinliği literatürde var olan yaklaşımlar üzerinden karşılaştırmalı olarak gösterilmiştir. Buna ek olarak, yine önerilen Lyapunov eşitliği temelli yöntemin olası diğer kullanım alanlarını vurgulamak amacıyla ayrık zamanlı sistemlerin kararlılığı ayrıntılı olarak tartışılmıştır. Bu durumda önerilen yaklaşımın nasıl değiştiği vurgulanmıştır. Lyapunov temelli yaklaşım ile kararlılık sınırlarının analitik ifadelerinin belirlenmesi de mümkündür. Bu durum da özellikle optimizasyon temelli tasarım yöntemlerinde farklı kullanım alanları açmaktadır. Bu kapsamda dayanıklı MPC problemi detaylı olarak ele alınmıştır. Lyapunov yöntemi kullanılarak belirlenen analitik kararlılık sınırları dayanıklı MPC problem formülasyonunda kullanılarak ele alınan problem nominal MPC problemine dönüştürülmüştür. Önerilen yöntemin etkinliği literatürde sıklıkla kullanılan bir sistem üzerinden de gösterilmiştir. Tam köşegenleştirme ile karşılaştırıldığında, köşegen baskınlık daha zayıf bir koşul olarak ortaya çıkar. Bu nedenle, parametre belirsizlikleri durumunda dahi bu koşulu sağlayan kontrolör parametrelerini belirlemek mümkün hale gelir. Bu tez kapsamında, TFM elemanlarının aralık tipi parametre belirsizliği içerdiği TITO sistemler detaylı olarak tartışılmıştır. Bu tür sistemleri parametre belirsizlikleri durumunda dahi köşegen baskın kılan statik köşegen kontrolörlerin belirlenmesi hedeflenmiştir. Bu hedef doğrultusunda üçgen eşitsizliği ve tarama yöntemlerine dayanan iki farklı konservatif yöntem önerilmiştir. Bu yaklaşımlar kullanılarak tartışılan problem ilk aşamada nominal sistemin ağırlıklandırılmış baskınlık problemine dönüştürülmüştür. Sonrasında da önceki bölümlerde elde edilen sonuçlar kullanılarak sonuca gidilmiştir. Son olarak da belirsiz parametre içeren çok değişkenli sistemlerin kararlılığı tartışılmıştır. Bu aşamada belirsiz parametreler için literatürde kullanılan iki farklı varsayıma yer verilmiştir. İlk varsayımda belirsiz parametreler üzerinde herhangi bir kısıtlama yoktur ve sistemi kararlı kılan tüm belirsiz parametre bölgelerinin belirlenmesi hedeflenmektedir. Bu durumda önerilen Lyapunov temelli yöntem direkt olarak uygulanabilir durumdadır. Bu yöntemin aksine literatürde var olan bir çok yöntemde ise belirsiz parametre sayısı ve türü üzerinde bir takım varsayımlarda bulunularak sonuçlar elde edilmiştir. Bu tez kapsamında önerilen yöntemin doğruluğu literatürde var olan farklı örnek durumlar üzerinden gösterilmiştir. Diğer taraftan, bazı durumlarda belirsiz sistem parametrelerinin alabileceği minimum ve maksimum değerler belirlidir. İlgili parametrenin bilinen bu değerler arasında bir değer aldığı tüm durumlarda polinom ailesinin kararlı kalıp kalmadığının belirlenmesi hedeflenir. SISO sistemler için bazı özel durumlarda sonlu sayıda polinomun kararlı olmasının tüm polinom ailesinin kararlığını garanti ettiği gösterilmiştir. MIMO sistemlerde ise en basit durumlarda bile kontrolör parametrelerinin ve TFM'yi oluşturan transfer fonksiyonlarının çarpımları karakteristik polinomda görünmektedir. %SISO sistemlerle karşılaştırıldığında bu tarz durumlarda dayanıklı kararlılığı sağlayan kontrolör parametre bölgelerinin belirlenmesi görece daha zordur. Tartışılan bu problemde karakteristik polinom, hem alt ve üst sınırları bilinen belirsiz parametreleri hem de serbest kontrolör parametrelerini içermektedir. Bu tez kapsamında yukarı yakınsama yaklaşımından da yararlanılarak, Kharitonov Teoremi ve önerilen Lyapunov eşitliği temelli yaklaşımla bu tarz sistemleri dayanıklı kararlı kılan kontrolör parametre bölgelerinin belirlenmesine yönelik bir yöntem önerilmiştir. Önerilen bu yöntem Kharitonov Teoremi de kullanıldığından hesaplama yükünü önemli oranda azaltmaktadır ancak değişmez kontrolör parametre bölgelerinin belirlenmesinde ek analiz adımlarını da beraberinde getirmektedir. Özetle, bu tez kapsamında nominal ve parametre belirsiz MIMO sistemeleri hem köşegen baskın kılan hem de kararlı yapan köşegen tipteki kontrolörlerin parametre bölgelerinin belirlenmesi hedeflenmiştir. Köşegen baskınlık açısından bakıldığında gerek ve yeter koşulların belirlenmesi hedeflendiğinden TITO sistemler üzerinden sonuçlar elde edilmiştir. Diğer taraftan kararlı kılan kontrolör parametrelerinin belirlenmesinde ise herhangi bir sistem veya kontrolör kısıtı bulunmamaktadır.Most of the industrial plants include more than one input and output variable. Compared to Single Input Single Output (SISO) systems, such systems include different structural properties. For instance, an output variable is effected by all input variables in general. On the other hand, in terms of controller structures, researchers have focused on two main approaches for such systems, which are "centralized" and "decentralized" controllers. However, it can be proposed that decentralized controllers are preferred more in practice due to various reasons like less number of tuning parameter, possibility to apply single loop