Disturbance Rejection Performance Research Articles

Single-layer neural-network based control of agricultural mobile robot

In this study, we propose a novel controller architecture and design for the automatic control of agricultural mobile robots to be used in farms and greenhouses. There are two novelties of this study. The first novelty is a completely new type of controller architecture proposed in which reference inputs and measured outputs are fed separately independent from each other to the controller. The controller architecture currently used in the literature uses only the difference between reference and measurement which is the error signal. The proposed architecture in this study is completely novel in the sense that not only the error information is used in the controller but also the information in reference inputs and information in measured outputs are used separately. This means a completely new type of look to control system by utilizing the information maximally in order to achieve superior performance. This performance boost is shown in the paper where the proposed architecture achieves up to 2000% better performance compared with state-of-the-art controllers. Second, controller architecture is grown to a complex structure from an initially simple PID structure. Using the maximal information comes with the cost of computational complexity to design the controller. The second novelty of growing the controller from initially simple PID equivalent controller tackles this difficulty by making the problem tractable and efficient to compute. This way the proposed novel controller can be designed within minutes in a commercially available laptop computer. The proposed controller is tested on a simulated agricultural mobile robot and results are compared with a previous state-of-the-art optimal controller. It is believed that the proposed architecture will be dominant in future automatic controllers and make current state-of-the-art controllers obsolete. This is because of the full utilization of information in controller design which results in robust disturbance rejection performance.

General proportional integral observer (GPIO) - based disturbance compensation for minimum variance time synchronization

Precise time synchronization is an enabling technology for mission-critical time-sensitive Industrial Internet of Things (IIoT). However, the crystal oscillator clock which is widely used in IIoT may suffer from periodic disturbances caused by repetitive motion or periodic vibration. To improve the time synchronization of distributed nodes subject to periodic disturbances, this paper proposes a novel disturbance rejection framework, General-Proportional-Integral-Observer-based Disturbance Compensation (GPIO-DC), with the proof of stability, and combined with a 2-freedom control design strategy to optimize both the disturbance rejection and clock tracking performance. And the GPIO’s unique feature of blocking zeros are fully exploited to reject the periodic disturbance at its frequencies and a zero-pole optimal design algorithm is given. With the disturbance being compensated, a disturbance-free minimum variance time synchronization protocol for a complex network is developed and optimized by using Linear Matrix Inequality (LMI) to minimize the variance of networked synchronization errors. The performance of the proposed method is devalued by intensive simulation. Comparing with recent relevant research, the proposed method achieves a better performance in disturbance rejection and minimum variance.

Adaptive super-twisting fast nonsingular terminal sliding mode control with ESO for high-pressure electro-pneumatic servo valve

In this paper, an adaptive super-twisting fast nonsingular terminal sliding mode controller (ASTFNTSMC) with active disturbance rejection is proposed to improve the response speed, control accuracy, and disturbance rejection ability of the high-pressure electro-pneumatic servo valve (HESV). This controller effectively combines sliding mode control (SMC), active disturbance rejection control (ADRC), and adaptive control. An improved fast nonsingular terminal sliding surface is constructed to speed up the dynamic response. This surface is characterized by the mutual decoupling between the control input and the system state in its derivative, so a super-twisting algorithm (STA) can be implemented to mitigate chattering. By using ADRC, system nonlinearities and external disturbances are regarded as a total disturbance. An extended state observer (ESO) is incorporated into the controller to estimate the total disturbance, and the estimation is applied as feedforward compensation. As a result, the switching term of STA only needs to suppress the residual disturbance, so chattering is further mitigated and disturbance rejection ability is enhanced simultaneously. Furthermore, an adaptive law is employed to reduce the conservativeness in the parameter selection. Finally, comparative experiments are carried out for HESV on the test platform. Experimental results are consistent with the theoretical analysis, showing that the proposed method can achieve faster dynamic response, higher tracking accuracy, and better disturbance rejection performance.

