Rejection Of Periodic Disturbances Research Articles

Rejection and Compensation of Periodic Disturbance in Control Systems

in this paper, a brief introduction to the disturbance rejection methods is given in general and to the periodic disturbance rejection methods in particular. Therefore in the following, methods of using only feedback technique to achieve both set point tracking and periodic disturbance rejection are presented. Also, the interaction problem between the set point design demands and the periodic disturbance rejection is discussed. Then, the interaction is minimized by using a separate feed-forward controller to reject the periodic disturbances as an add-on compensator to the pre-existing set point tracking feedback controller. Furthermore, the idea of the disturbance observer is introduced in general as well as the adaptive periodic disturbance cancelation method.

An adaptive feedforward method in active vibration control for the propulsion shafting system

This paper proposes a new adaptive feedforward control method for the rejection of multiple periodic disturbances in the propulsion shafting system. The active vibration control scheme of the propulsion shafting system is established by employing the equivalent-input-disturbance principle which reduces the complexity of the control system in applications. The adaptive control algorithm is designed by taking the scale transformation procedure and the frequency-tracking technique into consideration. The scale transformation normalizes the iso-surface of the optimization function by the frequency response characteristics of the control channel, which immensely improves the convergence rate of the control algorithm for multi-harmonic disturbance. Moreover, the adaptive controller tracks the fluctuating frequencies in a direct method, enhancing the efficiency and robustness of the algorithm for eliminating time-varying disturbances. Finally, numerical simulation and experimental validation are carried out to show that the proposed method has good performance on the application of the active vibration control of the propulsion shafting system.

Repetitive Control for Lur’e-Type Systems: Application to Mechanical Ventilation

Repetitive control (RC) has shown to achieve superior rejection of periodic disturbances. Many nonlinear systems are subject to repeating disturbances. The aim of this article is to develop a continuous-time RC design with stability guarantees for nonlinear Lur’e-type systems. Approximate output tracking is achieved by combining an internal model, consisting of a finite number of linear oscillators with frequencies at the reference frequency and at its multiples, with a stabilizer that guarantees a convergence property of the closed-loop system. The developed RC approach is applied to a nonlinear mechanical ventilation system for intensive care units (ICUs), which can be modeled as a Lur’e-type system. The experimental study confirms that the RC scheme is able to successfully follow the desired target pressure profile to properly support the ventilation needs of an adult patient.

A distributed delay based controller for simultaneous periodic disturbance rejection and input-delay compensation

The paper presents a controller design for systems suffering from multi-harmonic periodic disturbance and substantial input time-delay. It forms an alternative approach to Repetitive Control where the goal is to stabilize a close-loop that encapsulates an explicit time-delay model of the periodic signal. The proposed controller design is based on the Internal Model Control (IMC) framework, and it consists of the inverse system model and a tuneable distributed delay with an overall length related to the period of the disturbance. The properness of the controller can be ensured by utilizing a low-pass filter, however, such a component is shown to be unnecessary when the relative order of the system model is one. This fact makes the alternative approach especially suitable for systems approximated by a first-order model with input time-delay, leading to a straightforward controller design thanks to its simple structure and attainable conditions. Stability of the configuration is guaranteed by an ideal IMC framework. For further performance and robustness requirements for the non-ideal case the tuning of the controller is posed as a weighted-H∞ optimization problem where frequency-, spectral- and time-domain requirements are formulated as constraints. The overall control design is experimentally verified on a laboratory setup that has high-order dynamics approximated by a first-order model with input delay.

Discrete-Time Design of Dual Internal Model-Based Repetitive Control Systems

This paper presents a novel design of discrete-time dual internal model-based repetitive control systems. The design strategy is accomplished by combining general and high-order modified repetitive control schemes for simultaneous tracking repetitive tasks and rejection of uncertain periodic disturbances. The proposed controller is constructed from two different discrete-time internal models, rendering a dual internal model-based repetitive controller (DIMRC). The first internal model is intended to track repetitive commands with a fixed fundamental frequency. Meanwhile, the second internal model is coupled to compensate for an exogenous periodic disturbance with an uncertain frequency. The controller structure, stability conditions, and convergence analysis are discussed in this paper. The performance of the proposed controller is validated through simulation studies showing accurate tracking and excellent disturbance rejection simultaneously.

