Preview Control Research Articles

Flight Test Results of Disturbance Attenuation using Preview Feedforward Compensation

This paper demonstrates flight test results of disturbance attenuation of an aircraft by preview control, which was explained and its hardware-in-the-loop (HIL) simulation results were reported in a previous paper. The design methodology of preview control used here is the “two-stage” approach, in which a feedback gain is firstly designed by some standard design method and then a preview feedforward compensation is designed for the closed loop system. The flight test is carried out using a small research aircraft and a preview controller that alleviates disturbance response is designed for the aircraft model. Flight test results shows that the proposed preview controller alleviates vertical acceleration much better compared to the conventional feedback controller.

Optimal Feedforward Preview Control by FIR Filters

The paper presents a new method for designing an optimal feedforward preview controller for asymptotically stable single-input single-output (SISO) systems. We conduct an optimization based on an impulse response representation of the system’s dynamics for a chosen control horizon. This leads to an optimal deconvolution that proactively exploits the reference or disturbance signal’s preview information to calculate the control input for a desired output. In order to extend this deconvolution to arbitrarily long input signals, we show that, under certain circumstances, a finite impulse response (FIR) filter can be build from it. This filter can be seen as the system’s optimized inverse, which also applies to non-minimum phase systems. Since optimization is done offline, the resulting filter is computationally inexpensive and easily implemented. Its effectiveness is shown by applying the proposed method to a sample system.

Design of a robust H∞ preview controller for a class of uncertain discrete-time systems

The robust preview tracking control problem of uncertain discrete-time systems satisfying matching conditions is considered. First, we use the difference between a system state and its steady-state value, instead of the usual difference between system states, to derive an augmented error system that includes the future information on the reference signal and disturbance signal to transform the tracking problem into a regulator problem. Then, a robust preview controller of the augmented error system is proposed by integrating Lyapunov stability theory and LMI approach. Research shows that the preview controller gain matrix can be determined by solving a LMI. The proposed robust preview controller in this paper cannot only guarantee the asymptotic stability of the closed-loop system, but also enhance the interference rejection properties. An integrator is applied to make sure that the output tracks the reference signal with no static error. The numerical simulation example also illustrates the effectiveness of the results presented in the paper.

Cooperative global optimal preview tracking control of linear multi-agent systems: an internal model approach

ABSTRACTThis paper investigates the cooperative global optimal preview tracking problem of linear multi-agent systems under the assumption that the output of a leader is a previewable periodic signal and the topology graph contains a directed spanning tree. First, a type of distributed internal model is introduced, and the cooperative preview tracking problem is converted to a global optimal regulation problem of an augmented system. Second, an optimal controller, which can guarantee the asymptotic stability of the augmented system, is obtained by means of the standard linear quadratic optimal preview control theory. Third, on the basis of proving the existence conditions of the controller, sufficient conditions are given for the original problem to be solvable, meanwhile a cooperative global optimal controller with error integral and preview compensation is derived. Finally, the validity of theoretical results is demonstrated by a numerical simulation.

Effects of Preview on Human Control Behavior in Tracking Tasks With Various Controlled Elements.

This paper investigates how humans use a previewed target trajectory for control in tracking tasks with various controlled element dynamics. The human's hypothesized "near" and "far" control mechanisms are first analyzed offline in simulations with a quasi-linear model. Second, human control behavior is quantified by fitting the same model to measurements from a human-in-the-loop experiment, where subjects tracked identical target trajectories with a pursuit and a preview display, each with gain, single-, and double-integrator controlled element dynamics. Results show that target-tracking performance improves with preview, primarily due to the far-viewpoint response, which allows humans to cancel their own and the controlled element's lags, without additional control activity. The near-viewpoint response yields better target tracking at higher frequencies, but requires substantially more control activity. The control-theoretic approach adopted in this paper provides unique quantitative insights into human use of preview, which can help to explain human behavior observed in other preview control tasks, like driving.

