Observer-based Sliding Mode Control Research Articles

Extended State Observer-Based Sliding-Mode Control for Aircraft in Tight Formation Considering Wake Vortices and Uncertainty

The tight formation of unmanned aerial vehicles (UAVs) provides numerous advantages in practical applications, increasing not only their range but also their efficiency during missions. However, the wingman aerodynamics are affected by the tail vortices generated by the leading aircraft in a tight formation, resulting in unpredictable interference. In this study, a mathematical model of wake vortex was developed, and the aerodynamic characteristics of a tight formation were simulated using Xflow software. A robust control method for tight formations was constructed, in which the disturbance is first estimated with an extended state observer, and then a sliding mode controller (SMC) was designed, enabling the wingman to accurately track the position under conditions of wake vortex from the leading aircraft. The stability of the designed controller was confirmed. Finally, the controller was simulated and verified in mathematical simulation and semi-physical simulation platforms, and the experimental results showed that the controller has high tight formation accuracy and is robust.

Observer-based SMC for discrete semi-Markov switching models

This study focuses on the observer-based sliding mode control (SMC) for discrete stochastic switching models, where the semi-Markov kernel information is incomplete. Because the sensors do not always have direct access to the state vector in a complex environment, an observer-based output measurement is considered to estimate the system state. In contrast to previous works, the observer-based strategy is first investigated in studying the SMC for semi-Markov switching systems under the discrete framework. The sufficient condition for achieving mean-square stability is proposed to solve the desired observer and controller gains by utilizing the upper bound of sojourn time, along with the Lyapunov function that pertains to the system mode and the elapsed time. A mode-dependent SMC law is also constructed to ensure that the system state can reach the specified sliding region. Finally, the efficiency of the proposed method is demonstrated through the single-link robot arm model.

Nyquist criterion for chattering avoidance and global stability in observer-based sliding-mode control with parasitics

A novel output-feedback sliding-mode control for linear plants is proposed. An observer-based chattering avoidance technique (OBCAT) is incorporated to counteract the effect of parasitics (unmodeled dynamics). A variable-gain unit control is designed to ensure global stability even in the presence of unmodeled dynamics. A necessary and sufficient Nyquist-like criterion for global stability is obtained, encompassing systems with time-delays, without prior assumptions about the observer gain and the characteristic parameter of the unmodeled dynamics which is not required to be sufficiently small. Numerical simulations and experimental results with a commercial robot manipulator illustrate the performance and effectiveness in chattering avoidance of the proposed control scheme and confirm its increased robustness with higher observer gain.

Disturbance observer-based sliding mode control of active vertical suspension for high-speed rail vehicles

Disturbance observer-based sliding mode control (SMC) on the active vertical suspension (AVS) is developed to suppress the car body’s rigid and flexible vibration to improve ride comfort for a high-speed rail vehicle. A vertical-dynamics-intended vehicle model is foremost built with the bounce, pitch, and bending mode of the car body involved. Two sliding surfaces and disturbance observers are then designed for SMC, which only require the car body states, obviating the bogies’ states. The observer is successful in estimating the effect of unknown track irregularities perturbation as well as externally straightforwardly excitations on the car body with good accuracy. Control efficacy is verified through comparison with passive cases and sky-hook controls. With modal damping below 2% in passive cases, the mode shape function, especially with large displacement at the suspension support, would enlarge the car body acceleration. Moreover, the longitudinal traction rod can significantly multiply the flexible vibration at certain speeds. Comparative studies indicate that SMC provides satisfactory outcomes in the rigid and bending vibration suppression when all the car body’s three modes are considered in the sliding surface. However, it requires a high-frequency response actuator and allows a tighter tolerance of the control time delay than the sky-hook control.

Disturbance Observer-Based Sliding Mode Control Using Barrier Function for Output Speed Fluctuation Constraints of PMSM

Disturbance Observer-Based Sliding Mode Control Using Barrier Function for Output Speed Fluctuation Constraints of PMSM

Data Driven Fuzzy Sliding Mode Observer-Based Control Strategy for Time-Varying Suspension System of 12/14 Bearingless SRM

Data Driven Fuzzy Sliding Mode Observer-Based Control Strategy for Time-Varying Suspension System of 12/14 Bearingless SRM

Extended State Observer-Based Sliding Mode Control Design of Two-DOF Lower Limb Exoskeleton

Due to some model uncertainties and unknown friction disturbances that exist in the 2-DOF lower limb exoskeleton, a linear extended state observer (LESO) is proposed to estimate the unmeasurable angular velocity of two joints and the lumped uncertainties caused by friction disturbance and hydraulic parametric uncertainties. Meanwhile, by using the Lyapunov technique, a sliding mode controller is designed to improve the dynamic performance and the steady state accuracy of two joint angle responses in human–exoskeleton cooperative motion. By regulating the sliding mode controller gain, both the system state errors and estimation errors of the LESO are reduced in an arbitrary boundary of zero neighborhood. Finally, the effectiveness of the proposed control scheme is verified with both simulation and experimental results for one operator-wearable test, to guarantee that the joint position tracking performance and human–exoskeleton impedance torques are suppressed in a satisfactory boundary.

