Nonlinear Integral Sliding Mode Control Research Articles

Research on trajectory tracking control of ocean unmanned aerial vehicles based on disturbance observer and nonlinear sliding mode

This paper aims to solve the problem of real time tracking of unmanned aerial vehicle (UAV) with external disturbances, model uncertainty, and multiple control parameter tuning during wave glider (WG) navigation. Firstly, the dynamic model of UAV and WG is instituted; Secondly, an Expanded State Observer (ADOB) is proposed to estimate the total perturbations in real time, including model uncertainties and external wind perturbations; Moreover, the ADOB is integrated with a nonlinear integral sliding mode control to generate a nonlinear sliding mode controller (ASMC) with a compound disturbance observer for the trajectory tracking control strategy; Finally, the bandwidth parameterization theory is used to tune the parameters of the ASMC controller. Simulation and experimental results show that the UAV trajectory tracking landing control scheme proposed in this paper can effectively solve the real-time tracking problem of the UAV during WG navigation.

Robust Integral Sliding Mode Control for Transient Voltage Support From Bidirectional Converter-Based Active Filters in Microgrids

The DC-AC conversion in microgrids leads to second-order oscillations in the DC side voltages and source currents. These oscillations are mitigated using either active or passive filters. Active filters are preferred, as they mitigate oscillations with lesser component size than passive filters. The active filters are regulated to absorb the harmonic ripples at the ripple frequency, and do not provide any voltage support during DC bus voltage fluctuations due to load changes. In this paper, a Robust Integral Sliding Mode Control (RISMC) is proposed to regulate Bidirectional Converter (BDC) based DC active filters to facilitate voltage conditioning along with reduction of second-order harmonics which are caused due to DC-AC conversions. The proposed RISMC enhances capability of the BDC active filters to provide DC bus voltage conditioning in case of transience during load variations and uncertain voltage fluctuations. The proposed control consists of a nominal dual-loop PI control which regulates the voltage of the storage capacitor of BDC and a non-linear integral sliding mode control which regulates DC bus voltage. The proposed control mitigates voltage and current ripples hence preventing them to propagate towards the sources while providing additional voltage support functionality. The proposed control is verified through simulations and experimentation.

EXPERIMENTAL ANALYSIS OF HYBRID ENERGY STORAGE SYSTEM BASED ON NONLINEAR CONTROL STRATEGY

In this paper, a nonlinear integral sliding mode control for a hybrid energy storage system (HESS) based stand-alone dc microgrid has been proposed and applied experimentally. This hybrid system comprises a PV, super-capacitor, and battery. A classical PI-based linear control strategy has been designed to control battery and super-capacitor systems based on decoupling the high and low-frequency components to estimate reference current. Since the frequent discharge during operation, super-capacitor power can reach the lowest value, affecting controller performance and making the system unstable. From the experimental result, a nonlinear Integral sliding mode control ISMC is performed as an inner loop controller to regulate battery and super-capacitor power. Also, the PI controller is implemented as an outer loop controller to regulate the dc-link. The proposed control approach is compared with the linear PI controller to improve life extension and minimize stress on the battery. As a result, the proposed control strategy has achieved high dynamic system performance.

Adaptive fuzzy nonlinear integral sliding mode control for unmanned underwater vehicles based on ESO

An adaptive fuzzy nonlinear integral sliding mode control strategy based on an extended state observer (ESO) is proposed for trajectory tracking of unmanned underwater vehicles (UUVs) in the presence of unknown external disturbances and model parameter uncertainties. A nonlinear dynamics error model of the UUV is established; the estimation of the lumped disturbances are estimated using ESO, and the control variables are compensated for in real time. A nonlinear integral sliding mode controller with saturation characteristics is designed to improve the transient and steady-state performance of the system, and the switching gain of the sliding mode control is adaptively adjusted using the fuzzy logic system, such that the weight of the output changes with the sliding mode surface; thus, the chattering of the control variables is weakened. The asymptotic stability of the control system is verified using Lyapunov stability theory. The simulation and experimental results demonstrated that the designed control strategy effectively suppresses the system lumped disturbances with high tracking accuracy and robustness.

Nonlinear Integral Sliding Mode Control with Adaptive Extreme Learning Machine and Robust Control Term for Anti-External Disturbance Robotic Manipulator

Nonlinear Integral Sliding Mode Control with Adaptive Extreme Learning Machine and Robust Control Term for Anti-External Disturbance Robotic Manipulator

Chaotic synchronization based on improved global nonlinear integral sliding mode control☆

In order to avoid integral saturation of integral sliding mode surface, a new integral function which can magnify small errors and minify large errors is designed. Meanwhile, an attenuation function which can decay to zero in a finite time is designed to accelerate the convergence speed of global sliding mode surface. Then, an improved global nonlinear integral sliding mode surface (GNISMS) is constructed, and sliding mode control based on the proposed sliding mode surface is designed to accomplish the synchronization control of chaotic systems with external disturbances and internal parameters uncertainties. Simulation results show that the proposed sliding mode control method has good control performance, and it can be effectively applied to the chaotic secure communication system based on chaos synchronization control.

