Nonlinear Sliding Mode Control Research Articles

Design and real time implementation of nonlinear sliding surface with the application of super-twisting algorithm in nonlinear sliding mode control for twin rotor MIMO system

This paper proposes the design of a nonlinear sliding surface based on the principle of variable damping concept for 2-degree of freedom Twin Rotor Multiple input Multiple output System (2-dof TRMS). The implementation of the designed nonlinear sliding surface in real time is demonstrated. Super-twisting algorithm is applied in nonlinear sliding mode control. The nonlinear sliding surface enables the system trajectory to be highly robust and with the application of super-twisting algorithm in nonlinear sliding mode controller (SMC), the designed controller has minimized the problem of chattering considerably. The system is modeled in such a way that it includes all nonlinearities and coupling effects. A decoupler is designed to nullify the coupling effect. This scheme is capable of reducing both the settling time and peak overshoot simultaneously for 2-dof TRMS. The scheme also reduces the chattering. The proposed method is compared with the design using PID controller. The applicability of the designed nonlinear sliding surface and nonlinear SMC with super-twisting algorithm have been tested both in simulation and in real time. This research paper is mainly dealing with the modeling of Twin rotor MIMO system by including all nonlinearities and coupling effects, the decoupler design for 2-dof TRMS, the design of nonlinear sliding surface for 2-dof TRMS and application of super-twisting algorithm in nonlinear sliding mode control for 2-dof TRMS.

Sliding Mode Control for 2 Degrees of Freedom Upper Limb Rehabilitation Robotic System under Uncertainties

Rehabilitation of patients suffering from post-stroke injuries via robots is now adapted word widely. The aim of this therapy is to restore and improve the dysfunction and the performance of the affected limbs doing repetitive tasks with the help of rehabilitation robots, as robots are best way to perform repetitive task without any monotony failure. Control of these rehabilitation robots is an important part to consider because of nonlinearity and uncertainty of the system. This paper presents nonlinear sliding mode controller (SMC) for controlling a 2 degrees of freedom (DOF) upper limb robotic manipulator. Sliding mode control is able to handle system uncertainties and parametric changes. One drawback of using SMC is high frequency oscillations called as chattering. This chattering can be reduced by using boundary layer technique. Experiments have been carried out under perturbed conditions and results have shown that SMC performs well and remain stable and thus proves to robust controller for upper limb robotic manipulator.

Robust Frequency Regulation in Mobile Microgrids: HIL Implementation

It is undeniable that marine vessel systems play an important role to transfer huge loads and weapons with low cost. However, ship power systems produce a lot of greenhouse gases, which in turn lead to serious environmental pollution. Hence, the utilizing of wind turbines (WTs), solar generation, sea wave energy (SWE), and energy storage systems (ESSs) in marine vessel power systems have been attracting a lot of attention in recent years. In this paper, it is assumed that a marine vessel power system with photovoltaic (PV), WT, SWE, and ESS can be regarded as a mobile-islanded MG. Then, a novel topology for hybrid shipboard microgrids (MGs) is presented. Next, in order to make a balance between consumption and power generation in shipboard MGs, an optimal modified model-free nonlinear sliding mode controller is introduced for the secondary load frequency control. Since the quality of the control actions of the proposed model-free approach depends on its parameters, a hybrid version of the sine-cosine algorithm (SCA) and wavelet-mutation (WM), called SCAWM, is employed to find the best value of these coefficients. Comparisons are conducted with other existing methodologies, such as model predictive control, interval type-2 fuzzy logic controller, and conventional PI (PI) to establish the supremacy of the newly suggested control strategy. Finally, a real-time hardware-in-the-loop (HIL) simulation based on OPAL-RT is accomplished to affirm the applicability of the suggested controller, from a systemic perspective, for the load frequency control problem in the shipboard MG.

Sliding Mode Based Control of Dual Boost Inverter for Grid Connection

Single-stage voltage step-up inverters, such as the Dual Boost Inverter (DBI), have a large operating range imposed by the high step-up voltage ratio, which together with the converter of non-linearities, makes them a challenge to control. This is particularly the case for grid-connected applications, where several cascaded and independent control loops are necessary for each converter of the DBI. This paper presents a global current control method based on a combination of a linear proportional resonant controller and a non-linear sliding mode controller that simplifies the controller design and implementation. The proposed control method is validated using a grid-connected laboratory prototype. Experimental results show the correct performance of the controller and compliance with power quality standards.

