Distinguished Lecturers Program

Program Description

The Control Systems Society is continuing to fund a Distinguished Lecture Series.

The primary purpose is to help Society chapters provide interesting and informative programs for the membership, but the Distinguished Lecture Series may also be of interest to industry, universities, and other parties.

The Control Systems Society has agreed to a cost sharing plan which may be used by IEEE Chapters, sections, subsections, and student groups. IEEE student groups are especially encouraged to make use of this opportunity to have excellent speakers at moderate cost.

At the request of a Society Chapter, (or other IEEE groups as mentioned above), a lecture will be scheduled at a place and time that is mutually agreeable to both the Chapter and the Distinguished Lecturer. The Control Systems Society will pay ground transportation at the origin, and Economy Class air fare up to a maximum limit of $1,000 for trips within the same continent and $2,000 for intercontinental trips. The chapter will pay the ground transportation at the destination, hotel, meals, and other incidental expenses. Lecturers will receive no honorarium. Note that the group organizing the lecture must have some IEEE affiliation, the lecture must be free to attend by IEEE members.

Procedures

When you wish to use this program, you may contact the Distinguished Lecturer directly to work out a tentative itinerary. Then, you must submit a formal proposal to the Distinguished Lecturer Program Chair for his/her approval. The proposal should be sent to the Distinguished Lecturer Program Chair by someone in the local chapter, who should identify their role in the chapter, and provide some details of the invitation, including the dates. The proposal should contain a budgetary quotation for air fare from an authorized source (air line/ travel agent), and a confirmation that the local chapter will pay their share of the expenses associated with the trip. If the trip is approved, then IEEE CSS would pay ground transportation at the origin, and Economy Class air fare up to a maximum limit of $1,000 for trips within the same continent and $2,000 for intercontinental trips. The chapter will pay the ground transportation at the destination, hotel, meals, and other incidental expenses. Procedures for unusual situations (such as when the speaker has other business on the trip) should be cleared through the Distinguished Lecturer Program Chair.

The expense claim filed by the distinguished lecturer upon the conclusion of the trip should contain receipts for the airfare and ground transportation at the origin.
Each distinguished lecturer will be limited to two trips per year, out of which at most one can be inter-continental.

Distinguished Lecturers Program Chair

Distinguished Lecturers

John Baillieul Headshot Photo
Distinguished Lecturer

Information Gradients and Topology in Random Fields

Using concepts from differential topology and information theory, I shall describe a theoretical framework for search strategies aimed at rapid discovery of topological features (locations of critical points and critical level sets) of a priori unknown differentiable random fields. The theory enables study of efficient reconnaissance strategies in which the tradeoff between speed and accuracy can be understood. The proposed approach to rapid discovery of topological features has led in a natural way to to the creation of parsimonious reconnaissance routines that do not rely on any prior knowledge of the environment. The design of topology-guided search protocols uses a mathematical framework that quantifies the relationship between what has been discovered and what remains to be discovered. The quantification rests on an information theory inspired model whose properties allow us to treat search as a problem in optimal information acquisition.

Information Based Control and Control Communication Complexity

The interaction of information and control has been a topic of interest to system theorists that can be traced back to the 1950’s when the fields of communications, control, and information theory were new but developing rapidly.  Recent advances in our understanding of this interplay have emerged from work on the dynamical effect of state quantization and a corresponding understanding of how communication channel data rates affect system stability.  While a large body of research has now emerged dealing with communication constrained feedback channels and optimal design of information flows in networks, less attention has been paid to ways in which control systems should be designed in order to optimally mediate computation and communication.  Such optimization problems are of interest in the context of quantum computing, and similar problems have recently been discussed in connection with protocols for assembly of molecular components in synthetic biology.

The Standard Parts Problem and Quantization in Optimal Control

Recently W.S. Wong has proposed the concept of control communication complexity (CCC) as a formal approach for understanding how  a group of distributed agents can choose independent actions from a prescribed "action code book" that cooperatively realize common goals and objectives.  A prototypical goal is the computation of a function, and CCC provides a promising new approach to understanding complexity in terms of the cost of realizing a selected evaluation.  This lecture will introduce control communication complexity in terms of what are called standard parts optimal control problems. Problems in optimal ensemble averaged motion sequences and distributed control of dynamical systems defined on Lie groups are discussed.

Richard D. Braatz Headshot Photo
Distinguished Lecturer

Systems Nanotechnology: Identification, Estimation, and Control of Nanoscale Systems

Abstract: Nanometer length scale analogues of most traditional control elements, such as sensors, actuators, and feedback controllers, have been enabled by recent advancements in device manufacturing and fundamental materials research. However, combining these new control elements in classical systems frameworks remains elusive. Methods to address the new generation of systems issues particular to nanoscale systems is termed here as systems nanotechnology. This presentation discusses some promising control strategies and theories that have been developed to address the challenges that arise in systems nanotechnology. Specific examples are provided where the identification, estimation, and control of complex nanoscale systems have been demonstrated in experimental implementations or in high-fidelity simulations. Some control theory problems are also described that, if resolved, would facilitate further applications.