Preview predictive control layer design based upon known wind turbine blade‐pitch controllers

AbstractThe use of upstream wind measurements has motivated the development of blade‐pitch preview controllers for improving rotor speed tracking and structural load reduction beyond that achievable via conventional feedback control. Such preview controllers, typically based upon model predictive control (MPC) for its constraint handling properties, alter the closed‐loop dynamics of the existing blade‐pitch feedback control system. This can result in a deterioration of the robustness properties and performance of the existing feedback control system. Furthermore, performance gains from utilising the upcoming real‐time measurements cannot be easily distinguished from the feedback control, making it difficult to formulate a clear business case for the use of preview control. Therefore, the aim of this work is to formulate a modular MPC layer on top of a given output‐feedback blade‐pitch controller, with a view to retaining the closed‐loop robustness and frequency‐domain performance of the latter. The separate nature of the proposed controller structure enables clear and transparent quantification of the benefits gained by using preview control, beyond that of the underlying feedback controller. This is illustrated by results obtained from high‐fidelity closed‐loop turbine simulations, showing the proposed control scheme incorporating knowledge of the oncoming wind and constraints achieved significant 43% and 30% reductions in the rotor speed and flap‐wise blade moment standard deviations, respectively. Additionally, the chance of constraint violations on the rotor speed decreased remarkably from 2.15% to 0.01%, compared to the nominal controller. Copyright © 2017 John Wiley & Sons, Ltd.

Robust preview control for uncertain discrete‐time systems based on LMI

SummaryFor a class of uncertain discrete‐time systems, a preview controller based on linear matrix inequality is proposed. A new method is derived to construct an augmented error system instead of taking the difference of the error signal and the system equation. The new approach avoids applying the difference operator to the time‐varying matrix and can simplify the augmented error system. For the augmented error system of the uncertain system, state feedback is introduced. The sufficient condition of asymptotic stability of the closed‐loop system is derived for the performance index by using the relevant theorems of robust control theory. The condition can be realised by solving a linear matrix inequality optimization problem. By incorporating the controller obtained into the original system, we obtain the preview controller. Moreover, introducing an integrator allows the closed‐loop system to robustly track the desired tracking signal without steady‐state error.

H∞ Preview Control of A Class of Uncertain Discrete‐Time Systems

AbstractThis paper investigates the problem of H∞ preview tracking control with robust performance for uncertain discrete‐time systems. In order to avoid applying the difference operator to the time‐varying matrix, by taking advantage of the difference between the system state variables, input variables, and the corresponding auxiliary variables, instead of the usual difference between system states, an augmented error system including previewed information is constructed, which converts the tracking problem into a regulator problem. A sufficient condition based on the free‐weighting matrices technique and the Lyapunov stability theory is derived for the robust asymptotic stability of uncertain systems. Moreover, a state feedback control law with preview action design method is obtained via the linear matrix inequality approach. Based on these, a state observer for preview control systems is formulated. Previewable reference signals are fully utilized through reformulation of the output equation while designing the state observer. The proposed construction method of augmented error system is applicable to uncertain discrete‐time systems in which the uncertainties are general. Also an integrator is introduced to ensure the closed‐loop system tracking performance with no static error. The numerical results also show the effectiveness of the preview control law for uncertain systems in the paper.

Road disturbance estimation for the optimal preview control of an active suspension systems based on tracked vehicle model

This research investigates stochastic estimation of a look-ahead sensor scheme using the optimal preview control for an active suspension system of a full tracked vehicle (FTV). In this scheme, wheel disturbance input to the front wheels are estimated using the dynamic equations of the system. The estimated road disturbance input at the front wheels are utilized as preview information for the control of subsequently following wheels of FTV. The design of optimal preview control is used as a classical linear quadratic Gaussian problem by combining dynamics of the original system and estimation of previewed road inputs. The effectiveness of the preview controller is evaluated by comparing the estimated information with the measured information for different road profiles, where Kalman filter is used for the state-variables estimation of the FTV. This research also considers the reduced order estimation using commonly available sensors in order to decrease the number of sensors and measurements. The simulation results’ using an active suspension system with different preview information shows that the proposed system can be beneficial for the improvement of ride comfort of tracked vehicles without using any specialized sensors for preview information calculation.

Parameter‐dependent preview control with robust tracking performance

The problem of static output feedback preview tracking control is proposed for a class of polytopic uncertain discrete-time systems by combining parameter-dependent Lyapunov function method with linear matrix inequality (LMI) technique. First, the error system method of preview control theory is adopted and the difference operator is introduced, and then an augmented error system including previewed information is constructed, which transforms a tracking problem into a regulation problem. Then, a previewable reference signal is fully utilised through reformulation of the output equation for the derived augmented error system while considering the output feedback. Sufficient conditions for designing a robust static feedback preview controller are given in terms of solutions to a set of LMIs. Based on the criterion, a static output feedback controller with preview action is designed such that the output can asymptotically track the reference signal. Finally, the numerical simulation examples also illustrate the superiority of the desired preview controller for the uncertain system in the study.

