Conventional Sliding Mode Control Scheme Research Articles

Mechanical design and position-tracking control of a novel robotic joint with a circular rotary electro-hydraulic actuator

Robotic exoskeletons with different actuators have been extensively investigated for decades, but designing a robot joint with compact structure, sufficient output torque, and satisfactory kinematic performance still remains a challenge. The paper introduces the mechanical design and control scheme of a novel joint with a circular rotary electro-hydraulic actuator in order to provide walking assistance for the hip joint. First, measurement and analysis techniques are applied in the gait recognition to determine an accurate swing range of the target joint and provide essential information for the structure design of the hydraulic rotary drive joint. Secondly, the functional structure and working principle of the hydraulic rotary joint are described in detail and the corresponding mathematical model is established for the valve-controlled hydraulic servo system. In addition, an adaptive sliding mode control (ASMC) method is proposed for position-tracking and improving the anti-disturbance ability of the controlled system. The global asymptotic stability and finite-time convergence of the closed-loop system are proved by Lyapunov stability theory. Finally, the feasibility and position-tracking performance of the designed ASMC controller were experimentally verified. Compared to the PID controller and the conventional sliding mode control scheme, the proposed controller improved the position-tracking control accuracy by 20%.

Simplified Double-Integral Sliding-Mode Control of PWM DC-AC Converter with Constant Switching Frequency

In this paper, a simplified double-integral sliding-mode control method for pulse-width-modulated dc-ac buck conversion is introduced. The control equation is derived based on the equivalent control method, in which the control-oriented model is developed using the averaged dynamics of the power converter in continuous conduction mode. In contrast with the conventional sliding-mode control schemes, the complexity of adding a capacitor current sensor, variable ramp voltage, and other relevant components is avoided. Furthermore, the control equation is translated into a simple electronic circuit with minimal added components, which reduces the practical implementation cost. The proposed control method rejects large disturbances, tracks the reference signal, and maintains a constant switching frequency. Systematic design procedure, control parameters selection, and stability conditions are presented. The design methodology is verified via simulating the proposed control circuit using Simscape Electrical in MATLAB. The control method is also compared with the conventional double-integral sliding-mode control scheme under load disturbances. The results show that the simplified control approach provides a fast transient response and robust tracking performance.

Fixed-time disturbance observer-based chattering-free sliding mode attitude tracking control of aircraft with sensor noises

The challenging attitude tracking control problem of aircraft with external disturbance and sensor noises is investigated. A disturbance observer-based control approach is presented. In this approach, a fixed-time disturbance observer is preliminarily developed. The external disturbance is estimated with the estimation error governed to zero after a fixed-time regardless of any initial state. Moreover, with measurement noises explicitly considered, a discrete tracking differentiator extracting the real signals from the polluted measurement is introduced into that fixed-time observer to improve its application potential. Invoking the estimation information, a sliding mode attitude controller is then synthesized. The main feature of the proposed approach is that the closed-loop attitude tracking system is guaranteed to be exponentially stable. External disturbance rejection is achieved, while its upper bound is not required to implement that approach. In contrast to the conventional sliding mode control schemes, the proposed controller is chattering-free. Numerical simulation and experimental tests are finally carried out to verify the effectiveness of the proposed approach.

Sliding mode active disturbance rejection control for uncertain nonlinear fractional-order systems

It is recognized today that active disturbance rejection control (ADRC) is an effective control strategy in the presence of uncertainties and disturbances and especially in the absence of a model. Its advantages and its power have been demonstrated practically on numerous engineering applications. This control technique has been widely developed in the case of integer-order systems. On the other hand, fractional-order systems are gaining more and more interest due to their use in modeling of many physical phenomena. Some works have been dedicated to the design of the ADRC for linear and nonlinear fractional-order systems. However, the sliding mode technique has not yet been used for the design of ADRC of fractional-order systems. The aim of this paper is to propose a sliding mode active disturbance rejection controller (SMADRC) for nonlinear fractional-order systems with uncertainties and external disturbances for stabilization and tracking purposes. First, a step by step sliding mode extended state observer (SMESO) for both state variables and total disturbance (uncertainties and external disturbances) estimation is proposed. The finite time convergence of the proposed extended state observer is established. Then, a sliding mode controller using the estimated states and total disturbance is presented to realize stabilization and desired references tracking with compensation of the total disturbance. The closed loop stability is analyzed. Simulation results of the proposed SMADRC applied to the control of fractional-order chaotic systems are compared to those of the conventional sliding mode control scheme.

