High-order Disturbance Observer Research Articles

Adaptive sensor fault tolerant control with prescribed performance for unmanned autonomous helicopter based on neural networks

PurposeThis paper aims to study a neural network-based fault-tolerant controller to improve the tracking control performance of an unmanned autonomous helicopter with system uncertainty, external disturbances and sensor faults, using the prescribed performance method.Design/methodology/approachTo ensure that the tracking error satisfies the prescribed performance, the authors adopt an error transformation function method. A control scheme based on the neural network and high-order disturbance observer is designed to guarantee the boundedness of the closed-loop system. A simulation is performed to prove the validity of the control scheme.FindingsThe developed adaptive fault-tolerant control method makes the system with sensor fault realize tracking control. The error transformation function method can effectively handle the prescribed performance requirements. Sensor fault can be regarded as a type of system uncertainty. The uncertainty can be approximated accurately using neural networks. A high-order disturbance observer can effectively suppress compound disturbances.Originality/valueThe tracking performance requirements of unmanned autonomous helicopter system are considered in the design of sensor fault-tolerant control. The inequality constraint that the output tracking error must satisfy is transformed into an unconstrained problem by introducing an error transformation function. The fault state of the velocity sensor is considered as the system uncertainty, and a neural network is used to approach the total uncertainty. Neural network estimation errors and external disturbances are treated as compound disturbances, and a high-order disturbance observer is constructed to compensate for them.

Adaptive backstepping-extended state observer control for electrohydraulic position servo systems with multiple disturbances using the compound friction compensation

Multiple disturbances coming from friction, matched, and mismatched uncertainties make it difficult for electrohydraulic servosystems to obtain the satisfactory position-tracking performance. The existing adaptive backstepping controllers fail to effectively distinguish the difference of disturbance between the mechanical subsystem and the hydraulic subsystem, which limits the compensation effect of multiple disturbances, especially for friction nonlinearity. Therefore, the adaptive backstepping-extended state observer position-tracking controller combined with compound friction compensation is proposed to simultaneously compensate for the fast-varying friction disturbance of a mechanical subsystem and the slow-varying matched disturbance of a hydraulic subsystem. The extended state observer algorithm is integrated into the adaptive backstepping controller to suppress the null bias of the average tracking error. The compound friction compensation includes a LuGre model-based compensation and a high-order disturbance observer, which can improve the tracking performance of system and avoids the excessive gain of observer. A large number of comparative experiments are conducted to verify the effective of the proposed controller.

Discrete nonsingular terminal sliding mode control for trajectory tracking of space manipulators with mismatched multiple disturbances and noisy measurements

Accurate trajectory tracking is essential for the success of space robotic missions. However, challenges such as modeling uncertainty, measurement noise, and excessive sampling interval can degrade tracking performance and then deteriorate the control safety. In this study, a robust adaptive approach for trajectory tracking of space robotic manipulators is proposed to address the above challenges. The approach integrates the techniques of extended Kalman filter, high-order disturbance observer, and discrete nonsingular terminal sliding control. In particular, by introducing auxiliary variables into the filter, the accuracy of state estimation is significantly improved. In addition, an improved terminal sliding controller is developed based on an equivalent control design philosophy, which ensures both guaranteed tracking stability and mitigation of the adverse effects of long sampling times. Numerical simulation results demonstrate the effectiveness of the proposed techniques and highlight the advantages of the controller in terms of accuracy and robustness.

High-order disturbance observer-based safe tracking control for a class of uncertain MIMO nonlinear systems with time-varying full state constraints

This paper investigates a high-order disturbance observer-based safe tracking control scheme for a class of uncertain multiple-input and multiple-output systems under time-varying full state constraints and disturbances. To achieve the safe tracking objective, a boundary protection algorithm is introduced to generate new safe desired signals which are within corresponding state constraints. An improved second-order dynamic surface control technology is developed to deal with the piecewise differentiability of safe desired signals and the phenomenon of repeatedly differentiation, simultaneously. To handle the negative effects of system uncertainties and obtain better estimation effect of high order time-varying disturbances, the radial basis function neural networks and high-order disturbance observer methods are developed. The safety and performance of the closed-loop nonlinear system under the proposed control scheme have been rigorous proved and discussed by Lyapunov stability analysis. Finally, a two-link manipulator model has been given as an example, and the numerical simulations are given to express the availability of the proposed controller.