Robust optimal-integral sliding mode control for a pressurized water nuclear reactor in load following mode of operation

A nuclear reactor is a complex, nonlinear, and time-varying system. External disturbances and uncertainty due to neutronic and thermal-hydraulics parameters variation contribute to reactor control challenges and safe operations. Thus, this paper presents a hybrid control system for a nuclear reactor core power control in the presence of a matched disturbance and uncertainties. The hybrid controller combines Linear Quadratic Gaussian/Loop Transfer Recovery (LQG/LTR) optimal control and a nonlinear Integral sliding mode control (ISMC). The nonlinear system of the reactor, which is based on point kinetics equations with three delayed neutron group is linearized to design the LQG/LTR. The Lyapunov theory is used to prove the finite-time convergence of the Integral sliding mode control. Furthermore, a comparative analysis of the hybrid control scheme, LQG/LTR, PID, and an ISMC is conducted with the nonlinear model. Simulation experiments reveal that the closed-loop hybrid control system is stable and achieves the best performance specifications in the presence of external disturbance and uncertainties.

Capture dynamics and control of tethered space net robot for space debris capturing in unideal capture case

Tethered Space Net Robot (TSNR) is proposed as a hopeful solution for space debris capturing. An unideal case of net capture is studied in this paper, in which the net does not contact the target in the center of the net. For this case, the net cannot naturally close to wrap around the target completely after collision due to the asymmetric net configuration. Therefore, an integral adaptive Super-Twisting sliding mode control (IASTSMC) is designed to close the net. The control algorithm consists of a nonlinear integral sliding surface and adaptive Super-Twisting sliding mode control (ASTSMC), which not only has the property of “saturate the large error, magnify the small error”, but also provides a positive chattering alleviation effect. Compared with the nonlinear integral sliding mode control (ISMC) with equivalent control technique and the original Super-Twisting algorithm (STA), the proposed control method shows a better performance to close the net in this unideal case.

PMLSM Nonlinear Integral Sliding Mode Control Based on Gain Time- Varying Reaching Law

Background: The permanent magnet synchronous linear motor is a strongly coupled, nonlinear system. It has been applied in many fields, especially in the field of machining lathes and rail transportation. In order to ensure the permanent magnet synchronous linear motor has good dynamic performance and robustness, sliding mode control is gradually applied to the control system of permanent magnet synchronous linear motor. However, in the traditional sliding mode control, the convergence speed is slow, and the robust performance is poor when the sliding surface is not reached. Objective: The main purpose of this paper is to improve the dynamic performance and robustness of the permanent magnet synchronous linear motor during the process of approaching the sliding surface. Methods: Firstly, the type of nonlinear curve with "small error reduction, large error saturation" is introduced to design a nonlinear integral speed controller with global robustness. Secondly, the gain rate time-varying reaching law is introduced to reduce "chattering". Finally, using a symbolic tangent function instead of a sign function in designing a sliding mode observer reduces fluctuations in load observations. Results: Finally, the correctness and effectiveness of the control method are proved by simulation. Conclusion: The results of the simulation show that the nonlinear integral sliding mode controller based on gain time-varying reaching law is shown to have good global robustness and dynamic performance.

Active fault-tolerant attitude tracking control with adaptive gain for spacecrafts

In this paper, an active fault-tolerant control (AFTC) method with adaptive gain is proposed for spacecrafts which subject to model uncertainty, external disturbance and actuator fault. A novel adaptive-gain finite-time observer is designed to solely estimate fault in the presence of disturbance for fault diagnosis. By incorporating the dual-layer gain adaption scheme into the nonlinear integral sliding mode control (ISMC), a reconfigurable controller is designed to accommodate fault. Due to the reaching phase elimination of ISMC, the gain tracking to the unknown bounded disturbance can be accelerated while it is maintained that the control gain will not be overestimated and the bound knowledge of fault/disturbance is not required. Simulation results verify the effectiveness and improvement of the proposed FTC method.

Robust Control Designs of Payload’s Skew Rotation in a Boom Crane System

In this paper, a robust nonlinear integral sliding mode control (ISMC) is proposed as a vibration controller for the payload’s skew rotation process of a boom crane to cope with parametric uncertainties in the system parameters. By using the indirect Lyapunov method, algebraic inequality constraints for the ISMC gains are formulated to ensure the robust stability of the closed-loop system under the sliding mode and in a context where the reaching phase is completely eliminated. Moreover, a robust output feedback $H_{\infty }$ control is introduced as a benchmark to compare with the nonlinear ISMC. Specifically, $\mu $ -synthesis is utilized to establish the robust stabilization for the $H_{\infty }$ controller. An optimization routine based on the metaheuristic particle swarm optimization mechanism is established, which adopts the robust stability conditions with regard to each controller as the nonlinear constraints. By means of the proposed optimization procedure, minimization of desirable performance index and robust stabilization of the closed-loop system are guaranteed simultaneously in a single framework. Through both random simulation and experimental results, ISMC shows its superiority to the $H_{\infty }$ control; hence, ISMC is the preferable candidate for the actual implementation on the real-size system in use at the harbor.