controller design methods, ease of use for operators etc. Whereas, in general, performance and efficiency of such controllers reduce when there are significant interactions between different input-output pairs in a Multi Input Multi Output (MIMO) system. Reducing the interactions between different input-output pairs in MIMO systems is crucial in terms of decentralized controller design due to the previously mentioned reasons. Diagonal dominance which is a weaker condition compared to decoupling, is one of the approaches that can be used to reduce interactions in MIMO systems. One input variable is strongly related with one specific output variable in diagonal dominant systems. One of the main aims of this thesis is to determine controller parameter regions that achieve diagonal dominance conditions. Additionally, it is also aimed to determine stabilizing parameter spaces, since diagonal dominance does not indicate stability in general. As a result, controller parameter regions that achieve both diagonal dominance and stability conditions in closed loop are determined in this thesis as the first step of decentralized controller design. In literature, the diagonal dominance concept has gained attraction since the pioneering studies of Rosenbrock in early 1970s. However, in the meantime most of the researchers focused on determining a specific controller parameter pair that optimizes a predetermined condition. Such a case may restrict the designer in the next steps of the design process. Additionally, the number of studies are limited that investigates the diagonal dominance characteristics of the determined controller parameters in case uncertainties or checks how the system is close to the diagonal dominance boundaries. Two Input Two Output (TITO) systems are special subset of MIMO systems since in practice many MIMO systems can be treated as several TITO subsystems as proposed in literature. In terms of diagonal dominance, particularly, TITO systems and diagonal type controllers are discussed in detail, since it is aimed to determine necessary and sufficient conditions on diagonal dominance in terms of controller parameters. For such systems, exact conditions on the controller parameters in terms of both column and row diagonal dominance are derived at a given fixed frequency. Derived results are also valid for finite number of frequencies and practically applicable for a given frequency range. Moreover, weighting factors are added to the original definition of diagonal dominance in order to derive controller parameter regions that achieve better diagonal dominance ratios. Necessary and sufficient conditions on diagonal type controllers are also derived for the weighted diagonal dominance problem. Lastly, critical frequencies that may possibly change the interval characteristics of static diagonal controllers for the column diagonal dominance are derived. Effectiveness of the derived results in terms of diagonal dominance are demonstrated over several case studies using Gershgorin Disc plots and diagonal dominance ratio plots. On the other hand, a Lyapunov equation based stability mapping approach is proposed within the scope of this thesis to derive stabilizing controller parameter spaces of a given MIMO system. In the present approach, it is not necessary to calculate singular frequencies or apply frequency sweeping that most of the frequency based approaches require. From the Lyapunov point of view, positive definiteness of the Lyapunov matrix P(k) is necessary and sufficient for LTI systems. However, considering the numerators and denominators of the leading principal minors it is required to solve 2n parametric equation in order to determine positive definiteness of P(k). This number is reduced to n+1 at the first step. After that, Lyapunov matrix equation is reduced to the standard set of equation representation using the Kronecker products and vectorization operator. At this point, a new matrix M(k) is defined over the Kronecker products and it is shown that determinant of M(k) is the product of binary combinations of A(k). Using the relations between the system matrix A(k), Lyapunov matrix P(k) and M(k), it is shown that it is sufficient to solve at most 2 parametric equations which are |M(k)|=0 and |M(k)|->infinity. Determinant of M(k) includes redundant multiplications of binary combinations of eigenvalue pairs of A(k) due to the matrices P(k) and Q that are used in Lyapunov formulation are symmetric. In order to eliminate the redundant multiplications and reduce the computational complexity, elimination and duplication matrices are introduced as transformation matrices. In addition to MIMO systems, the proposed stability mapping approach is applicable to a broad range of systems, further system classes and sub problems where Lyapunov formulation is possible. In order to demonstrate these properties of the proposed approach, firstly, controller