Identification and Adaptive Control for High-performance AC Drive Systems.

High-performance AC machinery and drive systems can be found in a variety of applications ranging from motion control to vehicle propulsion. However, machine parameters can vary significantly with electrical frequency, flux levels, and temperature, degrading the performance of the drive system. While adaptive control techniques can be used to estimate machine parameters online, it is sometimes desirable to estimate certain parameters offline. Additionally, parameter identification and control are typically conflicting objectives with identification requiring plant inputs which are rich in harmonics, and control objectives often consisting of regulation to a constant set-point. In this dissertation, we present research which seeks to address these issues for high-performance AC machinery and drive systems. The first part of this dissertation concerns the offline identification of induction machine parameters. Specifically, we have developed a new technique for induction machine parameter identification which can easily be implemented using a voltage-source inverter. The proposed technique is based on fitting steady-state experimental data to the circular stator current locus in the stator flux linkage reference-frame for varying steady-state slip frequencies, and provides accurate estimates of the magnetic parameters, as well as the rotor resistance and core loss conductance. Experimental results for a 43 kW induction machine are provided which demonstrate the utility of the proposed technique by characterizing the machine over a wide range of flux levels, including magnetic saturation. The remainder of this dissertation concerns the development of generalizable design methodologies for Simultaneous Identification and Control (SIC) of overactuated systems via case studies with Permanent Magnet Synchronous Machines (PMSMs). Specifically, we present different approaches to the design of adaptive controllers for PMSMs which exploit overactuation to achieve identification and control objectives simultaneously. The first approach utilizes a disturbance decoupling control law to prevent the excitation input from perturbing the regulated output. The second approach uses a Lyapunov-based adaptive controller to constrain the states to the output error-zeroing manifold on which they are varied to provide excitation for parameter identification. Finally, a receding-horizon control allocation approach is presented which includes a metric for generating persistently exciting reference trajectories.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120862/1/davereed_1.pd

Control of an over-actuated nanopositioning system by means of control allocation

This Master’s Thesis is devoted to the analysis and design of a control structure for the nanopositioning system LAU based on the dynamic control allocation technique. The objective is to control the vertical displacement with nanometer precision under a control effort distribution criterion among the actuator set. In this case, the pneumatic actuator is used as a passive gravity compensator while the voice coil motor generates the transient forces. The analysis of the system characteristics allows defining the design criterion for the control allocation. In this direction, the proposed dynamic control allocation stage considers a frequency distribution of the control effort. The lower frequency components are assigned to the pneumatic actuator while the higher frequencies are handled by the voice coil drive. The significant actuator dynamics are compensated through a Kalman filter approach. The position controller is based on a feedback linearization framework with a disturbance observer for enhanced robustness. The experimental validation demonstrates the feasibility of the proposed technique.Diese Masterarbeit widmet sich der Analyse und dem Entwurf einer Regelungsstruktur für das Nanopositioniersystem LAU. Dabei werden Methoden untersucht, welche das notwendige Stellsignal auf zwei Aktoren aufteilen. Ziel ist es, die vertikale Verschiebung des LAU mit Nanometerpräzision zu regeln. In diesem Fall wird der pneumatische Aktor als passiver Schwerkraftkompensator verwendet, während die elktromagnetische Tauchspule die transienten Kräfte erzeugt. Die Analyse der Eigenschaften des LAUSystems ermöglicht die Definition der Entwurfskriterien zur Aufteilung der Stellgröße. In dieser Richtung berücksichtigt die vorgeschlagene dynamische Methode eine Aufteilung der Stellgröße bezüglich der Frequenzanteile. Die niederfrequenten Komponenten werden dem pneumatischen Aktor zugeordnet. Dem elektromagnetische Aktor werden die verbliebenen hochfrequenten Anteile zugeordnet. Die signifikanten Effekte der Aktordynamik in Bezug auf die Bewegungsdynamik werden durch einen Kalman- Filteransatz kompensiert. Nichtlineare Streckenanteile werden basierend auf dem Modell und einem Störbeobachter kompensiert, sodass der verbleibende Anteil des Positionsreglers mit linearen Methoden entworfen werden kann. Die experimentelle Validierung zeigt die Effektivität des untersuchten Konzeptes.Tesi

Autonomous thruster failure recovery on underactuated spacecraft using model predictive control

