Disturbance Rejection Performance Research Articles

Tracking and Vibration Control with a Parallel Structure Controller Based on a Flexible Ball Screw Drive System

In this paper, we present a parallel structure controller for flexible ball screw drive systems with dynamic variations mainly caused by variations in table position and workpiece mass. The controller consists of two parts: a linear quadratic regulator (LQR) controller with the aim of tracking reference trajectories with high response and accuracy and an interpolated gain-scheduled controller used to restrain system vibration. To damp out the varied resonant modes, the controller is obtained by a set of μ-synthesis linear time-invariant (LTI) controllers interpolated via Youla parameterization. Comparison experiments are conducted to confirm the performance of the proposed controller with a ball screw drive experimental setup. We demonstrate that the parallel structure controller achieves high performance in tracking, vibration suppression and disturbance rejection.

Coercivity modulation of FeCoCrMoTi films by artificial magnetic phase defects engineering based on multilayer structure

FeCoCr-based films have been considered as promising candidates for next-generation magnetic code disk materials used in high-accuracy magnetic rotary encoders. However, realizing high coercivity with sufficient remanent magnetization in FeCoCr-based films with in-plane anisotropy to ensure suitable disturbance-rejection performance and detectability of magnetic pole pairs is a critical issue, which hinders their practical applications. In this study, we demonstrated an in-plane anisotropic [Ta(20 nm)/FeCoCrMoTi(100 nm)]2/Ta(10 nm) multilayer film (M20 sample) with a high coercivity of 945 Oe and a sufficient remanent magnetization of 2890 Oe, which is 92.1% and 63.1% higher than FeCoCrMoTi(200 nm)/Ta(10 nm) film (SL sample), respectively. Detailed microstructure characterization using atomic resolution scanning transmission electron microscopy (STEM) indicates that the high coercivity originates from the domain-wall pinning effect induced by three factors including grain refinement and heterogeneous phases generation and composition fluctuation of modulated phases. X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) analyses reveal that the high remanent magnetization is ascribed to the higher relative content of Fe2Ta phases with strong ferromagnetism than that of Co2Ta phases with weak ferromagnetism.

Disturbance Rejection for Stewart Platform Based on Integration of Equivalent-Input- Disturbance and Sliding-Mode Control Methods

This study integrated an improved equivalent-input-disturbance (IEID) and a sliding-mode control (SMC) methods to ensure reference tracking and enhance disturbance-rejection performance for a Stewart platform. The internal principle ensures steady-state tracking of the system. A sliding-mode controller enhances the disturbance-rejection performance and tracking accuracy. The effects of the external disturbances are regarded as an overall disturbance. Then, a state observer and an IEID estimator estimate and compensate for the overall disturbance. The chattering phenomenon when implementing the SMC method is reduced because a small sliding-mode gain ensures the tracking precision in this control method. A stability condition of the closed-loop system is analyzed based on the Lyapunov stability theory. Gains of the IEID estimator and the state observer are designed by a linear matrix inequality that ensures the stability of the system. This method has been verified on an actual Stewart platform. Experimental results show that our method has better disturbance-rejection performance than an SMC method and an IEID method under external disturbances.

Tuning of PID/PIDD2 Controllers for Second-Order Oscillatory Systems with Time Delays

PID control is the longest history and the most vital basic control mode that has been widely applied in the production process. The oscillatory dynamics of the process have various features, and parameter tuning is complicated. To reduce the complexity of the parameter tuning process and improve the performance of the system, in this research, we propose a new tuning method for the PID/PIDD2 controllers for second-order oscillatory systems with time delays under the constraint of certain robustness. In comparison to existing PID for second-order oscillatory systems with time delays, simulation findings demonstrate that the tuning method of the proposed PID/PIDD2 controllers trades off robustness and disturbance rejection performance.