Fault-Tolerant Control Based on Sliding Mode Controller for Double-Star Induction Machine

This paper presents a fault-tolerant control (FTC) strategy for double-star induction machine subject to stator and rotor faults. To steer the speed and the flux to their desired references, a nonlinear sliding mode controller (SMC) is designed. However, the proposed SMC can’t deal with the faults effect which can achieve graceful system degradation. In order to compensate the faults effect, an appropriate combination between the proposed SMC and a new developed fault detection and compensation block is made. Simulation results are presented to show the effectiveness of the proposed FTC in terms of speed and flux responses using an estimator of rotor flux. Compared with SMC, the obtained results confirm the validity of the proposed FTC strategy and its ability to ensure a ripple-free operation when the fault occurs. In this kind of multiphase machines, the proposed controller is applied for the first time; its efficiency, robustness and simple design are promising for practical implementation and can be an alternative to the existing FTC.

Nonlinear SSR Damping Controller for DFIG Based Wind Generators Interfaced to Series Compensated Transmission Systems

This paper details a nonlinear Sliding Mode Control (SMC) based Sub-Synchronous Resonance (SSR) mitigation method for Doubly Fed Induction Generator (DFIG) based wind turbines interconnected to series compensated transmission systems. The proposed method is used to control the rotor side converter to mitigate SSR while ensuring decoupled torque and reactive power control ability of the DFIG is maintained. The proposed method is implemented on the detailed DFIG wind turbine model provided in the RTDS platform for validation via simulations. Results obtained indicate the controller is successful at damping SSR when tested under varying compensation levels and wind speeds.

Nonlinear adaptive sliding-mode control of the electronically controlled air suspension system

Recent years, electronically controlled air suspension has been widely used in vehicles to improve the riding comfort and the road holding ability. This article presents a new nonlinear adaptive sliding-mode control method for electronically controlled air suspension. A nonlinear dynamical model of electronically controlled air suspension is established, where the nonlinear dynamical characteristic of the air spring is considered. Based on the proposed nonlinear dynamic model, an adaptive sliding-mode control method is presented to stabilize the displacement of electronically controlled air suspension in the presence of parameter uncertainties. Parameter adaptive laws are designed to estimate the unknown parameters in electronically controlled air suspension. Stability analysis of the proposed nonlinear adaptive sliding-mode control method is given using Lyapunov stability theory. At last, the reliability of the proposed control method is evaluated by the computer simulation. Simulation research shows that the proposed control method can obtain the satisfactory control performance for electronically controlled air suspension.

Chaos Control of Third Order Phase Locked Loop Using Sliding Mode Nonlinear Controller

The nonlinear dynamics of a third-order phase locked loop (PLL) reveals a chaotic behavior for range values of loop parameter. Using bifurcation theory, it has been verified through mathematical analysis and simulation that such behavior pulls the PLL to an undesirable and unstable out-of-lock state. This paper aims to control such chaotic behavior and drive the PLL to the in-lock state, by applying a nonlinear controller based on sliding mode control theory to the PLL under consideration. The design process involves two phases. In the first phase, a sliding surface is designed such that the sliding motion meets the design specifications. In the second phase, a high-speed switching control law is selected such that the system state trajectory reaches the sliding surface. The validity of the proposed controller is tested through simulations. Results show the effectiveness of the designed nonlinear controller in stabilizing the system and driving the PLL to the phase locked state.

The Nonlinear Single Controller of DGEN380 Aero Engine Design

The advanced nonlinear sliding mode control method of DGEN380 aero engine is presented in this paper. This aero engine is a small high bypass ratio turbofan engine by which the nonlinear control approach of the aero engine is invested. And this paper focuses on the power management function of the aero engine control system which includes steady control and transient control. The mathematical model of DGEN380 aero engine is built by a set of nonlinear dynamic equation that is validated by experimental data. The single controller based on sliding mode approach is designed that can keep some certain thrust levels during steady state and maintain repeatable performance during transient operation from one requested thrust level to another. The single controller can offset the impact of the signal noise and harmonic disturbance at a certain power point. And the dynamic performance of the single controller is satisfactory at the transient process. The experiment is conducted by aero engine test bench for the single control.

Control por Modos Deslizantes de la Relación de Exceso de Oxígeno en una PEMFC Interconectada a un Motor de CD mediante un Convertidor Boost

In this work, a proton exchange membrane fuel cell (PEMFC) is used to electric energy supply to a permanent magnet DC motor in a sustainable way and the inlet air flow in the cathode is manipulated to ensure the PEM fuel cells efficient operation. A boost-type DC/DC converter is connected to the PEMFC, it is used with a PI linear control loop to regulate the speed of the DC motor under some possible load disturbances. In addition, a nonlinear sliding mode control (SMC) is designed for regulated the excess oxygen ratio considering constant the temperature and humidity of membrane, to achieve the PEM full cell operate in the ohmic region of the polarization curve, to avoid the oxygen starvation at the cathode and to prevent damage to fuel cell components. The results are validated using the internal models of the PEMFC and the power electronics from SimPowerSystems library of Matlab/Simulink.