Necessary and Sufficient Conditions for Harmonic Control in Continuous Time

In this article, we revisit the concepts and tools of harmonic analysis and control and provide a rigorous mathematical answer to the following question: When does an harmonic control have a representative in the time domain? By representative we mean a control in the time domain that leads by sliding Fourier decomposition to exactly the same harmonic control. Harmonic controls that do not have such representatives lead to erroneous results in practice. The main results of this article are: A one-to-one correspondence between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> functional spaces guaranteeing the existence of a representative, a strict equivalence between the Caratheorody solutions of a differential system and the solutions of the associated harmonic differential model, and as a consequence, a general harmonic framework for linear time periodic systems and bilinear affine systems. The proposed framework allows to design globally stabilizing harmonic control laws. We illustrate the proposed approach on a single-phase rectifier bridge. Through this example, we show how one can design stabilizing control laws that guarantee periodic disturbance rejection and low harmonic content.

Disturbance observer-based repetitive control with application to optoelectronic precision positioning system

Rejection of periodic disturbance and/or tracking of periodic reference is of importance in high-precision control systems. Conventional repetitive control is often used to solve the problem, but it cannot precisely set effective frequency points and adversely amplify the non-periodic component disturbance. Therefore, it is not applicable in actual systems where external disturbances exist in the whole frequency domain. In this paper, we propose an improved discrete-time repetitive control method based on the disturbance observer to correct the undesired deviation at repetitive frequencies and mitigate the amplification of the non-components. Moreover, in the observer structure, an intuitive and flexible Q-filter design is presented to suppress low-frequency broadband and intermediate-frequency narrowband disturbances. The conditions of closed-loop stability, performance analysis, and the implementation of the proposed scheme are provided in detail. Finally, the effectiveness of the method is verified by simulation and experimentation on an optoelectronic precision positioning system under the condition of disturbances, and the disturbance suppression and tracking error attenuation are improved.

Hybrid Dual-Loop Control for Current Regulation and Low-Frequency Ripple Rejection in Led Drivers

This paper presents a new hybrid dual-loop control system for the DC/DC LLC resonant converter, operating as a downstream DC/DC converter in a two independent stage offline LED driver. The outer loop employs a PI controller to maintain the average LED current regulated at the reference value and reject parametric variation. The inner loop implements an adaptive periodic disturbance rejection (APDR) subsystem, thus conceiving the hybrid PI\&amp;APDR controller. The APDR subsystem is designed to strictly reject the bus voltage ripple and limit its transmission to the LED current. Experimental results show the proposed controller feasibility in achieving good tracking behavior, reduced output current ripple under different bus voltage ripple amplitude and frequency, robustness against parametric variations, and simple implementation and design. For the sake of completeness, the proposed PI&amp;APDR is compared with the conventional proportional resonant controller employing experimental results and extra analysis based on simulations.

A New Control Architecture With Spatial Comb Filter and Spatial Repetitive Controller for Circulating Current Harmonics Elimination in a Droop-Regulated Modular Multilevel Converter for Wind Farm Application

Circulating current control is one of the critical issues in modular multilevel converters (MMCs). When a frequency-droop-regulated MMC is used to integrate an offshore wind farm into an high-voltage dc transmission system, the variation in its operating ac line frequency induces a change in circulating current harmonic frequencies. Hence, the conventional circulating current controllers, such as proportional-resonant or repetitive controller, which are tuned to a specific frequency, fail to alleviate the circulating current harmonics. In this paper, a new control architecture comprising of a spatial comb filter (SCF) and a spatial repetitive controller (SRC) is proposed to effectively attenuate the even-order harmonics in the circulating current independent of the operating ac line frequency of the MMC. The proposed controller incorporates the phase sampling technique to achieve the dynamic change in the sampling frequency, which is the key to strong periodic disturbance rejection capability of the SCF and SRC even under variable frequency operation. A system level simulation model has been developed on PLECS simulation software to demonstrate the performance of the proposed control architecture. In addition, a scaled-down laboratory prototype of a 1-kW, 400-V, five-level single-phase MMC is developed and the experimental results are presented to substantiate the performance of the proposed control scheme.

Rejection of varying-frequency periodic load disturbances in wind-turbines through active disturbance rejection-based control

Wind turbines are complex mechatronic systems subject to different kinds of disturbances. Among all disturbance sources, those from periodic nature are the most relevant and important for maintaining the structural health of the entire wind turbine. However, periodic disturbances in wind turbines, mainly given by wind shear, tower shadow and rotational sampling of turbulence, have a variable fundamental frequency that changes as function of the turbine angular speed. In consequence, conventional controllers have issues to mitigate such varying-frequency periodic loads. This paper proposes two individual pitch control schemes to attenuate the main periodic load components of blade flap-wise and hub yaw/tilt-wise bending moments in horizontal-axis wind turbines under varying-frequency conditions. Both proposals are founded on the paradigm of Active Disturbance Rejection Control (ADRC): the former is formulated in the time-domain using a Linear-Time-Invariant (LTI) standard controller, while the latter is designed in the angular position domain using a Linear-Position-Invariant (LPI) approach. Several realistic simulations with different wind turbulence intensities and average wind speeds are performed using a 5 MW three-bladed horizontal-axis wind turbine implemented in the FAST code by NREL. Simulation results of the proposed control schemes show improved load reductions compared with other control techniques.

