Second-order Disturbance Observer Research Articles

A novel second-order predictive disturbance observer for systems with input and output delays

This paper proposes a novel second-order predictive disturbance observer for systems experiencing external disturbance with both input and output measurement delays. The proposed observer uses the delayed system state and its derivative information to predict and compensate for future disturbance in real time, despite the delayed control input. Compared with the past studies about second-order disturbance observer, this paper analyses the impact of the disturbance derivatives on the estimation accuracy. This observer is designed using the Lyapunov–Razumikhin theorem and its exponential stability is proven. Comparative analysis and simulations demonstrate its advantages over second-order disturbance observers that do not consider delays.

Steering control of electric tracked vehicle based on second-order disturbance observer and multiobjective optimization

Autonomous and remote-controlled tracked vehicles are freeing humans from exhausting off-road maneuvers. Advanced motion control is a necessity to achieve high mobility and enhanced safety with less dependence on operator skill. Tracked vehicles may slide laterally or roll over under large centrifugal forces. Precise yaw motion and sideslip prevention are required for steering controller development. A switching control architecture is proposed for the underactuated tracked vehicle in this study. Two control laws for yaw rate tracking and anti-sideslip are proposed respectively based on second-order disturbance observers (DO-2s) with a given bandwidth. The controller is optimized for the two objectives using Nash bargaining method. The proposed steering controller is verified on a small electric track vehicle. Under large disturbance, the optimized DO-2-based controller prevents potential sideslip and reduces the yaw rate tracking error by 42.6% compared with LADRC. The chattering induced by switching is moderate because the estimated disturbances are smoothly switched.

Consensus control for multi-agent systems with input constraints based on disturbance observer

In this paper, a second-order-disturbance-observer-based distributed consensus control scheme is designed for a class of nonlinear multi-agent systems with input constraints. The second-order disturbance observer tracks the disturbance better than the common first-order disturbance observer. This paper provides the analysis of two kinds of disturbance observers and then compares the results from a simulation of the two types of observers. In the controller design process, a hyperbolic tangent function is used to limit output feedback in the control law. The overall closed-loop system reaches global stability with disturbance and the tracking errors exponentially converge without disturbance. The effectiveness of the proposed control law is illustrated by simulation results.

Disturbance Observer-Based Safe Tracking Control for Unmanned Helicopters with Partial State Constraints and Disturbances

In this paper, a disturbance observer-based safe tracking control scheme is proposed for a medium-scale unmanned helicopter with rotor flapping dynamics in the presence of partial state constraints and unknown external disturbances. A safety protection algorithm is proposed to keep the constrained states within the given safe-set. A second-order disturbance observer technique is utilized to estimate the external disturbances. It is shown that the desired tracking performance of the controlled unmanned helicopter can be achieved with the application of the backstepping approach, dynamic surface control technique, and Lyapunov method. Finally, the availability of the proposed control scheme has been shown by simulation results.

Observer-based attitude control of spacecraft under actuator dead zone and misalignment faults

The paper discusses the effect of non-smooth dead-zone (NDZ), and input actuator misalignment (AMA) during spacecraft attitude tracking maneuver in presence of parametric uncertainties and external perturbations. Initially, the input AMA and NDZ models are formulated to transform spacecraft attitude model dynamics. Subsequently, a new second order disturbance observer (SODO) is devised to get the total disturbance. The observer is developed considering system perturbations as extended states, with an additional term Introduced to improve the observer performance. Finally, a distinctive integral sliding mode control (ISMC) law is developed and integrated with the proposed SODO to perform spacecraft attitude control operations. Comparative simulations are conducted on the spacecraft attitude control model with input AMA, NDZ, system parametric uncertainties and external disturbances to show the effectiveness of the proposed control structure.

Model-Free Observer for Speed and Acceleration Estimations for Speed Servo System Applications

This brief presents a speed and acceleration estimation mechanism combining a Luenberger-type observer and a nonlinear second-order disturbance observer (DOB) using servo system angle measurements without system parameters and load information. The resultant observer has the following two contributions: (a) the inclusion of a system parameter information-free nonlinear DOB as a subsystem to ensure improved robustness and (b) the capability of performance assignment by tuning the scalar design factor without involving any matrix calculation processes. An experimental study validates the practical advantage of the proposed solution using a prototype 500 W dynamo system as a speed servo system.

