Improved sliding-mode control for a class of disturbed systems based on a disturbance observer

Objective: This study proposes the application of optimized Sliding Mode Control (SMC) with Nonlinear Disturbance Observer (NDO) for the Inverted pendulum, which is subjected to mismatched disturbances. Methods/Statistical Analysis: Sliding Mode Control (SMC) with Nonlinear Disturbance Observer (NDO) solves the main problem of chattering present in traditional sliding mode controllers while retaining the nominal performance even with mismatched disturbances. Chattering defines the presence of finite frequency and finite amplitude oscillations in the control input. Genetic Algorithm is used for searching the optimal controller parameters, which includes switching function coefficient, switching gain and observer gain. Findings: Simulation results shows the advantages of NDO based SMC and proves that NDOSMC can observe the mismatched disturbances very effectively. The conventional SMC method is also used in the control design the Inverted pendulum for comparison studies. The two main issues to be tackled in conventional Sliding Mode Control (SMC) are convergence time and chattering. Chattering and convergence time can be reduced in SMC by getting the optimal values of controller parameters using intelligent optimization techniques such as Genetic Algorithm (GA). In the present study convergence time and chattering of the controlled system are considered as the performance index of objective function. Application/Improvements: This study can further be extended for Multi-Input Multi-Output (MIMO) systems subjected to mismatched disturbances and parametric uncertainties.

This article seeks to achieve high tracking performance of the hybrid automobile electro-coating conveying mechanism with disturbances and uncertainties. An integral sliding mode control scheme is first presented to eliminate the reaching phase in sliding mode control. Then, an adaptive integral sliding mode controller is designed without knowing the disturbance information. Finally, a composite strategy, referred to as nonlinear disturbance observer (NDO)-based adaptive integral sliding model control, is put forward to further reduce the switching gain. By compensating the lumped disturbances via a NDO, the switching gain is only required to be higher than upper bound of the disturbance estimation error which is much smaller than actual disturbance. The results of both numerical simulations and experiments show that the proposed approach has good control performance especially in reducing the switching gain and alleviating the chattering problem.

An intelligence sliding mode controller for rotary steering drilling stabilized platform based on nonlinear disturbance observer is presented. Nonlinear disturbance observer which can converge exponentially with suitable design parameters is used to obs erve the uncertain disturbance of stabilized platform under work condition. Sliding mode controller is designed to guarantee the robustness of the closed-loop system. The adaptive rate of switching gain is designed and sign function is replaced by bipolar sigmoid function to weaken chattering. Finally, genetic algorithm is applied to search the optimal controller parameters, including switching function coefficient, switching gain adaptive coefficient, sigmoid function coefficient and observer coefficient. Simulation results show that nonlinear disturbance observer can observe the uncertain disturbance effectively, controller output is decreased and stabilized platform can get optimal control performance and robustness.

A guidance and control scheme utilizing nonlinear disturbance observer (NDO) technique for flexible hypersonic vehicle (FHV) is designed in this article. The motion model of FHV in glide phase in denoted. The elastic states of FHV are regarded as uncertainties and the relevant items in the dynamical model of FHV are compensated by NDO technique. In the guidance sub-system, the command of angle of attack is generated based on sliding mode control (SMC) method. The low pass filter (LPF) theory and parametric command method (PCM) are introduced to calculate the change rate of command of pitch angle and the commands of fin deflections are obtained based on SMC approach in the attitude control sub-system. The effectiveness and robustness of the designed scheme are validated based on simulation experiments.KeywordsFlexible hypersonic vehicleGuidance and controlSliding mode controlNonlinear disturbance observer

In order to improve the anti-disturbance performance of permanent magnet synchronous motor (PMSM) servo system, a sliding-mode control strategy using a new reaching law (NRL) is proposed. The NRL incorporates power term and switching gain term of the system state variables into the conventional exponential reaching law (CERL), which can effectively suppress the sliding-mode chattering and increase the convergence rate of system state reaching sliding-mode surface. Based on this new reaching law, a sliding-mode speed controller (SMSC) of PMSM is designed. At the same time, to solve the chattering problem caused by the large sliding-mode switching gain, an anti-disturbance sliding-mode speed controller method with an extended sliding-mode disturbance observer (ESMDO), called SMSC+ESMDO method, is developed. The sliding-mode disturbance observer is designed to accurately estimate the motor speed and external load disturbances, and the disturbance estimator is used as a feed-forward to compensate the sliding-mode speed controller (SMSC) to improve the system robustness and reduce the system chattering. Simulation and experimental results show that the proposed compound sliding-mode control strategy can effectively improve the dynamic performance and robustness of the system compared with the PI controller.