Thruster failures historically account for a large percentage of failures that have occurred on orbit. These failures are typically handled through redundancy, however, with the push to using smaller, less expensive satellites in clusters or formations there is a need to perform thruster failure recovery without additional hardware. This means that a thruster failure may cause the spacecraft to become underactuated, requiring more advanced control techniques. A model of a thruster-controlled spacecraft is developed and analyzed with a nonlinear controllability test, highlighting several challenges including coupling, nonlinearities, severe control input saturation, and nonholonomicity. Model Predictive Control (MPC) is proposed as a control technique to solve these challenges. However, the real-time, online implementation of MPC brings about many issues. A method of performing MPC online is described, implemented and tested in simulation as well as in hardware on the Synchronized Position-Hold, Engage, Reorient Experimental Satellites (SPHERES) testbed at the Massachusetts Institute of Technology (MIT) and on the International Space Station (ISS). These results show that MPC provided improved performance over a simple path planning technique

Energy-Optimal Control of Over-Actuated Systems - with Application to a Hybrid Feed Drive

Over-actuated (or input-redundant) systems are characterized by the use of more actuators than the degrees of freedom to be controlled. They are widely used in modern mechanical systems to satisfy various control requirements, such as precision, motion range, fault tolerance, and energy efficiency. This thesis is particularly motivated by an over-actuated hybrid feed drive (HFD) which combines two complementary actuators with the aim to reduce energy consumption without sacrificing positioning accuracy in precision manufacturing. This work addresses the control challenges in achieving energy optimality without sacrificing control performance in so-called weakly input-redundant systems, which characterize the HFD and most other over-actuated systems used in practice. Using calculus of variations, an optimal control ratio/subspace is derived to specify the optimal relationship among the redundant actuators irrespective of external disturbances, leading to a new technique termed optimal control subspace-based (OCS) control allocation. It is shown that the optimal control ratio/subspace is non-causal; accordingly, a causal approximation is proposed and employed in energy-efficient structured controller design for the HFD. Moreover, the concept of control proxy is proposed as an accurate causal measurement of the deviation from the optimal control ratio/subspace. The proxy enables control allocation for weakly redundant systems to be converted into regulation problems, which can be tackled using standard controller design methodologies. Compared to an existing allocation technique, proxy-based control allocation is shown to dynamically allocate control efforts optimally without sacrificing control performance. The relationship between the proposed OCS control allocation and the traditional linear quadratic control approach is discussed for weakly input redundant systems. The two approaches are shown to be equivalent given perfect knowledge of disturbances; however, the OCS control allocation approach is shown to be more desirable for practical applications like the HFD, where disturbances are typically unknown. The OCS control allocation approach is validated in simulations and machining experiments on the HFD; significant reductions in control energy without sacrificing positioning accuracy are achieved.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146104/1/molong_1.pd

A fast and parametric torque distribution strategy for four-wheel-drive energy-efficient electric vehicles

Electric vehicles (EVs) with four individually controlled drivetrains are over-actuated systems, and therefore, the total wheel torque and yaw moment demands can be realized through an infinite number of feasible wheel torque combinations. Hence, an energy-efficient torque distribution among the four drivetrains is crucial for reducing the drivetrain power losses and extending driving range. In this paper, the optimal torque distribution is formulated as the solution of a parametric optimization problem, depending on the vehicle speed. An analytical solution is provided for the case of equal drivetrains, under the experimentally confirmed hypothesis that the drivetrain power losses are strictly monotonically increasing with the torque demand. The easily implementable and computationally fast wheel torque distribution algorithm is validated by simulations and experiments on an EV demonstrator, along driving cycles and cornering maneuvers. The results show considerable energy savings compared to alternative torque distribution strategies

A review of convex approaches for control, observation and safety of linear parameter varying and Takagi-Sugeno systems

This paper provides a review about the concept of convex systems based on Takagi-Sugeno, linear parameter varying (LPV) and quasi-LPV modeling. These paradigms are capable of hiding the nonlinearities by means of an equivalent description which uses a set of linear models interpolated by appropriately defined weighing functions. Convex systems have become very popular since they allow applying extended linear techniques based on linear matrix inequalities (LMIs) to complex nonlinear systems. This survey aims at providing the reader with a significant overview of the existing LMI-based techniques for convex systems in the fields of control, observation and safety. Firstly, a detailed review of stability, feedback, tracking and model predictive control (MPC) convex controllers is considered. Secondly, the problem of state estimation is addressed through the design of proportional, proportional-integral, unknown input and descriptor observers. Finally, safety of convex systems is discussed by describing popular techniques for fault diagnosis and fault tolerant control (FTC).Peer ReviewedPostprint (published version

Méthodes scalables de commande par allocation pour le convertisseur modulaire multiniveaux : de la modélisation à l'implémentation temps réel