A New Sliding Mode Control Algorithm of IGC System for Intercepting Great Maneuvering Target Based on EDO.

To intercept the great maneuvering target, combining with the sliding mode and the extended disturbance observer, a new control algorithm for integrated guidance and control (IGC) system is proposed in this paper. Firstly, the paper formulates the Missile–Target problem. Then the paper establishes an uncertain IGC dynamic model where the nonlinearities, the perturbations and the maneuvering of the target are regarded as disturbance. Secondly, a second-order disturbance observer is designed to estimate the disturbance and their derivatives.. After this, combining with the second-order disturbance observer, a modified sliding surface and the corresponding reaching law are designed to obtain the rudder deflection command directly. Thus, the real sense of IGC system is achieved. Next, the paper uses the Lyapunov stability theory to prove the stability of the system. Finally, the paper provides different simulation cases, which have different maneuver modes of the target, to demonstrate the superiority of the proposed method in reducing the response time, increasing the rudder response, and having a high interception probability.

Memory Augmented Neural Network-Based Intelligent Adaptive Fault Tolerant Control for a Class of Launch Vehicles Using Second-Order Disturbance Observer

This paper focuses on the MANN-based intelligent adaptive fault tolerant control for a class of launch vehicles. Firstly, the attitude dynamic model of the launch vehicles suffering from the actuator faults and disturbances has been formulated. Secondly, the second-order disturbance observer has been designed for the launch vehicle to achieve the exact estimation and compensation of the time-varying disturbances. Meanwhile, the MANN has been introduced as online approximator, suppressing the adverse influence of the unknown nonlinearities. Moreover, several adaptive laws have been proposed to achieve the quick response to the actuator faults and the update of the MANN weights. As a result, the MANN-based intelligent adaptive fault tolerant control structure has been constructed for the launch vehicles. It has been proven that all the signals in the closed-loop system are bounded. Simulation results demonstrate the desired performance and the advantages of the proposed control algorithm.

A New Frequency Adaptive Second-Order Disturbance Observer for Sensorless Vector Control of Interior Permanent Magnet Synchronous Motor

In this article, a new frequency adaptive second-order disturbance observer (FASODO) for back electromotive force (EMF) and active flux estimation is proposed using the active flux model of interior permanent magnet synchronous motors. FASODO is a frequency adaptive approach and eliminates the phase delay compensator demand of the traditional sliding mode observer-based back EMF estimator. Besides, FASODO estimates the active flux and the back EMF simultaneously. As a result, a quadrature phase-locked loop (Q-PLL) using either the back EMF or the active flux and a tan inverse approach can be used for speed-position identification. Meanwhile, an integrally compensated Q-PLL is designed to overcome the traditional Q-PLL position estimation error during ramp frequency tracking. The design guideline of FASODO and the integrally compensated Q-PLL are provided. A comparative analysis with traditional SMO shows that the proposed approach can deliver a better sensorless control performance. Furthermore, a comparison with a frequency adaptive complex coefficient filter enhanced SMO shows a comparable result, while the proposed approach additionally delivers the active flux. The approach is verified using the Texas Digital Signal Processor (TMS320F28335) and RT-LAB Real-Time Simulator, taking into account different operating conditions.

A new sliding mode control design for integrated missile guidance and control system

A new sliding mode control algorithm for integrated guidance and control (IGC) system is proposed in this paper. Firstly, the IGC model is established and the nonlinearities, target maneuvers, perturbations caused by variations of aerodynamic parameters, etc. are viewed as disturbance, so that the IGC system becomes a mismatched uncertain linear system. Secondly, a second-order disturbance observer is used to estimate the disturbances and their derivatives. Thirdly, an integral sliding mode surface is designed to obtain the rudder deflection command directly instead of the back-stepping control (BC) algorithm used in conventional IGC system, which achieves the real sense of IGC, and the stability of the system is proven strictly by Lyapunov stability theory. Finally, the superiority of the proposed IGC method is verified by comparing the simulation results of different methods under different cases.

