Sequential Loop Closure Based Adaptive Autopilot Design for a Hypersonic Vehicle

This paper presents a sequential loop closure approach to designing a velocity and altitude tracking au- topilot for a hypersonic vehicle. The control architecture consists of two decoupled control subsystems, one for velocity, the other for altitude. The velocity control subsystem consists of an adaptive augmented baseline controller. The altitude control subsystem consists of an adaptive inner-loop designed to accommodate uncer- tainties in the stability and control derivatives of the aircraft, and track pitch-rate commands. The outer-loop is designed independent of the inner loop, and guarantees stability of the closed-loop system. The outer-loop uses components of a closed-loop reference model, and generates the appropriate pitch-rate commands for the inner loop such that the hypersonic vehicle tracks the desired altitude. A numerical example based on a scram- jet powered, blended wing-body generic hypersonic vehicle model is presented, demonstrating the efficacy of the proposed control design.Approved for Public Release; Distribution Unlimited. Case Number 88ABW-2015-5617

Adaptive Control Based on Retrospective Cost Optimization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83558/1/AIAA-46741-507.pd

2 Loop Nonlinear Dynamic Inversion Fuel Flow Controller Design for Air to Air Ducted Ramjet Rocket

Fuel Flow controller based ramjet propulsion system have a flexibility to change rocket velocity depending on guidance requirement by controlling the fuel flow rate as a function of atmospheric conditions like altitude, Mach no. and angle of attack. In this paper, Design objectives & requirements of fuel flow controller have been brought out from guidance loop for air-to-air target engagement. 2-loop non-linear dynamic inversion (DI) based controller design has been proposed to track the commanded thrust and to meet the time constant requirement as a function of altitude, Mach no. and angle of attack. The outer thrust loop is to control commanded thrust and to generate the demand for gas generator pressure loop and inner pressure loop is to meet outer loop demand by controlling throttle valve area. The engine state space plant model has been adapted with improvement of existing model. Throttle valve actuator specifications requirement are also brought out

Retrospective Cost Adaptive Control with Concurrent Closed-Loop Identification

Retrospective cost adaptive control (RCAC) is a discrete-time direct adaptive control algorithm for stabilization, command following, and disturbance rejection. RCAC is known to work on systems given minimal modeling information which is the leading numerator coefficient and any nonminimum-phase (NMP) zeros of the plant transfer function. This information is normally needed a priori and is key in the development of the filter, also known as the target model, within the retrospective performance variable. A novel approach to alleviate the need for prior modeling of both the leading coefficient of the plant transfer function as well as any NMP zeros is developed. The extension to the RCAC algorithm is the use of concurrent optimization of both the target model and the controller coefficients. Concurrent optimization of the target model and controller coefficients is a quadratic optimization problem in the target model and controller coefficients separately. However, this optimization problem is not convex as a joint function of both variables, and therefore nonconvex optimization methods are needed. Finally, insights within RCAC that include intercalated injection between the controller numerator and the denominator, unveil the workings of RCAC fitting a specific closed-loop transfer function to the target model. We exploit this interpretation by investigating several closed-loop identification architectures in order to extract this information for use in the target model.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138440/1/fsobolic_1.pd

Guidance and control for defense systems against ballistic threats

A defense system against ballistic threat is a very complex system from the engineering point of view. It involves different kinds of subsystems and, at the same time, it presents very strict requirements. Technology evolution drives the need of constantly upgrading system’s capabilities. The guidance and control fields are two of the areas with the best progress possibilities. This thesis deals with the guidance and control problems involved in a defense system against ballistic threats. This study was undertaken by analyzing the mission of an intercontinental ballistic missile. Trajectory reconstruction from radar and satellite measurements was carried out with an estimation algorithm for nonlinear systems. Knowing the trajectory is a prerequisite for intercepting the ballistic missile. Interception takes place thanks to a dedicated tactical missile. The guidance and control of this missile were also studied in this work. Particular attention was paid on the estimation of engagement’s variables inside the homing loop. Interceptor missiles are usually equipped with a seeker that provides the angle under which the interceptor sees its target. This single measurement does not guarantee the observability of the variables required by advanced guidance laws such as APN, OGL, or differential games-based laws. A new guidance strategy was proposed, that solves the bad observability problems and returns satisfactory engagement performances. The thesis is concluded by a study of the interceptor most suitable aerodynamic configuration in order to implement the proposed strategy, and by the relative autopilot design. The autopilot implements the lateral acceleration commands from the guidance system. The design was carried out with linear control techniques, considering requirements on the rising time, actuators maximum effort, and response to a bang-bang guidance command. The analysis of the proposed solutions was carried on by means of numerical simulations, developed for each single case-study

