Enhanced extended state observer-based control for systems with mismatched uncertainties and disturbances

Composite fault-tolerant and anti-disturbance control for switched fuzzy stochastic systems

This paper investigates the issue of fault-tolerant and anti-disturbance attenuation for a two-dimensional modified repetitive control system (2D MRCS) which is described by switched fuzzy systems with multiple disturbances. In particular, the multiple disturbances contain an exogenous disturbance and standard Wiener noise. Specifically, a generalized extended state observer (GESO) is incorporated with the 2D MRCS to estimate both fault and exogenous multiple disturbances so that the disturbances and faults can be attenuated in the control input. Further, the improved 2D MRCS relaxes the stability condition and provides an enhanced tracking performance. Based on the Lyapunov function approach, pole placement technique and average dwell time approach, the stability criteria for the considered system is developed in terms of linear matrix inequality (LMI). Then an algorithm for designing a GESO-based 2D MRC design is developed based on the obtained LMIs. Further, the results developed are validated in the simulation section through three numerical examples.

Sliding Mode Controller with Generalized Extended State Observer for Single Link Flexible Manipulator

This paper presents an enhanced generalized extended state observer (EGESO) based sliding mode control (SMC) technique for dealing with the disturbance attenuation problem for a class of non-integral chain systems with mismatched uncertainty. In the proposed control law, the robust SMC with reaching phase elimination is applied in the proposed control law, which uses the estimated states of a system. The stability analysis is thoroughly examined for both EGESO and SMC. The efficacy of the proposed controller is verified using specific examples, and later it is applied on a single-link flexible manipulator. Through simulation and experimentation analysis, it is observed that the proposed controller is giving a robust transient response as compared to existing GESO based controllers.

Predictive ESO-based control with guaranteed stability for uncertain MIMO constrained systems

In this paper, a novel predictive Extended State Observer (ESO)-based discrete controller with guaranteed input-to-state stability is developed. Predictive controllers based on ESOs are gaining acceptance for regulating MIMO systems with disturbances, uncertainties or actuator constrains. However, there is an important concern about this control structure regarding its closed-loop stability; a key property that is not strictly guaranteed with the most part of the previous formulations. This paper shows that -under the same assumptions that are normally taken in the ESO literature- a predictive ESO-based controller that is proved to be input-to-state stable can be easily constructed by adding two fixed terms in the cost-index definition. A simulation case study of the glucose control in patients with type-1 diabetes is additionally given in order to illustrate the main advantages of this control structure.

Improved generalized proportional integral observer based control for systems with multi-uncertainties

It is difficult to control systems with multi-uncertainties directly based on traditional active disturbance rejection control (ADRC) framework, due to the mismatched condition, non integral-chain form. Besides, the traditional Hurwitz bounded stability of the extended state observer (ESO) may not guarantee acceptable observation accuracy. To this end, this paper presents an improved generalized proportional integral observer (IGPIO) to estimate the multi-uncertainties and the derivatives, and an IGPIO based control (IGPIOBC) strategy is proposed to eliminate the multi-uncertainties actively and accurately. The proof of bounded stability for the IGPIO and the closed loop system are derived by the singular perturbation approach and Lyapunov theory. Meanwhile, the corresponding relationship between the gain parameters and the bandwidth of the IGPIO is deduced. The simulations of the numerical example, RLC circuit and DC motor system verify the effectiveness of the proposed method.

Hybrid extended state observer based control for systems with matched and mismatched disturbances

The conventional Extended State Observer-Based Control (ESOBC) technique is mostly applicable to a class of Integral Chain Form (ICF) structure with the matched kind of single-channel lumped disturbances. However, the systems having the non-ICF structure with the multi-channel matched and mismatched lumped disturbances are widely prevailing in the control applications, where the conventional ESOBC scheme may no longer applicable. To this end, it is recommended to upgrade the conventional ESOBC scheme for enhancing the feasibility and the applicability. This research work addresses the above-discussed recommendations using hybridizing the ESOBC with the Generalized ESOBC (GESOBC) which termed as Hybrid Extended State Observer Based Control (HyESOBC) in this paper. The proposed scheme is capable of estimating and controlling the multi-channel lumped disturbances (i.e., matched and mismatched) for a wide range of practical applications including the systems with the non-ICF structure. Simulation results and comparative analysis of numerical and practical application examples with the dual-channel lumped disturbances are presented to confirm the feasibility and the applicability of the proposed scheme.

