Adaptive Feedforward Compensation Research Articles

A fully actuated system approach: Desired compensation adaptive robust control for uncertain nonlinear systems

A desired compensation adaptive robust control (DCARC) framework is presented for two types of fully actuated systems (FASs) subject to both parametric and nonlinear uncertainties based on the Lyapunov theory. The designed controller consists of three parts: (i) a fundamental linear state error feedback term; (ii) an adaptive feedforward compensation term; (iii) a robust compensation term. Different from the existing FAS approaches, the adaptive compensation in the proposed controller relies on the noise-free desired trajectory and online parameter estimate only. A better overall tracking performance with an accelerated transient response is expected, arising from significantly reducing interaction between the robustness part and the adaptation part. Through theoretical analysis, the proposed controller ensures that the estimation error of the unknown parameter vector and the tracking error finally converge to a bounded ellipsoid. The comparative simulation of a permanent magnet (PM) stepper motor demonstrates the effectiveness of the presented approach.

Robust adaptive precision motion control of tank horizontal stabilizer based on unknown actuator backlash compensation

Backlash nonlinearity inevitably exists in the actuator of tank horizontal stabilizer and has adverse effect on the system control performance, however, how to effectively eliminate its effect remains a pending issue. To solve this problem, a robust adaptive precision motion controller is presented in this paper to address uncertainties and unknown actuator backlash of tank horizontal actuator. The controller handles the modeling uncertainties including parameter uncertainties and unmodeled disturbances by integrating adaptive feedforward compensation and continuous nonlinear robust law. Based on the backstepping method, a smooth backlash inverse model is constructed by combining the adaptive idea. Meanwhile, the unknown backlash parameters of the system can be approximated through the parameter adaptation, and the impact of the actuator backlash nonlinearity is effectively compensated via the inverse operation, which can availably improve the tracking performance. Moreover, the adaptive law can update the disturbance ranges of tank horizontal stabilizer online in real time, which enhances the feasibility in practical engineering applications. Furthermore, the stability analysis based on Lyapunov function shows that with the existence of unmodeled disturbances and unknown actuator backlash, the designed controller guarantees excellent asymptotic output tracking performance. Extensive comparative results verify the effectiveness of the proposed control strategy.

Input constraint control for hydraulic systems with asymptotic tracking

Due to the nonlinearity and various uncertainties, the controller design for hydraulic servo systems with input constraint is more complicated and challenging. This paper first proposes an asymptotic tracking controller for electrohydraulic servomechanisms considering input constraint, parametric uncertainties, and unmodeled disturbances. The core innovation of this controller is to decouple the control input and the input nonlinearity while guaranteeing the nonlinear decoupling term and its derivative to be available and bounded. Meanwhile, the decoupling operation could be skillfully integrated to realize accurate adaptive model-based compensation while remaining the unique feature of asymptotic control for residual disturbances. For this purpose, based on the desired trajectory and the estimated disturbance via an extended state observer (ESO), a desired load pressure signal is constructed to replace the actual load pressure and accomplish the required decoupling operation. In this case, a desired adaptive feedforward compensation in combination with a robust integral of the sign of the error (RISE) feedback is proposed to attenuate parametric uncertainties and residual unmodeled disturbances, respectively. Subsequently, a smooth hyperbolic tangent function is integrated into the controller to handle the input constraint. Theoretical analysis proves that the developed control strategy can achieve semi-global asymptotic tracking performance. Besides, numerical simulations and experimental tests demonstrate that the proposed control scheme can ensure high-precision tracking performance and simultaneously satisfy the preset control input range when encountering the input constraint and modeling uncertainties.

Adaptive feed-forward friction compensation through developing an asymmetrical dynamic friction model

This article presents an adaptive feed-forward method to compensate for the dynamic friction in the machine tool systems so that the tracking errors of the machine axes can be reduced. To achieve this aim, a dynamic friction model is firstly established by constructing a continuous and differentiable two-segmented arc tangent curve to characterize the asymmetrical and nonlinear static friction phenomenon in relation to the positive and negative velocity ranges of the machine axes. Subsequently, a new feed-forward method is proposed to compensate for the friction by constructing an adaptive controller with three advantages, i.e. no need of velocity and acceleration measurement, large adaptive rate and high steady-state accuracy. During the model establishment, a discontinuous projection mapping in the learning process is constructed. Especially, the stability of the adaptive controller is strictly proved by theoretical derivation. Besides, a new two-step adaptive method is formulated to analytically calculate the unobservable parameter z. Finally, both simulations and experiments confirm that the proposed compensation method can reach to lower tracking errors, especially in the velocity reversal area, by comparing with the existing approaches.