Distributed Adaptive Human-in-the-Loop Event-Triggered Formation Control for QUAVs With Quantized Communication

To improve the safety and reliability of quadrotor unmanned aerial vehicles (QUAVs) with limited communication, system uncertainties, and unknown external disturbances in a highly uncertain and safety-critical environment, a distributed adaptive human-in-the-loop (HiTL) event triggered (ET) formation controller is proposed. The non-autonomous leader are controlled by receiving control commands decided by the gesture recognition system, and the followers are controlled indirectly via the connected communication network. Thus, the safety and flexibility of the closed-loop system are improved. The designed controller is quantized and then sent to actuator only at the ET instants to further reduce the network burden. The radial basis function neural network (RBFNN) is used to approximate the system uncertainties. The unknown approximation error and the unknown external disturbance are viewed as a compound disturbance compensated by the high order disturbance observer (HODO). In addition, the uniformly ultimately bounded (UUB) stability of the closed-loop system is achieved through the Lyapunov method. Finally, comparative experiments are implemented on the QUAVs to demonstrate the validity of the presented control scheme.

Extended High-Order Disturbance Observer-Based Clutch Actuator Model Uncertainty Estimation of Ball-Ramp Dual-Clutch Transmission

The ball-ramp dual-clutch transmission (BR-DCT) was proposed to overcome the disadvantages of conventional DCT. Specifically, BR-DCT is designed to reduce the amount of clutch actuator energy consumption and reverse torque during tie-up, in which two clutches are engaged simultaneously. In addition, since the self-energizing principle is used, the actuator model can be used without the friction coefficient, which is the main uncertainty of the clutch actuator. These features can greatly contribute to enhancing the shift control performance of the BR-DCT. However, the measurement error due to friction between actuator parts causes a small amount of uncertainty. In this article, a method using extended high-order disturbance observer (EH-DOB) is proposed to estimate this uncertainty. The EH-DOB used in the proposed method guarantees convergence even in a system in which the gain of the disturbance is time-varying. The convergence of the estimation error was verified through proof of the proposed algorithm. Experimental verification of the proposed algorithm was performed using a test bench that simulates a powertrain equipped with BR-DCT. As a result, it was confirmed that the uncertainty estimation result using EH-DOB showed high accuracy. As a result, it was verified that the uncertainty estimation method using the proposed algorithm has high accuracy and stability enough to perform disturbance rejection control.

A Joint Acceleration Estimation Method Based on a High-Order Disturbance Observer

Joint acceleration feedback is widely used in the design of controllers and observers since joint accelerations reflect the joint dynamics of robots, especially in physical human-robot interaction. However, joint acceleration acquisition is a technical difficulty for robots. The dynamics-based methods can achieve joint acceleration estimation using only a nominal model. Still, the performance of these methods is limited by the fast time-varying disturbances in the system. This letter proposes a joint acceleration estimation method based on a high-order disturbance observer. This method can observe and compensate for fast time-varying lumped disturbances in the observer while maintaining joint acceleration estimation performance at low frequencies. The finite-time stability of the proposed estimation method is proved using the Lyapunov theory. Simulations and experiments with a lower limb rehabilitation robot are implemented to verify the performance of the proposed method.

Consensus Control for Multiple Euler-Lagrange Systems Based on High-Order Disturbance Observer: An Event-Triggered Approach

This letter addresses the leader-following consensus problem (LFCP) for multiple Euler-Lagrange (EL) systems with a directed topology. Firstly, a local high-order disturbance observer (HODO) is put forward to estimate the compound disturbance for each EL system itself, and the estimate error can ultimately achieve zero. Based on this HODO, an event-based distributed sliding mode control protocol is proposed to solve the LFCP of multiple EL systems. Furthermore, the reachability of the sliding mode surface is analyzed. Besides, it should be pointed out that the interval between any two triggering instants is a strictly positive value, hence the well-known Zeno behavior is avoided for the developed event-based protocol. Finally, the effectiveness of the proposed HODO and control protocol is further verified by a numerical simulation.