Robust Optimal Control of Finite-time Distributed Parameter Systems

Abstract: Most high value products such as in the pharmaceuticals, microelectronic, and nanotechnology industries are manufactured in a series of processing steps that operate over finite time. These processes are usually distributed parameter systems in which tight control is required. Computationally efficient methods are proposed for the robust optimal control of finite-time distributed parameter systems (DPS), in which robustness is ensured for either deterministic or stochastic parametric uncertainties. In the deterministic case, the effects of uncertainties on the states and product quality are quantified by power series expansions combined with linear matrix inequality or structured singular value analysis. In the stochastic case, the effects of uncertainties are quantified by power series or polynomial chaos expansions. The robust performance analysis have been incorporated into fixed controllers and model predictive control algorithms. The approaches are illustrated for several applications problems.

Control of Molecular Purity, Crystal Structure, and Particle Size Distribution in Pharmaceutical Crystallization

Abstract: An overview is provided on advances in the control of molecular purity, crystal structure, and particle size distribution of pharmaceutical crystals. A nonlinear feedback control strategy is described that is robust to orders-of-magnitude variations in the crystallization kinetics, which enables the same feedback controller to apply to completely different pharmaceutical compounds by just updating the drug solubility. The control strategy enables the manufacture of large drug crystals of uniform size and specified crystal structure, regardless of whether the crystal structure is thermodynamically stable or metastable. The control strategy forces the closed-loop operations to be within a tightly constrained trajectory bundle that connects the initial states to the desired final states. A modification of the methodology is able to achieve a target crystal size distribution by employing continual manipulation of seeds manufactured using a dual-impinging jet mixer. The methodology has been evaluated in theoretical, simulation, and experimental studies for a wide variety of pharmaceutical compounds. The presentation ends with a discussion of directions towards the simultaneous control of multiple properties, by the integration of feedback control with process design.

Linda Bushnell Headshot Photo
Distinguished Lecturer

Leader Title: Leader Selection for Performance and Control of Complex Networks

Control of complex networks, including unmanned vehicle networks, social networks, and biological systems, is an ever-growing challenge.  A standard approach is to directly control a subset of leader nodes, which then influence the remaining (follower) nodes.  While the choice of leader nodes is known to impact the performance, controllability, and security of complex networks, efficient algorithms for selecting optimal leaders are currently lacking.In this talk, we give an overview of our ongoing work on leader selection in complex networks.  We focus on three design criteria, namely, the robustness of the system to noise in the links between nodes, the time for the follower nodes to converge to their desired state, and the controllability to the follower nodes from the leader nodes.  We present a unifying framework based on submodularity, a diminishing returns property analogous to concavity of real-valued functions, for studying each of these criteria.  Our framework enables efficient leader selection based on the criteria above, with provable guarantees on the resulting system performance.  Moreover, we generalize our approach to time-varying networks, including networks with random failures, arbitrary topology variations due to node mobility, and attacks by an intelligent adversary targeting one or more links.  

Carlos Canudas de Wit Headshot Photo
Distinguished Lecturer

Modeling, Forecasting and control of Traffic systems

The Grenoble Traffic Lab (GTL http://necs.inrialpes.fr/pages/reseach/gtl.php) initiative is a real-time traffic data center (platform) intended to collect traffic road infrastructure information in real-time with minimum latency and fast sampling periods. This lecture includes several aspects on modeling, forecasting and control of traffic systems, which are applied to the GTL. In this presentation, we first review main flow-conservation models which are used as a basis to design physical-oriented forecasting & control algorithms. In particular we underline fundamental properties like downstream/upstream controllability and observability of such models, and present a new network set-up for analysis. Then we present advances in traffic forecasting using graph-constrained  macroscopic models which substantially reduce the number of possible affine dynamics of the system and preserve the number of vehicles in the network. This model is used to recover the state of the traffic network and precisely localize the eventual congestion front. The last part of the talk we discuss issues on density balancing control, where the objective is to design the homogeneous distribution of density on the freeway using the input flows as decision variables. The study shown, that a key-stone for the design of the balanced states is a necessary cooperation of ramp metering with  the variable speed limit control. 