Active vibration control for GyroWheel based on sliding mode observer and adaptive feedforward compensator

This article proposes an active vibration control method for the GyroWheel to ensure the attitude stability precision of the spacecraft. The method includes sliding mode disturbance observer and adaptive feedforward compensator. First, considering the disturbance torque caused by rotor imbalance, the dynamic equation adopting complex coefficients is derived with synchronous disturbances. To reduce the influence of model parameter perturbation, a finite time sliding mode observer is designed to estimate the rotor imbalance owing to its robustness. An integrator for the switching term is introduced in the sliding manifold, which attenuates the chattering phenomenon. Then, the observed unbalanced torque is utilized to generate the reference compensation tilting angle, which is fedforward to the command value to offset the synchronous frequency current. A variable step size seeking algorithm is adopted to tune the feedforward compensator gain adaptively. Finally, both numerical simulations and experiments have verified the effectiveness of the active vibration control scheme, achieving clean vibration torque.

Real‐time hybrid simulation of a space substructure based on high‐strength steel composite Y‐eccentrically braced frames

Real-time hybrid simulation (RTHS) is a novel structural seismic test method that has good application prospects. The applicability of RTHS for large-scale space frame structures is further investigated in this study based on high-strength steel composite Y-eccentrically braced frames (Y-HSS-EBFs). First, an RTHS system was established, which included OpenSees, OpenFresco, an xPC-Target, and an electrohydraulic servo control system. An adaptive feedforward delay compensator based on displacement prediction was introduced. Then, a shaking table test model of a three-story Y-HSS-EBF was taken as the prototype, the third-story frame with the strongest nonlinear performance was taken as the experimental substructure, and the remaining two stories were taken as the numerical substructure in order to perform the RTHS. The results of the RTHS were compared with those obtained in a purely numerical model and a shaking table test, and the stability of the RTHS system was analyzed. The results indicate that the RTHS results are in good agreement with the numerical simulation results and that RTHS can be used to obtain results similar to the ones obtained using the shaking table. In the typical seismic testing frequencies and the mass distribution ranges of the substructures, the RTHS system displayed good stability and reliability and was able to effectively evaluate the seismic performance of large-scale space frame structures.

Adaptive Pitch Controller of a Large-Scale Wind Turbine Using Multi-Objective Optimization

This paper deals with the control problems of a wind turbine working in its nominal zone. In this region, the wind turbine speed is controlled by means of the pitch angle, which keeps the nominal power constant against wind fluctuations. The non-uniform profile of the wind causes tower displacements that must be reduced to improve the wind turbine lifetime. In this work, an adaptive control structure operating on the pitch angle variable is proposed for a nonlinear model of a wind turbine provided by FAST software. The proposed control structure is composed of a gain scheduling proportional–integral (PI) controller, an adaptive feedforward compensation for the wind speed, and an adaptive gain compensation for the tower damping. The tuning of the controller parameters is formulated as a Pareto optimization problem that minimizes the tower fore-aft displacements and the deviation of the generator speed using multi-objective genetic algorithms. Three multi-criteria decision making (MCDM) methods are compared, and a satisfactory solution is selected. The optimal solutions for power generation and for tower fore-aft displacement reduction are also obtained. The performance of these three proposed solutions is evaluated for a set of wind pattern conditions and compared with that achieved by a classical baseline PI controller.

Adaptive RISE control for asymptotic rigid-body attitude tracking with additive disturbances

This paper presents a novel adaptive RISE (robust integral of the sign of the error) control method for the asymptotic rigid-body attitude tracking with inertia uncertainties and bounded unstructured external C2 disturbances. By virtue of a specially constructed synthesis of modified dynamic scaling mechanism, integration by parts, and finite escape analysis, the new design provides a simple but intuitive solution to the long-standing open problem in almost all RISE-based control schemes, that is, establishing global asymptotic tracking results without information about exact bounds of the external disturbances and its derivatives. Besides significant improvement on robustness, the proposed adaptation mechanism itself can also be regarded as a new kind of non-CE (non-certainty-equivalent) adaptive formulation, where very few extra dynamic extensions are required to largely recover ideal parameter estimation performance in commonly seen non-CE designs. The structure of the proposed controller is also equivalent to an adaptive feedforward compensator plus a stable low-pass filter whose input contains high gain feedback components, which allows flexible adjustments to establish ideal transient response and avoid chattering. Numerical simulations demonstrate that the above unique features of the proposed method lead to notable advantages over the composite adaptive RISE method.