Disturbance observer based fault-tolerant control for cooperative spacecraft rendezvous and docking with input saturation

A robust nonlinear control strategy is presented for a cooperative spacecraft rendezvous and docking maneuver, where the pursuer spacecraft is subject to input saturation and actuator faults. The nonlinear coupled models for relative attitude and relative position dynamics are expressed in the pursuer body-fixed frame. A novel control strategy based on feedback linearization framework is developed, and a second-order disturbance observer is employed to estimate and compensate all uncertainties including parametric uncertainties, external disturbances, input saturation and actuator faults. It is proved that the closed-loop systems are uniformly ultimately bounded by using Lyapunov theory. Numerical simulations are given to illustrate effectiveness of the proposed control strategy.

Disturbance observer based position tracking of electro-hydraulic actuator

A nonlinear controller based on an extended second-order disturbance observer is presented to track desired position for an electro-hydraulic single-rod actuator in the presence of both external disturbances and parameter uncertainties. The proposed extended second-order disturbance observer deals with not only the external perturbations, but also parameter uncertainties which are commonly regarded as lumped disturbances in previous researches. Besides, the outer position tracking loop is designed with cylinder load pressure as output; and the inner pressure control loop provides the hydraulic actuator the characteristic of a force generator. The stability of the closed-loop system is provided based on Lyapunov theory. The performance of the controller is verified through simulations and experiments. The results demonstrate that the proposed nonlinear position tracking controller, together with the extended second-order disturbance observer, gives an excellent tracking performance in the presence of parameter uncertainties and external disturbance.

Disturbance observer based finite-time attitude control for rigid spacecraft under input saturation

A novel finite-time controller integrated with disturbance observer is investigated for a rigid spacecraft in the presence of disturbance, actuator saturation and misalignment. As a stepping-stone, a second-order disturbance observer is designed firstly such that the reconstruction of lumped disturbances is accomplished in finite time with zero error. Then, with the reconstructed information, a finite-time controller is synthesized even under actuator input saturation and misalignment, and the closed-loop system/state is proved to be finite-time stable and converges to the specified time-varying sliding mode surface. Moreover, the input saturation constraint is overcome via introducing an auxiliary variable to compensate for the overshooting. Numerical simulation results for the in-orbit rigid spacecraft show good performances, which validate the effectiveness and feasibility of the proposed schemes.

AN ASYMPTOTIC SECOND‐ORDER SMOOTH SLIDING MODE CONTROL

ABSTRACTPresented is a method of smooth sliding mode control design to provide for an asymptotic second‐order sliding mode on the selected sliding surface. The control law is a nonlinear dynamic feedback that in absence of unknown disturbances provides for an asymptotic second‐order sliding mode. Application of the second‐order disturbance observer in a combination with the proposed continuous control law practically gives the second‐order sliding accuracy in presence of unknown disturbances and discrete‐time control update. The piecewise constant control feedback is “smooth” in the sense that its derivative numerically taken at sampling rate does not contain high frequency components. A numerical example is presented.

A MULTIPLE-LOOP SLIDING MODE CONTROL SYSTEM WITH SECOND-ORDER BOUNDARY LAYER DYNAMICS

Presented is a method of continuous sliding mode control design to provide for the second-order sliding mode on the selected sliding surfaces in a three-loop control system, where two outer-loop virtual control signals must be smooth enough to be tracked in the inner loops. The control law in the vicinity of the sliding surface is a nonlinear dynamic feedback that in absence of unknown disturbances provides for finite-time convergence of the second-order reaching phase dynamics. The controller with a second-order disturbance observer in a combination with the proposed continuous dynamic feedback attracts the system trajectories to boundary layers around two sliding surfaces of the outer control loops with the second-order sliding accuracy in presence of unknown disturbances and the discrete-time control update.