Highly redundant and fault tolerant actuator system: control, condition monitoring and experimental validation

This thesis is concerned with developing a control and condition monitoring system for a class of fault tolerant actuators with high levels of redundancy. The High Redundancy Actuator (HRA) is a concept inspired by biomimetics that aims to provide fault tolerance using relatively large numbers of actuation elements which are assembled in parallel and series configurations to form a single actuator. Each actuation element provides a small contribution to the overall force and displacement of the system. Since the capability of each actuation element is small, the effect of faults within the individual element of the overall system is also small. Hence, the HRA will gracefully degrade instead of going from fully functional to total failure in the presence of faults. Previous research on HRA using electromechanical technology has focused on a relatively low number of actuation elements (i.e. 4 elements), which were controlled with multiple loop control methods. The objective of this thesis is to expand upon this, by considering an HRA with a larger number of actuation elements (i.e. 12 elements). First, a mathematical model of a general n-by-m HRA is derived from first principles. This method can be used to represent any size of electromechanical HRA with actuation elements arranged in a matrix form. Then, a mathematical model of a 4-by-3 HRA is obtained from the general n-by-m model and verified experimentally using the HRA test rig. This actuator model is then used as a foundation for the controller design and condition monitoring development. For control design, two classical and control method-based controllers are compared with an H_infinity approach. The objective for the control design is to make the HRA track a position demand signal in both health and faulty conditions. For the classical PI controller design, the first approach uses twelve local controllers (1 per actuator) and the second uses only a single global controller. For the H_infinity control design, a mixed sensitivity functions is used to obtain good tracking performance and robustness to modelling uncertainties. Both of these methods demonstrate good tracking performance, with a slower response in the presence of faults. As expected, the H_infinity control method's robustness to modelling uncertainties, results in a smaller performance degradation in the presence of faults, compared with the classical designs. Unlike previous work, the thesis also makes a novel contribution to the condition monitoring of HRA. The proposed algorithm does not require the use of multiple sensors. The condition monitoring scheme is based on least-squares parameter estimation and fuzzy logic inference. The least-squares parameter estimation estimates the physical parameters of the electromechanical actuator based on input-output data collected from real-time experiments, while the fuzzy logic inference determines the health condition of the actuator based on the estimated physical parameters. Hence, overall, a new approach to both control and monitoring of an HRA is proposed and demonstrated on a twelve elements HRA test rig

Semi-blind robust indentification and robust control approach to personalized anemia management.

The homeostatic blood hemoglobin (Hb) content of a healthy individual varies between the range of 14-18 g/dL for a male and 12-16 g/dL for a female. This quantity provides an estimate of red blood cell (RBC) count in circulation at any given moment. RBC is a protein carrying substance that transports oxygen from the lungs to other tissues in the body and is synthesized by the kidney through a process known as erythropoiesis where erythropoietin is secreted in response to hypoxia. In this regard, the kidneys act not only as a controller but also as a sensor in regulating RBC levels. Patients with chronic kidney diseases (CKD) have dysfunctional kidneys that compromise these fundamental kidney functions. Consequently, anemia is developed. Anemics of CKD have low levels of Hb that must be controlled and properly regulated to the appropriate therapeutic range. Until the discovery of recombinant human erythropoietin (EPO) over three decades ago, treatment procedure of anemia conditions primarily involved repeated blood transfusions–a process known to be associated with several other health related complications. This discovery resulted in a paradigm shift in anemia management from blood transfusions to dosage therapies. The main objective of anemia management with EPO is to increase patients’ hemoglobin level from low to a suitable therapeutic range as defined by the National Kidney Foundation-Kidney Disease Outcomes Quality Initiative (NKF-KDOI) to be in the range of 10 - 12 g/dL while avoiding response values beyond 14 g/dL to prevent other complications associated with EPO medication. It is therefore imperative that clinicians balance dosage efficacy and toxicity in anemia management therapies. At most treatment facilities, protocols are developed to conform to NKF-KDOI recommendations. These protocols are generally based on EPO packet inserts and the expected Hb responses from the average patient. The inevitable variability within the patient group makes this “one-size-fits-all” dosing scheme non-optimal, at best, and potentially dangerous for certain group of patients that do not adhere to the notion of expected “average” response. A dosing strategy that is tailored to the individual patients’ response to EPO medication could provide a better alternative to the current treatment methods. An objective of this work is to develop EPO dosing strategies tailored to the individual patients using robust identification techniques and modern feedback control methods. First, a unique model is developed based on Hb responses and dosage EPO of the individual patients using semi-blind robust identification techniques. This provides a nominal model and a quantitative information on model uncertainty that accounts for other possible patient’s dynamics not considered in the modeling process. This is in the framework of generalized interpolation theory. Then, from the derived nominal model and the associated uncertainty information, robust controller is designed via the =H1-synthesis methods to provide a new dosing strategies for the individual patients. The H1 control theory has a feature of minimizing the influence of some unknown worst case gain disturbance on a system. Finally, a framework is provided to strategize dosing protocols for newly admitted patients