Fun-to-Drive by Feedback

This lecture is devoted to new challenging control problems arising in the automotive industry as a consequence  of the customer-driven performance specifications adopted by car builders which have dramatically increased the number of new proposed automated features where feedback interacts with the driver. The notion of "Fun-to-Drive by Feedback" relates, here, to the ability to design a control scheme  resulting in good ride comfort behavior as well as acceptable safe operation. The lecture shows how control techniques can be used to solve some of these problems, and discusses how these subjective notions can be formalized thanks to concepts such as passivity and model matching control. We present a series of examples concerning systems that provide assisted automated devices (assisted clutch synchronization, steer-by-wire system, and advanced inter-distance control), in which these aspects are assessed.

Jie Chen Headshot Photo
Distinguished Lecturer

Control Performance Limitation: A Revisit in the Information Age

It is well-known that feedback can be introduced to stabilize an unstable system, to attenuate the response of a system to disturbance, and to reduce the effect of plant parameter variations and modeling error. On the other hand, feedback design is also known to be contingent on various performance considerations and physical constraints, which invariably impose limitations on the achievable performance and necessitate tradeoffs among conflicting design objectives. An important step in the feedback design process, therefore, is to analyze how system properties may inherently impose constraints upon design and thus may fundamentally limit the performance attainable. In this talk I shall present a control theorist’s perspective into this intriguing area of scientific inquiry, from the early triumph of feedback theory to the latest development in networked control. The talk will begin with a tutorial review of Bode's classical integral relations, widely considered a pillar of feedback theory. This will then usher in the more recent progress, of which multivariable integral relations of Bode and Poisson type, and a number of canonical optimal control problems will constitute the primary theme. Interpretations of these results from control perspectives will be particularly emphasized. The talk will focus on multivariable systems and address a number of new, unique issues only found in multivariable systems, with a particular undertone to networked control systems.

When is a time-delay system stable and stabilizable?
A time-delay system may or may not be stable for different lengths of delay, and further, may or may not be stabilized via feedback. When will then a delay system be stable or unstable, and for what intervals of delay? What will be the largest range of delay that a feedback system can tolerate? Fundamental questions of this kind have long eluded engineers and mathematicians alike, yet ceaselessly invite new thoughts and solutions. In this talk I shall present an analytical tool that answers to these questions, seeking to provide exact and efficient computational solutions to stability and stabilization problems of time-delay systems. The approach consists of the development of eigenvalue perturbation series and intrinsic delay bounds for stabilization. The former seeks to characterize the analytical and asymptotic properties of eigenvalues of matrix functions or operators. When applied to stability problems, the essential issue dwells on the asymptotic behavior of the critical eigenvalues on the imaginary axis, that is, on how the imaginary eigenvalues may vary with respect to the varying parameter. This behavior determines whether the imaginary eigenvalues cross from one half plane into another, and hence plays a critical role in determining the stability of such systems. The latter characterizes analytically the largest range of delay for which a system can be stabilized by a feedback controller. These results depart from the currently pervasive, typically LMI conditions, and yet are conceptually appealing and computationally efficient, requiring only the solution of a generalized eigenvalue problem.  

Warren Dixon Headshot Photo
Distinguished Lecturer

Theoretical and Experimental Outcomes of Closed-Loop Neuromuscular Control Methods to Yield Human Limb Motion

Abstract: Neuromuscular Electrical Stimulation (NMES) is prescribed by clinicians to aid in the recovery of strength, size, and function of human skeletal muscles to obtain physiological and functional benefits for impaired individuals. The two primary applications of NMES include: 1) rehabilitation of skeletal muscle size and function via plastic changes in the neuromuscular system, and 2) activation of muscle to elicit movements that result in functional performance (i.e., standing, stepping, reaching, etc.) termed functional electrical stimulation (FES). In both applications, stimulation protocols of appropriate duration and intensity are critical for preferential results. Automated NMES methods hold the potential to maximize the treatment by self-adjusting to the particular individual (facilitating potential in-home use and enabling positive therapeutic outcomes from less experienced clinicians). Yet, the development of automated NMES devices is complicated by the uncertain nonlinear musculoskeletal response to stimulation, including difficult to model disturbances such as fatigue. Unfortunately, NMES dosage (i.e., number of contractions, intensity of contractions) is limited by the onset of fatigue and poor muscle response during fatigue. This talk describes recent advances and experimental outcomes of control methods that seek to compensate for the uncertain nonlinear muscle response to electrical stimulation due to physiological variations, fatigue, and delays.

Concurrent Learning-Based Adaptive Dynamic Programming for Autonomous Agents

Analytical solutions to the infinite horizon optimal control problem for continuous time nonlinear systems are generally not possible because they involve solving a nonlinear partial differential equation. Another challenge is that the optimal controller includes exact knowledge of the system dynamics. Motivated by these issues, researchers have recently used reinforcement learning methods that involve an actor and a critic to yield a forward-in-time approximate optimal control design. Methods that also seek to compensate for uncertain dynamics exploit some form of persistence of excitation assumption to yield parameter identification. However, in the adaptive dynamic programming context, this is impossible to verify a priori, and as a result researchers generally add an ad hoc probing signal to the controller that degrades the transient performance of the system. This presentation describes a forward-in-time dynamic programming approach that exploits the use of concurrent learning tools where the adaptive update laws are driven by current state information and recorded state information to yield approximate optimal control solutions without the need for ad hoc probing. A unique desired goal sampling method is also introduced as a means to address the classical exploration versus exploitation conundrum. Applications are presented for autonomous systems including robot manipulators, underwater vehicles, and fin controlled cruise missiles. Solutions are also developed for networks of systems where the problem is cast as a differential game where a Nash equilibrium is sought.  

