Finite-time extended state observer and fractional-order sliding mode controller for impulsive hybrid port-Hamiltonian systems with input delay and actuators saturation: Application to ball-juggler robots

This paper addresses the robust control problem of mechanical systems with hybrid dynamics in port-Hamiltonian form. It is assumed that only the position states are measurable, and time-delay and saturation constraint affect the control signal. An extended state observer is designed after a coordinate transformation. The effect of the time delay in the control signal is neutralized by applying Pade ́ approximant and augmenting the system states. An assistant system with faster convergence is developed to handle actuators saturation. Fractional-order sliding mode controller acts as a centralized controller and compensates for the undesired effects of unknown external disturbance and parameter uncertainties using the observer estimation results. Stability analysis shows that the closed-loop system states, such as the observer tracking error, and the position/velocity tracking errors, are finite-time stable. Simulation studies on a two ball-playing juggler robot with three degrees of freedom validate the theoretical results’ effectiveness

STABILITY, FINITE-TIME STABILITY AND PASSIVITY CRITERIA FOR DISCRETE-TIME DELAYED NEURAL NETWORKS

In this paper, we present the problem of stability, finite-time stability and passivity for discrete-time neural networks (DNNs) with variable delays. For the purposes of stability analysis, an augmented Lyapunov-Krasovskii functional (LKF) with single and double summation terms and several augmented vectors is proposed by decomposing the time-delay interval into two non-equidistant subintervals. Then, by using the Wirtinger-based inequality, reciprocally and extended reciprocally convex combination lemmas, tight estimations for sum terms in the forward difference of LKF are given. In order to relax the existing results, several zero equalities are introduced and stability criteria are proposed in terms of linear matrix inequalities (LMIs). The main objective for the finite-time stability and passivity analysis is how to effectively evaluate the finite-time passivity conditions for DNNs. To achieve this, some weighted summation inequalities are proposed for application to a finite-sum term appearing in the forward difference of LKF, which helps to ensure that the considered delayed DNN is passive. The derived passivity criteria are presented in terms of linear matrix inequalities. Some numerical examples are presented to illustrate the proposed methodology

Hierarchical control for multi-domain coordination of vehicle energy systems with switched dynamics

This dissertation presents a hierarchical control framework for vehicle energy management. As a result of increasing electrification, legacy integration and control approaches for vehicle energy systems have become limiting factors of performance and cannot accommodate the requirements of next-generation systems. Addressing this requires control frameworks that coordinate dynamics across multiple physical domains and timescales, enabling transformative improvements in capability, efficiency, and safety. To capture multi-domain storage and exchange of energy, a graph-based dynamic modeling approach is proposed and experimentally validated. This modeling approach is then leveraged for model-based control, in which the complex task of energy management is decomposed into a hierarchical network of model predictive controllers that coordinate decision-making across subsystems, physical domains, and timescales. The controllers govern both continuous and switched dynamic behaviors, addressing the hybrid nature of modern vehicle energy systems. The proposed hierarchical control framework is evaluated in application to a hardware-in-the-loop electro-thermal testbed representative of a scaled aircraft energy system, where it achieves significantly improved capability, efficiency, and safety as compared to legacy control approaches. Next, the structural information embedded in the graph-based modeling approach is shown to facilitate analysis. Closed-loop stability of decentralized MPC frameworks is guaranteed by analyzing the passivity of switched nonlinear graph-based systems and augmenting their controllers with a local passivity-based constraint. Lastly, a hierarchical control formulation guaranteeing satisfaction of state and input constraints for a class of switched graph-based systems is presented. This formulation is demonstrated in application to thermal management using both simulation and experimental implementation