Design of Nonlinear Conformable Fractional-Order Sliding Mode Controller for a Class of Nonlinear Systems

The paper aims to develop a new fractional-order nonlinear sliding mode controller with conformable fractional-order (CFO) derivative for a class of uncertain non-autonomous systems considering disturbance. The control method involves a novel CFO nonlinear surface as well as a new CFO switching function. The stability of the CFO controller is proved by means of the Lyapunov stability theorem. The simulation results show the improvement in the developed controller in terms of faster convergence speed, chattering reduction and lower control effort. Moreover, it needs simple calculations.

Fractional-order sliding mode control for deployment of tethered spacecraft system

This paper proposes a fractional-order integral sliding mode control with the order 0 < ν < 1 to stabilize the deployment of tethered spacecraft system with only tension regulation. The work in this paper is partially based on integer-order nonlinear sliding mode controller and improves its performance with fractional-order calculus. The proposed scheme makes use of integral sliding surface to obtain smaller convergence regions of state errors, and the fractional derivative is synthesized to enhance the flexibility of controller design by fining parameters for better dynamic and steady-state performance. Fractional-order observers help to eliminate external disturbances while the adaptive law is presented to remove the adverse effect in stability analyses, and fractional-order uniform ultimate boundedness is proved to guarantee the existence of the proposed sliding surface. According to theoretical analyses, the fractional order will indeed affect the dynamic and steady-state performance of control system, and the proposed method will be verified in numerical simulations compared with the nonlinear sliding mode counterpart.

Robust fixed-time sliding mode control for fractional-order nonlinear hydro-turbine governing system

This paper proposes a nonlinear sliding mode controller for effective fixed-time stabilization of a hydro-turbine governing system (HTGS). The HTGS is a highly nonlinear, multi-variable coupled and non-minimum phase system to maintain frequency stability by regulating the generation output in response to load variations. The state trajectories of HTGS under random load disturbances exhibit unstable behaviours on the rotor angle, rotor speed, and guide vane opening, which would affect the stable operation of hydroelectric stations. In the proposed approach, the fractional calculus technique is adopted to model the nonlinear dynamics of fractional-order hydro-turbine governing system (FOHTGS). In order to validate the system stabilization and convergence within a bounded time, a robust sliding mode controller is proposed to force the FOHTGS to reach the equilibrium point based on the fixed-time stability and Lyapunov stability theories. The proposed controller can guarantee the superior stabilization of FOHTGS with the bounded and quantifiable convergence time, and thus overcome the drawback of finite-time controllers whose convergence characteristics are heavily dependent on the initial conditions. Finally, numerical simulations have been implemented to confirm the effectiveness and superior performance of the fixed-time controller compared with the existing finite-time control methods.

Modular Integrated Longitudinal, Lateral, and Vertical Vehicle Stability Control for Distributed Electric Vehicles

There is a nonlinear coupling relationship between the vehicle in the longitudinal, lateral, and vertical directions, which brings great difficulties to the design of the controller. To tackle the chattering problem, a hierarchical integrated controller for distributed electric vehicle is proposed to improve driving safety, handling stability, ride comfort, and road tracking capabilities. The proposed algorithm has been developed to overcome a major challenge of the conventional method, which can improve only partial dynamic performance of the vehicle. The optimal pre-pointing lateral acceleration model is used to simulate the operator's expected reaction to the vehicle. The body control layer decouples complex problems to achieve multi-target independent tracking through a nonlinear sliding-mode control algorithm, and calculates the expected total body force to meet the upper level instructions. The tire force distribution layer is designed to optimize the function by reducing the tire load ratio and balancing the vertical dynamic load coefficient to improve the vehicle's driving stability and ride comfort. The lower actuator control layer controls the corresponding actuator to achieve the optimal tire force output from the middle layer. Finally, the effectiveness of the chassis integrated control system is verified in CarSim and MATLAB co-simulation.

Modelling and sliding‐mode control of a single‐phase single‐stage converter with application to plug‐in electric vehicles

In this study, a novel non-linear sliding-mode controller with a boundary layer solution and a redefined sliding manifold is proposed for a bidirectional converter utilised in plug-in electric vehicles. The proposed method employs a Lyapunov function to formulate the stability condition of the non-linear controller. The proposed switching regime and control strategy enforce a pseudo-resistive relation at the input terminals of the converter to ensure the unity power factor in power conversion. The input resistance of the converter is regulated and controlled to positive and negative values to facilitate both grid-to-vehicle and vehicle-to-grid features, respectively. Simulation and experimental results are provided to evaluate performance of the proposed modelling and feedback control scheme.