Mixed Dissipativity Control and Disturbance Rejection for Singular Systems

In this study, for a linear singular system, the dissipativity and disturbance-rejection problems are considered simultaneously. An improved equivalent-input-disturbance (IEID) method has shown good disturbance-rejection performance for linear systems. Therefore, the objective of this study is to obtain a satisfactory disturbance-rejection performance and dissipativity performance level based on the IEID method for singular systems. First, the influence of exogenous disturbances on the system is estimated based on the IEID method. The estimate is added to the control input channel to offset this influence. A necessary and sufficient condition is obtained to ensure that the singular system is admissible and satisfies dissipativity performance level. Subsequently, a state-feedback controller is designed based on the admissibility condition. Finally, a numerical example is used to demonstrate the validity of the proposed method.

Active disturbance rejection control with fractional-order model-aided extended state observer

Increasing the observer bandwidth of the extended state observer (ESO) can significantly enhance the disturbance rejection performance of the active disturbance rejection control (ADRC). However, a large observer bandwidth can also amplify the noise and degrade the control quality. This study proposes a novel fractional-order ADRC (FOADRC) approach. A fractional-order model-aided extended state observer (FOMESO) is designed by leveraging available plant information. Under a given observer bandwidth, the disturbance estimation performance of FOMESO is improved, while noise sensitivity is not aggravated. Additionally, FOMESO transforms a typical second-order plant into a fractional-order double-integrator model, reducing the phase lag to below 180∘. Consequently, the derivative component, which is sensitive to noise, is unnecessary in the feedback controller. Simulation and comprehensive comparisons demonstrate that the proposed FOADRC scheme outperforms the traditional ADRC in tracking, noise sensitivity, disturbance rejection, and stability. Furthermore, the proposed FOADRC approach is robust to plant parameter variations. The proposed method is validated through experiments on a permanent magnet synchronous motor speed servo system, confirming its superiority and effectiveness.

Design of Hypersonic Vehicle Time-Delay Compensation Controller based on Dynamic Surface Control

vehicles with input delays is described in this paper. Due to high dynamic characteristics of hypersonic vehicle, the strong uncertainties, high nonlinearity, strong coupling and control input time delays are challenging problems in the design of its control system. Therefore, it is necessary to design a control method that can handle input time delays. Finally, in this paper, the mathematical expression of the altitude nonlinear control theory problem of an aircraft with input time delay is given. Secondly, based on the backstepping method, the time delay compensation controller is designed. Thirdly, the backstepping method and dynamic control surface are used to design altitude angle control law. The stability and time delay compensation effect are proved. Finally, simulation results show that the suggested method can improve the stability and disturbance rejection performance for the system effectively, which has certain actual application value.

Disturbance rejection‐based cluster synchronization of nonlinear complex dynamical networks with hybrid‐driven mechanism

AbstractThe issue of cluster synchronization and disturbance rejection of multi‐weighted complex dynamical networks subject to nonlinearities and external disturbances are studied in this article. In particular, a hybrid‐triggering control scheme is implemented to mitigate the burden of the network transmission according to the prespecified triggering condition, under which each node will transmit its signal independently to the controller. To be more specific, a Bernoulli distributed stochastic variable is introduced to describe the switching law of the communication scheme. Also, the disturbance rejection performance is carried out with the aid of an improved equivalent input disturbance estimator approach. The sufficient criterion in the form of linear matrix inequalities is derived by constructing a suitable Lyapunov–Krasovskii functional and employing stochastic theory. Based on these settings, the feedback gain matrices and the trigger parameters affirming the desired cluster synchronization performance of the considered networks are established. Eventually, two illustrative examples including Lur'e networks with simulations are presented, which evidently proves the effectiveness of the obtained results.