Design of an Optimal Preview Controller for a Class of Linear Discrete-Time Descriptor Systems

The preview control problem of a class of linear discrete-time descriptor systems is studied. Firstly, the descriptor system is decomposed into a normal system and an algebraic equation by the method of the constrained equivalent transformation. Secondly, by applying the first-order forward difference operator to the state equation, combined with the error equation, the error system is obtained. The tracking problem is transformed into the optimal preview control problem of the error system. Finally, the optimal controller of the error system is obtained by using the related results and the optimal preview controller of the original system is gained. In this paper, we propose a numerical simulation method for descriptor systems. The method does not depend on the restricted equivalent transformation.

<i>H</i><sup>2</sup>予見出力フィードバックの導出とその負荷周波数制御への応用

This paper presents a continuous-time H2 preview control based on partial information, and its application to load frequency control (LFC). It is expected that preview supply and demand information improves load frequency control performances. In common power system, however, we have difficulties in measuring all the internal states which compose the overall generator. To solve this difficulty, a design method of H2 preview control system is proposed in an output feedback setting. The design method enables to treat the preview uncertainties by introducing an independent disturbance channel into the corresponding generalized plant. It is shown that the frequency variation in the power system is effectively attenuated by reflecting the bandwidth of load variation.

放射線モニタリング無人固定翼機の予見制御による高度制御性能向上

This paper is concerned with the design problem of preview altitude controller for Unmanned Airplane for Radiation Monitoring System\nobreakspace {}(UARMS) to improve its control performance. UARMS has been developed for radiation monitoring around Fukushima Dai-ichi nuclear power plant which spread radiation contaminant due to the huge tsunamis caused by the Great East Japan Earthquake. The monitoring area contains flat as well as mountain areas. The basic flight controller has been confirmed to have satisfactory performance with respect to altitude holding; however, the control performance for variable altitude commands is not sufficient for practical use in mountain areas. We therefore design preview altitude controller with only proportional gains by considering the practicality and the strong requirement of safety for UARMS. Control performance of the designed preview controller was evaluated by flight tests conducted around Fukushima Sky Park.

Back-stepping based anti-disturbance flight controller with preview methodology for autonomous aerial refueling

This paper proposes a novel back-stepping based flight controller for the receiver in Autonomous Aerial Refueling (AAR) by the combination of active disturbance rejection control (ADRC) and preview control methodology. Firstly, the proposed flight control law design is divided into five loops by the back-stepping technique. The 6 DOF model for aircraft is written into several strict-feedback nonlinear forms through tactful transformation, considering that the path dynamics are originally non-affine nonlinear forms and are intractable for controller design. Secondly, the influences of the unknown flow perturbations on a receiver in each loop are viewed as the components of the “total disturbances” which are estimated and compensated by extended state observer (ESO). Thirdly, the preview control methodology is introduced into the position loop design as the system dynamic of the receiver is much slower than drogue. The position loop determines the proper reference path angle by using a fuzzy-logic ADRC controller in which previewing error and current tracking error are both taken into consideration. And a novel adaptive look-ahead distance scheme based on the fuzzy logic control (FLC) is proposed for the selection of the preview point. Finally, extensive simulations and comparisons on the 6 DOF receiver model are carried out to demonstrate the effectiveness of the proposed flight controller.

Applications of the preview control method to the optimal problem for linear continuous-time stochastic systems with time-delay

This paper discusses the optimal control problem for a class of linear continuous-time stochastic systems with time-delay based on the preview control method. In the design procedure, the time-delay terms are formally eliminated and the augmented error system method is used. The optimal controller of the time-delay stochastic system is obtained based on dynamic programming principle. In the previous approaches, the preview control method is applied to continuous-time deterministic system. Consequently, compared with the existing results, the main contributions of this paper are: (1) the conclusion of the non-singular transformation is improved and (2) the conclusion in deterministic system is extended by using the methods of designing an assistant system and introducing an integrator when building the stochastic augmented error system. The optimal tracking of the stochastic system with time-delay is realized by solving the optimal regulation problem of the stochastic augmented error system. The simulation shows the effectiveness of the controller designed in this paper.