integrity problem of MIMO systems is discussed in detail. An approach is proposed to determine stabilizing controller parameter regions even in case of possible failures related with controller parameters. A benchmark case study is included and effectiveness of the proposed approach is shown over a comparative study with a currently existing approach. Additionally, discrete time systems is also discussed in detail to demonstrate the further application areas of the proposed Lyapunov equation based stability mapping approach. In this case, the structure of the Lyapunov equation varies slightly compared to the continuous time case. Another benefit of the proposed Lyapunov equation based approach is the opportunity to determine analytical expressions of stability boundaries. So that, it becomes possible to use Lyapunov equation based stability mapping approach in optimization based approaches by inserting the stability boundaries as constraints on such approaches. This case is also addressed through the robust Model Predictive Control (MPC) problem. Analytical stability boundaries which is derived in the off-line phase using the proposed stability mapping approach is inserted to the robust MPC problem formulation to achieve stability. In this way, robust MPC problem is transformed into the nominal MPC problem. The effectiveness of the proposed method is also demonstrated through a benchmark system that is frequently used in the literature. Diagonal dominance proposes weaker conditions compared to decoupling. As a result, it becomes possible to determine controller parameter regions that achieve diagonal dominance in case of parametric uncertainties. Within the scope of this thesis, two conservative approaches which are based on triangular inequality and griding are proposed for the systems that include interval type uncertainties in Transfer Function Matrix (TFM) elements. Using these approaches diagonal dominance problem of a parametric uncertain system is transferred to the weighted diagonal dominance problem of the nominal plant. After that, previously derived results are used to determine static diagonal controller parameter regions. Lastly, stability of parameter uncertain multivariable systems is discussed in order to determine robustly stabilizing parameter spaces. There are two main assumptions on uncertain parameters in literature. In the first assumption, there is no restriction on uncertain parameters and it is aimed to determine all uncertain parameter spaces that preserve stability of the closed loop system. In this case, proposed Lyapunov equation based stability mapping approach is directly applicable. Contrary to this approach, many methods that is currently available in the literature include the results obtained by making some assumptions on the number and the type of uncertain parameters. The validity of the Lyapunov equation based method has been demonstrated through different benchmark case studies. On the other hand, in some cases, it is assumed that upper and lower bounds of uncertain parameters are known. It is aimed to determine whether the whole polynomial family is stable in all cases where the uncertain parameters take any value between these known intervals. In some special cases, it was shown in literature that stability of finite number fixed polynomials guarantee the stability of whole uncertain polynomial family in case of SISO systems. However, the characteristic polynomial of MIMO systems includes the multiplication of free controller parameters and individual transfer functions even in the simplest cases. As a result, it can be proposed that compared to SISO systems, it is more difficult to determine the controller parameter areas that provide robust stability in such systems. In the discussed problem characteristic equation includes both uncertain parameters that have known upper and lower bounds and free controller parameters. In this thesis, an approach is presented to determine robustly stabilizing parameter spaces using the Kharitonov Theorem in accordance with the Lyapunov method by applying overbounding method on characteristic polynomial coefficients. The proposed method reduces the computational complexity significantly, since Kharitonov Theorem is used. However, it must also be noted that calculation of invariant controller parameter sub regions in terms of overbounding also introduces additional analysis steps. As a conclusion, in this thesis, it is mainly focused on determining controller parameter regions of the diagonal type controllers that make both nominal and parametric MIMO systems diagonal dominant and stable. The results are derived through TITO systems from the standpoint of diagonal dominance, since it is aimed to determine the necessary and sufficient conditions. On the other hand, there is no restriction on the system and controller type for the proposed stability mapping approach.DoktoraPh.D