Autonomous landing of fixed-wing aircraft on mobile platforms

E n esta tesis se propone un nuevo sistema que permite la operación de aeronaves autónomas sin tren de aterrizaje. El trabajo está motivado por el interés industrial en aeronaves con la capacidad de volar a gran altitud, con más capacidad de carga útil y capaces de aterrizar con viento cruzado. El enfoque seguido en este trabajo consiste en eliminar el sistema de aterrizaje de una aeronave de ala fija empleando una plataforma móvil de aterrizaje en tierra. La aeronave y la plataforma deben sincronizar su movimiento antes del aterrizaje, lo que se logra mediante la estimación del estado relativo entre ambas y el control cooperativo del movimiento. El objetivo principal de esta Tesis es el desarrollo de una solución práctica para el aterrizaje autónomo de una aeronave de ala fija en una plataforma móvil. En la tesis se combinan nuevos métodos con experimentos prácticos para los cuales se ha desarrollado un sistema de pruebas específico. Se desarrollan dos variantes diferentes del sistema de aterrizaje. El primero presta atención especial a la seguridad, es robusto ante retrasos en la comunicación entre vehículos y cumple procedimientos habituales de aterrizaje, al tiempo que reduce la complejidad del sistema. En el segundo se utilizan trayectorias optimizadas del vehículo y sincronización bilateral de posición para maximizar el rendimiento del aterrizaje en términos de requerimientos de longitud necesaria de pista, pero la estabilidad es dependiente del retraso de tiempo, con lo cual es necesario desarrollar un controlador estabilizador ampliado, basado en pasividad, que permite resolver este problema. Ambas estrategias imponen requisitos funcionales a los controladores de cada uno de los vehículos, lo que implica la capacidad de controlar el movimiento longitudinal sin afectar el control lateral o vertical, y viceversa. El control de vuelo basado en energía se utiliza para proporcionar dicha funcionalidad a la aeronave. Los sistemas de aterrizaje desarrollados se han analizado en simulación estableciéndose los límites de rendimiento mediante múltiples repeticiones aleatorias. Se llegó a la conclusión de que el controlador basado en seguridad proporciona un rendimiento de aterrizaje satisfactorio al tiempo que suministra una mayor seguridad operativa y un menor esfuerzo de implementación y certificación. El controlador basado en el rendimiento es prometedor para aplicaciones con una longitud de pista limitada. Se descubrió que los beneficios del controlador basado en el rendimiento son menos pronunciados para una dinámica de vehículos terrestres más lenta. Teniendo en cuenta la dinámica lenta de la configuración del demostrador, se eligió el enfoque basado en la seguridad para los primeros experimentos de aterrizaje. El sistema de aterrizaje se validó en diversas pruebas de aterrizaje exitosas, que, a juicio del autor, son las primeras en el mundo realizadas con aeronaves reales. En última instancia, el concepto propuesto ofrece importantes beneficios y constituye una estrategia prometedora para futuras soluciones de aterrizaje de aeronaves.In this thesis a new landing system is proposed, which allows for the operation of autonomous aircraft without landing gear. The work was motivated by the industrial need for more capable high altitude aircraft systems, which typically suffer from low payload capacity and high crosswind landing sensitivity. The approach followed in this work consists in removing the landing gear system from the aircraft and introducing a mobile ground-based landing platform. The vehicles must synchronize their motion prior to landing, which is achieved through relative state estimation and cooperative motion control. The development of a practical solution for the autonomous landing of an aircraft on a moving platform thus constitutes the main goal of this thesis. Therefore, theoretical investigations are combined with real experiments for which a special setup is developed and implemented. Two different landing system variants are developed — the safety-based landing system is robust to inter-vehicle communication delays and adheres to established landing procedures, while reducing system complexity. The performance-based landing system uses optimized vehicle trajectories and bilateral position synchronization to maximize landing performance in terms of used runway, but suffers from time delay-dependent stability. An extended passivity-based stabilizing controller was implemented to cope with this issue. Both strategies impose functional requirements on the individual vehicle controllers, which imply independent controllability of the translational degrees of freedom. Energy-based flight control is utilized to provide such functionality for the aircraft. The developed landing systems are analyzed in simulation and performance bounds are determined by means of repeated random sampling. The safety-based controller was found to provide satisfactory landing performance while providing higher operational safety, and lower implementation and certification effort. The performance-based controller is promising for applications with limited runway length. The performance benefits were found to be less pronounced for slower ground vehicle dynamics. Given the slow dynamics of the demonstrator setup, the safety-based approach was chosen for first landing experiments. The landing system was validated in a number of successful landing trials, which to the author’s best knowledge was the first time such technology was demonstrated on the given scale, worldwide. Ultimately, the proposed concept offers decisive benefits and constitutes a promising strategy for future aircraft landing solutions

CFD Analysis, Sensing and Control of a Rotary Pulse Width Modulating Valve to enable a Virtually Variable Displacement Pump