Headshot Photo
Distinguished Lecturer

Control of Multi-Robot Systems: From Formations to Human-Swarm Interactions

The last few years have seen significant progress in our understanding of how one should structure multi-robot systems. New control, coordination, and communication strategies have emerged and in this talk, we summarize some of these developments. In particular, we will discuss how to go from local rules to global behaviors in a systematic manner in order to achieve distributed geometric objectives, such as achieving and maintaining formations, area coverage, and swarming behaviors. We will also investigate how users can interact with networks of mobile robots in order to inject new information and objectives. The efficacy of these interactions depends directly on the interaction dynamics and the structure of the underlying information-exchange network. We will relate these network-level characteristics to controllability and manipulability notions in order to produce effective human-swarm interaction strategies. 

Choreographic Abstractions in Robotics

When programming robots to perform tasks, one is inevitably forced to make abstractions at different levels in order to answer questions such as “What should the robot be doing?” and “How should it be doing it?” In this talk, we draw inspiration from choreography in order to produce these abstractions in a systematic manner. Manifestations of this idea will include robotic marionettes and humanoid, dancing robots that execute complex motions, and we will develop a formal framework for specifying and executing such motions by combining tools and techniques from hybrid optimal control theory and linear temporal logic.

Li-Chen Fu Headshot Photo
Distinguished Lecturer

Design and Control of Atomic Force Microscope

 Atomic Force Microscope (AFM) opens a new window to the nano-world. It features high resolution in vacuum, gases, or liquid operational environments, and has now become a widely used tool in the sectors of, for example, nano measurement and machining, biotech and medical testing etc. Many top research institutions in the world have put a lot of effort into this area.

 Most conventional AFMs use piezoelectric devices to achieve their positioning. Even though the precision is up to nano-level, it has a serious problem: short travel-range. In addition, when they are operated in liquids, large measurement error will occur, mainly because the damping is substantially increased when they are immersed in liquids. To overcome the problems of short travel-range and large measurement error in liquid environments existing in conventional AFMs, a long travel-range, two-state (gases and liquids) AFM needs to be designed and developed, which has equal precision capability for both operation environments and is capable of scanning areas up to the level of millimeter. Since electromagnetic actuator has the capability of providing long travel-range and piezoelectric actuator can offer high precision, the first aforementioned problems in conventional AFMs can be overcome by integrating these two advantages, which accounts for the need of introducing hybrid control in the resulting AFM. On the other hand, as the liquid operation environment is very critical to the cantilever scan, to cope with the resulting lower resolution of those AFM measurements made in liquids, as compared with those made in gases, becomes imperative. An adaptive Q controller has therefore been developed to resolve such problems. 

Real-Time Visual Tracking with Bayesian Filters

Visual tracking in a dynamic environment has drawn a great deal of attention nowadays. It spans a wide research spectrum, such as for access control, human or vehicle detection and identification, detection of anomalous behaviors, crowd statistics or congestion analysis, human-machine interaction in an intelligent space, etc.

Many problems in science require estimation of the state of a system that changes over time using a sequence of noisy measurements made on the system. Bayesian filter provides a rigorous general framework for dynamic state estimation problems. Visual tracking is also one kind of this problem. The sensed sequence of 2D image data, which may lose some 3D information and is usually noisy, includes the target, similar objects, and cluttered background, etc. The visual tracker designed with the spirit of Bayesian filter can overcome these problems and result in the successful multi-target tracking when the objects interacting in a group. 

For utilizing the information obtained from visual tracking, such as the visual servoing of robot motion or human-machine interaction, the visual tracking of one image frame must be processed as fast as possible, otherwise the information may be changed in the processing interval. In order to reduce the computational time, the dimension of the image processing can be efficiently constrained by some spatial and temporal hypotheses which are generated from the predictions of target motion model. Other sampling schemes, such as the particle filtering, would also be employed to achieve the real-time tracking purpose.

Another issue in this talk includes the wide-area surveillance with active camera tracking and multi-camera cooperation. Since the field of view of one camera is limited, a camera platform is usually equipped with some degree of freedoms to extend its observing range. The observing range can be extended more by combining multiple active cameras. The overall surveillance capability of the entire set of cameras could be effectively utilized through the well-designed strategies of camera task assignment and camera action selection. Integrating the distributed camera agents, which can track targets alone and collaborate with other agents tightly, the prospect of seamless tracking would be realized stage by stage.