Flow-oriented anomaly-based detection of denial of service attacks with flow-control-assisted mitigation

Flooding-based distributed denial-of-service (DDoS) attacks present a serious and major threat to the targeted enterprises and hosts. Current protection technologies are still largely inadequate in mitigating such attacks, especially if they are large-scale. In this doctoral dissertation, the Computer Network Management and Control System (CNMCS) is proposed and investigated; it consists of the Flow-based Network Intrusion Detection System (FNIDS), the Flow-based Congestion Control (FCC) System, and the Server Bandwidth Management System (SBMS). These components form a composite defense system intended to protect against DDoS flooding attacks. The system as a whole adopts a flow-oriented and anomaly-based approach to the detection of these attacks, as well as a control-theoretic approach to adjust the flow rate of every link to sustain the high priority flow-rates at their desired level. The results showed that the misclassification rates of FNIDS are low, less than 0.1%, for the investigated DDOS attacks, while the fine-grained service differentiation and resource isolation provided within the FCC comprise a novel and powerful built-in protection mechanism that helps mitigate DDoS attacks

Computational intelligence approaches to robotics, automation, and control [Volume guest editors]

No abstract available

A generic architecture style for self-adaptive cyber-physical systems

Die aktuellen Konzepte zur Gestaltung von Regelungssystemen basieren auf dynamischen Verhaltensmodellen, die mathematische Ansätze wie Differentialgleichungen zur Ableitung der entsprechenden Funktionen verwenden. Diese Konzepte stoßen jedoch aufgrund der zunehmenden Systemkomplexität allmählich an ihre Grenzen. Zusammen mit der Entwicklung dieser Konzepte entsteht eine Architekturevolution der Regelungssysteme. In dieser Dissertation wird eine Taxonomie definiert, um die genannte Architekturevolution anhand eines typischen Beispiels, der adaptiven Geschwindigkeitsregelung (ACC), zu veranschaulichen. Aktuelle ACC-Varianten, die auf der Regelungstheorie basieren, werden in Bezug auf ihre Architekturen analysiert. Die Analyseergebnisse zeigen, dass das zukünftige Regelungssystem im ACC eine umfangreichere Selbstadaptationsfähigkeit und Skalierbarkeit erfordert. Dafür sind kompliziertere Algorithmen mit unterschiedlichen Berechnungsmechanismen erforderlich. Somit wird die Systemkomplexität erhöht und führt dazu, dass das zukünftige Regelungssystem zu einem selbstadaptiven cyber-physischen System wird und signifikante Herausforderungen für die Architekturgestaltung des Systems darstellt. Inspiriert durch Ansätze des Software-Engineering zur Gestaltung von Architekturen von softwareintensiven Systemen wird in dieser Dissertation ein generischer Architekturstil entwickelt. Der entwickelte Architekturstil dient als Vorlage, um vernetzte Architekturen mit Verfolgung der entwickelten Designprinzipien nicht nur für die aktuellen Regelungssysteme, sondern auch für selbstadaptiven cyber-physischen Systeme in der Zukunft zu konstruieren. Unterschiedliche Auslösemechanismen und Kommunikationsparadigmen zur Gestaltung der dynamischen Verhalten von Komponenten sind in der vernetzten Architektur anwendbar. Zur Bewertung der Realisierbarkeit des Architekturstils werden aktuelle ACCs erneut aufgenommen, um entsprechende logische Architekturen abzuleiten und die Architekturkonsistenz im Vergleich zu den originalen Architekturen basierend auf der Regelungstheorie (z. B. in Form von Blockdiagrammen) zu untersuchen. Durch die Anwendung des entwickelten generischen Architekturstils wird in dieser Dissertation eine künstliche kognitive Geschwindigkeitsregelung (ACCC) als zukünftige ACC-Variante entworfen, implementiert und evaluiert. Die Evaluationsergebnisse zeigen signifikante Leistungsverbesserungen des ACCC im Vergleich zum menschlichen Fahrer und aktuellen ACC-Varianten.Current concepts of designing automatic control systems rely on dynamic behavioral modeling by using mathematical approaches like differential equations to derive corresponding functions, and slowly reach limitations due to increasing system complexity. Along with the development of these concepts, an architectural