Non-singular terminal sliding mode control for redundantly actuated parallel mechanism

In this article, the trajectory tracking control is developed by implementing a non-singular terminal sliding mode control for the redundantly actuated parallel mechanism system. The proposed control scheme could guarantee that the tracking errors converge to zero asymptotically. The problem of singularity with regard to conventional terminal sliding mode control scheme can be eliminated with the presented novel non-singular terminal sliding mode surface as well. The corresponding stability of the proposed control scheme has also been proved theoretically in terms of Lyapunov method. In addition, simulations and experiments are conducted for trajectory tracking to validate the effectiveness of the proposed scheme. The illustrative results demonstrate that the proposed scheme is available to solve the uncertainties and external disturbances with self-tuning in real time. Furthermore, the prominent characteristics of the presented control scheme are quick convergence, high accuracy, and high robustness, which can achieve excellent tracking performance as compared with computed torque control scheme and conventional sliding mode control scheme.

An Improved Sliding Mode Control Technique to Mitigate Mismatched Parameter Uncertainties of Three-Phase Voltage Source Inverters

This paper proposes a theoretical and experimental implementation of an advanced sliding mode control (SMC) for a three-phase voltage source inverter (VSI) to achieve robustness against the unknown uncertainties of an LC filter. The significant contributions of the proposed SMC are summarized as considerations for the matched and mismatched uncertainties of the LC filter, more relaxed norm-bounds, dynamic characterization of sliding surface, and unique stability analysis. Unlike the conventional SMC techniques with matched uncertainties, the mismatched uncertainties in the state matrix are taken for the design of the proposed SMC. Also, the relaxed norm-bound designed for matched and mismatched uncertainties allows a wide range of variations in the values of LC filter. The voltage tracking errors are significantly reduced and the total harmonic distortions (THDs) are highly suppressed by characterizing the sliding surface in terms of flexible linear matrix inequalities (LMIs). Next, the stability analysis and reachability conditions are given using the Lyapunov criterion. The authenticity of the proposed SMC method is proved by TMS320LF28335 DSP based experimental results with a prototype 1-kVA test-bed. The comparative experimental results and analysis for the proposed SMC scheme, the conventional SMC scheme, and the conventional PI-PI control scheme are presented under the load step change, unbalanced load, and non-linear load step change with the parameter uncertainties to demonstrate the excellent performance of the proposed controller such as fast transient response, small steady-state error, and low THD.

Reduction of power consumption on quadrotor vehicles via trajectory design and a controller-gains tuning stage

This work presents a methodology for reducing power consumption on quadrotor vehicles. The proposed methodology combines both, a trajectory design procedure and a controller-gains tuning stage. The quadrotor is operated in closed-loop by means of a terminal sliding modes controller, whose stability analysis is provided by using a strict Lyapunov function. The trajectory design stage allows designing an optimal trajectory with smooth transitions by minimizing a criterion function using dynamic optimization theory. Furthermore, in order to reduce power consumption, a performance index depending on the tracking error and the quadrotor inputs is used on a control-gains tuning stage based on a nature inspired evolutionary meta-heuristic algorithm, namely the cuckoo search algorithm. The quadrotor terminal sliding modes controller is compared to another sliding mode control algorithm, and the performance of each controller is assessed by considering aero-dynamical disturbances and parametric uncertainties. Numerical simulations show that the tracking error and power consumption are reduced when the trajectory tracking and controller-gains tuning stages are used. Besides, it is shown that the proposed terminal sliding modes controller outperforms a conventional sliding mode control scheme.

Four-phase interleaved DC/DC boost converter interfaces for super-capacitors in electric vehicle application based onadvanced sliding mode control design

Electric vehicles (EVs) has received an increasing interest from the power community and have become increasingly popular due to their importance in fighting climate change. An advanced power electronic converter remains the main and common topic for research in this area. In this paper, an advanced sliding mode control (ASMC) is designed for Four Phase Interleaved Boost Converter (FP-IBC). The novelty of the proposed controller relies on the use of an adaptive delay-time block with the conventional sliding mode control scheme which is designed based on chattering elimination method. The new scheme succeed to reduce the ripple contents in the converter's output voltage and inputs currents, and achieve fast convergence and transient response. An experimental comparison study has been investigated between the proposed controller and Self-tuning Lead Lag Compensator (SLLC). The comparison study is performed at different loading conditions using Super-Capacitor (SC) module. The experimental results show that the dynamic response of FP-IBC is significantly improved based on the proposed control design.

