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In this study, a fuzzy logic system to tune the parameters of terminal sliding mode control with a sliding perturbation observer (TSMCSPO) in real-time is proposed according to the system’s state changes to improve the control performance of TSMCSPO for a 5-DOF robot manipulator used for nuclear reactor dismantlement. Accurate trajectory tracking control is required when using a multi-DOF robot manipulator to cut the decommissioned nuclear reactor. A TSMCSPO scheme using TSMC in SPO has been proposed in previous research, which improves the estimation and convergence performance of traditional SMCSPO. In TSMCSPO, the parameters of the controller are important to enhance the control performance. Moreover, due to the influence of the working environment and the uncertainty of the system, the characteristics of the system will be changed during the trajectory tracking control of the multi-degree-of-freedom robot manipulator. Therefore, real-time optimal parameter tuning is required. In this regard, using fuzzy logic to tune the parameters is an effective method. By designing fuzzy rules, the controller parameters can be optimized. In this study, the proposed algorithm and, the trajectory tracking control simulation of the robot manipulator in the nuclear reactor vessel internal (RVI) are implemented in MATLAB/Simulink environment. The control algorithm is verified by the experiments on a real robot manipulator platform. The outstanding control performance of the algorithm is demonstrated by comparing the trajectory tracking error between the proposed fuzzy TSMCSPO scheme and TSMCSPO with fixed parameters.

Robot manipulators have complex dynamics and are affected by significant uncertainties and external disturbances (perturbations). Consequently, determining the exact mathematical model of a robot manipulator is a tedious task. Accordingly, accurate trajectory tracking is a dominant feature in the design of position control for robot manipulators. The main objective of this research is to design a robust and accurate position control for a robot manipulator despite the absence of an exact model. For this purpose, an extended state observer (ESO)-based sliding mode control (SMC) is proposed. The main concept in the ESO is to define and estimate the assumed perturbation, which includes known and unknown system dynamics, uncertainties, and external disturbances. Additionally, the ESO estimates the system states. This estimated perturbation information, which is combined with the SMC input, is utilized as a feedback term to compensate for the effect of the actual perturbation. The perturbation compensation improves the controller performance, resulting in a slight position error, less sensitivity to perturbation, and a small switching gain required for the SMC. The advantage of the proposed algorithm is that it only requires partial state information and position feedback. Thus, identifying the system parameters for the nominal model before designing the controller is unnecessary. The proposed algorithm is implemented and compared with the conventional SMC and the SMC with a sliding perturbation observer (SMCSPO) in a virtual environment based on MATLAB SimMechanics. The comparison results validate the robustness of the proposed technique in the presence of perturbation and show that the technique has a significantly reduced trajectory tracking error than the conventional SMC and SMCSPO.

Solution to the safe and collision-free trajectory of the wheeled mobile robot in cluttered environments containing the static and/or dynamic obstacle has become a very popular and challenging research topic in the last decade. Notwithstanding of the amount of publications dealing with the different aspects of this field, the ongoing efforts to address the more effective and creative methods is continued. In this article, the effectiveness of the real-time harmonic potential field theory based on the panel method to generate the reference path and the orientation of the trajectory tracking control of the three-wheel nonholonomic robot in the presence of variable-size dynamic obstacle is investigated. The hybrid control strategy based on a backstepping kinematic and regressor-based adaptive integral sliding mode dynamic control in the presence of disturbance in the torque level and parameter uncertainties is employed. In order to illustrate the performance of the proposed adaptive algorithm, a hybrid conventional integral sliding mode dynamic control has been established. The employed control methods ensure the stability of the controlled system according to Lyapunov’s stability law. The results of simulation program show the remarkable performance of the both methods as the robust dynamic control of the mobile robot in tracking the reference path in unstructured environment containing variable-size dynamic obstacle with outstanding disturbance suppression characteristic.