Flight controller design for aircraft low altitude airdrop

Purpose During low altitude airdrop operations, the heavy cargo moving inside and the sudden dropping out exert serious threats on the aircraft safety and mission performance. This paper aims to propose an efficient flight control method for the airdrop operations. Design/methodology/approach A novel controller which combines feedback linearization with nonlinear integral sliding mode control is proposed. The aircraft airdrop model is decoupled and linearized by using the feedback linearization technique. On this basis, an integral sliding mode controller is designed to stabilize the speed and pitch attitude of the aircraft. In the sliding manifold, one class of nonlinear functions with the property of “smaller errors correspond to bigger gains and bigger errors correspond to saturated gains” is introduced to form the integral term; thus, the overcompensation of the integral term to big errors is omitted, and the dynamic response performance is improved. Lyapunov-based stability analysis shows that the controller could completely reject model uncertainties by choosing proper controller parameters. Findings The flight control system with strong robustness could meet the low altitude airdrop indexes in the maximum weight cargo airdrop task. Originality/value This paper fulfils an urgent need to study how to control the aircraft to guarantee mission performance and flight safety during the low altitude airdrop operations.

Nonlinear Integral Sliding Mode Control for a Second Order Nonlinear System

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.

Current-based direct power control of a DFIG under unbalanced grid voltage

A novel current-based direct power control (CB-DPC) strategy for a grid-connected doubly-fed induction generator (DFIG) is proposed. The reported control scheme is applicable to DFIG-based variable-speed wind turbines that operate under unbalanced network voltages. The required DFIG rotor voltage for precise regulation of the stator active and reactive output powers and accurate elimination of their inherent pulsations are directly obtained using a nonlinear integral sliding-mode control (ISMC) scheme. Compared with other control methods, the proposed strategy is simpler since it is not based on the symmetrical components theory, does not need multiple synchronous coordinate transformations, and only requires DFIG voltage and current values as its inputs. Constant switching frequency of the rotor-side converter (RSC) is achieved by means of space vector pulse-width modulation (SVPWM) technique. Uncertainties in the parameters of the generator are included in the design. A compensation strategy is also proposed for tracking error mitigation of the powers that occur due to elimination of the chattering phenomena in the ISMC scheme. Simulation results on a 2MW DFIG under different operating conditions are presented to validate the effectiveness and robustness of the proposed method.

GPI observer-based non-linear integral sliding mode control and synchronisation of uncertain chaotic system

An output feedback control scheme for a class of triangular chaotic systems in the presence of system uncertainties, unknown disturbances, parameter perturbations and measurement noises is proposed in this paper. A high gain general proportional integral (GPI) observer is used for the accurate linear estimation of the error states, non-linear endogenous and exogenous disturbances from the noisy output signals of the system, and then a non-linear integral sliding mode controller with active disturbance cancellation is proposed for the tracking control and synchronisation of the chaotic systems. The uncertain Gesino chaotic system is used to validate the proposed control method and the convincing numerical results illustrate the proposed method is effective to deal with various system uncertainties only based on the utilisation of the input-output data.

Active adaptive fuzzy integral sliding mode control for unified chaotic system with uncertainties and disturbance

An active adaptive fuzzy integral sliding mode controller is proposed for a unified chaotic system with parametric uncertainties under external perturbation. An improved control method is designed to guarantee the stability, while maintaining the transient performances of the original nonlinear integral sliding mode control. The proposed method reduces the effects of both the uncontrollable state of unified chaotic system and approximation error of adaptive fuzzy compensator on system state error. The stability of the controller is analyzed by Lyapunov stability theorem. The simulation results show that the system states can be controlled to target points with parametric uncertainties under external perturbation. The effectiveness of this method is illustrated by the numerical simulation.

NETMAT: A knowledge-based grid system analysis tool

A novel current-based direct power control (CB-DPC) strategy for a grid-connected doubly-fed induction generator (DFIG) is proposed. The reported control scheme is applicable to DFIG-based variable-speed wind turbines that operate under unbalanced network voltages. The required DFIG rotor voltage for precise regulation of the stator active and reactive output powers and accurate elimination of their inherent pulsations are directly obtained using a nonlinear integral sliding-mode control (ISMC) scheme. Compared with other control methods, the proposed strategy is simpler since it is not based on the symmetrical components theory, does not need multiple synchronous coordinate transformations, and only requires DFIG voltage and current values as its inputs. Constant switching frequency of the rotor-side converter (RSC) is achieved by means of space vector pulse-width modulation (SVPWM) technique. Uncertainties in the parameters of the generator are included in the design. A compensation strategy is also proposed for tracking error mitigation of the powers that occur due to elimination of the chattering phenomena in the ISMC scheme. Simulation results on a 2MW DFIG under different operating conditions are presented to validate the effectiveness and robustness of the proposed method.