Disturbance Rejection Ability Research Articles

Observer-Based Fixed-Time Consensus Tracking for a Class of Nonlinear Multi-Agent Systems

In this paper, the problem of fixed-time consensus tracking for a class of nonlinear multi-agent systems (MASs) with uncertainties and external disturbances is addressed. To solve this problem, a new fixed-time consensus tracking protocol with disturbance rejection abilities is proposed that consists of a fixed-time distributed observer (FTDO), a fixed-time disturbance observer (FDO), and a nonsmooth backstepping controller with lumped disturbance compensation (NBCDC). The fixed-time stabilities are analyzed correspondingly. Firstly, an FTDO is designed to estimate a leader’s output by using the topology of communication networks for each follower. Second, an FDO is developed to observe the lumped disturbances composed of model uncertainties and external disturbances. Finally, an NBCDC is proposed for improving the closed-loop performance. The simulation results show that the proposed method is effective.

Adaptive iterative learning control for enhancing the dynamic path tracking accuracy of 6-degrees of freedom industrial robots

In this article, an adaptive iterative learning control (AILC) scheme has been proposed to enhance the accuracy of the dynamic path tracking of 6-degrees of freedom industrial robots. Based on the memorized data and current feedback from a three-dimensional visual measurement instrument, an adaptive algorithm is developed to update the time-varying control parameters of the AILC scheme iteratively. A new compensation signal is calculated to adjust the control inputs produced by the dynamic path tracking control module at each time interval. Through the adaptation algorithm, the identical initial conditions can be relaxed to some extent with the AILC scheme. Moreover, the stability analysis of the proposed AILC scheme is presented. Experimental results on FANUC M20iA, using C-Track 780 as a photogrammetry sensor, demonstrate the superior performance of the developed AILC scheme in terms of pose accuracy, disturbance rejection ability, and control performance.

Lower-order linear active disturbance rejection control for electro-hydraulic servo system based on structural invariance compensation

High observer gain is the key to ensuring the full-order active disturbance rejection control (ADRC) performance for electro-hydraulic servo (EHS) systems. However, the noise sensitivity and output time delay limit the observer gain. In this paper, a lower-order linear ADRC is proposed with lower gain and uncompromised disturbance rejection ability. First, the internal nonlinear dynamics and external unknown disturbances of the EHS system are eliminated by introducing the structural invariance compensation (SIC). Then, the original EHS model is transformed into a one-order integral chain structure. A one-order linear ADRC, solving the compensation error of SIC caused by model parameter uncertainty, could be directly developed based on the equivalent model. In addition, a practical and novel b0 tuning method and frequency-domain stability analysis technology are developed. Extensive comparative experiments are carried out to illustrate the effectiveness of the proposed method.

Research on morphing aircraft maneuver control based on active disturbance rejection control

Aiming at the problems of model uncertainties caused by morphing aircraft during morphing process and disturbance encountered when maneuvering, a morphing aircraft maneuver control method based on active disturbance rejection control (ADRC) is proposed to eliminate the influences of model uncertainty and external disturbance and improve the rapidity and accuracy of maneuver control. Firstly, a nonlinear model for morphing aircraft is established and the impact mechanism of morphing process is analyzed. Then, the ADRC technique is used to design the angular rate robust control law and the control performance of ADRC law is analyzed under the influence of disturbance. Finally, the immelmann turn maneuver is selected to verify the performance of the designed control law with aerodynamic parameters perturbation combined with the morphing process. The simulation results show that the method possesses good decoupling effect and strong disturbance rejection ability. Moreover, the aircraft's maneuverability and the control margin of control surface can be effectively improved through morphing

Composite sliding mode control for cyber‐physical systems with multi‐source disturbances and false data injection attack

AbstractThis paper investigates the sliding mode control problem for cyber‐physical systems subject to multi‐source disturbances and actuator false data injection attacks simultaneously. Firstly, a series of extended state observers are designed to estimate the unknown multi‐source disturbances. For the actuator false data injection attacks, a sliding mode observer is designed to online estimate the values of attacks. Then, by introducing the disturbance and attack estimations, a dynamic sliding manifold and a composite sliding mode controller are constructed. Under the proposed approach, the unknown disturbances and false data injection attacks can be timely estimated and compensated, which can improve the disturbance rejection ability and guarantee security of the cyber‐physical system. Lyapunov theory is utilized to prove the stability of the closed‐loop system. Finally, simulations of both the numerical example and application to a power converter system demonstrate the effectiveness and superiority of the proposed composite sliding mode control approach.