evolution of automatic control systems is raised. This dissertation defines a taxonomy to illustrate the aforementioned architectural evolution relying on a typical example of control application: adaptive cruise control (ACC). Current ACC variants, with their architectures considering control theory, are analyzed. The analysis results indicate that the future automatic control system in ACC requires more substantial self-adaptation capability and scalability. For this purpose, more complicated algorithms requiring different computation mechanisms must be integrated into the system and further increase system complexity. This makes the future automatic control system evolve into a self-adaptive cyber-physical system and consistitutes significant challenges for the system’s architecture design. Inspired by software engineering approaches for designing architectures of software-intensive systems, a generic architecture style is proposed. The proposed architecture style serves as a template by following the developed design principle to construct networked architectures not only for the current automatic control systems but also for self-adaptive cyber-physical systems in the future. Different triggering mechanisms and communication paradigms for designing dynamic behaviors are applicable in the networked architecture. To evaluate feasibility of the architecture style, current ACCs are retaken to derive corresponding logical architectures and examine architectural consistency compared to the previous architectures considering the control theory (e.g., in the form of block diagrams). By applying the proposed generic architecture style, an artificial cognitive cruise control (ACCC) is designed, implemented, and evaluated as a future ACC in this dissertation. The evaluation results show significant performance improvements in the ACCC compared to the human driver and current ACC variants

Remote maintenance of real time controller software over the internet

The aim of the work reported in this thesis is to investigate how to establish a standard platform for remote maintenance of controller software, which provides remote monitoring, remote fault identification and remote performance recovery services for geographically distributed controller software over the Internet. A Linear Quadratic Gaussian (LQG) controller is used as the benchmark for the control performance assessment; the LQG benchmark variances are estimated based on the Lyapunov equation and subspace matrices. The LQG controller is also utilized as the reference model of the actual controller to detect the controller failures. Discrepancies between control signals of the LQG and the actual controller are employed to a General Likelihood Ratio (GLR) test and the controller failure detection is characterized to detect sudden jumping points in the mean or variance of the discrepancies. To restore the degraded control performance caused by the controller failures, a compensator is designed and inserted into the post-fault control loop, which serially links with the faulty controller and recovers the degraded control performance into an acceptable range. Techniques of controller performance monitoring, controller failure detection and maintenance are extended into the Internet environment. An Internet-based maintenance system for controller software is developed, which provides remote control performance assessment and recovery services, and remote fault identification service over the Internet for the geographically distributed controller software. The integration between the mobile agent technology and the controller software maintenance is investigated. A mobile agent based controller software maintenance system is established; the mobile agent structure is designed to be flexible and the travelling agents can be remotely updated over the Internet. Also, the issue of heavy data process and transfer over the Internet is probed and a novel data process and transfer scheme is introduced. All the proposed techniques are tested on sirnulations or a process control unit. Simulation and experimental results illustrate the effectiveness of the proposed techniques.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Evolutionary design automation for control systems with practical constraints