Disturbance Compensation-Based Nonlinear Control for Pneumatic Artificial Muscle Systems With Hardware Experiments

Owing to variable stiffness, natural compliance, and similarities with skeletal muscles, pneumatic artificial muscles (PAMs) have been widely utilized in the fields of bionic robots, medical rehabilitation, and industrial manufacturing. However, in addition to high nonlinearities, time variation, and uncertainties, PAMs are extremely sensitive to external disturbances in practical applications, most of which are unknown, complicated, and constantly changing. Regarding these challenging issues, a disturbance compensation-based robust control method is proposed in this paper, which realizes satisfactory tracking control of PAM systems without a prior knowledge of exact models. Particularly, without assuming that disturbances or their first-order derivatives are invariable, a high-order disturbance observer is proposed to estimate lumped disturbances and their nth-order derivatives. On this basis, a nonlinear feedback controller is designed to simultaneously ensure that the observation errors converge to zero in finite time and the tracking error converges to zero asymptotically. Further, based on Lyapunov techniques, the stability analysis for the equilibrium point of the closed-loop system is provided in detail. Finally, the practicability and the robustness of the proposed method are validated by hardware experiments on a self-built horizontal PAM platform.

Design and Analysis of a Generalized High-Order Disturbance Observer for PMSMs With a Fuzy-PI Speed Controller

This paper proposes a generalized high-order observer for estimating total disturbance of permanent magnet synchronous motors (PMSMs). This total disturbance is dominated by load torque but also includes many other terms such as frictions, viscous force, Eddy and flux pulling forces, and noises. Comprehensive experimental results and analyses under various scenarios will be presented to find the appropriate order of the observer. We will compare the performance of zero-order observer (ZDO), first-order observer (FDO), and second-order observer (SDO) under three different scenarios of load torque. Additionally, the results of an state observer (ESO) under the same conditions are also presented. The experimental results show that FDO and SDO achieve similar performance and both of them are notably better than the ZDO and ESO. However, during the severe conditions of load torque, the SDO-based controller can achieve better performance compared to that of FDO-based controller. Moreover, fuzzy algorithm is applied to online tune the PI gains in the speed loop. The results also show that the SDO-based fuzzy-PI control scheme is effective in disturbance rejection and high-performance speed tracking. All of the experiments are carried out on a 300-W PMSM testbed with a digital signal processor (DSP).

A robust passivity based model predictive control for buck converter suppling constant power load

In this paper, the instability problem caused by the constant power load in Buck converter is addressed. In order to solve this instability problem, a composite controller is proposed. Due to the double loop structure of this controller, the passivity based control (PBC) is adopted in the voltage loop to track the reference voltage and make the system stable, while a simplified continuous control set model predictive control (CCS-MPC) is selected as the current controller to track the current reference. Moreover, in order to improve the robustness of the controller and avoid the static error in output, a high order disturbance observer (HODO) is designed out to compensate the negative effects caused by the disturbance and uncertainty. Then, a mixed potential theory based large signal stability analysis is conducted to investigate the large signal stability of the studied system. In order to verify the proposed method, MATLAB simulation, OPAL-RT based hardware in loop and rapid control prototype experiments are conducted.