Modified active disturbance rejection control based on gain scheduling for circulating fluidized bed units

Circulating fluidized bed (CFB) units are extensively operated in China due to their wide fuel adaptability, low emissions and high combustion efficiency. Nevertheless, CFB units are facing many control challenges due to their strong nonlinearity and large lag characteristics. To handle these control challenges, a modified active disturbance rejection control based on gain scheduling is structured in this paper. Firstly, a decentralized active disturbance rejection control strategy based on gain scheduling is designed by analyzing control difficulties of CFB units. Then, the parameter tuning and scheduling methods are provided, and the convergence of the extended state observer during the scheduling process is derived theoretically. The advantages of the proposed method in tracking performance, disturbance rejection performance, and ability to reject fuel quality fluctuation and uncertain heat transfer coefficients are illustrated by comparative simulations. Finally, the proposed control strategy is practically applied to the main steam pressure system of a 300 MW CFB unit. Running data demonstrate that it has a faster tracking performance and better disturbance rejection ability in [50∼100]% of the rated load, where the hourly average integral absolute error index has decreased obviously, and it shows a good field application prospect.

Fixed-time solution of inequality constrained time-varying linear systems via zeroing neural networks

Zeroing neural network (ZNN) has been explored and applied in a variety of time-varying problems solving. However, ZNN models for inequality constrained time-varying linear equation (ICTVLE) solving are rarely reported. Generally, numerous practical problems can be mathematically modeled as ICTVLE problems. Motivated by the above mentioned issue, a nonlinear tunable activation function activated ZNN (NTAF-ZNN) model is constructed to effectively solve ICTVLE problems. To further improve the performances of NTAF-ZNN model, a fuzzy nonlinear tunable activation function (FNTAF) is also designed. Based on the FNTAF, a fuzzy nonlinear tunable activation function-based ZNN (FNTAF-ZNN) model is realized. Firstly, the fixed-time convergence property and disturbance rejection ability of the NTAF-ZNN and FNTAF-ZNN models are proved by theoretical analysis. Then, comparative simulation results of the two models with other existing ZNN models for solving the ICTVLE problem are provided to further verify their robustness and effectiveness. Additionally, the two models and other existing ZNN models are also employed to realize inequality constrained manipulator trajectory tracking under ideal and noisy environments for further comparisons. Finally, the superior performances of the FNTAF-ZNN model for manipulator trajectory tracking are further verified by physical experiment results.

Controlling flat-foot limit cycle walkers with compliant joints based on local stability variation.

This study investigates local stability of a four-link limit cycle walking biped with flat feet and compliant ankle joints. Local stability represents the behavior along the solution trajectory between Poincare sections, which can provide detailed information about the evolution of disturbances. The effects of ankle stiffness and foot structure on local stability are studied. In addition, we apply a control strategy based on local stability analysis to the limit cycle walker. Control is applied only in the phases with poor local stability. Simulation results show that the energy consumption is reduced without sacrificing disturbance rejection ability. This study may be helpful in motion control of limit cycle bipedal walking robots with flat feet and ankle stiffness and understanding of human walking principles.