A model-free continuous integral sliding mode controller for robust control of robotic manipulators

<p>This paper proposes a model-free continuous integral sliding mode controller for robust control of robotic manipulators. The highly nonlinear dynamics of robots and load disturbances cause control challenges. To achieve tracking control under load disturbances and nonlinear parameter variations, the controller is constructed with three continuous terms including an integral term that acts as an adaptive controller. The proposed controller is able to accomplish a non-overshoot transient response, a short settling time, and strong disturbance rejection performance for robotic manipulators. The developed model-free control method is implemented on the PUMA 560 robotic manipulator, and its performance is compared with the proportional-derivative (PD) plus gravity controller. Numerical results under measurement noise and load disturbances are provided in order to show the efficacy, validity, and feasibility of the method.</p>

Intelligent controller for unmanned surface vehicles by deep reinforcement learning

With the development of the applications of unmanned surface vehicles (USVs), USV automation technologies are attracting increasing attention. In the industry, through the subtask division, it is generally believed that course-keeping is a critical basic sub-system in a series of complex automation systems and affects USV automation performance to a great extent. By course-keeping, we mean USV adjusts its angle to the desired angle and keeps it. In recent decades, course-keeping has been mainly achieved through classical first principles technologies, such as proportion–integral–differential (PID) controllers, leading to extremely laborious parameter tuning, especially in changeable wave environments. With the emergence and extensive application of data-driven technologies, deep reinforcement learning is conspicuous in sequential decision-making tasks, but it introduces a lack of explainability and physical meaning. To take full advantage of the data-driven and first principles paradigm and easily extend to the industry, in this paper, we propose an intelligent adaptive PID controller enhanced by proximal policy optimization (PPO) to achieve USV high-level automation. We then further verify its performance in path-following tasks compared with the PID controller. The results demonstrate that the proposed controller inherits the merits of explainability from PID and excellent sequential decision making from PPO and possesses excellent disturbance rejection performance when facing the disturbance of a changeable wave environment.

SRFPI-LADRC Based Control Strategy for Off-Grid Single-Phase Inverter: Design, Analysis, and Verification

Linear active disturbance rejection control (LADRC) has been extensively used in various areas due to its excellent disturbance suppression capability. When LADRC is applied to a single-phase inverter for tracking a sinusoidal reference signal, there is an inherent tracking inaccuracy problem. The steady-state error can be removed with the synchronous reference frame proportional-integral (SRFPI) control, which generates two orthogonal signals. In this paper, a modified control method based on compound SRFPI and LADRC for an off-grid single-phase inverter is put forward, where both output signals of SRFPI are employed as the reference signals of LADRC. Furthermore, a selective harmonic compensation method is performed by paralleling multiple SRFPI controllers to further reduce the selective harmonic components. Detailed theoretical analyses including system stability, robustness, performance of voltage tracking error and disturbance rejection are presented, which indicate that this organic combination fuses the merits of both SRFPI and LADRC without complicating the control design. Additionally, contrast experiments are conducted to demonstrate its effectiveness and superiority. These findings demonstrate that the system realizes a slight voltage tracking error and steady-state error, rapid dynamic response, and low total harmonic distortion (THD), especially under highly nonlinear load conditions.

Smith predictor-based feedforward controller for measurable disturbances

This paper proposes a feedforward extension for the simplified filtered Smith predictor (SFSP) to deal with measurable disturbances. The proposed strategy uses a state-space formulation and can be applied in unified manner to stable, unstable, and integrating linear dead-time processes of any order. The main advantage with using the predictor approach in comparison with other control strategies is the ability to deal with processes with large dead time. The structure improves the disturbance rejection performance by feedforwarding the disturbance while maintaining the good robustness and noise attenuation properties of the SFSP. Simulation results show better performance indices compared with other strategies from the recent literature. In addition, the proposed strategy is applied to control the temperature in a newborn intensive care unit (NICU) to show its effectiveness in a real process.