Real-time hybrid simulation on high strength steel frame with Y-shaped eccentric braces

In recent years, real-time hybrid simulation (RTHS) has been widely examined by researchers as a new, economical, and reliable seismic testing technology for structural analysis. In this paper, RTHS is applied to the space structure experiment of a high strength steel frame with Y-shaped eccentric braces (HSYE). First, the proposed RTHS method utilized the upper stories of the prototype as the experimental substructure, and the lower stories was taken as the numerical substructure and simulated in finite element software. Then, the OpenFresco test platform and xPC-Target with an adaptive feed-forward delay compensator were used to realize real-time loading. Before conducting the RTHS, the method of adding an adaptive stage before seismic acceleration record was proposed to compensate the initial delay. On this basis, the seismic behavior of the HSYE was tested using selected seismic acceleration records. The results indicated that the RTHS results are stable and reliable. Under an earthquake simulated load, the HSYE structure can give full play to the local energy dissipation characteristics of the shear link and ensure the elasticity of the main frame, which has vast engineering application prospects.

Adaptive Feedforward and Feedback Compensation Method for Real-time Hybrid Simulation Based on a Discrete Physical Testing System Model

ABSTRACT This study proposed a general framework for adaptive delay compensation in real-time hybrid simulation(RTHS). This framework is composed of two main parts: an adaptive feedforward controller to handle variable time delay and amplitude discrepancies, and a feedback controller to enhance the robustness of compensation. In particular, the adaptive feedforward controller is determined using a discrete physical testing system (PTS) model, whose parameters are estimated using the least-squares method. Moreover, the feedback controller is introduced to reduce dependency on the PTS model of the feedforward controller. Results of virtual and actual RTHS alongside five other compensation strategies revealed the superiority of the proposed compensation method.

Adaptive feedforward control of a collaborative industrial robot manipulator using a novel extension of the Generalized Maxwell-Slip friction model

Collaborative industrial robots often use strain-wave transmissions which display a highly nonlinear behavior. In particular, the friction torque depend on the load torque and the hysteresis characteristics were recently found to depend on the joint angular position.This paper presents a novel extension of the Generalized Maxwell-Slip friction model to describe said phenomena in a combined framework. The method overcomes the discontinuity around zero velocity of existing models. Experiments on the Universal Robots UR5e manipulator show superior performance in terms of torque prediction accuracy and tracking performance of the proposed method.An adaptive feedforward friction compensator is proposed based on the extended Generalized Maxwell-Slip friction model to compensate the time-variations of the Coulomb and viscous friction due to, respectively, wear and mispredictions of the lubricant temperature. The adaptive estimator relies on the sensing hardware readily available in the joints of the Universal Robots manipulators, i.e. two absolute rotary encoders; one at each side of the transmission, current sensing for the electric actuator, and a temperature sensor. Results show a considerable reduction of the torque prediction error and tracking error.

Algorithms for Adaptive Feedforward Noise Attenuation—A Unified Approach and Experimental Evaluation

Adaptive feedforward broadband noise compensation is currently used when a correlated measurement with the disturbance (an image of the disturbance) is available. Most of the active feedforward noise control systems feature an internal “positive” acoustical feedback between the compensation system and the disturbance measurement, which has to be taken into account. Adaptive algorithms for active feedforward noise attenuation have been developed since 1985 from a local optimization point of view. This article presents two classes of adaptive configurations for active feedforward noise compensation developed from a stability point of view. The first class uses a standard infinite impulse response (IIR) [finite impulse response (FIR)] compensator structure, while the second class uses the Youla-Kučera parameterization of the feedforward noise compensator. This allows separating the problem of stabilizing the internal positive feedback loop from the minimization of the residual noise. These adaptive schemes have been developed in the context of active vibration control, but, as will be shown, they can be used also in active noise control. This article presents, in a unified manner, the available algorithms and compensator structures for adaptive feedforward noise attenuation and provides a comparative experimental evaluation on a relevant experimental test bench (a duct silencer).