An adaptive sliding-mode control technique for three-phase UPS system with auto-tuning of switching gain

This paper presents an adaptive sliding-mode control (ASMC) technique for a three-phase UPS system with an auto-tuning mechanism of the switching gain. First, a sliding-mode control (SMC) scheme for the three-phase UPS inverter is designed to guarantee the robustness against the system uncertainties and external disturbances. Then, through addition of an adaptive control term, the ASMC algorithm is developed to optimize the switching gain without the prior information of the unknown and bounded uncertainties. It is shown that the upper bounds of the uncertainties are not required to be known in the SMC design. Also, the chattering problem in the reaching mode is considerably alleviated and the excessive use of electric power can be reduced by avoiding overestimation of the switching gain. Both the stability and robustness of the proposed ASMC method are proven by using the Lyapunov theory. In addition, a simple sliding-mode observer is used to estimate the load current without any additional current sensors. Therefore, the proposed ASMC system can accomplish the superior control performance (such as faster voltage recovery under a sudden load change, smaller steady-state error under parameter deviations, and lower THD under nonlinear load) compared to the conventional SMC scheme. Finally, the performance verifications of the proposed algorithm are carried out through the comparative simulation and experimental results on a prototype 1-kVA three-phase UPS inverter using TMS320F28335 DSP.

Research of a fuzzy global sliding mode control scheme: A stability control scheme for anti-aircraft missile with swing nozzle thrust vector control

In order to suppress the high-frequency chattering at control input in the premise of keeping robust against system uncertainties, a novel fuzzy global sliding mode controller (FGSMC) is proposed. A nonlinear switching function is designed in order that system trajectory can be set on sliding mode surface at initial time. A fuzzy decision maker, which can adaptively obtain the gain of signum term according to novel fuzzy logic, is proposed and introduced to guarantee the comprehensive properties with respect to the reachability of sliding mode and the smoothness of control input. Moreover, it possesses simple fuzzy inference rules and is easy to be realized in application. The FGSMC is employed to construct the stability control scheme for anti-aircraft missile with swing nozzle thrust vector control. Simulation results on researched anti-aircraft missile present that, in the existence of sustained disturbances, the proposed FGSMC scheme not only possesses better convergent performance, but also suppresses high-frequency chattering to a large extent, compared with conventional sliding mode control scheme.

Fuzzy-neural-network inherited sliding-mode control for robot manipulator including actuator dynamics.

This paper presents the design and analysis of an intelligent control system that inherits the robust properties of sliding-mode control (SMC) for an n-link robot manipulator, including actuator dynamics in order to achieve a high-precision position tracking with a firm robustness. First, the coupled higher order dynamic model of an n-link robot manipulator is briefy introduced. Then, a conventional SMC scheme is developed for the joint position tracking of robot manipulators. Moreover, a fuzzy-neural-network inherited SMC (FNNISMC) scheme is proposed to relax the requirement of detailed system information and deal with chattering control efforts in the SMC system. In the FNNISMC strategy, the FNN framework is designed to mimic the SMC law, and adaptive tuning algorithms for network parameters are derived in the sense of projection algorithm and Lyapunov stability theorem to ensure the network convergence as well as stable control performance. Numerical simulations and experimental results of a two-link robot manipulator actuated by DC servo motors are provided to justify the claims of the proposed FNNISMC system, and the superiority of the proposed FNNISMC scheme is also evaluated by quantitative comparison with previous intelligent control schemes.

Robust finite-time control for spacecraft attitude stabilization under actuator fault

A finite-time convergent sliding mode control (SMC) scheme is developed to solve the problem of fault-tolerant control for a rigid spacecraft attitude stabilization manoeuvre in the presence of uncertain inertia parameters and external disturbances. A new terminal sliding surface is first presented. Based on the sliding manifold designed, a robust sliding mode controller is then derived for automatically compensating the external disturbances, uncertain inertia matrix, and even time-varying actuator faults. One feature of the proposed strategy is that the design of the fault-tolerant control does not require a fault detection and isolation mechanism to detect, separate, and identify actuator faults. Lyapunov stability analysis shows that finite-time convergence of spacecraft attitude orientation to the equilibrium point can be accomplished with great robustness to disturbance and actuator faults guaranteed. Numerical simulation results are also presented that not only highlight the closed-loop performance benefits from the control law derived here, but also illustrate the proposed procedures and their effectiveness when compared with a conventional SMC scheme for spacecraft attitude stabilization control.