Receding Galerkin Optimal Control with High-Order Sliding Mode Disturbance Observer for a Boiler-Turbine Unit

The control of the boiler-turbine unit is important for its sustainable and robust operation in power plants, which faces great challenges due to the control unit’s serious nonlinearity, unmeasurable states, variable constraints, and unknown time-varying lumped disturbances. To address the above issues, this paper proposes a receding Galerkin optimal controller with a high-order sliding mode disturbance observer in a composite scheme, in which a high-order sliding mode disturbance observer is first employed to estimate the lumped disturbances based on a deviation form of the mathematical model of the boiler-turbine unit. Subsequently, under the hypothesis of state constraint, a receding Galerkin optimal controller is designed to compensate the lumped disturbances by embedding their estimates into the mathematically based predictive model at each sampling time instant. With the help of an interpolation polynomial, Gauss integration, and nonlinear solvers, an optimal control law is then obtained based on a Galerkin optimization algorithm. Consequently, disturbance rejection, target tracking, and constraint handling performance of a controlled closed-loop system are improved. Some simulation cases are conducted on a mathematical boiler-turbine unit model to demonstrate the effectiveness of the proposed method, which is supported by the quantitative result analysis, such as tracking and disturbance rejection performance indexes.

Voltage Control Strategy for Improving Disturbance Rejection Performance in Stationary Reference Frame During Parallel Operation of Multimodular UPS

This paper proposes a voltage control strategy to improve the disturbance rejection performance during the parallel operation of multi-modular uninterruptible power supply (UPS). In the standalone operation of UPS, feed-forward control can improve the dynamic performance of output voltage regulation. However, a circulating current can occur when feedforward control is applied in the parallel operation of UPS modules, causing uneven load sharing among the modules. In this study, the reason for the occurrence of the circulating current was analyzed using a circulating current impedance model. A partial feedforward control technique was proposed, which compensates for a portion of the load current by considering the circulating current impedance in the parallel operation of the UPS. However, this reduced the disturbance rejection performance compared with the standalone operation of the UPS, which uses full feedforward compensation gain. Therefore, an additional feedforward control technique was proposed to enhance the disturbance rejection performance. The effectiveness of the proposed control strategy was verified through the experimental result of the parallel operation of 500 W modular double-conversion UPSs.

Offset-Free Model Predictive Control of Fuel Cell DC–DC Boost Converter With Low-Complexity and High-Robustness

This paper proposes an easily implementable and computationally effective model predictive control (MPC) scheme for fuel cell DC-DC boost converter. The proposed control scheme contains an explicit MPC method just with a single-step predictive horizon. Thus, the computational burden can be greatly reduced. To further enhance its anti-disturbance ability, the observer technique is adopted to respectively estimate the load impedance and input voltage for the predictive models. Since the estimated variables can be directly sent to the cost function, the satisfactory disturbance rejection performance can be guaranteed with optimal control. Besides, an additional reference current generation module based on the flatness theory is built to deal with the inevitable parameter uncertainties and the estimation errors. Thus, the nominal system model can be directly adopted to further reduce the design complexity. Some simulation and experimental tests based on a multi-phase interleaved fuel cell DC-DC boost converter are conducted to verify the superiority of the proposed control scheme. Results show that, with the proposed control scheme, both the dynamic performance and robustness of the closed-loop system are satisfactory, which can help to contribute to the fuel cell applications in transportation electrification.

Enhanced LADRC for Permanent Magnet Synchronous Motor With Compensation Function Observer

Aiming at the problem of one-degree-of-freedom characteristic and unsatisfactory anti-disturbance ability in linear active disturbance rejection control (LADRC) method of permanent magnet synchronous motor (PMSM), an enhanced LADRC with compensation function observer (CFO-LADRC) is proposed. Firstly, based on the refined PMSM mathematical model containing the total disturbances, a speed controller adopting CFO-LADRC is designed to address the tradeoff between dynamic and anti-disturbance performance and improve the disturbance rejection performance of the system simultaneously. Moreover, the analysis of the proposed method reveals the decoupling characteristic, stability, robustness, and relationship between each controller parameter and control performance. Besides, a practical parameter configuration process is proposed to consider both the anti-disturbance and noise rejection. Finally, simulations and experiments are conducted to compare with the conventional LADRC and the proposed CFO-LADRC. The results demonstrate that the proposed method retains the advantages of the conventional method while effectively improving the anti-disturbance capability.