Guidelines to Classical Frequency-Domain Disturbance Observer Redesign for Enhanced Rejection of Periodic Uncertainties and Disturbances

The paper suggests a method aimed to improve the performance of dynamical systems with periodic uncertainties and disturbances (ac power converters are typical representatives of such systems) utilizing frequency-domain disturbance observer (DOB)-based control structure. In such control arrangement, DOB filter is the key component and should be designed so that its magnitude (phase) is as close to unity (zero) as possible at frequencies where the total uncertainty and disturbance exists. The methodology for designing DOB filters is well established mostly for systems with slow-varying uncertainties/disturbances and has been barely extended to systems with periodic excitation (such as grid-connected or stand-alone ac power converters). In this study, systematic enhancement of DOB filters, designed according to the classical methodology, is suggested based on appropriate mixing with a series multiresonant term. The proposed approach allows attaining improved periodic signals rejection capability while significantly sacrificing neither the dc gain nor the crossover frequency. Quantitative design guidelines are provided, and possible tradeoffs are revealed. The proposed methodology is validated by application to current control of LCL -filter-based inverter connected to a distorted ac grid. Feasibility and performance of the suggested approach are well supported by simulations and experiments.

Reference tracking control and attenuation of unknown periodic disturbances in the presence of noise for unknown minimum‐phase LTI plants

SummaryThe rejection of unknown periodic disturbances in the plant output through adaptive feedback has been an active area of research. In most successful efforts, it is assumed that the plant model is a known LTI stable system. In this paper, we relax the assumption of stable known plant and consider the case where the plant model can be unstable with unknown parameters. We do assume, however, that the plant model is minimum phase and use the model reference adaptive control structure to meet the objectives of reference tracking and unknown periodic disturbance rejection without amplifying the effect of broadband noises. The cost of achieving these objectives is the use of overparameterization that adds to the number of computations. The main contribution of this paper is that it shows that the problem of rejecting unknown periodic disturbances can be solved for unstable plants with unknown parameters as long as they are minimum phase. Numerical examples illustrate the effectiveness of the proposed control methodology.

Bioinspired Jet Propulsion for Disturbance Rejection of Marine Robots

This investigation takes the first step toward characterizing autonomous underwater vehicle (AUV) behavior trying to perform station keeping using bioinspired thrusters under the influence of disturbances with multiple amplitudes and frequencies. We describe the similarities between periodic disturbance rejection and the frequency response of the AUV performing oscillating maneuvers, and the significance of maneuvering regimes previously identified for this type of propulsion. We measured the exact position/orientation of the AUV using an underwater motion capture system and provide position data to the AUV controller in real time for feedback control. A wave disturbance generator was developed for this study in order to characterize the vehicle tracking performance in the presence of both high-amplitude low-frequency disturbances and low-amplitude high-frequency disturbances. The bioinspired maneuvering technique is demonstrated to provide adequate control capabilities for both types of disturbances maintaining in all cases position errors less than half the vehicle diameter, and proved especially adept at compensating for low-amplitude high-frequency disturbances, which can be difficult to overcome using traditional marine thrusters.

A Fractional-Order Repetitive Controller for Periodic Disturbance Rejection

A fractional-order repetitive controller is here proposed to reject a periodic disturbance acting on a time-invariant linear stable, possibly nonminimum phase, plant. The controller is designed assuming that the frequency response of the plant, in a particular range of frequencies, belongs to a generic half-plane of the complex plane. No information about the structure of the system, i.e., number and locations of zeros/poles, is required. It is shown that, if this half-plane entirely contains the frequency response of the plant, then the controller can be designed without gain constraints. In the presence of saturation nonlinearities, conditions on the system absolute stability are discussed.