 

Pose Estimation and Gesture Recognition Based on Visual Tracking

Human motion analysis from image sequence has many important applications in the fields of computer vision and robotics. With vision based interpretation of human motion in image sequence, HMI can be experienced more naturally without hand held device. Therefore, this talk will start with introduction of a two-hands tracking method with a monocular camera. To cope with the situations of self-occlusion, similar color distracters and cluttered environment, this methodology is based on different kinds of image cues including locally discriminative color, motion history, gradient orientation feature, and depth order reasoning. Specifically, the multiple importance sampling (MIS) particle filter generates the tracking hypotheses of merged targets by the skin blob mask and the depth order estimation. These merged hypotheses are then evaluated by the visual cues of occluded face template, hand shape orientation and motion continuity. Next, the talk will also address pose estimation, where MIS particle filter will be used to integrate multiple clues to track both arms with arbitrary motion. Due to lack of depth information, a sequential pose estimation based on structure-from-motion (SFM) is proposed to online estimate 3D posture of the arms. With reliable tracking methodology, we feed the tracking result into the hidden Markov models (HMM) to on-line spot and recognize the performed action. 

Headshot Photo
Distinguished Lecturer

Model-Based Testing and Monitoring for Embedded Software

In many application domains, Simulink/Stateflow serves as a platform for model-based development of the reactive embedded code, that interacts with its environment in real-time fashion. The talk will present a model-based approach for testing Simulink/Stateflow code, based on its automated translation to input-output extended finite automaton (I/O-EFA), followed by automated test-generation, guaranteeing user-defined code as well as requirements coverage, and also support for automated test-execution and error-localization. While testing is useful for design-time error analysis, the talk will further discuss our model-based approach for run-time error monitoring, detection and localization. Monitoring at system level (as opposed to software level) is necessarily stochastic, and a more general I/O-Stochastic Hybrid Automaton (I/O-SHA) model is used, and condition is obtained for bounded-delay detectability, and achieving desired levels of false-positives/-negatives. 

Frank Lewis Headshot Photo
Distinguished Lecturer

Reinforcement Learning Structures for Real-Time Optimal Control and Differential Games

Reinforcement Learning Structures for Real-Time Optimal Control and Differential Games

F. L. Lewis, National Academy of Inventors
IEEE Fellow, IFAC Fellow, Fellow UK Inst. Measurement & Control
Moncrief-O’Donnell Endowed Chair
Head, Advanced Controls & Sensors Group
UTA Research Institute
The University of Texas at Arlington, USA

This talk will discuss some new adaptive control structures for learning online the solutions to optimal control problems and multi-player differential games.  Techniques from reinforcement learning are used to design a new family of adaptive controllers based on actor-critic learning mechanisms that converge in real time to optimal control and game theoretic solutions.  Continuous-time systems are considered.  

Optimal feedback control design has been responsible for much of the successful performance of engineered systems in aerospace, industrial processes, vehicles, ships, robotics, and elsewhere since the 1960s.  H-infinity control has been used for robust stabilization of systems with disturbances.  Optimal feedback control design is performed offline by solving optimal design equations including the algebraic Riccati equation and the Game ARE.  It is difficult to perform optimal designs for nonlinear systems since they rely on solutions to complicated Hamilton-Jacobi-Bellman or HJI equations.  Finally, optimal design generally requires that the full system dynamics be known.

Optimal Adaptive Control.  Adaptive control has provided powerful techniques for online learning of effective controllers for unknown nonlinear systems.  In this talk we discuss online adaptive algorithms for learning optimal control solutions for continuous-time linear and nonlinear systems.  This is a novel class of adaptive control algorithms that converge to optimal control solutions by online learning in real time.  In the linear quadratic (LQ) case, the algorithms learn the solution to the ARE by adaptation along the system motion trajectories.  In the case of nonlinear systems with general performance measures, the algorithms learn the (approximate smooth local) solutions of HJ or HJI equations.  The algorithms are based on actor-critic reinforcement learning techniques.  Methods are given that adapt to optimal control solutions without knowing the full system dynamics. Application of reinforcement learning to continuous-time (CT) systems has been hampered because the system Hamiltonian contains the full system dynamics.  Using a technique known as Integral Reinforcement Learning (IRL), we will develop reinforcement learning methods that do not require knowledge of the system drift dynamics.  

Online Algorithms for Zero-Sum Games.  We will develop new adaptive control algorithms for solving zero-sum games online for continuous-time dynamical systems.  Methods based on reinforcement learning policy iteration will be used to design adaptive controllers that converge to the H-infinity control solution in real-time. An algorithm will be given for partially known systems where the drift dynamics is not known. 