Distributed tube model predictive control for string stability of heterogeneous vehicle platoons

This article develops a distributed tube model predictive control method to guarantee the string stability of the heterogeneous vehicle platoon under external disturbance and controller saturation. The error model of each vehicle is proposed based on the desired distance and velocity, where the coupled factor between vehicles is treated as a random disturbance. The linear feedback controller is devised to reject disturbances by keeping the actual trajectory within a tube around the nominal trajectory, and a model predictive controller is proposed by treating the input saturation and string stability as state constraints in the optimization problem. Compared with previous results, the proposed control strategy achieves a better performance of disturbance rejection and greatly reduces the online computation burden, which would be more favorable in engineering applications. The method proposed in this article is illustrated to be effective by simulation.

Iterative Design Algorithm for Robust Disturbance-Rejection Control

An iterative design algorithm is developed for robust disturbance–rejection control of uncertain systems with time-varying parameter perturbations in this paper. For more design degrees of freedom, a generalized equivalent-input-disturbance estimator is adopted to approximate the effect of both disturbances and uncertainties. By the bound real lemma, the H∞ norm is used to evaluate the robust disturbance–rejection performance of the closed-loop uncertain system. To avoid the constraints introduced by the widely used commutative condition, the control gains are divided into two groups and calculated by steps. Further, two robust quadratic stability conditions are derived, and an iterative design algorithm is developed to optimize the robust H∞ disturbance–rejection performance. Finally, the effectiveness and advantages of the developed method are demonstrated by a case study of a suspension system of modern vehicles.

Generalized Active Disturbance Rejection With Reduced-Order Vector Resonant Control for PMSM Current Disturbances Suppression

A control strategy that combines a novel reduced-order vector resonant controller and a generalized active disturbance rejection control (ROVR-GADRC) is proposed in this paper to suppress the current disturbances containing periodic harmonics of permanent magnet synchronous motor (PMSM). Firstly, the ROVR controller is designed, which integrates the advantages of both the complex coefficient filter and the vector resonant controller. Compared with the existing resonant control methods, the proposed ROVR can separate and extract the positive and negative sequence harmonics, and avoid the phase delay and peak point simultaneously. Secondly, a generalized extended state observer (GESO) is introduced to enhance the suppression of low-frequency disturbance. Then, the composite control strategy is developed. Besides, the stability, disturbance rejection performance, parameters configuration, robustness and tracking performance of the proposed ROVR-GADRC are comprehensively analyzed. The proposed current controller simultaneously performs harmonics suppression of specific phase sequence and other unknown disturbances attenuation. Finally, the feasibility and effectiveness of the proposed method is verified on a PMSM platform through the experimental results.

Ultrasound Imaging-Based Closed-Loop Control of Functional Electrical Stimulation for Drop Foot Correction

Open-or closed-loop functional electrical stimulation (FES) has been widely investigated to treat drop foot syndrome, which is typically caused by weakness or paralysis of ankle dorsiflexors. However, conventional closed-loop FES control mainly uses kinematic feedback, which does not directly capture time-varying changes in muscle activation. In this study, we explored the use of ultrasound (US) echogenicity as an indicator of FES-evoked muscle activation and hypothesized that including US-derived muscle activation, in addition to kinematic feedback, would improve the closed-loop FES control performance compared to the closed-loop control that relies only on the kinematic feedback. A sampled-data observer (SDO) was derived to continuously estimate FES-evoked muscle activations from low-sampled US echogenicity signals. In addition, a dynamic surface controller (DSC) and a delay compensation (DC) term were incorporated with the SDO, denoted as the US-based DSC-DC, to drive the actual ankle dorsiflexion trajectory to the desired profile. The trajectory tracking error convergence of the closed-loop system was proven to be uniformly ultimately bounded based on the Lyapunov–Krasovskii stability analysis. The US-based DSC-DC controller was validated on five participants with no disabilities to control their ankle dorsiflexion during walking on a treadmill. The US-based DSC-DC controller significantly reduced the root-mean-square error of the ankle joint trajectory tracking by 46.52% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 7.99% ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p&lt;0.001$</tex-math> </inline-formula> ) compared to the traditional DSC-DC controller with only kinematic feedback but no US measurements. The results also verified the disturbance rejection performance of the US-based DSC-DC controller when a plantarflexion disturbance was added. Our control design, for the first time, provides a methodology to integrate US in an FES control framework, which will likely benefit persons with drop foot and those with other mobility disorders.