Periodic disturbance rejection to the Nyquist frequency and beyond

In this paper, we address periodic disturbance rejection for sampled-data control systems, where the frequency of the disturbance can be beyond the Nyquist frequency of the limited measured plant output sampling rate. The disturbance effect on steady-state response of the fictitious fast-rate plant output including intersample information is obtained using discrete-time Fourier series. A sufficient condition for disturbance rejection together with a sufficient and necessary condition for perfect disturbance elimination are provided by employing the steady-state response. A simple but effective controller design procedure combining H∞ loop shaping, Youla–Kucera parameterization, and gradient methods is provided to achieve the two conditions. The proposed approach is applied on vibration control beyond the Nyquist frequency in a commercial hard disk drive. The effectiveness of the proposed approach is verified by our simulation results showing disturbance rejection of 62% and perfect disturbance elimination, as well as by our experimental results showing disturbance rejection of 54%.

EID‐Estimation‐Based Periodic Disturbance Rejection for Sintering Ignition Process with Input Time Delay

AbstractSintering plays a key role in generating blast furnace burden in metallurgical processes. The continuous production and stable quality of sintering significantly depends on the stable and precise control of sintering ignition, which, however, is achieved through an input time delay system, and suffers from different and unknown disturbances. To reject disturbances and enhance the control precision of ignition temperature, this paper introduces a modified equivalent input disturbance (EID)‐based disturbance compensation that is suitable for controlling sintering ignition. First, the periodic properties of disturbances induced by gas pressure fluctuations are obtained based on spectral density decomposition. Second, to obtain the dynamics of sintering ignition, an iterative subspace modeling method is developed, which estimates not only the model parameters but also the length of time delay. By considering the periodic property, a control structure of sintering ignition based on the modified EID‐based compensation is proposed, in which an additional time‐delay element is designed to make the phase difference between EID estimation and real disturbance close to zero. Finally, the validity of the proposed method is verified by a simulation.

Periodic Disturbance Rejection Control Based on Observer and Switching in Photo-Conductor Drum with Planetary Gear System

A servo control architecture is proposed for the photo-conductor drum drive using planetary gears in a production printer. The velocity fluctuation of the photo-conductor drum is one of the main causes of color banding. Most of the velocity fluctuations come from gear eccentricity that is particularly large in injection molded plastic gear. In order to obtain high image quality, a servo controller design for periodic disturbance reduction is needed. Feedback and feedforward controllers are used to achieve higher performance. This paper proposes a new feedforward control strategy to reduce the effects of the periodic disturbances that are caused by the transmission error of the planetary gears. The proposed control strategy, based on a switching scheme and an open-loop observer, compensates the periodic disturbances. The advantage of the proposed method is that periodic disturbances can be reduced without sacrificing feedback performance. An experiment on a prototype is carried out to verify the control performances. The results show that 90[%] of periodic disturbances are reduced by the proposed control algorithm.

A new approach for periodic disturbance rejection in input-time-delay systems

An innovative approach combining equivalent-input-disturbance (EID) theory with the internal model principle is applied to achieve periodic disturbance rejection in input-time-delay systems. The EID estimator, which exhibits the synthetic effect of the time-delay and the periodic disturbance as an input-dependent disturbance, is constructed by inserting appropriate time-delay elements to compensate for the total influence of the input-time-delay and the periodic disturbance. A sufficient stability criterion is derived based on the separation theorem and the small-gain theorem. A design algorithm is developed for the system based on the stability criterion. Design and simulation results for the example are also employed to compare our method with the disturbance observer approach, and to demonstrate the validity of our method.

Smith predictor-based multiple periodic disturbance compensation for long dead-time processes

ABSTRACTMany disturbance rejection methods have been proposed for processes with dead-time, while these existing methods may not work well under multiple periodic disturbances. In this paper, a multiple periodic disturbance rejection is proposed under the Smith predictor configuration for processes with long dead-time. One feedback loop is added to compensate periodic disturbance while retaining the advantage of the Smith predictor. With information of the disturbance spectrum, the added feedback loop can remove multiple periodic disturbances effectively. The robust stability can be easily maintained through the rigorous analysis. Finally, simulation examples demonstrate the effectiveness and robustness of the proposed method for processes with long dead-time.

The consistency control of mold level in casting process

A new multiple periodic disturbance rejection control for casting process is proposed in this paper. Firstly, a high-precision multiple periodic disturbance detection method is designed. The accurate frequencies of the disturbance can be obtained. By using the disturbance observer and a group of filters with additional delay items, multiple periodic disturbance can be suppressed under time-delay environment. Then systematic control design is achieved based on the robust stability analysis. Finally, the efficiency of the proposed method is shown by comparisons between different methods and time-varying disturbance rejection in the consistency control of mold level.