This paper proposes a perturbation estimation based nonlinear adaptive power decoupling controller for doubly fed induction generator based wind turbines (DFIG-WTs). Perturbation states are defined to include the nonlinearities, uncertainties of the system model, the cross-coupling between control loops, and external disturbances. Perturbation observers are designed to estimate the fast time-varying perturbation states. With perturbation estimation, the DFIG-WT system is fully decoupled, and an output feedback control can be designed for the control of rotor currents. Rotor current references are calculated based on the steady-state relation between active/reactive power and rotor current, and stator dynamic is ignored. The performance of the proposed controller is evaluated and verified via both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

In this paper, an event-based control strategy for mobile robots is proposed. The solution includes new features that minimize the effects of the noise on the system. Two methodologies have been developed to compensate the perturbations. To avoid the effects of such perturbations, a threshold calculator and a perturbation estimator are included in the system. The proposed system is compared with classical control systems based on discrete time. Different scenarios are analyzed in the experiments to check its performance. The stability and the improvements of the proposed control strategy are also analyzed in the experimental results.

Let be the set of all complex matrices. For any Hermitian positive semi-definite matrices A and B in , their new common upper bound less than is constructed, where denotes the Moore–Penrose inverse of , and is the parallel sum of A and B. A factorization formula for is derived, where are any Hermitian positive semi-definite perturbations of A and B, respectively. Based on the derived factorization formula and the constructed common upper bound of X and Y, some new and sharp norm upper bounds of are provided. Numerical examples are also provided to illustrate the sharpness of the obtained norm upper bounds. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a robust maximum power point tracking (MPPT) control scheme for a grid-connected permanent magnet synchronous generator based wind turbine (PMSG-WT) using perturbation observation based nonlinear adaptive control. In the proposed control scheme, system nonlinearities, parameter uncertainties, and external disturbances of the PMSG-WT are represented as a lumped perturbation term, which is estimated by a high-gain perturbation observer. The estimate of the lumped perturbation is employed to compensate the actual perturbation and further achieve adaptive feedback linearizing control of the original nonlinear system, without requiring the detailed system model and full state measurements. The effectiveness of the proposed control scheme is verified through both simulation studies and experimental tests. The results show that, compared with the conventional vector controller and the standard feedback linearizing controller, the proposed control strategy provides higher power conversion efficiency and has better dynamic performances and robustness against parameter uncertainties and external disturbances. Highlights • A perturbation observation based nonlinear adaptive MPPT control (PONAC-MPPT) scheme is proposed for PMSG-WT. • The PONAC-MPPT increases energy conversion efficiency under time-varying wind. • The PONAC-MPPT enhances robustness against system parameter uncertainties and tower shadow. • The PONAC-MPPT do not require the detailed system model and full state measurements. • Both simulation and experimental results verify the effectiveness of the PONAC-MPPT. [ABSTRACT FROM AUTHOR]

This paper develops a perturbation estimation based robust state feedback control (PER-SFC) scheme of doubly-fed induction generator (DFIG) for maximum power point tracking (MPPT). The combinatorial effect of nonlinearities originally stemmed from wind turbine aerodynamics, generator modelling uncertainties and wind speed randomness is aggregated as a perturbation, which is rapidly estimated online by a sliding-mode state and perturbation observer (SMSPO). Then, a linear state feedback controller is designed to fully compensate the perturbation estimate in real-time. Furthermore, only the measurement of rotor speed and reactive power is needed while no accurate DFIG model is required by the proposed approach. Under such framework, the elegant merits of conventional linear state feedback control (favourable implementation simplicity and high reliability) and nonlinear robust control (global control consistency and considerable robustness) can be wisely incorporated. Meanwhile, their inherent drawbacks could be significantly reduced. Case studies are undertaken which verify the effectiveness and superiority of PER-SFC compared to that of other classical methods. [ABSTRACT FROM AUTHOR]

An adaptive non‐singular backstepping control with perturbation estimation scheme is designed for a class of multi‐input systems with matched and mismatched perturbations to solve the regulation problems. The design procedure of this control scheme mainly contains two parts. The first part is the design of the virtual control inputs, the second part is the design of control input functions and perturbation estimation mechanism. The main advantage of the proposed control scheme is that, without knowing the upper bounds of perturbations, the controlled system is still capable of suppressing the perturbations so that the controlled states are able to reach zero within a finite time. Another advantage is that there is no singular problem at all. Finally, a numerical example and a practical application are given for demonstrating the feasibility of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Piezoelectric actuators (PEAs) are the key devices in micro/nano positioning system. However, the PEA performance is significantly degraded by the inherent non-linear behaviour. This behaviour is a consequence of the hysteresis properties contained within PEAs. Therefore, in micro/nano positioning applications, a robust control system has to be adopted for such actuators. This paper proposes a systematic control method that utilises a fast non-singular terminal sliding mode (FNTSM) based on online perturbation estimation technique for PEAs. Unlike other sliding mode methods, the FNTSM control method is characterised by chatter free. Besides, a zero error convergence can be guaranteed in finite time in the presence of disturbance and system uncertainties (i.e., hysteresis and gain changes). The design of the FNTSM control based on perturbation estimation (FNTSMPE) is presented. A model-free robust exact differentiator is used to estimate the states of the feedback system from merely measurable position signal. Theoretical analysis and the experimental results of FNTSMPE control reveal that high-precision and robust performance is achieved in comparison with ordinary FNTSM control. [ABSTRACT FROM PUBLISHER]