Tracking and Synchronization Control Strategy of Vehicle Dual-Motor Steer-by-Wire System via Active Disturbance Rejection Control

A novel vehicle dual-motor steer-by-wire (SBW) system is proposed to improve the reliability and safety of traditional SBW system. However, the biggest challenge of dual-motor SBW is its tracking and synchronization control issues. In order to solve the problems of poor tracking and synchronization of the vehicle dual-motor SBW system caused by load disturbance, parameter perturbation, and model mismatch, a tracking and synchronization control strategy of the vehicle dual-motor SBW system via the active disturbance rejection control is proposed. First, the driving mechanism of dual-motor SBW system is analyzed, and the system dynamics model is established. Then, considering the system disturbance and parameter uncertainty, a second-order active disturbance rejection controller is designed for the position loop of the steering motor, which is composed of a third-order extended state observer and a state error feedback control law. Next, in order to simplify the adjustment difficulty of the controller, the bandwidth method is introduced to greatly reduce the number of controller parameters and the difficulty of parameter adjustment. Based on this, the disturbance rejection performance and stability of the designed active disturbance rejection controller are proved. Furthermore, the cross-coupling control structure is employed to enhance the synchronization performance of the dual-motor system. Finally, the performance of the controller to suppress the external disturbance and internal parameter perturbation is analyzed in step condition and double lane change condition, respectively, and the effectiveness of the proposed control strategy is verified on the dual-motor experimental platform.

Disturbance Rejection and Control System Design Using $\lbrace 1\rbrace$-Inverse-Based Equivalent-Input-Disturbance Approach

This article develops an improved equivalent-input-disturbance (EID) approach that rejects disturbances for a plant. A control system based on the approach includes an improved EID estimator, which is newly devised using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lbrace 1\rbrace$</tex-math></inline-formula> inverse of the plant input matrix. Compared with a conventional EID estimator, the improved EID estimator has an additional free matrix. This free matrix enables the control system to improve the disturbance rejection performance but not increase the configuration complexity. An analysis of the control system explains how the free matrix improves the disturbance rejection performance. The experiments of a posture control system for a Stewart platform demonstrate the validity of the approach.

Enhanced Reduced-Order Extended State Observer for Motion Control of Differential Driven Mobile Robot.

Motion control is critical in mobile robot systems, which determines the reliability and accuracy of a robot. Due to model uncertainties and widespread external disturbances, a simple control strategy cannot match tracking accuracy with disturbance immunity, while a complex controller will consume excessive energy. For precise motion control with disturbance immunity and low energy consumption, a control method based on an enhanced reduced-order extended state observer (ERESOBC) is proposed to control the motor-wheels dynamic model of a differential driven mobile robot (DDMR). In this method, only unknown state error and negative disturbance are estimated by the enhanced reduced-order extended state observer (ERESO), which reduces the required energy of the observer. In addition, a simple state-feedback-feedforward controller is used to track the reference signal and compensate for negative disturbance. Through numerical simulation and application example, the tracking performance and disturbance rejection performance of DDMR are compared with the traditional control method based on enhanced extended state observer (EESOBC), and the results show the superiority of the ERESOBC method.

Robust Consensus Tracking Control of Uncertain Multi-Agent Systems With Local Disturbance Rejection

In this paper, a new distributed consensus tracking protocol incorporating local disturbance rejection is devised for a multi-agent system with heterogeneous dynamic uncertainties and disturbances over a directed graph. It is of two-degree-of-freedom nature. Specifically, a robust distributed controller is designed for consensus tracking, while a local disturbance estimator is designed for each agent without requiring the input channel information of disturbances. The condition for asymptotic disturbance rejection is derived. Moreover, even when the disturbance model is not exactly known, the developed method also provides good disturbance-rejection performance. Then, a robust stabilization condition with less conservativeness is derived for the whole multi-agent system. Further, a design algorithm is given. Finally, comparisons with the conventional one-degree-of-freedom-based distributed disturbance-rejection method for mismatched disturbances and the distributed extended-state observer for matched disturbances validate the developed method. Manuscript received May 13, 2022; accepted June 12, 2022. This work was supported by the National Natural Science Foundation of China (62003010, 61873006, 61673053), the Beijing Postdoctoral Research Foundation (Q6041001202001), the Postdoctoral Research Foundation of Chaoyang District (Q1041001202101), and the National Key Research and Development Project (2018YFC1602704, 2018YFB1702704). Recommended by Associate Editor Xiaohua Ge. (Corresponding author: Pan Yu.)