This paper presents a novel adaptive sliding mode control based on nonlinear sliding surface with disturbance observer (ANSMC-DOB) for precision trajectory tracking control of a surface mount technology (SMT) assembly machine. A two-degree-of-freedom model with time-varying parameter uncertainties and disturbances is built to describe the first axial mode of the pick-place actuation axis of the machine. According to the principle of variable damping ratio coefficient which makes the system have a nonovershoot transient response and a short settling time in the second-order system, the nonlinear sliding surface is designed for the sliding mode control (SMC). Since the upper bound value of the disturbances is unknown, the adaptive gain estimation is applied to replace the switching gain in the SMC. In order to settle the problem of SMC unrobust to the mismatched parameter uncertainties and disturbances, the nonlinear disturbance observer is introduced to estimate the mismatched disturbances and form the novel controller of ANSMC-DOB. The stability of sliding surfaces and control laws are verified by the Lyapunov functions. The simulation research and comparative experiments are conducted to verify the improvement of positioning accuracy and robustness by the proposed ANSMC-DOB in the SMT assembly machine.

In this paper a novel concept of event triggering control (ETC) for effective resource utilization is proposed for dc microgrid. Matched uncertainty elimination is possible through sliding mode control (SMC) itself as addressed in the literatures. This paper proposes a new approach for suppression of both matched and unmatched uncertainties in grid connected and islanded mode through an integral disturbance observer (IDO) which is designed with super twisting SMC to provide dual filtering phenomena pertaining to system perturbations. The IDO facilitates control algorithm to manage effective event counts during disturbance conditions. The proposed controller is designed in order to regulate DC bus voltage and enhance the microgrid capability to perform stable operation in presence of uncertainties. Chattering free finite time convergent SMC is designed with super twisting reaching law to obtain robust behavior of dc microgrid. Results are compared with power rate reaching SMC, Nonlinear disturbance observer (NDO) based controller and PI controller. In the proposed work event triggering condition is designed first time under super twisting reaching law. Comparative assessment is accomplished in lieu of demonstrating the superior performance of event trigger SMC through MATLAB/Simulink and Typhoon based controller hardware in loop (CHIL) platform.

Based on a nonlinear disturbance observer, a backstepping sliding mode robust control is proposed for a wire-driven parallel robot (WDPR) system used in the wind tunnel test to dominate the motion of the end effector. The control method combines both the merits of backstepping control and sliding mode robust control. The WDPR is subject to different types of disturbances, and these disturbances will affect the motion precision of the end effector. To overcome these problems, a nonlinear disturbance observer (NDO) is designed to reject such disturbances. In this study, the design method of the nonlinear disturbance observer does not require the reliable dynamic model of the WDPR. Moreover, the design method can be used not only in the WDPR but also in other parallel robots. Then, a backstepping design method is adopted and a sliding mode term is introduced to construct a desired controller, and the disturbances are compensated in the controller to reduce the switching gain and guarantee the robustness. For the sake of verifying the stabilization of the closed-loop system, the Lyapunov function is constructed to analyze the stabilization of the system. Finally, the feasibility and validity of the proposed control scheme are proved through both simulation and experimental results.

The control of unmanned aerial vehicles (UAVs) has been an active area of research over the past decade, particularly for operations in complex environments. This paper addresses the finite-time fault-tolerant control problem for UAV subjected to simultaneous actuator faults and wind disturbances. A novel adaptive finite-time disturbance observer-based fault-tolerant control (AFTDO-FTC) scheme is proposed. This scheme integrates a finite-time sliding surface, a nonlinear disturbance observer, and an adaptive controller to achieve accurate tracking of position and attitude. First, a nonlinear disturbance observer is designed to estimate the lumped uncertainty arising from combined faults and wind disturbances. Then, a finite-time sliding surface, formulated using weighted error vectors, is introduced to effectively mitigate the adverse effects of estimation errors from the disturbance observer. Furthermore, adaptive finite-time position and attitude controllers are developed based on the estimates provided by the adaptive disturbance observer. Finally, the effectiveness of the proposed method is verified through comparative simulations and Lyapunov stability analysis.