SMC for nonlinear systems with mismatched uncertainty using Lyapunov-function integral sliding mode

In this paper, the mismatched uncertainty and disturbance rejection is addressed for uncertain nonlinear systems by a class of integral sliding mode (ISM) design. First, after describing the system control problem, the ISM design problem is given. Then, two kinds of ISM are presented that have the ability to reject the mismatched uncertainty and disturbance. One is called Lyapunov-function integral sliding mode (LFISM) and the other is called assistant-Lyapunov-function integral sliding mode (ALFISM). The system state in the ideal sliding mode of the two ISM surfaces is proved to be robustly stable despite the existence of the mismatched uncertainty and disturbance. In the presented framework, a general case of single input nonlinear system was studied and verified by a simulation application to a one-link robotic manipulator. Additionally, applications to a unicycle using the ISM with the mismatched-disturbance minimisation (ISM-MDM) method, the high-order disturbance observer (HODO) technique, and the LFISM method were reported. The simulation results confirmed that the LFISM's rejection effect to the mismatched disturbance is better.

Fuzzy Robust Constrained Control for Nonlinear Systems With Input Saturation and External Disturbances

This article proposes a high-order disturbance observer (HODO) and dynamic surface control (DSC) technique-based adaptive fuzzy control scheme for nonlinear systems subjected to input saturation and external time-varying disturbances. First, based on a Sigmoid function, the saturation input is tackled by utilizing a well-defined nonlinear smooth function. Furthermore, HODO and fuzzy logic systems are used to estimate the external disturbances and to handle the lumped unknown functions, respectively. Then, by using the backstepping method and DSC technique, a HODO-based adaptive fuzzy tracking control scheme is proposed for nonlinear systems with saturation nonlinearity, uncertainties, and external disturbances. The Lyapunov analysis method is used to prove that all signals in the entire system are semiglobally uniformly ultimately bounded (SGUUB). In addition, the tracking error converges to a compact set with a tunable error bound determined by some design parameters. Finally, a numerical simulation of two-stage chemical reactor shows the effectiveness of the developed tracking control strategy.

Disturbance observer based discrete PI control system with back-calculation anti-windup technique for improvement transient performance of PMSM

In this paper disturbance observer-based control (DOBC) system for PMSM has been proposed. The cascade structure of the discrete-time PI-PI control system with back-calculation anti-windup scheme for both loops has been adopted. High order disturbance observer (HODO) has been adopted to estimate the total disturbance and compensate it in the speed loop of the PMSM control system. In the HODO, the disturbance estimation is based on the motion equation which takes into account torque losses due to the drug resulting from the time-varying flux, hysteresis, and friction. Unlike the traditional observers, the HODO does not require the derivatives of the disturbance to be zero, which is considered as its main advantage. The fast-varying disturbance as cogging torque and a high-frequency electromagnetic noise in the PMSM system also affect on the performance of control system, which are analyzed in the study. In the real-time experiments, the proposed control system achieves less speed errors and faster response comparing with controller without disturbances observer. The experimental results have proved the feasibility of the proposed control scheme.

High Order Disturbance Observer Based PI-PI Control System With Tracking Anti-Windup Technique for Improvement of Transient Performance of PMSM

This paper focuses on designing a disturbance observer-based control (DOBC) system for PMSM drives. The cascade structure of the discrete-time PI-PI control system with tracking anti-windup scheme has been designed for both loops. In this study, high order disturbance observer (HODO) based control is used to improve the speed tracking performance of the control system for the PMSM prototyping kit regardless of the disturbance and unmodelled dynamics. The motion equation was modified in the HODO in which torque losses due to the drug resulting from the time-varying flux, hysteresis, and friction have been taken into account to estimate the total disturbance. The HODO does not require the derivatives of the disturbance to be zero, like in the traditional ones. It demonstrates its ability to estimate along with a load torque the high order disturbances caused by a cogging torque and a high-frequency electromagnetic noise in the PMSM system. In the real-time experiments, the proposed algorithm with HODO achieves less speed errors and faster response comparing with the baseline controller. The performances with proposed and baseline control have been evaluated under mechanical speed and load torque variation cases. The experimental results have proved the feasibility of the proposed control scheme. The proposed disturbance observer-based control system was implemented with a Lucas-Nuelle 300 W PMSM prototyping kit.