Observer-based SMC design for stochastic systems with Levy noise

Abstract This work addresses the problem of sliding mode control (SMC) design for a continuous-time non-linear stochastic system with Levy-type noise. A state observer model is constructed to estimate the unavailable state information. Furthermore, Levy-type noise is considered to analyse small perturbations and to characterize the appearance of large samples that will occur in the system. Lyapunov stability and SMC theory are used to provide some sufficient conditions that ensure the stochastic stability of the error system and reachability of the predefined sliding surface. Finally, an example is given to demonstrate the feasibility of the proposed approach.

Neural learning-based dual channel event-triggered deployment control of space tethered system with intermittent output

In this paper, we investigate the dual-channel event-triggered deployment control for the space tethered system with intermittent output. Two different dynamic event-triggered mechanisms are designed to implement the event-based state sampling and the event-based input sampling, in which the data transmission frequencies are reduced at the dual channel, namely sensor-to-controller and controller-to-actuator. Then, the neural network (NN) state observer based on the intermittent output is designed to estimate the unmeasurable state under external disturbance, and the observer-based sliding mode controller is designed. Furthermore, because of the non-periodic sampling of the state signal and the output signal, the closed-loop system is proved via the analysis of the hybrid system, and the Zeno behavior is avoidance under these two event-triggered conditions. Finally, the simulation tests are implemented to verify the effectiveness of the proposed scheme.

Modified Three-Element Modeling and Robust Tracking Control for a Planar Pneumatic Soft Actuator

In pneumatic soft robotics systems, pneumatic soft actuators (PSAs) are the most important components, so it is necessary to study the precise modeling and control over PSAs for application. This paper focuses on a self-designed planar PSA, named pneumatic bellow actuator (PBA), and proposes a modified three-element model (MTEM) and a nonlinear disturbance observer-based sliding mode control (NDO-based SMC) method to achieve the robust tracking control objective of the PBA with multiple uncertainties. Firstly, the dynamic characteristics of the PBA are analyzed based on experimental data obtained from open-loop experiments of the PBA. Then, based on these dynamic characteristics, a semi-phenomenological MTEM is established considering coupling between the dynamics of the PBA and load as well as friction, which can describe the dynamics of the PBA with changing loads in the rough horizontal plane precisely. Model parameters are then identified by Levenberg-Marquardt (LM) algorithm. Next, identification errors, device disturbances and external disturbances are regarded as the multiple uncertainties of the PBA, and the NDO-based SMC method is proposed based on the MTEM to realize the robust tracking control objective of the PBA. The stability of the control system is proved. The effectiveness of the proposed method is verified by experiments.

Robust and Collision-Free Formation Control of Multiagent Systems With Limited Information.

This article investigates the collision-free cooperative formation control problem for second-order multiagent systems with unknown velocity, dynamics uncertainties, and limited reference information. An observer-based sliding mode control law is proposed to ensure both the convergence of the system's tracking error and the boundedness of the relative distance between each pair of agents. First, two new finite-time neural-based observer designs are introduced to estimate both the agent velocity and the system uncertainty. The sliding mode differentiator is then employed for every agent to approximate the unknown derivatives of the formation reference to further construct the limited-information-based sliding mode controller. To ensure that the system is collision-free, artificial potential fields are introduced along with a time-varying topology. An example of a multiple omnidirectional robot system is used to conduct numerical simulations, and necessary comparisons are made to justify the effectiveness of the proposed limited-information-based control scheme.

A novel control system for synchronizing chaotic systems in the presence of communication channel time delay; case study of Genesio-Tesi and Coullet systems

Time delay is one of the challenges that may occur in the communication channels. The control of chaotic systems due to time delay is a challenging purpose. This paper defines a synchronization system where the Genesio-Tesi is the master, and the Coullet is the slave system. A suitable observer-based sliding mode controller is designed for the goal of synchronization with the communication channel’s time delay. The proposed control system consists of state and disturbance observers and a controller. The state, disturbance observers, and controller are designed to synchronize the chaotic systems. The state observer estimates the master system states, the disturbance observer estimates the model of the uncertainties and external disturbances, and the controller uses the information from the state and disturbance observers in real time. These state and disturbance observers and controller work simultaneously. The proposed controller is based on the Sliding Mode Control (SMC) method and fixed-time stability concepts. This control system is compared with finite-time and asymptotical control systems by defining three performance criteria IAE, ITAE, and ISV. The proposed control method is robust against uncertainties and external disturbances and chattering-free. The MATLAB/Simulink software simulates the control systems and compares their results.