Cooperative/Non-Cooperative Multi-Player Differential Games.  New algorithms will be presented for solving online non zero-sum multi-player games for continuous-time systems.  We use an adaptive control structure motivated by reinforcement learning policy iteration.  Each player maintains two adaptive learning structures, a critic network and an actor network.  The parameters of these two networks are tuned based on the actions of the other players in the team.  The result is an adaptive control system that learns based on the interplay of agents in a game, to deliver true online gaming behavior.

 

Optimal Design for Cooperative Control Synchronization and Games on Comunication Graphs

Optimal Design for Cooperative Control Synchronization and Games on Comunication Graphs

F. L. Lewis, National Academy of Inventors
IEEE Fellow, IFAC Fellow, Fellow UK Inst. Measurement & Control
Moncrief-O’Donnell Endowed Chair
Head, Advanced Controls & Sensors Group
UTA Research Institute
The University of Texas at Arlington, USA

ABSTRACT

Distributed systems of agents linked by communication networks only have access to information from their neighboring agents, yet must achieve global agreement on team activities to be performed cooperatively.  Examples include networked manufacturing systems, wireless sensor networks, networked feedback control systems, and the internet.  Sociobiological groups such as flocks, swarms, and herds have built-in mechanisms for cooperative control wherein each individual is influenced only by its nearest neighbors, yet the group achieves consensus behaviors such as heading alignment, leader following, exploration of the environment, and evasion of predators.  It was shown by Charles Darwin that local interactions between population groups over long time scales lead to global results such as the evolution of species.

In this talk we present design methods for cooperative controllers for distributed systems.  The developments are for general directed graph communication structures, for both continuous-time and discrete-time agent dynamics.  Cooperative control design is complicated by the fact that the graph topology properties limit what can be achieved by the local controller design.  Thus, local controller designs may work properly on some communication graph topologies yet fail on other topologies.  Our objective is to provide local agent feedback design methods that are independent of the graph topology and so function on a wide range of graph structures.  

An optimal design method for local feedback controllers is given that decouples the control design from the graph structural properties.  In the case of continuous-time systems, the optimal design method guarantees synchronization on any graph with suitable connectedness properties.  In the case of discrete-time systems, a condition for synchronization is that the Mahler measure of unstable eigenvalues of the local systems be restricted by the condition number of the graph.  Thus, graphs with better topologies can tolerate a higher degree of inherent instability in the individual node dynamics.

A theory of duality between controllers and observers on communication graphs is given, including methods for cooperative output feedback control based on cooperative regulator designs.

In Part 2 of the talk, we discuss graphical games.  Standard differential multi-agent game theory has a centralized dynamics affected by the control policies of multiple agent players.  We give a new formulation for games on communication graphs.  Standard definitions of Nash equilibrium are not useful for graphical games since, though in Nash equilibrium, all agents may not achieve synchronization.  A strengthened definition of Interactive Nash equilibrium is given that guarantees that all agents are participants in the same game, and that all agents achieve synchronization while optimizing their own value functions.

 

Stability vs. Optimality of Cooperative Multiagent Control

Stability vs. Optimality of Cooperative Multiagent Control

F. L. Lewis, National Academy of Inventors
IEEE Fellow, IFAC Fellow, Fellow UK Inst. Measurement & Control
Moncrief-O’Donnell Endowed Chair
Head, Advanced Controls & Sensors Group
UTA Research Institute
The University of Texas at Arlington, USA

ABSTRACT

Distributed systems of agents linked by communication networks only have access to information from their neighboring agents, yet must achieve global agreement on team activities to be performed cooperatively.  Examples include networked manufacturing systems, wireless sensor networks, networked feedback control systems, and the internet.  Sociobiological groups such as flocks, swarms, and herds have built-in mechanisms for cooperative control wherein each individual is influenced only by its nearest neighbors, yet the group achieves consensus behaviors such as heading alignment, leader following, exploration of the environment, and evasion of predators.  It was shown by Charles Darwin that local interactions between population groups over long time scales lead to global results such as the evolution of species.

Natural decision systems incorporate notions of optimality, since the resources available to organisms and species are limited. This talk investigates relations between the stability of cooperative control and optimality of cooperative control.  

Stability.  A method is given for the design of cooperative feedbacks for the continuous-time multi-agent tracker problem (also called pinning control or leader-following) that guarantees stable synchronization on arbitrary graphs with spanning trees.  It is seen that this design is a locally optimal control with infinite gain margin.  In the case of the discrete-time cooperative tracker, local optimal design yields stability on graphs that satisfy an additional restriction based on the Mahler instability measure of the local agent dynamics.