A Foot Placement Strategy for Robust Bipedal Gait Control

This thesis introduces a new measure of balance for bipedal robotics called the foot placement estimator (FPE). To develop this measure, stability first is defined for a simple biped. A proof of the stability of a simple biped in a controls sense is shown to exist using classical methods for nonlinear systems. With the addition of a contact model, an analytical solution is provided to define the bounds of the region of stability. This provides the basis for the FPE which estimates where the biped must step in order to be stable. By using the FPE in combination with a state machine, complete gait cycles are created without any precalculated trajectories. This includes gait initiation and termination. The bipedal model is then advanced to include more realistic mechanical and environmental models and the FPE approach is verified in a dynamic simulation. From these results, a 5-link, point-foot robot is designed and constructed to provide the final validation that the FPE can be used to provide closed-loop gait control. In addition, this approach is shown to demonstrate significant robustness to external disturbances. Finally, the FPE is shown in experimental results to be an unprecedented estimate of where humans place their feet for walking and jumping, and for stepping in response to an external disturbance

Design and verification of Guidance, Navigation and Control systems for space applications

In the last decades, systems have strongly increased their complexity in terms of number of functions that can be performed and quantity of relationships between functions and hardware as well as interactions of elements and disciplines concurring to the definition of the system. The growing complexity remarks the importance of defining methods and tools that improve the design, verification and validation of the system process: effectiveness and costs reduction without loss of confidence in the final product are the objectives that have to be pursued. Within the System Engineering context, the modern Model and Simulation based approach seems to be a promising strategy to meet the goals, because it reduces the wasted resources with respect to the traditional methods, saving money and tedious works. Model Based System Engineering (MBSE) starts from the idea that it is possible at any moment to verify, through simulation sessions and according to the phase of the life cycle, the feasibility, the capabilities and the performances of the system. Simulation is used during the engineering process and can be classified from fully numerical (i.e. all the equipment and conditions are reproduced as virtual model) to fully integrated hardware simulation (where the system is represented by real hardware and software modules in their operational environment). Within this range of simulations, a few important stages can be defined: algorithm in the loop (AIL), software in the loop (SIL), controller in the loop (CIL), hardware in the loop (HIL), and hybrid configurations among those. The research activity, in which this thesis is inserted, aims at defining and validating an iterative methodology (based on Model and Simulation approach) in support of engineering teams and devoted to improve the effectiveness of the design and verification of a space system with particular interest in Guidance Navigation and Control (GNC) subsystem. The choice of focusing on GNC derives from the common interest and background of the groups involved in this research program (ASSET at Politecnico di Torino and AvioSpace, an EADS company). Moreover, GNC system is sufficiently complex (demanding both specialist knowledge and system engineer skills) and vital for whatever spacecraft and, last but not least the verification of its behavior is difficult on ground because strong limitations on dynamics and environment reproduction arise. Considering that the verification should be performed along the entire product life cycle, a tool and a facility, a simulator, independent from the complexity level of the test and the stage of the project, is needed. This thesis deals with the design of the simulator, called StarSim, which is the real heart of the proposed methodology. It has been entirely designed and developed from the requirements definition to the software implementation and hardware construction, up to the assembly, integration and verification of the first simulator release. In addition, the development of this technology met the modern standards on software development and project management. StarSim is a unique and self-contained platform: this feature allows to mitigate the risk of incompatibility, misunderstandings and loss of information that may arise using different software, simulation tools and facilities along the various phases. Modularity, flexibility, speed, connectivity, real time operation, fidelity with real world, ease of data management, effectiveness and congruence of the outputs with respect to the inputs are the sought-after features in the StarSim design. For every iteration of the methodology, StarSim guarantees the possibility to verify the behavior of the system under test thanks to the permanent availability of virtual models, that substitute all those elements not yet available and all the non-reproducible dynamics and environmental conditions. StarSim provides a furnished and user friendly database of models and interfaces that cover different levels of detail and fidelity, and supports the updating of the database allowing the user to create custom models (following few, simple rules). Progressively, pieces of the on board software and hardware can be introduced without stopping the process of design and verification, avoiding delays and loss of resources. StarSim has been used for the first time with the CubeSats belonging to the e-st@r program. It is an educational project carried out by students and researchers of the “CubeSat Team Polito” in which StarSim has been mainly used for the payload development, an Active Attitude Determination and Control System, but StarSim’s capabilities have also been updated to evaluate functionalities, operations and performances of the entire satellite. AIL, SIL, CIL, HIL simulations have been performed along all the phases of the project, successfully verifying a great number of functional and operational requirements. In particular, attitude determination algorithms, control laws, modes of operation have been selected and verified; software has been developed step by step and the bugs-free executable files have been loaded on the micro-controller. All the interfaces and protocols as well as data and commands handling have been verified. Actuators, logic and electrical circuits have been designed, built and tested and sensors calibration has been performed. Problems such as real time and synchronization have been solved and a complete hardware in the loop simulation test campaign both for A-ADCS standalone and for the entire satellite has been performed, verifying the satisfaction of a great number of CubeSat functional and operational requirements. The case study represents the first validation of the methodology with the first release of StarSim. It has been proven that the methodology is effective in demonstrating that improving the design and verification activities is a key point to increase the confidence level in the success of a space mission