Observer-based Sliding Mode Control for Fractional Order Singular Fuzzy Systems

Observer-based Sliding Mode Control for Fractional Order Singular Fuzzy Systems

H∞ observer-based sliding mode control for uncertain discrete-time singularly perturbed systems

This paper studies the sliding mode control (SMC) problem of discrete-time singularly perturbed systems (DTSPSs) with external perturbations and nonlinear inputs. First, to estimate the state of the original system, a novel state observer is constructed. Under this condition, the observer error system is ensured to be input-to-state stable (ISS) and satisfies the given H∞ performance index. Then, an appropriate sliding mode control law is proposed to satisfy the reachability condition. On this basis, the ISS criterion for the sliding mode dynamics (SMDs) is given, and the controller gain matrix is also obtained. In addition, a feasible algorithm is given to compute the upper bound for the small parameter. Finally, two numerical examples are given to demonstrate the effectiveness of the proposed method.

Active fault-tolerant control of quadrotor UAVs with nonlinear observer-based sliding mode control validated through hardware in the loop experiments

Multirotor unmanned aerial vehicles (UAV) are highly prone to motor faults, which can arise from defective motors or damaged propellers. Motor faults severely change the multirotor UAV’s dynamics and therefore endanger flight safety and reliability since the controller loses its efficiency. To cope with such crucial problems, a fault-tolerant controller is proposed in this paper for full control of a quadrotor UAV with motor faults. The proposed fault-tolerant approach consists of the nonlinear observer technique and the Sliding Mode Control (SMC). The designed novel nonlinear observer predicts the effects of motor faults on quadrotor dynamics and it is augmented with an SMC to create a fault-tolerant controller. In addition, the nonlinear observer enhances the robustness of the SMC against the uncertainties and disturbances acting on the quadrotor during flight. Any actuator fault will be treated as a disturbance detected by the nonlinear observer and will be attenuated directly by the proposed SMC. The disturbance attenuation capability achieved by the nonlinear observer decreases the amount of control action expected from the SMC, which results in advanced robustness without sacrificing the nominal control performance. The performance of the proposed nonlinear observer SMC (NOSMC) is demonstrated through simulations and testbed experiments. The results show that the proposed fault-tolerant controller effectively recovers the full control of the quadrotor with motor faults up to 40% while tracking the predefined trajectory and rotation angles as desired.

Event-Triggered Sliding-Mode Control for Polynomial Fuzzy Singular Systems

This article focuses on the problem of the observer-based sliding-mode control (SMC) for polynomial fuzzy singular systems via a novel dynamic event-triggered (DET) mechanism. First, the DET mechanism is introduced to reduce the transmission burden in the communication network. Second, the DET-based observer is constructed to estimate the unavailable state variables. On this basis, the integral sliding variable is provided, and the observer dynamics can be obtained. A sufficient condition is then proposed to make sure that the whole closed-loop system composed of the observer dynamics and the estimation error system is admissible and passive by utilizing the sum-of-squares approach. Meanwhile, the sliding surface parameter matrix, the observer gain, and the trigger weighting matrix are co-designed. It should be emphasized that the common equality constraints, nonstrict and nonlinear inequality constraints are removed through equivalent sets and several inequality techniques in this design process. Moreover, the DET observer-based SMC law is derived to assure the reachability of the specified sliding surface. Finally, the theoretical results are verified by simulation results.

An extended state observer-based sliding mode control method for hydraulic servo system of marine stabilized platforms

The marine stabilized platform is a critical apparatus to ensure the stability of offshore equipment and operations with respect to the inertial coordinate system. However, the hydraulic actuating system of the platform is challenging to control due to the severe offshore environment and hydraulic parameter perturbations. Therefore, to improve the stability and anti-disturbance performance of the hydraulic actuators on the marine stabilized platform, an extended state observer-based sliding mode control (ESO-SMC) method is proposed in the paper. We first analyze the kinematic model of the platform and the dynamic model of the hydraulic servo system. Then, ESO-SMC is designed, and its stability is verified. The novel Marine Predator Algorithm (MPA) is used to optimize the parameters in ESO-SMC design. Simulation is performed in MATLAB/Simulink using an engineering ship model and a stabilized platform model on the ship. Compared with the traditional Sliding Mode Control (SMC), Velocity Feedforward PID (VFPID), and PID methods, ESO-SMC performs best in resisting external wave load disturbances and flow gain parameter perturbations. In conclusion, ESO-SMC is a reliable control approach for enhancing the anti-interference performance of the hydraulic servo system on marine stabilized platforms in the simulation.