A Novel Higher-Order Sliding Mode Control Scheme for Uncertain Nonlinear Systems: Short-period Missile Control Application

The paper proposes a novel higher-order sliding modes (HOSM) control scheme for a class of uncertain nonlinear systems. The HOSM-based control scheme is developed based on the Filippo

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Department of Mechanical EngineeringSmall fixed-wing UAVs are increasingly attracting attention due to many applications in both military operations such as surveillance, and civilian domains such as powerline patrol and aerial photography. Their popularity growth has reduced the weight and size of small fixed-wing UAVs. They are vulnerable to external disturbances, such as wind due to their reduced size and weight. Disturbance has adverse effects on small fixed-wing UAVs, as it lowers the stability and performance of the control system during the operation. The disturbance includes modeling errors caused by the uncertainty of the system parameters as well as the wind from the external environment. The disturbance effects acting on small fixed-wing UAVs must be considered explicitly and eliminated eventually. In this regard, various control techniques for compensating the disturbance have been actively studied in control fields. Representative controller design techniques for compensating the disturbance include robust control (RC), sliding mode control (SMC) and adaptive control (AC), and disturbance observer-based control (DOBC). Most of the control techniques cause a slow response in attenuating disturbance effects since feedback control is performed based on tracking errors. Therefore, there is a need to compensate directly for disturbance through feedforward control. The disturbance observer-based control scheme directly estimates the uncertainty of the system, external disturbance, and directly compensates the estimated disturbance through the feedforward. This paper proposes a nonlinear disturbance observer-based path following controller for a small fixed-wing UAV affected by disturbance such as wind. We used a nonlinear disturbance observer-based control (NDOBC) method for precise path following for a small fixed-wing UAV along with the Lyapunov guidance vector field (LGVF) technique. The disturbance is estimated by a nonlinear disturbance observer, and then it is incorporated into the LGVF path following controller to compensate disturbance effects. The numerical simulation is first carried out through the MATLAB Simulink environment. Software in the loop simulation (SITL) is carried out to verify its performance. Outdoor flight experiments are performed to demonstrate its performance in a real-world environment.ope

Development of Robust Control Laws for Disturbance Rejection in Rotorcraft UAVs

Inherent stability inside the flight envelope must be guaranteed in order to safely introduce private and commercial UAV systems into the national airspace. The rejection of unknown external wind disturbances offers a challenging task due to the limited available information about the unpredictable and turbulent characteristics of the wind. This thesis focuses on the design, development and implementation of robust control algorithms for disturbance rejection in rotorcraft UAVs. The main focus is the rejection of external disturbances caused by wind influences. Four control algorithms are developed in an effort to mitigate wind effects: baseline nonlinear dynamic inversion (NLDI), a wind rejection extension for the NLDI, NLDI with adaptive artificial neural networks (ANN) augmentation, and NLDI with L1 adaptive control augmentation. A simulation environment is applied to evaluate the performance of these control algorithms under external wind conditions using a Monte Carlo analysis. Outdoor flight test results are presented for the implementation of the baseline NLDI, NLDI augmented with adaptive ANN and NLDI augmented with L1 adaptive control algorithms in a DJI F330 Flamewheel quadrotor UAV system. A set of metrics is applied to compare and evaluate the overall performance of the developed control algorithms under external wind disturbances. The obtained results show that the extended NLDI exhibits undesired characteristics while the augmentation of the baseline NLDI control law with adaptive ANN and L1 output-feedback adaptive control improve the robustness of the translational and rotational dynamics of a rotorcraft UAV in the presence of wind disturbances