The aim of this work is to explore the potential and to enhance the capability of evolutionary computation in the development of novel and advanced methodologies that enable control system structural optimisation and design automation for practical applications. Current design and optimisation methods adopted in control systems engineering are in essence based upon conventional numerical techniques that require derivative information of performance indices. These techniques lack robustness in solving practical engineering problems, which are often of a multi-dimensional, multi-modal nature. Using those techniques can often achieve neither global nor structural optimisation. In contrast, evolutionary mechanism learning tools have the ability to search in a multi-dimensional, multi-modal space, but they can not approach a local optimum as a conventional calculus-based method. The first objective of this research is to develop a reliable and effective evolutionary algorithm for engineering applications. In this thesis, a globally optimal evolutionary methodology and environment for control system structuring and design automation is developed, which requires no design indices to be differentiable. This is based on the development of a hybridised GA search engine, whose local tuning is tremendously enhanced by the incorporation of Hill-Climbing (HC), Simulated Annealing (SA) and Simplex techniques to improve the performance in search and design. A Lamarckian inheritance technique is also developed to improve crossover and mutation operations in GAs. Benchmark tests have shown that the enhanced hybrid GA is accurate, and reliable. Based on this search engine and optimisation core, a linear and nonlinear control system design automation suite is developed in a Java based platform-independent format, which can be readily available for design and design collaboration over corporate Intranets and the Internet. Since it has also made cost function unnecessary to be differentiable, hybridised indices combining time and frequency domain measurement and accommodating practical constraints can now be incorporated in the design. Such type of novel indices are proposed in the thesis and incorporated in the design suite. The Proportional plus Integral plus Derivative (PID) controller is very popular in real world control applications. The development of new PID tuning rules remains an area of active research. Many researchers, such as Åström and Hägglund, Ho, Zhuang and Atherton, have suggested many methods. However, their methods still suffer from poor load disturbance rejection, poor stability or shutting of the derivative control etc. In this thesis, Systematic and batch optimisation of PID controllers to meet practical requirements is achieved using the developed design automation suite. A novel cost function is designed to take disturbance rejection, stability in terms of gain and phase margins and other specifications into account in-the same time. Comparisons made with Ho's method confirm that the derivative action can play an important role to improve load disturbance rejection yet maintaining the same stability margins. Comparisons made with Åström’s method confirm that the results from this thesis are superior not only in load disturbance rejection but also in terms of stability margins. Further robustness issues are addressed by extending the PID structure to a free form transfer function. This is realised by achieving design automation. Quantitative Feedback Theory (QFTX, method offers a direct frequency-domain design technique for uncertain plants, which can deal non-conservatively with different types of uncertainty models and specifications. QFT design problems are often multi-modal and multi-dimensional, where loop shaping is .the most challenging part. Global solutions can hardly be obtained using analytical and convex or linear programming techniques. In addition, these types of conventional methods often impose unrealistic or unpractical assumptions and often lead to very conservative designs. In this thesis, GA-based automatic loop shaping for QFT controllers suggested by the Research Group is being furthered. A new index is developed for the design which can describe stability, load rejection and reduction of high frequency gains, which has not been achieved with existing methods. The corresponding prefilter can also be systematically designed if tracking is one of the specifications. The results from the evolutionary computing based design automation suite show that the evolutionary technique is much better than numerical methods and manual designs, i.e., 'high frequency gain' and controller order have been significantly reduced. Time domain simulations show that the designed QFT controller combined with the corresponding prefilter performs more satisfactorily

Investigation in the application of complex algorithms to recurrent generalized neural networks for modeling dynamic systems