Anti-disturbance control design of Exoskeleton Knee robotic system for rehabilitative care

In this study, Active Disturbance Rejection Control (ADRC) has been designed for motion control of knee-joint based on exoskeleton medical robot. The extended state observer (ESO) is the main part of ADRC structure, which is responsible for estimating both actual states and system uncertainties. The proposed control scheme has adopted two versions of observers as disturbance estimators: linear extended state observer (LESO) and nonlinear extended state observer (NESO). The efficacy of proposed ADRC is strongly related to the performance of used ESO. As such, a comparison study has been conducted to evaluate the performance of two ADRCs in terms of disturbance-rejection capability and robustness to variation in system parameters under two version of ESO (LSO and NLESO). In order to enhance the dynamic performance of ADRC, Particle Swarm Optimization (PSO) algorithm has been used to optimally tune the design parameters of control scheme. To show the effectiveness of proposed LESO-based ADRC and NLESO-based ADRC, numerical simulation have been conducted. The proposed controllers have tested for an uncertain exoskeleton-knee system, where a 20% change in parameters was permitted over their nominal values. The results indicate that the ADRC algorithm based on LESO outperforms the one based on NESO in terms of disturbances rejection ability and robustness to parameters’ variations.

Active Disturbance Rejection Control Design with Sensitivity Constraint for Drum Water Level

The drum water level plays a crucial role in the safety and economy of heat recovery boilers. However, the control of the drum water level faces many challenges, such as external disturbances and system uncertainties. To enhance the control performance of the drum water level, a modified active disturbance rejection control (MADRC) optimized with sensitivity constraint is proposed in this paper. Firstly, the control structure of the three-element control system for the drum water level is introduced and analyzed. Based on the regular active disturbance rejection control (ADRC) structure, the structure of the MADRC is introduced and the convergence of the proposed MADRC is proven. Then a modified whale optimization algorithm (MWOA) with sensitivity constraint is applied to optimize the parameters of the MADRC. With different sensitivity constraints, the parameters of the MADRC and comparative controllers are obtained, and their control performance for tracking and disturbance rejection abilities is compared. Moreover, the ability to handle system uncertainties is analyzed. Simulation results and performance indexes show that the proposed MADRC can obtain the best tracking and disturbance rejection abilities with satisfactory robustness. The satisfactory control performance shows that the proposed MADRC has wide application potential for heat recovery boilers and other industrial processes.

Maximum Sensitivity Constrained Graphical Controller Tuning for a DC–DC Boost Converter Loaded With a CPL

Owing to the negative impedance instability of the constant power load (CPL), oscillations are induced in the output voltage of the boost converter which may lead to voltage collapse. This paper proposes a graphical strategy to tune a PID controller for the boost converter loaded with a CPL. The idea of root crossing boundaries is applied to compute the all stability region. Robustness and relative stability of the system are addressed by obtaining the desired maximum sensitivity region (DMSR) within the all stability region. Required controller parameters are obtained by finding the centroid of the DMSR. A novel technique to select the derivative gain of the PID controller from the trade-off curve between disturbance rejection and noise suppression abilities, is also proposed. Experimental results with comparison are provided to show the effectiveness of the presented scheme.

High-Precision Position Control of PMLSM Using Fast Recursive Terminal Sliding Mode With Disturbance Rejection Ability

High-Precision Position Control of PMLSM Using Fast Recursive Terminal Sliding Mode With Disturbance Rejection Ability

Disturbance observer‐based model predictive control of a coaxial octorotor with variable centre of gravity

AbstractThis paper presents a model predictive control (MPC) approach based on the extended disturbance observer (EDOB) for trajectory tracking of a coaxial octorotor unmanned aerial vehicle (UAV). First, the system dynamic model is derived using Newton–Euler relations in the presence of time‐varying centre of gravity (COG); then, a two‐loop cascade structure is presented to perform the trajectory tracking task. Both loops are controlled using MPC with feedforward compensation based on the EDOB to improve disturbance rejection abilities. When the mass changes, the moment of inertia and COG are affected. The EDOB simultaneously estimates the effects of time‐varying mass, external disturbances, and parametric uncertainties in six degrees of freedom. After obtaining virtual control inputs using designed controllers, constrained control allocation is used to obtain rotors speed in a valid range. The proposed control scheme is evaluated using simulation. The simulation results show the ability of the developed control strategy in accurate trajectory tracking and stable flight in different conditions and being robust to uncertainty and disturbance.