Observer-based Finite-time Event-triggered Asynchronous Sliding Mode Control for Interval Type-II Fuzzy Semi-Markov Jump Systems with Quantization and Fading Channels

In this paper, we investigate the finite-time event-triggered sliding mode control(SMC) issue of a class of interval type-II fuzzy semi-Markov jump systems affected by quantization and fading channels. Firstly, the data needs to be quantized by logarithmic quantizers before being transmitted over the channel. To alleviate network pressure, a periodic event-triggered scheme is introduced to govern whether the data are sent to the sensor-tocontroller(S/C) channel or not. As the transmitted data passes through the S/C channel, it could undergo fading. Then, considering the asynchronous issue between the system mode and the controller mode, an asynchronous control scheme is applied; Thereafter, a feasible fuzzy observer-based SMC law is developed, which enables the state trajectories of the system to reach the specified sliding surface within finite-time; And with the aid of the time partition strategy, sufficient conditions for the system to be bounded in finite-time during the arrival and sliding stages are derived. Besides, by means of the linear matrix inequality(LMI) toolbox, the controller and the observer gains are computed. Finally, the advantages of the SMC strategy are validated by emulation products.

ESO-based adaptive event-triggered load following control design for a pressurized water reactor with samarium–promethium dynamics

Conventional control systems used in nuclear reactors rely on real-time information transmission between the controllers and the actuators, which is unnecessary and imposes a heavy communication burden. To this end, this paper proposes an extended state observer-based adaptive event-triggered control (ESO-AETC) scheme for the load following problem of a pressurized water reactor (PWR) in the presence of uncertainties and limited communication resources. Different from most of the previous controllers presented in the literature, the samarium–promethium dynamics are considered in the constructed PWR model in this paper. Based on the PWR model with the load-dependent parameters and the samarium–promethium dynamics, an ESO, which can estimate lumped uncertainties and unmeasured system states including the relative density of the delayed neutron precursor, the average fuel temperature, the xenon concentration, the iodine concentration, the samarium concentration, the promethium concentration, and the total reactivity, is designed. With the help of the ESO and the event-triggered techniques, an AETC scheme is developed to avoid the real-time communication in the controller-to-actuator channel of the PWR system. It is rigorously proved that the control error can converge to any prescribed residual set in a finite time according to Lyapunov stability theory, excluding the Zeno behavior. Finally, simulation studies involving comparisons with existing works, estimation performance verification, and sensitivity analysis are conducted to assess the proposed ESO-AETC scheme. Simulation results reveal that (1) relative to the pre-existing model-free controller (MFC) and the disturbance observer-based sliding mode controller (DO-SMC), the proposed ESO-AETC scheme is found to provide better load following performance with at least 56.12% lower maximum absolute error (MAE), at least 15.05% lower integral absolute error (IAE), and 87.58% reduced communication resources in the controller-to-actuator channel, (2) the ESO possesses strong estimation capability for system states and lumped uncertainties, and (3) the proposed ESO-AETC scheme yields a low sensitivity with respect to the change of the controller parameters.

Fast finite-time observer-based sliding mode controller design for a class of uncertain nonlinear systems with input saturation

In this paper, a novel fast finite-time velocity observer-based terminal sliding mode controller is proposed for a class of multi-input multi-output nonlinear systems in the presence of unknown time-varying matched uncertainties and input saturation constraint. The considered nonlinear system is a chain of interdependent second-order nonlinear subsystems that can describe a multitude of real practical applications. The notion of an auxiliary system is introduced and utilized to deal with the input saturation. Due to the hardship of measuring and accessibility to all the system states, a robust output feedback sliding mode controller is designed based on nonsingular fast terminal sliding surfaces exploiting the estimated states and the auxiliary system’s states which is capable of alleviating the control signal gains and enhancing the convergence rate. By noticing that the separation principle does not hold in nonlinear systems, analyzing the finite-time stability of the closed-loop system is a challenging problem and will be assured via an innovative Lyapunov function candidate. Moreover, an explicit adjustable finite convergence time is derived. Simulation results on two practical systems consisting of a two-degree-of-freedom rigid robotic manipulator and Van der Pol oscillator illustrate the effectiveness and superiority of the suggested control scheme.