University of Minnesota Ph.D. dissertation. August 2017. Major: Mechanical Engineering. Advisors: Perry Li, Thomas Chase. 1 computer file (PDF); xi, 174 pages.Hydraulic systems have been widely utilized for heavy duty industries for their competitive advantages of high power density, low cost, and flexible circuit design. However, the efficiency of hydraulic systems typically is not very competitive due to high throttling losses, which limits their applications. On/off valve based control of a hydraulic system is an approach that can potentially increase the hydraulic system's efficiency significantly. This approach combines the strengths of throttling valve control and variable displacement unit control. The former has the advantage of high control bandwidth and precision, but the disadvantage of low efficiency due to throttling loss; the latter has the advantage of high efficiency, but the disadvantage of being bulky, heavy, costly, and the control bandwidth is low when compared to valve control. To create a potentially high efficiency with relatively low cost solution, a fixed displacement pump, an accumulator, and a high speed on/off valve are combined to create a virtually variable displacement pump (VVDP). By pulse width modulating (PWM) the flow from the supply to the load via the on/off valve, the average output flow can be varied by adjusting the PWM duty ratio. The key technology to this hydraulic configuration is the pulse width modulated on/off valve. A novel rotary high speed on/off valve concept has been proposed. This concept can enable different digital hydraulic configurations, such as VVDP, VVDPM (pump/motor), and virtually variable displacement transformer. Research conducted in this dissertation supports the design, modeling, and control of the rotary on/off valve. A 3-way, high-speed, rotary, self-spinning on/off valve was developed for the VVDP configuration. The valve has two degrees of freedom. The spool's rotary motion realizes the high-speed switching required for the PWM function. This motion can be self-driven by capturing the fluid's angular momentum via a unique valve spool turbine design. The spool's axial motion determines the valve PWM duty ratio, and this motion is driven externally. Firstly, to understand the flow inside the valve, and to quantify the valve pressure drop with the key valve parameters, a computational fluid dynamics (CFD) analysis is conducted in chapter 2. Analytical and semi-empirical formulas to model the pressure drop across the valve spool as a function of flow rate and key valve geometrical parameters are developed. The torque generated by the valve turbines are also analyzed using CFD to validate the analytical models which calculate the torque as a function of flow rate and key valve geometrical parameters. These equations are utilized in an optimization analysis to optimize the valve geometry, targeted at reducing the valve's power loss. CFD is also utilized to optimize the valve's interior flow path to reduce the fluid volume inside the valve while maintaining a low pressure drop, so that both the compressible loss and the throttling loss of the valve are reduced. The CFD analysis enabled reducing the throttling loss pf a prototype valve design by 62.5% and reducing the compressible loss by 66%. Secondly, the sensing and estimation of the valve spool's rotary position and velocity are addressed in chapter 5. Given the limitation on sensing distance and the requirement of a simple sealing structure, a coarse, non-contacting, optical sensor is proposed to measure the spool's angular position. Measurement events in the form of encoder count changes are obtained at irregular times and infrequently. An event-based Kalman filter is developed to improve the resolution and to provide continuous estimates of the spool's angular position and velocity. Thirdly, the spool's axial motion actuation, sensing, and control development are addressed. The on/off valve's duty ratio is regulated by controlling the valve spool's axial position. In chapter 4, a driving mechanism to work with the self-spinning valve's feature and the corresponding sensing and control methods are developed to manipulate the spool's axial position. In the first generation's driving system, a geroter pump is hydro-statically connected to both ends of the spool chamber to move the spool axially. This design simplifies the sealing structure in order to achieve self-spinning. An optical sensor is utilized as a non-contact approach to measuring the spool's axial displacement. The measurement is corrupted by a structured noise caused by the spool's rotary motion. A periodic time varying model is proposed to model the structured noise, which can capture the main dynamics with a low order system. An analysis of the observability of the augmented system (plant plus structured noise) is conducted. A state observer can be built to distinguish between the axial spool position and the structured noise, and the estimated position can then be used in the control law. The sleeve chamber pressure dynamics are ignored, and a linear feed-forward with a Proportional-Integral controller is developed for spool axial positioning. The self-spinning function ties the spool rotary speed with the valve flow. The controller was experimentally implemented, and achieved good spool regulation results. In order to investigate the PWM frequency and the flow rate properties independently, an external driving mechanism is developed in chapter 5. A new passivity based nonlinear controller has been proposed which considers the pressure dynamics inside the sleeve chamber. This controller can provide more robust axial position control. From theoretical analysis' point of view, a passivity framework for hydraulic actuators is developed by considering the compressibility energy function for a fluid with a pressure dependent bulk modulus. It is shown that the typical actuator's mechanical and pressure dynamics model can be obtained from the Euler-Lagrange equations for this energy function and that the actuator is passive with respect to a hydraulic supply rate. The hydraulic supply rate contains the flow work $(PQ)$ and the compressibility energy, whereas the latter one has typically been ignored. A storage function for the pressure error is then proposed and the pressure error dynamics are shown to be a passive two port subsystem. Trajectory tracking control laws are then derived using the storage function. Since some of the states utilized in the passive controllers are from an estimator instead of being directly measured, the chapter also provides the analysis on the convergence of both tracking errors and the estimation errors to zero. This passivity-based nonlinear controller implemented with a high gain observer is applied experimentally on the valve. Experimental results validate the effectiveness of this new control system. Lastly, the VVDP is implemented as the variable displacement pump in a direct displacement control open circuit, as presented in chapter 6. A variable flow source (VVDP), a directional valve, and a proportional valve are coordinated to manipulate the motion of the hydraulic actuator in an energy efficient way. The passivity-based nonlinear controller as discussed in chapter 5 is proposed to realize accurate actuator trajectory tracking. A nominal method to optimally distribute the control efforts between the control valve and the variable flow pump is proposed. This method can accommodate different control bandwidths from the valve and the pump, so that the valve has a large nominal opening to reduce the throttling loss. Experimental results validate the effectiveness of the control strategy

Mission oriented R and D and the advancement of technology: The impact of NASA contributions, volume 2

NASA contributions to the advancement of major developments in twelve selected fields of technology are presented. The twelve fields of technology discussed are: (1) cryogenics, (2) electrochemical energy conversion and storage, (3) high-temperature ceramics, (4) high-temperature metals (5) integrated circuits, (6) internal gas dynamics (7) materials machining and forming, (8) materials joining, (9) microwave systems, (10) nondestructive testing, (11) simulation, and (12) telemetry. These field were selected on the basis of both NASA and nonaerospace interest and activity