A nonlinear adaptive sliding mode control strategy for modular high-temperature gas-cooled reactors

Modular high-temperature gas-cooled nuclear reactor (MHTGR) has attracted comprehensive attention for its reliable inherent safety, and an effective control strategy is needed to control the output power of the MHTGRs at desired levels. This paper aims to develop a nonlinear power-level tracking controller based on sliding mode control (SMC) strategy for the MHTGRs. By introducing Takagi-Sugeno (TS) fuzzy system for nonlinear modeling, the MHTGR model is represented by TS models. The control law is designed based on the TS models and the sliding mode surface that is defined as the tracking error, and an adaptive algorithm is also included in the proposed control law to reduce the chattering phenomenon of SMC. In addition, the stability of the closed-loop control system is also guaranteed by the proposed control law. To evaluate the performance of the proposed nonlinear adaptive sliding mode control (NASMC) strategy, a traditional nonlinear sliding mode control (TNSMC) strategy and a Proportional-Integral-Derivative (PID) control strategy are presented for comparison. Simulation results show the effectiveness and the advantages of the proposed NASMC strategy, and most importantly, the proposed NASMC strategy does not suffer from chattering.

Tuning and Feasibility Analysis of Classical First-Order MIMO Non-Linear Sliding Mode Control Design for Industrial Applications

Model-based control techniques have been gaining more and more interest these days. These complex control systems are mostly based on theories, such as feedback linearization, model predictive control, adaptive and robust control. In this paper the latter approach is investigated, in particular, sliding mode (SM) control is analyzed. While several works on the description and application of SM control on single-input single-output systems can easily be found, its application on multi-input multi-output systems is not examined in depth at the same level. Hence, this work aims at formalizing some theoretical complements about the necessary conditions for the feasibility of the SM control for multi-input-multi-output systems. Furthermore, in order to obtain the desired performance from the control system, a method for parameter tuning is proposed in the particular case in which the relative degree of the controlled channels is equal to one. Finally, a simple control problem example is shown with the aim of stressing the benefits derived from the application of the theoretical complements described here.

On robust controllers for active steering systems of articulated heavy vehicles

This paper examines the robustness of different controllers for active steering systems (ASSs) of articulated heavy vehicles (AHVs) in terms of the directional performance. Controllers based on the linear quadratic regulator (LQR) technique were designed for ASSs. The success of the LQR-based controllers is dependent on the accuracy of linear models for AHVs. When designing ASS controllers, linearisation of the AHV models is usually necessary; this results in model inaccuracy and un-modelled dynamics, and the robustness of the LQR-based controllers may be degraded. ASSs for AHVs are assessed in the time-domain, which may lead to an incomplete performance evaluation. This paper assesses the robustness of the ASS controllers designed with the techniques of sliding mode control (SMC), nonlinear sliding mode control (NSMC), and mu-synthesis (MS). The ASS controllers are evaluated using numerical simulation in terms of the trade-off between the manoeuvrability and the lateral stability at high speeds.

Direct power control of three-phase PWM AC/DC converter based on intelligent approach with dc-bus voltage regulation using sliding mode controller

This research aims to present a novel direct power control (DPC) strategy of three-phase PWM AC/DC converters. In this strategy, the regulation of the dc-bus voltage is based on nonlinear sliding mode controller (SMC), the control of the instantaneous active and reactive power is performed by fuzzy logic controllers (FLC) and also the artificial neural networks (ANN) approach is used to select the switching states of PWM AC/DC converter. The sliding mode control is an effective tool to minimise disturbances. Nevertheless, the chattering phenomenon depicts a major problem for variable structure systems (VSS). To overcome this drawback, a saturation function is employed to decrease chattering effects. The proposed method allows, on the one hand, to steer the dc-bus voltage, the instantaneous active and reactive power to their reference values. On the other hand, it enables to reduce the harmonic disturbances, the power ripples and to realise a unity power factor (UPF) operation. Simulation results are provided to confirm the efficiency, the robustness and the performances of the proposed DPC scheme in different conditions of simulation.

Grid Connected Photovoltaic Energy Conversion System Modeling and Control Using SMC-BSC Approach

The photovoltaic generators are characterized by a nonlinear electrical characteristics that admit one only maximum power point (MPP). Therefore, the maximum power point tracking (MPPT) is very essential to improve the photovoltaic systems efficiency. This paper presents a robust method to control and optimization of a grid-connected photovoltaic (PV) energy conversion system .The control design is based on a nonlinear sliding mode control (SMC)-Backstepping control (BSC) approach. The principal aim of this work is to develop the sliding mode technique for having a grid-connected PV system with a goods performances. The SMC is ameliorated by associate it with the Backstepping technique, it is applied to track the maximum power from the PV panels, and also, to ensure an independent control of the active (P) and reactive (Q) powers. In this control strategy the stability is verified by the Lyapunov approach. The simulations results has been realized in Simulink/Matlab and they have shown that the proposed system present a good robustness with the SMC-BSC method.