High-Order Disturbance Observer-Based Neural Adaptive Control for Space Unmanned Systems With Stochastic and High-Dynamic Uncertainties

In this paper, a high order disturbance observer based stochastic adaptive anti-disturbance control algorithm has been designed for the space unmanned systems (SUSs) with high dynamic disturbances and stochastic uncertainties. Firstly, to suppress the adverse influence of the high dynamic disturbances, a high order disturbance observer is designed for the SUSs to maintain the accurate approximation. Secondly, to overcome the infaust effects of the stochastic uncertainties, a novel variable has been introduced and the corresponding adaptive law has been proposed. Moreover, the neural networks have been employed to enhance the adaptability with respect to the nonlinearities and modeling errors. Based on the stochastic control theory and the fourth-order Lyapunov function, the stochastic stability of the closed-loop control system has been proved. Finally, the performance of high-order disturbance observer has been verified in two cases of simulations, and the effectiveness of the stochastic adaptive anti-disturbance control strategy has been demonstrated simultaneously.

High-Order Observer-Based Sliding Mode Control for the Isolated Microgrid with Cyber Attacks and Physical Uncertainties

System security is essential for the operation of the island microgrid. However, the system security is generally threatened due to the presence of physical uncertainties and cyber attacks. In this article, a novel sliding mode load control strategy is proposed for the microgrid to mitigate cyber attacks and physical uncertainties. Firstly, a high-order disturbance observer (HODO) is designed to estimate the unmeasurable factors in the microgrid. Secondly, a HODO-based sliding mode control (SMC) strategy is proposed where the estimated value observed by the HODO is applied to the sliding mode surface and control law. It can better guarantee the security of the isolated microgrid. Then, the stability of the HODO-based SMC is demonstrated by Lyapunov stability theory. Finally, simulation results show that the proposed control strategy has excellent control performance.

Uncalibrated Visual Servoing for Underwater Vehicle Manipulator Systems with an Eye in Hand Configuration Camera.

This paper presents an uncalibrated visual servoing scheme for underwater vehicle manipulator systems (UVMSs) with an eye-in-hand camera under uncertainties. These uncertainties contain vision sensor parameters, UVMS kinematics and feature position information. At first, a linear separation approach is addressed to collect these uncertainties into vectors, and this approach can also be utilized in other free-floating based manipulator systems. Secondly, a novel nonlinear adaptive controller is proposed to achieve image error convergence by estimating these vectors, the gradient projection method is utilized to optimize the restoring moments. Thirdly, a high order disturbance observer is addressed to deal with time-varying disturbances, and the convergence of the image errors is proved under the Lyapunov theory. Finally, in order to illustrate the effectiveness of the proposed method, numerical simulations based on a 9 degrees of freedom (DOFs) UVMS with an eye-in-hand camera are conducted. In simulations, the UVMS is expected to track a circle trajectory on the image plane, meanwhile, time-varying disturbances are exerted on the system. The proposed scheme can achieve accurate and smooth tracking results during simulations.

Notice of Removal: A Disturbance Observer Based Sliding Mode Control for a Class of Underactuated Robotic System With Mismatched Uncertainties

In this note, a high-order disturbance observer for a class of underactuated robotic systems with mismatched uncertainties is proposed. To improve its estimation performance, a choice method of optimal gain matrices of the high-order disturbance observer is obtained as the solution of an optimization problem. A high-order disturbance observer based sliding mode control method is also designed for this class of underactuated robotic system with mismatched disturbance. The stabilities of both the disturbance observer and the controlled closed-loop system are proved by the Lyapunov theorem. Simulations on a benchmark Acrobot system demonstrate the efficiency of proposed approaches.

Improved disturbance observer based control for airborne photoelectric stabilized platform

The aim of this work was to solve the problem that the stabilization accuracy of photoelectric stabilized platforms is affected by disturbance. An improved disturbance observer was established to observe the disturbance. By using the ultra-high control bandwidth of the current loop, the observer was used as the input of the current loop. The design of the improved disturbance observer consists of an inverse model of the control object and an improved filter. The high-order disturbance observer not only has good suppression ability compared to the high order disturbance model, but also has good robustness, meeting the application requirements of photoelectric stabilized platforms.