Design of Voltage Tracking Control for DC–DC Boost Converter Via Total Sliding-Mode Technique

In this paper, a total sliding-mode control (TSMC) scheme is designed for the voltage tracking control of a conventional dc-dc boost converter. This control strategy is derived in the sense of Lyapunov stability theorem such that the stable tracking performance can be ensured under the occurrence of system uncertainties. The salient feature of this control scheme is that the controlled system has a total sliding motion without a reaching phase as in conventional sliding-mode control (CSMC). Moreover, the effectiveness of the proposed TSMC scheme is verified by numerical simulations and realistic experimentations, and the advantages of good transient response and robustness to uncertainties are indicated in comparison with a conventional proportional-integral control system and a CSMC scheme.

Interaction control of robotic manipulators via second‐order sliding modes

AbstractThis paper deals with the interaction control of robot manipulators. The ideal goal is to control the manipulator so that its end‐effector reaches a desired position in the operative space. The attainment of this goal can be prevented by the fact that during its motion the end‐effector can interact with the environment. So, a realistic goal is regarded as control objective in the paper, that of asymptotically reaching an equilibrium position jointly determined by the choice of the ideal desired position, and by the presence of the environment. The model of the manipulator is supposed to be affected by uncertainties, so that a classical impedance control scheme cannot be adopted. The approach proposed in this paper relies on the theory of sliding mode control. In general, this methodology is deemed nonappropriate to control mechanical systems like robot manipulators, since it introduces the so‐called chattering phenomenon, which produces undesired wear and vibrations. Yet, the final control solution proposed in this paper is based on the generation of sliding modes of the second order, which practically reduces the degradation of performances, and the mechanical stress due to the chattering effect. Indeed, the proposed second‐order sliding mode control scheme relies on the use of a continuous control law, in contrast to conventional sliding mode control schemes. Copyright © 2007 John Wiley & Sons, Ltd.

Sliding mode control with perturbation compensation for a class of uncertain systems

In this study, a perturbation compensator is introduced in the sliding mode control (SMC) through a function of the prespecified sliding function, which is capable of estimating the lumped uncertainty and external disturbance with a known bandwidth. The approaches are designed to ensure a stable attraction and to attenuate the perturbation, which can be determined through the frequency domain analysis. Furthermore, an upper bound on the perturbation estimating error can be obtained based on the designed parameters, which depend on the bandwidth of the perturbation and the resonant frequency of the proposed estimator. Owing to the fact that the gain margin at zero frequency is infinity, the constant load disturbance can be estimated exactly. Combining the estimator with the sliding mode control method not only drastically reduces the gain of the discontinuous control term as compared with a conventional sliding mode control scheme but also achieves a chattering alleviated performance. In contrast to the SMC, the switching action is then performed in the bandwidth of the proposed compensator. For a disturbance-free system, this scheme not only establishes the sliding condition but also directly specifies the dynamic characteristics of the controlled system during the reaching stage, in which a discontinuous term is not needed. Experimental studies for the design of a turntable spindle servo system are conducted to illustrate its feasibility and effectiveness.

Design of a perturbation estimator using the theory of variable-structure systems and its application to magnetic levitation systems

A perturbation estimator using the theory of variable structure systems is proposed to enhance the robustness of a pole-placement controller design. In its ideal form, the pole-placement design using feedback-linearization technique achieves a desired performance in nonlinear time-varying systems. However, its performance deteriorates rapidly with the presence of disturbance and parametric uncertainties, referred to as perturbation. The estimate generated by the proposed perturbation estimator is incorporated as an additional input to rectify the uncertainties in the nominal control model of the pole-placement design. The proposed scheme requires neither the measurement of the time derivative of the state vector nor the precise knowledge of system parameters, hut rather the bounds on system perturbation. Chatter and the adverse effects of conservative bounds on system perturbation, often encountered in conventional sliding-mode control (SMC), are alleviated for the controlled plant by the proposed scheme. The benefits of this scheme are demonstrated in this study practically on a magnetic levitation system and its performance is compared with that of the conventional SMC scheme. >