Summary of Research 1994

The views expressed in this report are those of the authors and do not reflect the official policy or position of the Department of Defense or the U.S. Government.This report contains 359 summaries of research projects which were carried out under funding of the Naval Postgraduate School Research Program. A list of recent publications is also included which consists of conference presentations and publications, books, contributions to books, published journal papers, and technical reports. The research was conducted in the areas of Aeronautics and Astronautics, Computer Science, Electrical and Computer Engineering, Mathematics, Mechanical Engineering, Meteorology, National Security Affairs, Oceanography, Operations Research, Physics, and Systems Management. This also includes research by the Command, Control and Communications (C3) Academic Group, Electronic Warfare Academic Group, Space Systems Academic Group, and the Undersea Warfare Academic Group

The optimal control of power electronic embedded networks in More Electric Aircraft

With the advancement of power electronic technologies over recent decades, there has been an overall increase in the utilisation of distributed generation and power electronic embedded networks in a large sphere of applications. Probably one of the most prominent areas of utilisation of new power electronics embedded systems is the use in power networks onboard military and civilian aircraft. With environmental concerns and increased competition in the civil aviation sector, more aircraft manufactures are replacing and interfacing electrical alternatives over heavier, less efficient and costly pneumatic, hydraulic and mechanical systems. In these modern power systems, the increased proliferation of power electronic converters and distributed generation raises important issues in regards to the performance, stability and robustness between interfaced switching units. These phenomena, such as power electronic sub-system interactions, become even more prominent in micro-grid applications or other low voltage distribution systems where interfaced converters are in close proximity to one another. In More Electric Aircraft (MEA), these interfaced power electronic converters are connected to the same non-stiff low power AC grid, which further increases the interactive effects between converter sub-systems. If these effects are not properly taken into account, then external disturbances to the system at given operating conditions can result in degradation of the system performance, failure in meeting the operating requirements of the grid, or in the worst case, instability of the whole grid. With much research in the area of decreasing the size and weight of systems, there is much literature proposing optimisation methods which decrease the size of filters between interfacing converters. Whilst effectively decreasing the size of these systems, interactions between interfaced converters gets worse, and is often improperly accounted for. The work presented in this thesis proposes a novel approach to the decentralisation and optimisation of converter controls on a power electronics embedded power network. In order to account for the interactive dynamics between sub-systems in the environment of reduced passive filter networks, all the system dynamics including the interactive terms are modelled globally. An optimal controller design approach based on the H2 optimisation is proposed to synthesise and generate automatically the controller gains for each power electronic sub-system. H2 optimisation is a powerful tool, which not only allows the submission, optimisation and development of closed loop controls for large dynamic systems, but offers the ability to the user to construct the controller for given structures. This enables the development of decentralised controllers for every sub-system with intrinsic knowledge of the closed loop dynamics of every other interconnect sub-system. It is shown through simulation and by experimental validation that this novel approach to grid control optimisation not only can improve overall dynamic performance of all sub-systems over 15traditional methods of design, but can also intrinsically reduce or better yet mitigate against the interactive effects between all converters. In addition, this method of controller design will be shown to not only be scalable to expanding sizes of grids, but the Phase-locked loops (PLLs) integrated to grid connected devices can also be considered in the optimisation procedure. PLLs are widely known to further cause interactive behaviours between grid interfaced devices. Including this into the optimisation also has been validated experimentally to prevent interactions on the grid, and improve performance over traditional design methods. Adaptations to the controller are performed to ensure operation in variable frequency environments (as is common in MEA), as well as methods of single converter optimisation when interfacing to an unknown grid. Additionally some initial research towards an adaption of the H2 controller to incorporate robustness as well as performance into the optimisation procedure is presented with mathematical concepts shown through simulation