This paper proposes an active-current control strategy for large-scale wind turbines (WTs) to improve the transient stability of power systems based on a perturbation estimation (PE) approach. The main idea of this control strategy is to mitigate the generator imbalance of mechanical and electrical powers by controlling the active-current of WTs. The effective mutual couplings of synchronous generators and WTs are identified using a Kron-reduction technique first. Then, the control object of each WT is assigned based on the identified mutual couplings. Finally, an individual controller is developed for each WT using a PE approach. In the control algorithm, a perturbation state (PS) is introduced for each WT to represent the comprehensive effect of the nonlinearities and parameter variations of the power system, and then it is estimated by a designed perturbation observer. The estimated PS is employed to compensate the actual perturbation, and to finally achieve the adaptive control design without requiring an accurate system model. The effectiveness of the proposed control approach on improving the system transient stability is validated in the modified IEEE 39-bus system.

Based on the background of atomic force microscope (AFM) driven by piezoelectric actuators (PEAs), this paper proposes a sliding mode control coupled with an inverse Bouc–Wen (BW) hysteresis compensator to improve the positioning performance of PEAs. The intrinsic hysteresis and creep characteristics degrade the performance of the PEA and cause accuracy loss. Although creep effect can be eliminated by the closed-loop control approach, hysteresis effects need to be compensated and alleviated by hysteresis compensators. For the purpose of dealing with the estimation errors, unmodeled vibration, and disturbances, a sliding mode control with perturbation estimation (SMCPE) method is adopted to enhance the performance and robustness of the system. In order to validate the feasibility and performance of the proposed method, experimental studies are carried out, and the results show that the proposed controller performs better than a proportional-integral-derivative (PID) controller at 1 and 2 Hz, reducing error to 1.2% and 1.4%, respectively.

This paper proposes a perturbation estimation based coordinated adaptive passive control (PECAPC) of generators excitation system and thyristor-controlled series capacitor (TCSC) devices for complex, uncertain and interconnected multimachine power systems. Discussion begins with the PECAPC design, in which the combinatorial effect of system uncertainties, unmodelled dynamics and external disturbances is aggregated into a perturbation term, and estimated online by a perturbation observer (PO). PECAPC aims to achieve a coordinated adaptive control between the excitation controller (EC) and TCSC controller based on the nonlinearly functional estimate of the perturbation. In this control scheme an explicit control Lyapunov function (CLF) and the strict assumption of linearly parametric uncertainties made on system structures can be avoided. A decentralized stabilizing EC for each generator is firstly designed. Then a coordinated TCSC controller is developed to passivize the whole system, which improves system damping through reshaping the distributed energies in power systems. Case studies are carried out on a single machine infinite bus (SMIB) and a three-machine system, respectively. Simulation results show that the PECAPC-based EC and TCSC controller can coordinate each other to improve the power system stability, finally a hardware-in-the-loop (HIL) test is carried out to verify its implementation feasibility. [ABSTRACT FROM AUTHOR]

The fault ride-through capability (FRTC) of a full- rated converter wind turbine relies on the operation and control of the grid-side converter. To enhance the FRTC of the wind power generation system (WPGS), this paper investigates a novel controller for the grid-side converter, based on nonlinear adaptive control (NAC). Lumped perturbation terms are defined in the NAC to include all unknown and time-varying dynamics and external disturbances of the WPGS, and can be estimated by designing perturbation observers. The estimate of the perturbation terms is used to compensate the real perturbations and finally achieve an adaptive feedback linearizing control of the original nonlinear system, without requiring the accurate system model and full state measurements. The proposed NAC is an output feedback control and adaptive to parameter uncertainties and unknown nonlinearities of the WPGS, and time-varying external disturbances including grid faults, voltage dips and intermittent wind power inputs. The effectiveness of the proposed NAC is verified by simulation studies and compared with conventional vector controller and feedback linearizing controller, which show that it can provide better FRTC even though the grid voltage levels are far below their nominal values. [ABSTRACT FROM AUTHOR]