Disturbance rejection model predictive control for solar collector fields based on fast Fourier transform

Stability of fluid temperature in the collector field guarantees for the safe operation of a trough solar power plant. As a control algorithm that handles process characteristics, the model predictive control (MPC) algorithm provides good effectiveness in temperature control of the collector field. In order to compensate for model errors and unmeasurable disturbances, this paper proposes a novel model predictive control algorithm based on the Fast Fourier Transform (FFT) to control the temperature of the collector field. During the control process, the dominant frequencies of model deviations and disturbances are acquired by the FFT. Then, the effects brought by these factors can be estimated and compensated in advance by the expansion of the prediction model and the calculation of the estimator. Simulation results show that the proposed FFT-based MPC algorithm has good disturbance rejection ability, especially for periodic disturbances.

Improved Disturbance Rejection Ability for Speed Control of PMSM Drives Using a Modified Cascaded Extended State Observer

Improved Disturbance Rejection Ability for Speed Control of PMSM Drives Using a Modified Cascaded Extended State Observer

A hierarchical reinforcement learning GPC for flexible operation of ultra-supercritical unit considering economy

With the growing proportion of renewable energy sources in power grid, the demands for deep peak shaving and rapid load regulation of ultra-supercritical (USC) unit to provide more flexible and stable power services is further enhanced. Simultaneously, the load tracking speed is no longer the only significant task in the flexible operation of USC unit, the operational economy is more and more important. To this end, a hierarchical reinforcement learning GPC control scheme with a better economy is proposed and apply to USC unit. Firstly, the model mismatch problem in control process is taken into account, and an integral mode is added into the GPC to eliminate the steady state error during the load regulation. Secondly, the hierarchical reinforcement learning GPC scheme integrated the GPC and twin delayed deep deterministic policy gradient algorithms is presented. The complex flexibility demand problem is decomposed into rapid load regulation and economic operation and then respectively solved in the GPC-based upper layer and reinforcement learning agent-based lower layer. Thirdly, under the flexibility demand, a multi-criteria optimization function including the load tracking cost, main steam throttling loss and coal consumption rate of unit is constructed. Then, via the accurate trajectory tracking by GPC and on-line control sequence optimization by reinforcement learning agent, the operational flexibility and economy of USC unit are simultaneously improved within safe boundaries. Finally, to verify the availability of the proposed hierarchical reinforcement learning GPC strategy, large-scale load variations and disturbance rejection ability tests cover the 30%–100 % rated load of a 1000 MW USC unit are carried out, and the load regulation performance is compared to other strategies. Results confirm that the designed hierarchical reinforcement learning GPC control scheme is profit for the flexible and economic operation capability promotion of USC unit.

Nonlinear Extended State Observer Based Super-Twisting Terminal Sliding Mode Synchronous Control for Parallel Drive Systems

Addressing the issue to restrain the nonlinear coupling disturbance in the multimotor parallel drive system and acquiring perfect driving control performance, a novel super-twisting terminal sliding mode synchronous control (STSC) is proposed. In this control scheme, a lumped error (LE) with a synchronization coefficient is designed to transform coupled control into LE convergence. Then, a recursive terminal sliding mode function with two layers is introduced. Based on this sliding mode function, the STSC scheme is proposed, and it can guarantee the LE finite-time convergence and the continuous control action in nature. A nonlinear extended state observer (NESO) is introduced to enhance robustness. Moreover, the NESO not only provides an estimation of disturbance but also provides a smooth velocity signal. Therefore, differential operations and filtering operations are avoided. Finally, a compound control scheme is obtained. Compared with conventional super-twisting algorithm (STA), the robustness is enhanced by embedding NESO-based disturbance compensation, and the advantage of continuous control action is inherited. The major advantages of this scheme are characterized by output-based information only used, good model adaptability, and strong disturbance rejection ability. Experimental results show the effectiveness of the proposed control law.

