Trim Optimization of Over-Actuated Rotorcraft Using Extremum Seeking Control
Restricted (Penn State Only)
- Author:
- Scaramal, Mariano Daniel
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 28, 2024
- Committee Members:
- Amy Pritchett, Program Head/Chair
Constantino Lagoa, Outside Unit & Field Member
Joseph Horn, Chair & Dissertation Advisor
Edward Smith, Major Field Member
Jacob Langelaan, Minor Field Member
Umberto Saetti, Special Member - Keywords:
- Extremum Seeking Control
Over-Actuated Rotorcraft
Trim Optimization
Automatic Flight Control System
AFCS
Scheduled Controller
Dynamic Inversion Controller
eVTOL - Abstract:
- This thesis presents an exploration into the application of Extremum-Seeking Control (ESC) within automatic flight control systems to enhance efficiency in over-actuated rotorcraft. Through a comprehensive investigation, the study delves into the utilization of ESC for optimizing various performance metrics, including load alleviation, energy consumption, and fuel efficiency. Leveraging ESC’s adaptive capabilities, the research demonstrates its effectiveness in dynamically adjusting control inputs to achieve optimal performance across a range of flight conditions and maneuvers. Additionally, the study explores the integration of ESC with other control strategies to further enhance efficiency, stability, and response characteristics. The findings shed light on the potential of ESC as a versatile tool for advancing the efficiency and effectiveness of rotorcraft operations, paving the way for future developments in autonomous flight control systems. The thesis is divided into three research projects related to different over-actuated rotorcraft. The first part focuses on the design of controllers to achieve load alleviation for a compound rotorcraft in trim and in quasi-steady maneuvering flight. These controllers are implemented on a compound utility rotorcraft airframe with properties resembling those of a UH-60A along with lifting wings. The nonlinear model is developed in FLIGHTLAB® from where the vehicle dynamics and critical fatigue loads are extracted as a linear time-periodic system due to its cyclic nature. Via harmonic decomposition, this model is converted to a high-order linear time-invariant (LTI) system and then a reduced-order method is applied to extract a more tractable system for controller design over a range of airspeeds. The designs were tested in both the high-order LTI and the nonlinear system. These results demonstrate a significant reduction in peak-to-peak pitch link loads with minimum impact on response characteristics. As a result of this research, two control systems were developed, each utilizing a Dynamic Inversion (DI) controller and Direct Load Feedback (DLFB). The first controller was designed to solely reduce the amplitude of the pitch link load during maneuvering. The second controller utilized ESC to provide better performance for load alleviation in trim and maneuvering flight. The second research introduces a controller system designed to minimize electric energy usage during trim level flight for an eVTOL rotorcraft. The methodology employs an ESC approach with bounded update rates and is implemented on an eVTOL with a lift plus cruise configuration, featuring four lift rotors and a pusher propeller. The optimal control strategy utilizes the energy consumption of all five rotors as the cost function while simultaneously controlling the rotorcraft’s pitch angle and lift rotor speeds. Nonlinear simulations, conducted with various initial conditions at a velocity close to the transition between rotorcraft and airplane modes, depict the controller’s effectiveness. Results show that upon controller activation, significant reductions in electric energy are achieved within 50 seconds, maintaining rotorcraft stability. While minor effects of the dither signal on attitude, lift rotor speeds, and collective responses are observed, a heuristic solution eliminates the dither signal by deactivating the controller upon achieving stability and minimizing the cost function. The third part presents a controller system designed to improve fuel efficiency by reducing fuel flow in trim and quasi-steady maneuvering flight conditions. The primary control system incorporates an inner loop controller for governing attitude rates and an outer loop controller for velocity and altitude regulation, based on the linearized model. Utilizing extremum-seeking control, the proposed controller operates within the null space of the velocity and altitude dynamic control matrix to achieve fuel flow reduction. The demonstrated effectiveness of the controller system resulted in fuel flow reductions of up to 21% in approximately 15 seconds, in cases not affected by turbulence. Testing under various turbulence levels also resulted in fuel flow reduction, albeit to a lesser extent. In summary, this thesis explores the application of ESC in automatic flight control systems for over-actuated rotorcraft. Specifically, it examines: the application of ESC with DLFB for load alleviation on compound rotorcraft; the use of ESC to design an in-flight optimization method for electric energy consumption on eVTOL aircraft; and the utilization of ESC through the null space of the control matrix to reduce the effects of the dither signal while minimizing fuel flow on coaxial rotorcraft. Through innovative methodologies and rigorous testing, it demonstrates the transformative potential of ESC. These findings significantly advance rotorcraft technology, enhancing efficiency and effectiveness in various flight conditions and environments.