Sliding-mode anti-disturbance speed control of permanent magnet synchronous motor based on an advanced reaching law

In order to improve the performance of a permanent magnet synchronous motor (PMSM) speed controller, an advanced reaching law sliding mode control (ASMC) strategy is proposed in this study. The advanced sliding mode reaching law (ASMRL) introduces a power term of the system state and a checkmark function term about the sliding mode function based on the traditional constant-proportional rate reaching law(TSMRL) , and replaces the sign function with a hyperbolic tangent function. A detailed theoretical analysis of the characteristics of the ASMRL is then presented. The theoretical analysis shows that the ASMRL converges to the sliding mode surface more quickly and with less chattering than the TSMRL. In addition, a sliding mode disturbance observer (SMDO) is designed to estimate the total disturbance of the system, and the estimated disturbance is compensated to ASMC. Then the stability of the system with ASMC and the stability of the system with ASMC+SMDO is proved by Lyapunov’s theorem. Finally, the proposed control strategy is validated on an experimental platform of PMSM. The experimental results show that the ASMC has a faster convergence speed, smaller chattering, better disturbance rejection performance than the traditional constant-proportional rate reaching law sliding mode control(TSMC), and better performance with the addition of SMDO.

외란관측기를 이용한 비선형 자기부상 시스템의 제어 성능 향상

Magnetic levitation system (MLS) is a typical nonlinear system that controls the position of a steel ball with the magnetic force of the electromagnetic actuator. Since disturbances, due to various external forces and modeling errors, may cause excessive vibration or poor command following, disturbance suppression is necessary to improve the control performance of the MLS. This paper presents a control performance improvement approach of an MLS with a disturbance observer (DOB). First, a mathematical model of the MLS was introduced and validated with the measured frequency response. The MLS steel ball was levitated with a proportional–integral–derivative (PID) controller and a DOB was designed based on the physical model of the MLS. Both disturbance rejection and command tracking performances of the MLS with the DOB were investigated with several design parameters such as PID gains and Q filter. The disturbance rejection and command tracking performances were improved by 76.1% and 64.7%, respectively by using DOB. Finally, the disturbance rejection and command-following performances of the MLS with the DOB were verified experimentally. The effectiveness and limitations of DOB were explained with measured closed-loop frequency responses.

Generalized-Extended-State-Observer and Equivalent-Input-Disturbance Methods for Active Disturbance Rejection: Deep Observation and Comparison

Active disturbance-rejection methods are effective in estimating and rejecting disturbances in both transient and steady-state responses. This paper presents a deep observation on and a comparison between two of those methods: the generalized extended-state observer (GESO) and the equivalent input disturbance (EID) from assumptions, system configurations, stability conditions, system design, disturbance-rejection performance, and extensibility. A time-domain index is introduced to assess the disturbance-rejection performance. A detailed observation of disturbance-suppression mechanisms reveals the superiority of the EID approach over the GESO method. A comparison between these two methods shows that assumptions on disturbances are more practical and the adjustment of disturbance-rejection performance is easier for the EID approach than for the GESO method.

Disturbance Rejection Performance Comparison of PSO and ZN Methods for Various Disturbance Frequencies

In this study Proportional-Integral-Derivative (PID) control of brushed DC Motor is analyzed. The parameters of the PID controller are tuned with two different approaches, namely Ziegler-Nichols (ZN) and Particle Swarm Optimization (PSO). The system is tested under sinusoidal disturbance of varying frequencies in order to evaluate and compare disturbance rejection performances. It is shown that PSO approach has clearly higher performance compared with ZN approach for all disturbance frequencies. Simulations are done using Python programming language with trapezoid rule for differentiation and integration. Results are given in both figures and tables. Comments are done on results and future study is planned.