Optimality.  Global optimal control of distributed systems is complicated by the fact that, for general LQR performance indices, the resulting optimal control is not distributed in form.  Therefore, it cannot be implemented on a prescribed communication graph topology.  A condition is given for the existence of any optimal controllers that be implemented in distributed fashion.  This condition shows that for the existence of global  optimal controllers of distributed form, the performance index weighting matrices must be selected to depend on the graph structure.  

 

Andrea Serrani Headshot Photo
Distinguished Lecturer

Adaptive Guidance and Flight Control Systems Design for Air-Breathing Hypersonic Vehicles

Air-breathing hypersonic vehicles (HSVs) are intended to be a reliable and cost-effective technology for access to space. In the past few years, a considerable research effort has been spent to further their development and design. Notwithstanding the recent success of NASA's X-43A and AFRL's X-51 experimental vehicles, the design of robust guidance and control systems for HSVs is still an open problem, due to the complexity of the dynamics and the unprecedented level of coupling between the airframe and the propulsion system. The slender geometries and light structures required for these aircraft cause significant flexible effects, and a strong coupling between propulsive and aerodynamic forces results from the integration of the scramjet engine. Because of the variability of the vehicle characteristics with flight conditions, significant uncertainties affect the models, which are known to be unstable and non-minimum phase with respect to the regulated output. Finally, the presence of unavoidable constraints on the control inputs render the design of robust control systems an even harder endeavor, especially concerning controlling the propulsion system. In this talk, we give an overview of fundamental issues in control-oriented modeling and control system design for HSVs, and present an account of the state of the art in nonlinear and adaptive control methodologies that in the past few years have been developed and applied to address these issues. In particular, we present a flight control system architecture that comprises a robust adaptive inner-loop controller and a self-optimizing guidance system. Finally, we discuss open problems and current research directions.

Feedback Suppression of Resonance in Shallow Cavities: A Case Study in Aerodynamic Flow Control

An established benchmark problem in active aerodynamic flow control is the suppression of pressure oscillations induced by flow over a shallow cavity. In this talk, we summarize the research activity of the Gas Dynamics and Turbulence Lab at The Ohio State University that has been devoted in the past few years to the design and experimental evaluation of model-based controllers for subsonic cavity flows. Proper orthogonal decomposition and Galerkin projection techniques are used to obtain a reduced-order model of the flow dynamics from experimental data. The model is made amenable to control design by means of an optimization-based control separation technique, which makes the control input appear explicitly in the equations. The design of a two-DOF controller based on the reduced-order model and its experimental validation are presented. An inner-loop controller based on mixed-sensitivity minimization with delay compensation is used to linearize the actuator response. An adaptive outer-loop controller based on extremum-seeking optimization is employed to suppress the cavity tones from pressure measurements. Experimental results, in qualitative agreement with the theoretical analysis, show that  the controller achieves a significant attenuation of the resonant tone with a redistribution of the energy into other frequencies. The benefits of parameter adaptation over controllers of fixed structure under varying or uncertain flow conditions are also demonstrated experimentally.

 

Adaptive Feedforward Compensation of Harmonic Disturbances for Convergent Nonlinear Systems

Internal model-based control for nonlinear systems has experienced a vigorous growth in the past decade. The classic solution relies on augmenting the plant model with a suitable "nonlinear copy" of the model of the disturbance generator, and, as a second stage, on designing a robust stabilizing unit that achieves stabilization of an error-zeroing manifold with prescribed domain of attraction. The closely related approach of designing the stabilizing unit first, and then looking for a suitable adaptive feedforward control to offset the disturbance (a technique known as AFC in linear systems) has received little or no attention for nonlinear systems. In this talk, we investigate the problem of adaptive feedforward compensation for a class of nonlinear systems, namely that of input-to-state (and locally exponentially) convergent systems. It is shown how, under a set assumptions reminiscent of those found in the LTI literature, the proposed scheme succeeds in achieving disturbance rejection of a harmonic disturbance at the input of a convergent nonlinear system, with a semi-global domain of convergence. The suitability of the proposed solution is demonstrated by combining classic results from averaging analysis with modern techniques for semi-global stabilization.

Anna G. Stefanopoulou
Distinguished Lecturer

Control of powertrain systems at the high efficiency limit

Abstract: Powerful model-based control tools have enabled the realization of modern clean and efficient automobiles. Our effort to minimize automotive pollution and fuel consumption at low cost is pushing us to control powertrain systems at their high efficiency limit where poorly understood phenomena occur. This presentation will highlight a few of these frontiers.

In the realm of internal combustion engines, a highly efficient gasoline engine with seemingly chaotic behavior will be controlled at the lean combustion stability limit. In the electrification realm, stressed-out batteries and dead-ended fuel cells will highlight the challenges and successes in understanding, modeling, and controlling highly efficient power conversion on-board a vehicle. With these highlights it will become clear that as we race to improve mileage by 50% over the next decade powertrain control engineers will take the driver's seat! 

