Caroline Bérard

Gain scheduling with guardian maps for longitudinal flight control

A new approach to gain scheduling of linear controllers is proposed and applied to a longitudinal flight control pro-blem. Traditionally, gain scheduling is done a posteriori by the interpolation of controller gains designed for several operating points or conditions. The method proposed here is based on guardian maps and does not require as many linear controller syntheses as there are design points. Rather, it extends the performance of an initial single controller carried out on an arbitrary operating point to the entire domain while ensuring generalized stability all along the process. The method, which uses a given fixed architecture controller, is successfully applied on the longitudinal flight control of a business jet aircraft.

Development of a VTOL mini UAV for multi-tasking missions

Recent developments in the field of Mini-UAVs lead to successful designs in both hovering rotorcraft and fixed wing aircraft. However, a polyvalent MAV capable of stable hovering and fast forward flight is still expected. A promising candidate for such versatile missions consists of a tilt-body tail-sitter configuration. That concept is studied in this paper both from the flight mechanics and control points of view. Developments are based on an existing prototype called Vertigo. It consists of a tail sitter fixed-wing mini-UAV equipped with a contra-rotating pair of propellers in tractor configuration. A wind-tunnel campaign was carried out to extract experimental results from the Vertigo aerodynamic characteristics. A 6-component sting balance was fitted in the powered model enabling excursion in angles of attack and sideslip angles up to 90°. Thus, a detailed understanding of the transition mechanism could be obtained. An analytical model including propwash effects was derived from experimental results. The analytical model was used to compute stability modes for specific flight conditions. This allowed an appropriate design of the autopilot capable of stabilisation and control over the whole flight envelope. A gain sequencing technique was chosen to ensure stability while minimising control loop execution time. A MATLAB-based flight simulator including an analytical model for the propeller slipstream has been developed in order to test the validity of airborne control loops. Simulation results are presented in the paper including hover flight, forward flight and transitions. Flight tests lead to successful inbound and outbound transitions of the Vertigo.

LFT modelling of the 2-DOF longitudinal nonlinear aircraft behaviour

The objective of this paper is to illustrate that the standard form or Linear Fractional Transformation LFT framework is a unique and powerful framework to treat with nonlinear systems during control law synthesis and analysis. It is also shown that the expression linear in the acronym LFT is too restrictive as a nonlinear behaviour can be simulated by using the LFT framework. Within this paper, a precise and as small as possible LFT for a nonlinear 2-DOF aircraft with time varying parameters is derived. This LFT is validated both in a linear and nonlinear framework.

A Novel Parameter Varying Controller Synthesis Method for Quadrotor Control

This paper presents a method to design robust gain scheduled controller for parameter varying plants. The controller is to be used in an adaptive control architecture to obtain better performance than a robust controller for the control of multiple configuration of quadrotors. The proposed approach is based on the a priori selection of an interpolation formula. It takes advantage of recent advances in structured and multi-channel fixed-order Hinf synthesis to derive a low order controller with a meaningful structure. The resulting observer/state feedback controller remains easy to implement. The efficiency of the controller is demonstrated with its implementation on quadrotors UAV and the subsequent flight tests.

Structured H ∞ control for a launch vehicle

This work presents an application of structured H∞ synthesis, a novel robust controller synthesis technique that takes the benefits of the classic H∞ synthesis imposing additional restrictions to the controller structure. These restrictions allows the designer to synthesize controllers with a more understandable structure and help in the optimization process. This technique is applied to the atmospheric ascent phase of a launch vehicle.

Investigation of Flight Dynamics and Automatic Controls for Hovering Micro Air Vehicles

The present work describes the development of an automatic control system and the investigation of the flight dynamics of fixed-wing micro air vehicles (MAVs) with vertical take-off and landing (VTOL) capabilities. Specifically, the hovering phase of the flight was studied in detail. A state-space model was formulated and used in a control law design. The effects of propeller slip stream impinging on the airframe are discussed in the context of control design. Feedback control laws based on a proportional, integral, and derivative (PID) control design were developed and programmed into the autopilot. The development and evaluation of two VTOL MAVs with wingspans of 65 and 31 cm are presented. A number of test flights of vehicles with attitude stabilization and altitude hold were conducted with telemetry acquisition. Despite the difference in size, similarities were noted in the dynamic response for both aircraft. The actuation delays in the propulsion systems caused a systematic error in an altitude. Average amplitudes of rotational oscillations in all three axes were also about the same for both aircraft. Higher roll rates can be explained by lower inertia in roll axis.

Motion Planning and Control of a Space Robot to Capture a Tumbling Debris

Space robotics has emerged as one of the key technology for on-orbit servicing or debris removal issues. In the latter, the target is a specific point of a tumbling debris, that the ≪ chaser ≫ satellite must accurately track to ensure a smooth capture by its robotic arm. Based on recent works by Aghili, an optimal capture trajectory is presented to match position and speed, but also acceleration of the target. Two controllers are simultaneously synthesized for the satellite and the arm, using the fixed-structure H ∞ synthesis. Their tracking performance is validated for the tumbling target capture scenario. The main goal is to efficiently track the optimal trajectory while using simple PD-like controllers to reduce computational burden. The fixed-structure H ∞ framework proves to be a suitable tool to design a reduced-order robust controller compatible with current space processors capabilities.

Self-scheduled and structured H ⋡ synthesis : A launch vehicle application

This paper presents a new application of structured H∞ synthesis to tune self-scheduled controllers. Newly available MATLAB-based tools allow to tune fixed-structure linear controllers while satisfying H∞ constraints. Moreover multi-model synthesis capabilities can extend their application to self-scheduled controllers. This technique is successfully applied to the attitude control of a launch vehicle in atmospheric ascent phase.

Robust control of a launch vehicle in atmospheric ascent based on guardian maps

A robust control design for a space launcher during its atmospheric ascent is presented. Considering a typical wind profile during flight, the launcher controller has to first stabilize the open-loop unstable system, and then maintain verticality. The model available takes into account flexible modes and nozzle actuator dynamics, and is time-variant. Aside from launcher stability, additional requirements pertaining to frequency and damping of rigid launcher modes as well as flexible ones, must be fulfilled. The synthesis relies on guardian maps, making possible to characterize the sets of all controller gains which meet the requirements, by specifying areas of interest where the systems closed-loop poles must be located.

Robust scheduled control of longitudinal flight with handling quality satisfaction

Classic flight control systems are still widely used in the industry because of acquired experience and good understanding of their structure. Nevertheless, with more stringent constraints, it becomes difficult to easily fulfil all the criteria with these classic control laws. On the other hand, modern methods can handle many constraints but fail to produce low order controllers. The following methodology proposed in this paper addresses both classic and modern flight control issues, to offer a solution that leverages the strengths of both approaches. First, an H∞ synthesis is performed in order to get controllers which satisfy handling qualities and are robust withrespect to mass and centre of gravity variations. These controllers are then reduced and structured by using robust modal control techniques. In conclusion, a self-scheduling technique is described that will schedule these controllers over the entire flight envelope.