A New Adaptive RISE Feedforward Approach based on Associative Memory Neural Networks for the Control of PKMs

In this paper, a RISE (Robust Integral of the Sign Error) controller with adaptive feedforward compensation terms based on Associative Memory Neural Network (AMNN) type B-Spline is proposed to regulate the positioning of a Delta Parallel Robot (DPR) with three degrees of freedom. Parallel Kinematic Manipulators (PKMs) are highly nonlinear systems, so the design of a suitable control scheme represents a significant challenge given that these kinds of systems are continually dealing with parametric and non-parametric uncertainties and external disturbances. The main contribution of this work is the design of an adaptive feedforward compensation term using B-Spline Neural Networks (BSNNs). They make an on-line approximation of the DPR dynamics and integrates it into the control loop. The BSNNs’ functions are bounded according to the extreme values of the desired joint space trajectories that are the BSNNs’ inputs, and their weights are on-line adjusted by gradient descend rules. In order to evaluate the effectiveness of the proposed control scheme with respect to the standard RISE controller, numerical simulations for different case studies under different scenarios were performed.

Adaptive feedforward vibration compensation control strategy of bearingless induction motor

In order to solve the unbalanced vibration problem of bearingless induction motor caused by the rotor mass eccentricity, an adaptive feedforward vibration compensation control strategy is researched. Firstly, the inverse dynamic decoupling control me

Adaptive Feedforward Compensator Based on Approximated Causal Transfer Function for CACC with Communication Delay

Abstract In this paper, we propose an adaptive feedforward compensator using parameter estimation to compensate for the communication time delay in cooperative adaptive cruise control (CACC). When CACC uses a feedforward controller to improve tracking performance and satisfy the string stability, it should take into account the communication delay between vehicles. Pade approximation of the time delay can be used for the design of feedforward compensator, but there is a limitation since the approximated system becomes the non-minimum system. To cope with this inherent non-causality problem, we propose an approximated causal transfer function for the feedforward compensator. Then, we apply extended Kalman filter as one of parameter estimation methods with a nonlinear model from the state augmented by a parameter of the approximated causal transfer function. Numerical simulation results show that the proposed system not only mitigates spacing error in time-varying communication delay but also satisfies string stability in a platoon.

Beyond the delay barrier in adaptive feedforward active noise control using Youla–Kučera parametrization

Adaptive feedforward broad-band noise compensation is currently used when a correlated measurement with the disturbance (an image of the disturbance) is available. Most of the active feedforward noise control systems feature an internal “positive” acoustical feedback between the compensation system and the reference source (a correlated measurement with the disturbance) that has to be taken into account. Adaptive algorithms for active feedforward noise attenuation have been implemented such that the propagation delay between the compensatory actuator and the measurement of the residual noise (the secondary path) be much smaller than the propagation delay between the reference source (image of the incoming noise) and the measurement of the residual noise (the primary path). Nevertheless, there are potential fields of applications in which the propagation delay of the secondary path may be larger than the one of the primary path. The present paper explores the behaviour of the available adaptive feedforward compensation algorithms in this new context. The algorithms have been tested experimentally on a relevant test bench. All the algorithms except the Youla–Kučera finite impulse response (YKFIR) adaptive compensator and the standard FIR adaptive compensator using a stability based filtered adaptation (FUSBA) lead to an unstable behaviour. In terms of performance the YKFIR provides the best performance.

On the use of Youla–Kucera parametrisation in adaptive active noise and vibration control – a review

ABSTRACTYoula–Kucera parametrisation plays a very important role in adaptive active vibration control and adaptive active noise control. This concerns both vibration and noise attenuation by feedback as well as by feedforward compensation when a measurement of an image of the disturbance (noise or vibration) is available. The paper will review the basic algorithms and various extensions trying to emphasise the advantages of using Youla–Kucera parametrisation. Specific aspects related to the use of this approach in adaptive active vibration and noise control will be mentioned. A brief review of applications and experimental testing will be provided.Abbreviations: ANC: Active noise control system; AVC: Active vibration control system; FIRYK: Youla–Kucera parametrised FIR adaptive feedforward compensator using an FIR Youla–Kucera filter; IIR: IIR adaptive feedforward compensator; IIRYK:Youla–Kucera parametrised IIR adaptive feedforward compensator using an IIR Youla–Kucera filter; IMP: Internal model principle; PAA: Parameter adaptationalgorithm; QFIR: Youla–Kucera FIR filter; QIIR: Youla–Kucera IIR filter; SPR: Strictly positive real (transfer function); YK: Youla–Kucera