Suppressions of vibration in the Tip-Tilt mirror control system by add-on controller

Tip-Tilt mirrors play an important role in astronomical telescopes requiring the tracking performance at the level of microradian or sub-microradian. However, the closed-loop performance suffers a lot from the low-sample rate and time delay of image sensors. Especially, this issue is under the condition of vibrations, because dynamic behaviors are complex and the models are difficult to be obtained accurately. Another challenging issue comes from the measurement of vibrations and its extraction for the closed-loop control. This paper proposes a new method based on an add-on controller of the Tip-Tilt mirror to mitigate telescope vibrations. The proposed method only uses Tip-Tilt errors from an image sensor to implement a disturbance observer, which is not being restricted by an accurate model. As a result, the closed-loop performance can be optimized by designing of a proper Q-filter. To suppress the low-frequency and high-frequency vibrations, a novel Q-filter combining a lowpass filter and a bandpass filter is proposed here. The improved control method is validated by both simulation and experiment in the tip-tilt mirror control system under the condition of vibrations.

Reset observers alleviating the peaking and the robustness tradeoffs: A case study on force estimation in teleoperation

The peaking phenomenon is an undesirable effect appearing in observers and destroying controller performance. Several solutions have been proposed to mitigate peaking in state estimation. The literature shows that reset or impulsive observers are superior to linear (Luenberger) observers. However, the comparisons are based on particular choices of linear observers. This paper investigates this issue. First, comparative frameworks are proposed based on two traded-off performance indices: ensemble maximum-peak versus ensemble settling time for nominal conditions, and ensemble settling time versus size of the error asymptotic invariant set for quadratically bounded uncertain plants. Next, performance limitations of linear observers are represented by Pareto-optimal boundaries. In this way, not previously considered in the literature as far as known, the superiority of the chosen reset observer is more rigorously assessed. The framework is finally applied to force estimation in haptic teleoperation.

Adaptive Sliding Mode Trajectory Tracking Control for WMR Considering Skidding and Slipping via Extended State Observer

When the wheeled mobile robot (WMR) is required to perform specific tasks in complex environment, i.e., on the forestry, wet, icy ground or on the sharp corner, wheel skidding and slipping inevitably occur during trajectory tracking. To improve the trajectory tracking performance of WMR under unknown skidding and slipping condition, an adaptive sliding mode controller (ASMC) design approach based on the extended state observer (ESO) is presented. The skidding and slipping is regarded as external disturbance. In this paper, the ESO is introduced to estimate the lumped disturbance containing the unknown skidding and slipping, parameter variation, parameter uncertainties, etc. By designing a sliding surface based on the disturbance estimation, an adaptive sliding mode tracking control strategy is developed to attenuate the lumped disturbance. Simulation results show that higher precision tracking and better disturbance rejection of ESO-ASMC is realized for linear and circular trajectory than the ASMC scheme. Besides, experimental results indicate the ESO-ASMC scheme is feasible and effective. Therefore, ESO-ASMC scheme can enhance the energy efficiency for the differentially driven WMR under unknown skidding and slipping condition.

Finite-time tracking control for uncertain robotic manipulators using backstepping method and novel extended state observer

This article considers finite-time trajectory tracking control problem for robotic manipulators with parameter uncertainties and external disturbances. A finite-time controller that achieves high precision and strong robustness is proposed without the requirement of the exact dynamic model. First, a novel finite-time model-assisted extended state observer is designed to compensate the system uncertainties with complex and uncertain dynamics. Then, a composite finite-time controller is developed for trajectory tracking control with the help of finite-time model-assisted extended state observer. Compared to the classic extended state observer, it is proved that the estimation error of finite-time model-assisted extended state observer can be stabilized in finite time. Meanwhile, the finite-time convergence of the closed-loop system with the proposed controller can also be proved through Lyapunov’s stability theory. A variable structure term is employed to compensate the estimation errors of finite-time model-assisted extended state observer. The validity of the control scheme is demonstrated by simulations and experiments.

Gain-scheduled predictive extended state observer for time-varying delays systems with mismatched disturbances

In this paper, a novel control scheme for systems with input and output time-varying delays is provided in discrete-time domain. The control strategy combines predictor-like techniques with a delay-dependent gain-scheduled extended state observer. The main goal is twofold: (i) to minimize the negative effect of time-varying delays in the closed-loop performance and, (ii) to actively compensate the effect of mismatched disturbances in the controlled output. Moreover, a sufficient condition based on Linear Matrix Inequalities (LMI) is provided to obtain the maximum delay interval that ensures the stability of the closed-loop system. Finally, the achieved benefits of the proposal are shown by simulation in open-loop unstable plants, and experimentally validated in a test-bed quadrotor platform.

Active steering wheel shimmy control for electric vehicle by sampled-data output feedback

In this paper, a new two Degree of Freedom (DOF) shimmy dynamic model of an Electric Vehicle (EV) with independent suspension subject to uncertain disturbances is built via Lagrange's theorem firstly. Secondly, Based on the built model, an active control method is proposed to solve the shimmy problem of the steering system via a sampled-data output feedback controller. The output feedback domination approach is also used to dominate uncertain disturbances by using a scaling gain. With the help of these tools, the sampling period and scaling gain are calculated to guarantee global stability and disturbance attenuation for the closed-loop control system. Finally, simulations and tests are conducted to verify the effectiveness of the sampled-data output feedback controller for the EV's shimmy problem under different conditions.