Many researchers have focused on force tracking improvement in teleoperation systems. Various methods have been utilized to reach this aim. This paper focuses on force-reflecting passivity-based architecture. Adding a force error term to conventional passivity-based architecture, a controller has been introduced to improve transparency. A condition has been obtained, which guarantees the stability of the system, while it holds. Moreover, a sliding mode perturbation estimation algorithm has been proposed. The method proved to be asymptotically converging to perturbations. The transparency of system has been compared in simple and force-reflecting passivity-based architectures, and also with and without perturbation estimator. Experiments on a 2-DOF non-linear delayed teleoperation system were conducted to investigate the system’s performance. Experimental results have shown that the controller is stable and force tracking has been improved compared with previous research. Furthermore, the perturbation in the system has been successfully estimated and cancelled. Conclusively, the paper introduces a controller that is stable and compares its performance in force tracking with previous research. [ABSTRACT FROM PUBLISHER]

Piezoelectric actuators (PEAs) are frequently used in a wide variety of micromanipulation systems. However, the hysteresis non-linearity and the creep reduce their fidelity and cause difficulties in the micromanipulation control procedure. Besides, variation of temperature and external loads could change the model parameters identified for the piezo actuator. In this paper, a robust feedforward–feedback controller is proposed for precise tracking control of PEAs, under external disturbances. A Bouc–Wen hysteresis model is integrated with a second-order linear dynamic, to represent the behaviour of a PEA. Based on the Bouc–Wen model, a hysteresis observer is developed to estimate the hysteresis non-linear effect. Then, for real-time compensation of the observer error and the thermal and external load disturbances, a sliding mode control (SMC) strategy with a perturbation estimation function is utilized. To verify the efficiency of the proposed method, a comparison between the proposed approach and a classical SMC is presented. [ABSTRACT FROM AUTHOR]

A novel modeling and control methodology is proposed in this paper for real-time compensation of nonlinearities along with precision trajectory control of piezoelectric actuators in various range of frequency operation. By integrating a modified Prandtl-Ishlinskii hysteresis operator with a second-order linear dynamics, a nonlinear dynamic model and an inverse feedforward controller are developed and experimentally validated for a piezoelectrically driven nanopositioning stage. This modeling and control framework, however, lacks the accuracy due to the hysteresis model limitation, parametric uncertainties, and ever present unmodeled dynamics. Utilizing the sliding mode control strategy coupled with a perturbation estimation technique, a robust controller is then proposed for trajectory tracking of the actuator displacement. The controller gains are adjusted based on an intelligent comparison of the dynamic model and the control law. Eventually, the performance of the proposed controller is verified for the nanopositioning stage which is equipped with a high resolution capacitive position sensor. Experimental results demonstrate that the controller is capable of precisely tracking triangular and multiple frequency sinusoidal trajectories, which are common practices in many scanning probe microscopy systems. [ABSTRACT FROM AUTHOR]

This paper presents a robot manipulator tracking controller based on output feedback linearization. A sliding mode perturbation observer (SPO) is designed to estimate unmeasurable states and system perturbations that involve system nonlinearities, disturbances and unmodelled dynamics. The use of SPO allows to input/output linearize and decouple the strongly coupled nonlinear robot manipulator system merely by the feedback of joint angles. The controller design does not need an accurate model of the robot manipulator. Simulation studies are undertaken based on a two-link robot manipulator to evaluate the proposed approach. The simulation results show that the proposed controller has more superior tracking control performance, with payload changing in a wide range, in comparison with a sliding mode controller (SMC) designed based on state feedback linearization with full states available. [ABSTRACT FROM AUTHOR]