Design and PIL implementation of a new robust backstepping based low-complexity voltage-oriented control method for four-leg rectifiers

This paper proposes a low computational complexity enhanced voltage-oriented control strategy (EVOC) based on robust backstepping controllers (BSC) in the synchronous rotating frame (dq0 frame) for a PWM four-leg voltage-source-rectifier (FLVSR). Unlike traditional VOC strategies, the suggested EVOC approach does not need any synchronization method and Park transformations, and it has the similar architecture and same features as the traditional VOC when it’s synchronization loop for grid voltage phase angle detection is properly operated. In addition to controlling the FLVSR, the suggested EVOC strategy is also used to develop the model of the three phase FLVSR in the dq0 frame using the concepts of direct instantaneous power control (DPC) theory, which combine the benefits of traditional DPC and traditional VOC with less computational complexity. The robust BSC is adopted for accurate regulation of FLVSR input currents and dc bus voltage simultaneously while taking into account the FLVSR parameter uncertainties. It produces sinusoidal currents with lower ripples and has high robustness against parametric variations. It is also simple to implement and has a relatively high grid voltage disturbance rejection ability. Finally, comparisons with both the traditional VOC strategy using PI controllers (VOC-PIC) and the EVOC strategy using PI controllers (EVOC-PIC) under various conditions demonstrate the superiority and benefits of the proposed EVOC-BSC strategy.

Improved Inverted Pendulum Control through PID and EPID Controllers

This presentation is on studies of application of combined constant rate reaching law and proportional-integral-derivative (PID) control law (EPID) for the control of inverted pendulum system. The inverted pendulum system is similar to a typical attitude control of booster rocket undergoing the takeoff process. Recent studies indicated records of higher rates of accidents in aircrafts. The records show that about half results due to malfunctions of aircraft systems and close to one-third from propulsion system malfunctions. Others are higher complexities of modern aircraft systems and in trying to reduce cost of maintenance. Therefore, the need enhanced automation, fault detection, faults isolation, faults tolerance, faults diagnosis and faults correction. Linear control techniques may not yield the desired performances in aircraft systems due to high levels of system nonlinearities. Applications of the intelligent control counterparts may not guarantee the generation of mathematical model for in-depth analysis. The major demerit of nonlinear control methods is higher requirement of computational burden making practical implementation difficult. The model of the inverted pendulum system is a linearized analytical model. The system performance of the system was observed with the EPID and PID controllers. Furthermore the effect of sudden changes such as wind, gust or other related variations on the system was also studied using step disturbance. It was a simulation studies using MATLAB/SIMULINK software. Results showed that with the EPID a near zero deviation was achieved. Whereas with PID controller was able to only maintain a deviation of about 40. Results also indicated a near zero disturbance rejection ability with the EPID, while the PID was able to only suppress the disturbance to some extent. It implies a more robust control with the EPID was achieved for aircraft/inverted pendulum control. Hence, it implies enhanced performance and with further improvement it can be used for application in this class of systems as well as similar systems. The work would help to for basic researches in aircraft/inverted pendulum control for beginners as well as experienced researchers in the field.

A smith-predictor-assisted adaptive load disturbance rejection controller for speed variation suppression of PMSM drive

The load disturbance rejection ability of the electrical machine systems is an important consideration factor in many applications, including both power generation (e.g., wind power generator) and consumption (e.g., servo systems such as high-precision machining and continuous motion in manufacturing automation). Existing studies on load disturbance rejection mainly focus on developing disturbance observers with improved steady state and dynamic performance. However, the performance of the disturbance rejection control is not only determined by the performance of the disturbance observers but also influenced by the speed response control during the transient. The latter problem might require more attention, especially due to the fact that speed filter is widely used in many actual systems to suppress the speed ripples or noise. The speed control performance would suffer from the delay caused by the filter and result in an undesired oscillatory speed response. In this paper, load disturbance rejection control based on a sliding mode disturbance observer is considered as an investigation platform, where an adaptive filter is proposed to further improve the performance of the observer. More importantly, a Smith predictor-based speed filter delay compensator is proposed to mitigate the undesired variation in the speed response caused by speed filter, achieving enhanced transient speed response under load disturbance. This structure is simple to implement, and no control parameters need to be tuned. The effectiveness of the proposed solution has been verified on a permanent magnet synchronous machine drive system.