Disturbance rejection enhancement using predictive control for the fixed‐wing UAV with multiple ailerons

SummaryThe performance of small fixed‐wing unmanned aerial vehicles (UAVs) is easily degraded by exogenous disturbances. In an attempt to improve the performance, the structural change is made in conventional small fixed‐wing UAV through segmentation of each aileron control surface into multiples. Detailed system identification experiments are performed on each aileron pair in the wind tunnel to acquire linear dynamic models for the roll attitude of the UAV. These experiments have provided the transfer functions for the aileron control surfaces based on corresponding frequency response. Three distinctive model predictive controllers are designed and deployed in real‐time hardware to achieve the roll attitude control. The roll attitude control experiments are validated in wind tunnel under both normal and turbulent environments. The results show that multiple input and single output control system provides significant improvement in the roll attitude and disturbance rejection performance. The collective actuation of multiple control surfaces improves roll stability by to when compared to the single aileron pair based conventional control in the presence of turbulent flight conditions.

Smith predictor–based sliding mode control with hyperbolic tangent function for unstable processes

In this work, a modified Smith predictor–based sliding mode control (SP-SMC) method is proposed for unstable plus time-delay processes. Sliding mode control has a discontinuous part in its control law which may cause chattering in the control signal if conventional switching strategy is used. A hyperbolic tangent function is employed as a switching element in the suggested SP-SMC technique to minimize the chattering effect. Optimal values of the controller’s unknown parameters are obtained using whale optimization algorithm which is a meta-heuristic technique. The process model used in the proposed Smith predictor control architecture is identified using measurements of limit cycle output which is obtained from online relay test. The proposed controller is found to be robust towards process parameter uncertainties and load disturbance. Suggested control technique results in fast set-point tracking response and significantly improved disturbance rejection performance compared to some other related methods.

Fractional order internal model control of non‐minimum phase and time‐delayed plants

AbstractSeveral applications on fractional order (FO) control have gained considerable significance in the recent years, which led to the evolution of novel tuning strategies of the generalized order FO controllers. Some of the methods in available literatures are based on constrained minimization optimization techniques or analytical method defined only for specific plants. They are valid only for some special model cases. On the contrary, in this technical note, a generalized non‐integer order internal model control (IMC) framework is realized for any order non‐minimum phase (NMP) plants with right half plane (RHP) zero as well as time delayed plants having any finite relative order. Its parameters are graphically interpreted satisfying the frequency domain design stipulations for single input and single output (SISO) higher order linear time invariant (LTI) plants. The performance of the same on a bioreactor fermentation process for its temperature control is found to have outperformed in contrast to its integer order (IO)‐IMC. It is therefore inferred here that this new approach pledges to impart unique solution of the controller parameters, formulating a highly efficient tool outperforming the existing paradigms. Simulation and real time experimentation are presented to validate the method put forward providing satisfactory performance in reference tracking, disturbance rejection, and robustness to various plant parameter perturbations.

Active disturbance rejection controller design for alleviation of gust-induced aeroelastic responses

This paper develops an active disturbance rejection control technology that uses the equivalent input disturbance (EID) approach to reduce the aeroelastic vibrations and structural loads caused by wind gusts. The influence of gust disturbance is evaluated by the EID estimator and actively compensated in the control input channel, giving a high disturbance rejection performance of the aeroelastic system. The suitable design of the state observer and low-pass filter is essential for the disturbance estimation and rejection. However, the conventional low-pass filter simply specified by a cutoff frequency may lead to a degraded estimation performance. To this end, a new structure of low-pass filter is proposed, and the design algorithms for the observer gain and filter parameters are also given. By specifying bandwidth constraints, the control system with guaranteed performance can be automatically generated. Numerical results show that for the acceleration measurement-based control, the proposed design method can achieve better disturbance estimation performance than that obtained by the conventional one, resulting in smaller gust responses. Finally, the proposed design method is further extended to the folding wing parameter-varying system. A parameterized version of the EID-based controller is constructed by using the concept of gain-scheduling. It is demonstrated that the gust responses can be significantly reduced in the entire range of folding angle. This study provides an effective solution for gust alleviation of the aeroelastic system with fixed or variable configurations.