Neural networks are mathematical formulations that can be "trained" to perform certain functions. One particular application of these networks of interest in this thesis is to "model" a physical system using only input-output information. The physical system and the neural network are subjected to the same inputs. The neural network is then trained to produce an output which is the same as the physical system for any input. This neural network model so created is essentially a "blackbox" representation of the physical system. This approach has been used at the University of Saskatchewan to model a load sensing pump (a component which is used to create a constant flow rate independent of variations in pressure downstream of the pump). These studies have shown the versatility of neural networks for modeling dynamic and non-linear systems; however, these studies also indicated challenges associated with the morphology of neural networks and the algorithms to train them. These challenges were the motivation for this particular research. Within the Fluid Power Research group at the University of Saskatchewan, a "global" objective of research in the area of load sensing pumps has been to apply dynamic neural networks (DNN) in the modeling of loads sensing systems.. To fulfill the global objective, recurrent generalized neural network (RGNN) morphology along with a non-gradient based training approach called the complex algorithm (CA) were chosen to train a load sensing pump neural network model. However, preliminary studies indicated that the combination of recurrent generalized neural networks and complex training proved ineffective for even second order single-input single-output (SISO) systems when the initial synaptic weights of the neural network were chosen at random. Because of initial findings the focus of this research and its objectives shifted towards understanding the capabilities and limitations of recurrent generalized neural networks and non-gradient training (specifically the complex algorithm). To do so a second-order transfer function was considered from which an approximate recurrent generalized neural network representation was obtained. The network was tested under a variety of initial weight intervals and the number of weights being optimized. A definite trend was noted in that as the initial values of the synaptic weights were set closer to the "exact" values calculated for the system, the robustness of the network and the chance of finding an acceptable solution increased. Two types of training signals were used in the study; step response and frequency based training. It was found that when step response and frequency based training were compared, step response training was shown to produce a more generalized network. Another objective of this study was to compare the use of the CA to a proven non-gradient training method; the method chosen was genetic algorithm (GA) training. For the purposes of the studies conducted two modifications were done to the GA found in the literature. The most significant change was the assurance that the error would never increase during the training of RGNNs using the GA. This led to a collapse of the population around a specific point and limited its ability to obtain an accurate RGNN. The results of the research performed produced four conclusions. First, the robustness of training RGNNs using the CA is dependent upon the initial population of weights. Second, when using GAs a specific algorithm must be chosen which will allow the calculation of new population weights to move freely but at the same time ensure a stable output from the RGNN. Third, when the GA used was compared to the CA, the CA produced more generalized RGNNs. And the fourth is based upon the results of training RGNNs using the CA and GA when step response and frequency based training data sets were used, networks trained using step response are more generalized in the majority of cases

Efficiency and Sustainability of the Distributed Renewable Hybrid Power Systems Based on the Energy Internet, Blockchain Technology and Smart Contracts-Volume II

The climate changes that are becoming visible today are a challenge for the global research community. In this context, renewable energy sources, fuel cell systems, and other energy generating sources must be optimally combined and connected to the grid system using advanced energy transaction methods. As this reprint presents the latest solutions in the implementation of fuel cell and renewable energy in mobile and stationary applications, such as hybrid and microgrid power systems based on the Energy Internet, Blockchain technology, and smart contracts, we hope that they will be of interest to readers working in the related fields mentioned above

Visual Servoing in Robotics

Visual servoing is a well-known approach to guide robots using visual information. Image processing, robotics, and control theory are combined in order to control the motion of a robot depending on the visual information extracted from the images captured by one or several cameras. With respect to vision issues, a number of issues are currently being addressed by ongoing research, such as the use of different types of image features (or different types of cameras such as RGBD cameras), image processing at high velocity, and convergence properties. As shown in this book, the use of new control schemes allows the system to behave more robustly, efficiently, or compliantly, with fewer delays. Related issues such as optimal and robust approaches, direct control, path tracking, or sensor fusion are also addressed. Additionally, we can currently find visual servoing systems being applied in a number of different domains. This book considers various aspects of visual servoing systems, such as the design of new strategies for their application to parallel robots, mobile manipulators, teleoperation, and the application of this type of control system in new areas