This paper deals with the tracking control problem of quadrotor unmanned aerial vehicles (QUAVs) with external disturbances. First, because the QUAV model contains two non-integrity constraints, the dynamic model of the QUAV is decomposed into two subsystems which are independently controlled, so as to reduce controller design complexity. Secondly, the nonlinear disturbance observer (DOB) technique is integrated into a backstepping control method to design the controller for the first subsystem, in which a DOB is applied to estimate the lumped uncertainty. Based on the double power reaching law and the DOB, a multivariable sliding mode control (MSMC) scheme is developed for the second subsystem. Thirdly, based on Lyapunov theory, the closed-loop system is proved to be asymptotically stable. Finally, our comparative simulation results demonstrate that the presented control scheme behaves better in terms of tracking performance than the adaptive backstepping control (ABC) approach.

A model-free fractional-order sliding mode control (MFFOSMC) method based on a non-linear disturbance observer is proposed for the electric drive system in this paper. Firstly, the ultra-local model is established by using the mathematical model of electric drive system under parameter perturbation. Then, aiming at reducing the chattering of the sliding mode controller and improving the transient response, a model-free fractional-order sliding mode controller is designed based on fractional-order theory. Next, considering that the traditional sliding mode control can only suppress matched disturbance and that it is sensitive to mismatched disturbance, a non-linear disturbance observer is used to estimate disturbance, and the estimated variables are used in the design of a sliding mode surface to improve the tracking accuracy of the system. Finally, the experiment is completed on an asynchronous motor drive platform. Compared with the model-free integer-order sliding mode control (MFIOSMC), the results show that the proposed method has good dynamic response and strong robustness. Meanwhile, the proposed method reduces the dependence on mathematical models.

ABSTRACTTo enhance the power quality of microgrid inverters and reduce the influence of changes in inductance parameters and external disturbances on the direct power control of the inverter system, a terminal sliding mode control strategy with a variable exponential power reaching law has been proposed. The designed new reaching law comprises a variable exponential term and an enhanced power term. The variable exponential term contains an arctangent function, and the power term coefficient is replaced by a function about the sliding mode. Therefore, the convergence rate can be adaptively adjusted based on different stages of the system, ensuring a faster rate of convergence throughout the process of approaching the sliding mode surface. To weaken the effects of changes in inductance parameters, a power disturbance observer is designed to estimate the internal disturbances induced by the filtered inductance in the system. Subsequently, a sliding mode control law containing disturbance observations is derived. Moreover, a variable exponential terminal sliding surface is designed to adjust the convergence rate of system errors on the sliding surface in stages, thereby enhancing the control performance of the system. The simulation results show that the new reaching law has faster convergence rate and better dynamic performance. The convergence speed of the system error can be accelerated by the designed variable exponential terminal sliding surface. The sliding mode control strategy with the variable exponential power reaching law is applicable to the power control system of three‐phase inverters in microgrids, thereby significantly enhancing the dynamic performance and robustness of the system.

The following topics are dealt with: renewable energy sources; energy conservation; computer aided engineering; thermal power stations; solar power stations; solar absorber-convertors; distributed power generation; photovoltaic power systems; domestic appliances; humidity.

A nonlinear integral sliding-mode control (NISMC) scheme is proposed for second order nonlinear systems. The new control scheme is characterized by a nonlinear integral sliding manifold which inherits the desired properties of the integral sliding manifold, such as robustness to system external disturbance. In particular, compared with four kinds of sliding mode control (SMC), the proposed control scheme is able to provide better transient performances. Furthermore, the proposed scheme ensures the zero steady-state error in the presence of a constant disturbance or an asymptotically constant disturbance is proved by Lyapunov stability theory and LaSalle invariance principle. Finally, both the theoretical analysis and simulation examples demonstrate the validity of the proposed scheme.

For the mismatched uncertain system, a novel spiking-free disturbance observer (DO)-based sliding-mode control (SMC) scheme is developed. First, a DO is proposed to estimate the mismatched uncertainty. A new sliding-mode surface is developed by using the system states, the estimation of mismatched uncertainty, and a spike suppression term. Then, an SMC method is proposed by using the developed sliding-mode surface. Compared with existing SMC schemes, the proposed spiking-free DO-based SMC has two advantages: (1) the mismatched uncertainty can be effectively suppressed; (2) the harmful spike problem of extended disturbance observer (EDO)-based and extended state observer (ESO)-based SMC schemes when the observer gain is high can be avoided. Finally, the simulation is presented to show the effectiveness of the proposed scheme by comparing the proposed and existing SMC schemes.