Prescribed Performance Back-Stepping Tracking Control for a Class of High-Order Nonlinear Systems via a Disturbance Observer.

Due to the widespread presence of disturbances in practical engineering and widespread applications of high-order systems, this paper first pays attention to a class of high-order strict-feedback nonlinear systems subject to bounded disturbance and investigates the prescribed performance tracking control and anti-disturbance control problems. A novel composite control protocol using the technique of a disturbance observer-prescribed performance control-is designed using the back-stepping method. The disturbance observer is introduced for estimating and compensating for unknown disturbances in each step, and the prescribed performance specifications guarantee both transient and steady-state performance of the tracking error to improve the control performance and result in better disturbance rejection. Moreover, the technique of adding a power integrator is modified to tackle controller design problems for the high-order systems. The Lyapunov function method is utilized for rigorous stability analysis. It is revealed that while the control performance completely remains in the prescribed bound, all states in the closed-loop system are input-to-state stable, and the tracking error and the disturbances estimating error asymptotically converge to zero simultaneously. Then, the feasibility and effectiveness of the proposed control protocol are verified by a simulation result.

Band-Passing Nonlinearity in Reset Elements

This article addresses nonlinearity in reset elements and its effects. Reset elements are known for having less phase lag based on describing function (DF) analysis compared to their linear counterparts; however, they are nonlinear elements and produce higher-order harmonics. This article investigates the steady-state higher-order harmonics for reset elements with one resetting state and proposes an architecture and a method of design that allows for band-passing the nonlinearity and its effects, namely, higher-order harmonics and phase advantage. The nonlinearity of reset elements is not entirely useful for all frequencies, for example, they are useful for reducing phase lag at crossover frequency regions; however, higher-order harmonics can compromise tracking and disturbance rejection performance at lower frequencies. Using the proposed “phase shaping” method, one can selectively suppress the nonlinearity of a single-state reset element in a desired range of frequencies and allow the nonlinearity to provide its phase benefit in a different desired range of frequencies. This can be especially useful for the reset elements in the framework of the “constant in gain, lead in phase” (CgLp) filter, which is a newly introduced nonlinear filter, bound to circumvent the well-known linear control limitation—the waterbed effect.

Improving Disturbance Rejection Performance of EID-Based Control by Employing PLTD

Improving Disturbance Rejection Performance of EID-Based Control by Employing PLTD

Systematic Filter Design by Convex Optimization for Disturbance Rejection in Dual-Stage Actuated Hard Disk Drives

To enhance storage capacity in hard disk drive systems (HDDs), dual-stage actuated systems employing both piezoelectric and voice coil motors (VCMs) are utilized in the positioning of magnetic heads. However, external disturbances, such as rotational vibrations and cooling fan vibrations, necessitate the design of controllers with robust disturbance rejection performance to further improve positioning precision. In this paper, we propose an auto-tuning method for a fixed-structure filter in a dual-stage actuated HDD system. The filter parameters are determined using our proposed frequency response data-based convex optimization process. Furthermore, the initial guess for the optimization is selected from the Robust Bode (RBode) plot which is a visible tool in designing robust controllers. Simulation results confirm the effectiveness of our proposed method.

Frequency Response Data-based Resonant Filter Design considering Phase Stabilization and Stroke Limitation applied to Dual-Stage Actuator Hard Disk Drives

Disturbance rejection of a Hard Disk Drive (HDD) enables a large amount of data storage in a recent information society. The aim is to design a feedback controller which rejects disturbances at multiple frequencies in HDDs. The disturbance rejection is achieved using resonant filters which have a large peak at disturbance frequencies. The developed approach enables the convex optimization of resonant filters with phase stabilization and stroke limitation using frequency response data of a controlled system. The disturbance rejection performance of the optimized resonant filters is validated in a dual-stage actuator HDD benchmark problem.