This paper presents a sliding mode controller based on a sliding mode perturbation observer (SMPO) for the tracking control of robot manipulators. The SMPO is designed to estimate unmeasurable states and system perturbations that involve system non-linearities, disturbances, and unmodelled dynamics. The use of an SMPO allows the linearization of the input/output and the decoupling of the strongly coupled non-linear robot manipulator system merely by the feedback of joint angles, waiving the need for expensive tachometers. The controller design does not need an accurate model of the robot manipulator. Simulation studies are undertaken based on a two-link robot manipulator to evaluate the proposed approach. The simulation results show that the SMPO has more superior tracking control performance, with a wide range of payloads, in comparison with a sliding mode controller designed based on state feedback linearization with full states available. [ABSTRACT FROM AUTHOR]

This paper presents an observer-based nonlinear control method that was developed and implemented to provide accurate tracking control of a limited angle torque motor following a 50Hz reference waveform. The method is based on a robust nonlinear observer, which is used to estimate system states and perturbations and then employ input-output feedback linearization to compensate for the system nonlinearities and uncertainties. The estimation of system states and perturbations allows input-output linearization of the nonlinear system without an accurate mathematical model of nominal plant. The simulation results show that the observer-based nonlinear control method is superior in comparison with the conventional model-based state feedback linearizing controller. [ABSTRACT FROM AUTHOR]

This paper presents a novel nonlinear adaptive controller (NAC) for the co-ordinated control of generators and thyristor-controlled series compensators (TCSCs) in multimachine power systems. Discussions begin with power system de-coupling which is achieved by Lie differentiation. For each subsystem, the nonlinear adaptive control strategy is, at first, investigated based on the input/output feedback linearizing control. In this strategy, a fictitious state is defined to represent the combined effect of system nonlinearities, uncertainties and external disturbances and an extended-order sliding mode observer is employed to estimate the states and the fictitious state of the subsystem, which allows the NAC to be designed without requiring the knowledge of system nonlinearities and parameters. The NAC is then implemented locally, involving the external dynamics of the subsystem, which is estimated by the observer, for the co-ordinated control of generators and TCSCs in the multimachine power system. Simulation studies are undertaken based on a three-machine power system to evaluate the effectiveness of the NAC. The simulation results show that the locally installed NACs can co-ordinate each other to improve the power system stability. [ABSTRACT FROM AUTHOR]

The modal injection mechanism ensures the exponential convergence of an observer in a continuous tubular reactor in dependence with the system parameters, the sensor location, and the observer gains. In this paper, it is shown that by simple considerations in the boundary conditions, the observer convergence is improved regardless of the presence of perturbations, the sensor locations acquire a meaningful physical meaning, and by simple numerical manipulations, the perturbations in the inflow can be numerically estimated. [ABSTRACT FROM AUTHOR]

This paper proposes an active-current control strategy for large-scale wind turbines (WTs) to improve the transient stability of power systems based on a perturbation estimation (PE) approach. The main idea of this control strategy is to mitigate the generator imbalance of mechanical and electrical powers by controlling the active-current of WTs. The effective mutual couplings of synchronous generators and WTs are identified using a Kron-reduction technique first. Then, the control object of each WT is assigned based on the identified mutual couplings. Finally, an individual controller is developed for each WT using a PE approach. In the control algorithm, a perturbation state (PS) is introduced for each WT to represent the comprehensive effect of the nonlinearities and parameter variations of the power system, and then it is estimated by a designed perturbation observer. The estimated PS is employed to compensate the actual perturbation, and to finally achieve the adaptive control design without requiring an accurate system model. The effectiveness of the proposed control approach on improving the system transient stability is validated in the modified IEEE 39-bus system. [ABSTRACT FROM AUTHOR]

Based on the background of atomic force microscope (AFM) driven by piezoelectric actuators (PEAs), this paper proposes a sliding mode control coupled with an inverse Bouc–Wen (BW) hysteresis compensator to improve the positioning performance of PEAs. The intrinsic hysteresis and creep characteristics degrade the performance of the PEA and cause accuracy loss. Although creep effect can be eliminated by the closed-loop control approach, hysteresis effects need to be compensated and alleviated by hysteresis compensators. For the purpose of dealing with the estimation errors, unmodeled vibration, and disturbances, a sliding mode control with perturbation estimation (SMCPE) method is adopted to enhance the performance and robustness of the system. In order to validate the feasibility and performance of the proposed method, experimental studies are carried out, and the results show that the proposed controller performs better than a proportional-integral-derivative (PID) controller at 1 and 2 Hz, reducing error to 1.2% and 1.4%, respectively. [ABSTRACT FROM AUTHOR]