Mixed Skyhook and FxLMS Control of a Half-Car Model with Magnetorheological Dampers

The problem of vibration attenuation in a semiactive vehicle suspension is considered. The proposed solution is based on usage of the information about the road roughness coming from the sensor installed on the front axle of the vehicle. It does not need any preview sensor to measure the road roughness as other preview control strategies do. Here, the well-known Skyhook algorithm is used for control of the front magnetorheological (MR) damper. This algorithm is tuned to a quarter-car model of the front part of the vehicle. The rear MR damper is controlled by the FxLMS (Filtered-x LMS) taking advantage of the information about the motion of the front vehicle axle. The goal of this algorithm is to minimize pitch of the vehicle body. The strategy is applied for a four-degree-of-freedom (4-DOF) vehicle model equipped with magnetorheological dampers which were described using the Bouc-Wen model. The suspension model was subjected to the road-induced excitation in the form of a series of bumps within the frequency range 1.0–10 Hz. Different solutions are compared based on the transmissibility function and simulation results show the usefulness of the proposed solution.

Robust preview tracking control for a class of uncertain discrete-time systems

AbstractThe robust preview control problem of uncertain discrete-time systems satisfying matching conditions is considered. First, for the nominal system, we use the difference between a system state and its steady-state value, instead of the usual difference between system states, to derive an augmented error system that includes the future information on the reference signal and disturbance signal to transform the tracking problem into a regulator problem. Then, the robust controller design problem based on the optimal controller of the augmented error system is proposed for uncertain system. And the proposed robust preview control law is obtained in terms of the linear matrix inequality (LMI) technique and the Lyapunov stability theory. Bringing the resulting controller back to the original system, a controller with preview actions achieving robust tracking performance is presented. The numerical simulation example also illustrates the effectiveness of the results presented in the paper.

Adaptive preview control for piecewise discrete-time systems using multiple models

In this paper, the problem of multi-model adaptive preview control is proposed for discrete-time systems with unknown piecewise constant coefficients. Following preview control theory, corresponding augmented error systems for piecewise discrete-time systems are constructed. By making use of the Heine–Borel covering theorem, a finite set of fixed augmented systems covering the range of the unknown parameters is established, and associated fixed preview controllers are derived. Based on the core idea of multi-model adaptive control, switching law of the controllers is designed, and eventually, an adaptive preview controller is obtained. The exponential asymptotic stability of closed-loop systems with large uncertainties is discussed in detail. Finally, simulation results are given to demonstrate the effectiveness of the theoretical results.

Stable walking in a biped robot with force-feedback-induced center-of-mass regulation

We report on a novel ZMP feedback control strategy which regulates the center of mass trajectory of a robot based on the measured zero-moment point (ZMP). Based on the trajectory generated by preview control and the linear inverted pendulum model, the controller has an extra model-based control input which is driven by the center-of-mass (CoM) acceleration, which provides sensitive response to disturbance. Thus, the robot motion is balanced between the long-term nominal CoM/ZMP trajectory tracking and the short-term trajectory modification for disturbance rejection. In addition, the controller has two layers of adjustment strategy. When the disturbance is small, the robot is regulated by merely adjusting its CoM trajectory. In contrast, when the disturbance is large, the foot position of the robot is simultaneously changed to provide a more effective response with characteristics of larger intrinsic stability. The performance of the control strategy is also experimentally evaluated using a child-size biped robot.

Constrained Optimal Preview Control of Dual-Stage Actuators

This paper proposes constrained optimal trajectories for the preview control of dual-stage actuators (DSA). Relying on the redundancy of actuators preview control allows the primary stage to move before the transition instant, and uses the secondary stage to compensate its movements. Contrasting existing strategies that consider the secondary stage infinitely fast during preview control, this study takes into account its dynamic limitations when designing the trajectories to be followed during preactuation. It will be shown that the problem may be cast in terms of quadratic programming providing an optimal solution with respect to a quadratic criterion. Experimental results validated the proposed strategy, which is able to achieve a 30% improvement over state-of-the-art high-performance DSA controllers, while respecting the limitations of both actuators.