The optimal control of power electronic embedded networks in More Electric Aircraft

With the advancement of power electronic technologies over recent decades, there has been an overall increase in the utilisation of distributed generation and power electronic embedded networks in a large sphere of applications. Probably one of the most prominent areas of utilisation of new power electronics embedded systems is the use in power networks onboard military and civilian aircraft. With environmental concerns and increased competition in the civil aviation sector, more aircraft manufactures are replacing and interfacing electrical alternatives over heavier, less efficient and costly pneumatic, hydraulic and mechanical systems. In these modern power systems, the increased proliferation of power electronic converters and distributed generation raises important issues in regards to the performance, stability and robustness between interfaced switching units. These phenomena, such as power electronic sub-system interactions, become even more prominent in micro-grid applications or other low voltage distribution systems where interfaced converters are in close proximity to one another. In More Electric Aircraft (MEA), these interfaced power electronic converters are connected to the same non-stiff low power AC grid, which further increases the interactive effects between converter sub-systems. If these effects are not properly taken into account, then external disturbances to the system at given operating conditions can result in degradation of the system performance, failure in meeting the operating requirements of the grid, or in the worst case, instability of the whole grid. With much research in the area of decreasing the size and weight of systems, there is much literature proposing optimisation methods which decrease the size of filters between interfacing converters. Whilst effectively decreasing the size of these systems, interactions between interfaced converters gets worse, and is often improperly accounted for. The work presented in this thesis proposes a novel approach to the decentralisation and optimisation of converter controls on a power electronics embedded power network. In order to account for the interactive dynamics between sub-systems in the environment of reduced passive filter networks, all the system dynamics including the interactive terms are modelled globally. An optimal controller design approach based on the H2 optimisation is proposed to synthesise and generate automatically the controller gains for each power electronic sub-system. H2 optimisation is a powerful tool, which not only allows the submission, optimisation and development of closed loop controls for large dynamic systems, but offers the ability to the user to construct the controller for given structures. This enables the development of decentralised controllers for every sub-system with intrinsic knowledge of the closed loop dynamics of every other interconnect sub-system. It is shown through simulation and by experimental validation that this novel approach to grid control optimisation not only can improve overall dynamic performance of all sub-systems over 15traditional methods of design, but can also intrinsically reduce or better yet mitigate against the interactive effects between all converters. In addition, this method of controller design will be shown to not only be scalable to expanding sizes of grids, but the Phase-locked loops (PLLs) integrated to grid connected devices can also be considered in the optimisation procedure. PLLs are widely known to further cause interactive behaviours between grid interfaced devices. Including this into the optimisation also has been validated experimentally to prevent interactions on the grid, and improve performance over traditional design methods. Adaptations to the controller are performed to ensure operation in variable frequency environments (as is common in MEA), as well as methods of single converter optimisation when interfacing to an unknown grid. Additionally some initial research towards an adaption of the H2 controller to incorporate robustness as well as performance into the optimisation procedure is presented with mathematical concepts shown through simulation

Six Decades of Flight Research: An Annotated Bibliography of Technical Publications of NASA Dryden Flight Research Center, 1946-2006

Titles, authors, report numbers, and abstracts are given for nearly 2900 unclassified and unrestricted technical reports and papers published from September 1946 to December 2006 by the NASA Dryden Flight Research Center and its predecessor organizations. These technical reports and papers describe and give the results of 60 years of flight research performed by the NACA and NASA, from the X-1 and other early X-airplanes, to the X-15, Space Shuttle, X-29 Forward Swept Wing, X-31, and X-43 aircraft. Some of the other research airplanes tested were the D-558, phase 1 and 2; M-2, HL-10 and X-24 lifting bodies; Digital Fly-By-Wire and Supercritical Wing F-8; XB-70; YF-12; AFTI F-111 TACT and MAW; F-15 HiDEC; F-18 High Alpha Research Vehicle, F-18 Systems Research Aircraft and the NASA Landing Systems Research aircraft. The citations of reports and papers are listed in chronological order, with author and aircraft indices. In addition, in the appendices, citations of 270 contractor reports, more than 200 UCLA Flight System Research Center reports, nearly 200 Tech Briefs, 30 Dryden Historical Publications, and over 30 videotapes are included