On the Accuracy and Estimation of Battery Behavior

Abstract: Many multi-scale physics-based models and their reduced-order renditions are used to estimate the lithium concentration and over-potential distributions throughout the battery electrode. The models let us meet time varying power demands while avoiding locally damaging phenomena. We show how to evaluate the accuracy of various electrochemical battery models by using neutron imaging as in situ measurement of the lithium concentration along the anode and cathode electrode layers. The observations from an operating Lithium Iron Phosphate (LFP) pouch cell battery with typical commercial electrodes are used to define the limits of the validity of the electrode-averaged models used in observers.

We then establish a simple thermal model than can be parameterized using the surface temperature measurement of the cell casing. The algorithm employs non-uniform forgetting factors to capture the long term resistance growth, and thus heat generation, due to aging or degradation. The algorithm accounts for the nonlinear dependency of the electric resistance (hence heat generation) on temperature in healthy cells and can be critical for avoiding the onset of thermal run-aways.

 

Lihua Xie Headshot Photo
Distinguished Lecturer

Minimum Data Rate and Channel Capacity for Stabilization of Linear Systems over Lossy Networks

One of the main challenges in networked control systems is the analysis and synthesis of control over limited rate feedback channels. The problem of minimum data rate for stabilization of linear systems has attracted significant interest in the past decade and it is now well known that under perfect communications the minimum data rate is related to the unstable engenvalues of the open-loop system. Another important issue in networked control is the uncertainties induced by the network such as packet losses. In this lecture, we shall discuss the minimum data rate for mean square stabilization over lossy networks. The packet losses process is modeled as an i.i.d. or Markov process. We show that the minimum data rate can be explicitly given in terms of the unstable eigenvalues of the open-loop system and the packet loss rate for the i.i.d. case or the transition probabilities of the Markov chain for the Markovian packet losses case. The number of additional bits required to counter the effect of the packet losses on stabilizability is completely quantified.  We shall also discuss the problem of minimum channel capacity for mean square stabilization of linear systems.

State Estimation over Rate limited Uncertain Channels

The problem of estimation and control over a communication network has attracted recurring interests in recent years due to the fact that there are more and more applications where communication networks are used to connect  sensors, controllers and actuators. While having many advantages of using communication works for transmitting data/signals, the limited data rate and network uncertainties such as packet losses pose significant challenges for analysis and design. In particular, in wireless sensor networks, power consumption is a critical design factor and communications cost much more energy as compared with computation. As such, there is a clear motivation for minimizing the communications. In this lecture, we shall discuss issues of quantized estimation and stability of Kalman over lossy channels. For the quantized estimation problem, we focus on how to jointly design quantizer and estimator to minimize the mean square estimation error. Under the Gaussian assumption of the predicted density, the quantized MMSE filter is shown to have a similar form as the Kalman filter with the raw measurement simply replaced by its quantized version. Quantization effects are explicitly quantified in terms of the number of quantization levels and quantization thresholds. The stability of the quantized estimator in relation to the system dynamics is examined. We then discuss the stability of Kalman filtering over a network subject to random packet losses, which are modeled by a time-homogeneous ergodic Markov process. Necessary and sufficient conditions for stability of the mean estimation error covariance matrices are derived by taking into account the system structure. Stability criteria are expressed by simple inequalities in terms of the largest eigenvalue of the open loop matrix and transition probabilities of the Markov process. Their implications and relationships with related results in the literature are discussed.

Network Topology and Communication Data Rate for Consensusability of Multi-agent Systems

Multi-agent cooperation involves a collection of decision-making components with limited processing, limited sensing and limited communications capabilities, all seeking to achieve a collective objective. Well known examples include mobile sensor networks for environment monitoring and surveillance and multi-UAV (unmanned aerial vehicle) formation flight. The distributed nature of information processing, sensing and actuation makes these applications a significant departure from the traditional centralized control system paradigm. In this lecture, we shall discuss the joint effects of agent dynamic, network topology and communication data rate on the consensusability  of linear discrete-time multi-agent systems. Neglecting the finite data rate constraint, a necessary and sufficient condition for consensusability under a set of distributed control protocols is given which explicitly reveals how the intrinsic entropy rate of the agent dynamic and the communication  graph affect consensusability. The result is established by solving a discrete-time simultaneous stabilization problem. A lower bound of the optimal convergence rate to consensus, which is shown to be tight for some special cases, is given as well. The consensus problem under a finite communication data rate is also investigated. We shall present a systematic approach to the design of encoder, decoder and control protocol to achieve the exact consensus. The consensus convergence rate in relation to the bit rate, network synchronizability and the size of the network is established. The implementation of the algorithm on a real multi-robot system as well as on a virtual platform will be demonstrated.