Loop Transfer Recovery Controller Research Articles

Design and Flight Evaluation of Primary Control System for Learjet-25B Aircraft

In this paper, a multi-input/multi-output servomechanism primary flight controller is presented. Also discussed are flight data related to the system performance and pilot assessments of handling qualities. The data were collected during flight-test experiments (March 2018) on the Calspan Variable Stability In-Flight Simulator Learjet-25B aircraft. Aircraft body angular rates and linear accelerations are used to enable decoupled command tracking in pitch, roll, and yaw axes. Angle of attack and angle of sideslip measurements are not required for the system to operate. The developed primary flight controller translates pilot controls into the corresponding pitch, roll, and yaw commands for the aircraft to track. The system consists of a gain-scheduled robust linear baseline augmented with a direct adaptive model reference output feedback. The baseline is designed via the Observer-Based Loop Transfer Recovery method. The adaptive component incorporates the closed-loop reference model, whereby a state observer from the baseline Observer-Based Loop Transfer Recovery system also acts as the reference model for the adaptive augmentation. In March 2018, the Observer-Based Loop Transfer Recovery controller was successfully flight verified on the Calspan Learjet-25B aircraft, at the U.S. Air Force Test Pilot School, Edwards Air Force Base, California. Flight-test results are discussed, and a brief summary is given at the end.

Feedforward Feedback Linearization Linear Quadratic Gaussian With Loop Transfer Recovery Control of Piezoelectric Actuator in Active Vibration Isolation System

Hysteresis exists widely in intelligent materials, such as piezoelectric and giant magnetostrictive ones, and it significantly affects the precision of vibration control when a controlled object moves at a range of micrometers or even smaller. Many measures must be implemented to eliminate the influence of hysteresis. In this work, the hysteresis characteristic of a proposed piezoelectric actuator (PEA) is tested and modeled based on the adaptive neuro fuzzy inference system (ANFIS). A linearization control method with feedforward hysteresis compensation and proportional–integral–derivative (PID) feedback is established and simulated. A linear quadratic Gaussian with loop transfer recovery (LQG/LTR) regulator is then designed as a vibration controller. Verification experiments are conducted to evaluate the effectiveness of the control method in vibration isolation. Experiment results demonstrate that the proposed vibration control system with a feedforward feedback linearization controller and an LQG/LTR regulator can significantly improve the performance of a vibration isolation system in the frequency range of 5–200 Hz with low energy consumption.

Adaptive Output-Feedback Control with Closed-Loop Reference Models for Very Flexible Aircraft

This paper proposes a model reference adaptive controller for a class of multi-input/multi-output plants where the number of outputs is larger than the number of inputs: an example of which is very flexible aircraft. A dominant presence of model uncertainties and actuator anomalies necessitates an adaptive approach for control of very flexible aircraft. The proposed controller, denoted as the adaptive strictly positive real / loop transfer recovery controller, combines a baseline observer-based design with loop transfer recovery properties and an adaptive design based on strictly positive real transfer functions. In addition to accommodating the absence of full-state measurements, the controller includes a reference model that also plays the role of an observer through a closed-loop component. Conditions are delineated under which this controller can guarantee asymptotic reference tracking, and the control design is validated using a very flexible aircraft model around a single equilibrium flight condition with 707 states, 12 outputs, and 2 control inputs. Simulation results show that the adaptive controller not only ensures stability but also recovers a nominal performance in both the time domain and frequency domain, despite the presence of varying wing shapes and actuator anomalies.

A New Look at the Target Feedback Loop Parameterization for $$\mathcal {H}_{\infty }$$ H ∞ /LTR Control

In this paper, a new approach on the target feedback loop (TFL) parameterization for the \(\mathcal {H}_{\infty }\)/loop transfer recovery (LTR) control is presented. The proposed procedure, which is based on a similarity transformation, allows to obtain a first-order system behavior through a particular shaping of the TFL sensitivity in terms of singular values. Furthermore, the proposed methodology makes possible to augment the design plant model with any stable real-finite pole, and not only a pole at the origin, as classical TFL parameterization procedures suggest. Thus, the proposed methodology should gather great attention by LTR-based control applications in which the use of integrators in the open-loop is undesirable or even prohibitive. Additional properties are derived if the design plant model does not have poles at the open right-half plane. Since \(\mathcal {H}_{\infty }\)/LTR control can be viewed as a generalization of well-known LQG/LTR control, the proposed methodology in this paper to shape the TFL can be properly extended to the LQG/LTR control.

Study of autonomous underwater vehicle wave disturbance rejection in the diving plane

Autonomous underwater vehicles operating near the sea surface are subject to wave disturbances in their motion, which can affect severely the data acquisition during the vehicle motion. Bathymetric maps, for example, may suffer a big loss in quality due to such kind of disturbances that can impose oscillations in the vehicle depth and attitude. This article describes a controller structure for compensating the wave disturbances in the vertical plane for a torpedo-like autonomous underwater vehicle, based on a modified version of the linear quadratic Gaussian with loop transfer recovery control combined with a wave filter. The proposed methodology uses additional to the classic linear quadratic Gaussian with loop transfer recovery design the measurement of non-controlled states, such as the pitch rate and heave velocity, in the control action. The wave disturbances were filtered away by a shaping filter fitted to the sea spectrum, and the sensor signals were integrated by an extended Kalman filter. The proposed control methodology was tested against the classical linear quadratic Gaussian with loop transfer recovery controller in a 6-degree-of-freedom non-linear autonomous underwater vehicle simulator, producing a better performance in most demanding conditions such high wave crests. The tests also revealed the impact of the hydroplane geometry on the controller performance, which should not be underestimated by the autopilot designer.

Nonlinear quadratic Gaussian control with loop transfer recovery

A nonlinear quadratic Gaussian with loop transfer recovery control method called NQG/LTR method is presented, which is the integration of statistical linearization, loop-shaping and loop transfer recovery techniques. The proposed NQG/LTR method is a powerful one for designing controllers of nonlinear systems with hard nonlinearities such as Coulomb friction, backlash and dead-zone. In order to show the effectiveness of the proposed method, the LQG/LTR and NQG/LTR methods are applied to a timing-belt driving cart system with Coulomb friction and dead-zone. The results of simulation and experiment for a cart system show that the performance and stability robustness of the NQG/LTR control system are insensitive to the effects of the nonlinear elements of a cart system.

Quasi-linear H2/H.INF./LTR Control of Vertical Parallel Flexible Structures Connected by a Spring.

The quasi-linear H2/H∞/LTR control method is presented for the robust control of hardnonlinear multivariable systems. The hard nonlinear elements such as Coulomb friction, dead-zone and backlash are replaced by their random input describing functions (RIDF) to develop a quasi-linear model for designing a quasi-linear H2/H∞ controller. However, a nonlinear correction term appears in the coupled Riccati equations when the quasi-linear H2/H∞ method is applied for a quasi-linear model. It is shown that a nonlinear correction term can be ignored using the loop transfer recovery (LTR) under the appropriate condition. Thus, the quasi-linear H2/H∞ controller can be synthesized by introducing the inverse random input describing function (IRIDF). To show the effectiveness of the proposed control method, it will be applied to a flexible parallel inverted pendulum with Coulomb friction. The results of simulation show that the proposed control method is robust to nonlinear effects and the vibration of end tip.