Independent Control of Multiple Degrees of Freedom Local Magnetic Actuators With Magnetic Cross-Coupling Compensation

This letter tackles the problem of independent control of multiple degrees of freedom (DoF) systems based on local magnetic actuation (LMA). This is achieved by means of a modular disturbance rejection scheme, with the aim of enhancing the range of use of multiple-DoF LMAs in dexterous surgical manipulators. An LMA actuation unit consists of a pair of permanent magnets, characterized by diametrical magnetization, acting as magnetic gears across the abdominal wall. In this study, the model of the LMA and the time-varying magnetic disturbances owing to the proximity of multiple units are discussed. Subsequently, the developed model is capitalized in order to establish a Kalman state observer for the purpose of developing a sensor-free endoscopic manipulator suited to infer the state of the internal side of the LMA. Afterwards, the same model is used to develop an adaptive feedforward compensator system, with the aim of balancing the magnetic torques acting on the LMAs from the neighboring units in the case of unknown and frequency-varying sinusoidal disturbances. The effect of a magnetic shield, realized by means of MuMetal is also analyzed. The overall control system is modular with respect to the number of units and requires no centralized intelligence. The proposed scheme is subsequently validated by means of experiments performed on a benchtop platform, showing the effectiveness of the proposed approach. In particular, the proposed state observer presents a root mean square error (RMSE) ranging from $\boldsymbol {\text{28}}$ to $\boldsymbol {\text{47}}$ $\boldsymbol {\text{rpm}}$ in the estimation of the rotational velocity of the internal magnet and an RMSE of $\boldsymbol {\text{1.18}}$ $\boldsymbol {}$ to $\boldsymbol {\text{1.41}}$ $\boldsymbol {\text{mNm}}$ in the estimation of a load torque. The disturbance compensation system provides a reduction of ${\text{40}}$ $\%$ to $\boldsymbol {\text{50}}$ $\%$ in the disturbance caused by interacting LMA units.

Adaptive Feedforward Compensation for Voltage Source Disturbance Rejection in DC–DC Converters

Jumping disturbances and large noises in input voltage sources to a power converter can cause substantial excursion of its output voltage even under a well-designed feedback controller. Predictive compensation can achieve improved disturbance rejection and tracking performance in such scenarios, resulting in a two-degree-of-freedom design. While the feedback controller has embedded robustness, designing feedforward controllers, which are open-loop compensators, is challenging due to the fact that converter internal parameters change from aging and variations in operating conditions, and loads themselves are part of the converter dynamics. When converter dynamics change, system performance deteriorates significantly, making adaptation mandatory. By integrating system identification with the feedforward compensator, an adaptive feedforward compensation design is proposed in this brief. Working on a boost dc–dc converter as a typical platform, combined feedback and adaptive feedforward design is explored. The results show that the two-degree-of-freedom adaptive design results in much improved performance in rejecting disturbances from input power sources.

Direct adaptive feedforward compensation of narrowband disturbances without explicit identification of the secondary path model

The effectiveness of common algorithms for feedforward compensation of narrowband disturbance depends mainly on the model quality. To avoid this dependency several direct adaptive control algorithms without explicitly identified secondary path models have been developed over the last years. However an overview of their properties and a comparison of their performances in a standardized benchmark is still lacking. In this paper the three most promising algorithms are modified for narrowband feedforward vibration control for the use in rotating machinery. As in this application the reference signal is generated using the frequency measurement from a speed sensor it can be assumed that there is no coupling between reference measurement and the secondary path. First the algorithms are tested in simulation, then they are implemented on a test rig for active vibration control of unbalance induced rotor vibration. In simulation as well as for the test rig the performances of the algorithms are compared to each other. Advantages and drawbacks of the algorithms are discussed and practical instructions for implementation are given. The work is intended to serve as starting point and motivation for future research in this field of study.