Dans le cadre de la montée en puissance des convertisseurs statiques, les différents avantages qu’il y a à utiliser les Convertisseurs Modulaires Multiniveaux (MMC) ont mené à leur popularisation. Cependant, à mesure que le nombre de niveaux de tension et le nombre de phase augmentent, ces convertisseurs présentent un nombre de plus en plus important de degrés de liberté pour en effectuer la commande. Ainsi les MMC représentent un défi pour la commande car le nombre de variables de commande est alors supérieur aux contraintes à satisfaire, faisant d’eux des systèmes redondants ou encore sous-déterminés ce qui ouvre la voie de l’optimisation. D’abord apparues dans les années 1980 dans l’aéronautique pour tirer profit de la multiplicité des surfaces aérodynamiques et des redondances associées que présente un avion afin d’en contrôler sa trajectoire (volets, ailerons, gouvernes…), les méthodes de commande par allocation ont fait leurs preuves en étant progressivement appliquées dans différents domaines technologiques. En parallèle ces algorithmes ont fait l’objet de travaux pour améliorer les performances obtenues et notamment s’adapter aux systèmes commandés. Le sujet de la thèse concerne donc le développement et l’implémentation en temps réel de méthodes de commande par allocation, avec un souci d’optimisation en ligne, pour un système de conversion d’énergie à base de MMC. La première partie de la thèse portent sur la modélisation du convertisseur MMC en vue de sa commande à partir de méthodes d’allocation. Ce qui implique le développement de différents modèles de commande avec différents niveaux de détails et de complexité. Un résultat fort issu de cette première partie est un modèle de commande dont la complexité n’est plus influencée par le nombre de phases du système électrique considéré. La deuxième étape des travaux concerne le développement d’une nouvelle méthode d’allocation qui met à profit les avantages des méthodes présentes dans l’état de l’art pour en concevoir une nouvelle plus adaptée. Ainsi cette démarche a conduit à la programmation d’un nouvel algorithme d’allocation présentant des caractéristiques dynamiques et statiques réglables et adaptables simplement, son intégration aux méthodes déjà existantes est aisée et presque immédiat. La troisième étape des travaux combine les travaux précédents. Tout d’abord en simulation, la méthode de commande par allocation du convertisseur est programmée puis testée pour finalement être validée. Pour la commande différentes architectures sont conçues permettant de réaliser des comparatifs afin d’évaluer leur capacité à atteindre les performances requises pour le bon fonctionnement du système. Il en découle une analyse des différents algorithmes de commande proposés. Le résultat principal de cette partie est la conception d’un nouvel algorithme d’allocation permettant de contrôler les tensions aux bornes des condensateurs ainsi que les tous les courants du convertisseur dans chacune des branches et ce indépendamment du nombre de phases. La quatrième étape porte sur la validation expérimentale des méthodes développées. Pour se faire, le convertisseur MMC disponible au laboratoire LAPLACE est utilisé ainsi qu’un ensemble d’outils de prototypage rapide (OPAL-RT) permettant de tester et mettre au point les algorithmes de façon sûre et efficace. La cinquième partie des travaux concerne l’extension, hors de la zone de fonctionnement nominale du convertisseur, des algorithmes de commande développés. En effet une ouverture est proposée mettant en exergue les capacités des méthodes d’allocation à reconfigurer le fonctionnement du MMC lorsqu’un défaut apparait dans l’un des sous-modules. Les résultats obtenus en simulation montrent une amélioration de la disponibilité du convertisseur, c’est-à-dire une continuité de fonctionnement en présence de défauts ce qui justifie l’intérêt de poursuivre les travaux dans cette direction

Gaussian process adaptive incremental backstepping flight control

The presence of uncertainties caused by unforeseen malfunctions in the actuation system or changes in aircraft behaviour could lead to aircraft loss of control during flight. The paper proposes almost model-independent control law combining recent developments in nonlinear control theory, data-driven methods, and sensor technologies by considering Gaussian Processes Adaptive augmentation for Incremental Backstepping control (IBKS) algorithm. IBKS uses angular accelerations and current control deflections to reduce the dependency on the aircraft model. However, it requires knowledge of control effectiveness. Conducted research shows that if the input-affine property of the IBKS is violated, e.g., in severe conditions with a combination of multiple failures, the IBKS can lose stability. Meanwhile, the GP-based estimator provides fast identification and the resultant GP-adaptive IBKS algorithm demonstrates improved stability and tracking performance. The performance of the algorithm is validated using a large transport aircraft flight dynamics model