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To improve the control performance and energy efficiency of the hydrostatic transmission (HST) system of wheel loaders, this study proposes a novel variable structure dual-motor hydrostatic transmission system, accompanied by a multivariable control strategy based on fuzzy sliding mode control. By constructing a simulation model of the transmission system, the performance of the novel transmission system is verified, and the control effects of common control strategies are compared. The simulation results show that the proposed control strategy and system have good matching and can adapt to disturbances actively. Field experiment results show that the proposed solution can achieve smooth automatic shifting of wheel loaders, while effectively adjusting system pressure, flow, and power. Compared with the traditional hydrodynamic torque converter loader transmission system, its transmission efficiency is effectively increased by 30%, and the efficiency is increased by 8% compared with the traditional hydrostatic transmission system This achievement is of great significance for improving the working efficiency of wheel loaders and reducing energy consumption. The future research focus is to further improve the multivariable control strategy, achieve intelligent operation, and improve the efficiency and reliability of the transmission system. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control of a symmetrical six-phase induction generator based on a variable structure strategy is experimentally tested and compared with a classical proportional-integral controller. For this, we use a linear feedback sliding mode controller with switched feedback gains in such a way to control the inner current loops of this machine. One main drawback of the classical three-phase induction generator is that it is no longer possible to generate electrical power if only one phase is lost on the stator side. To overcome this issue, we will use a squirrel cage six-phase induction machine that can still operate when at least three phases remain on the stator side. This article proposes to use a variable structure control in order to cope with unbalanced currents and also maintain the generation of power when a loss of the stator's phases occurs. The proposed controller shows its robustness and good regulation performance in healthy and faulty modes. The simulation and experimental tests were carried out with a 24 kW induction machine that represents 1/100 of the electrical power of a real wind turbine. [ABSTRACT FROM AUTHOR]

This paper presents a load frequency control (LFC) design using the variable structure model predictive controller (VSMPC) for gain scheduling (GS) of PI controller in PV connected thermal for multi‐area system. Due to the increasing impact of renewable energy sources into the grid system, the system frequency deteriorates. The proposed PV connected thermal system is evaluated under varying load conditions under increased penetration of the PV source. The combination of renewable energy into the thermal power system aggravates the frequency and it is indispensable to mitigate such a problem by introducing an optimal controller. Perturbation in load greatly affects the system frequency and this problem is addressed by using VSMPC based gain scheduling knowing the effect of proportional and integral in transient and steady‐state conditions. The oscillations in frequency are controlled by a proposed controller and the impact of frequency under penetration of PV is monitored. Further verification of the proposed technique is accomplished through communication delay in the governor and turbine. The Hardware in the loop (HIL) which validates the accuracy and real time performance of the controller. Finally, the validation of the proposed controller is compared with MPC to tune PI controller and renowned evolutionary tuned techniques like particle swarm optimization (PSO), genetic algorithm (GA) and firefly algorithm (FA) to optimize PI controller. The VSMPC with GS of PI controller shows promising results. [ABSTRACT FROM AUTHOR]

In this article, a new discrete-time sliding mode predictive control (DSMPC) with a PID sliding function is proposed for synchronous DC–DC buck converter, and its stability analysis is reported. The model predictive control, along with digital sliding mode control (DSMC), is able to further reducing the chattering phenomenon, steady-state error, overshoot and undershoot. The proposed control implementation only requires output error voltage evaluation. The effectiveness of the proposed DSMPC is proved through simulation results executed by the MATLAB/SIMULINK software. These results demonstrate its superior performance to DSMC. In other words, it represents a significant reduction of the chattering, overshoot and undershoots of output voltage response by an optimised control law during load and line variations. The proposed DSMPC almost overcomes the steady-state error (0.02%) and decreases the ripple value to about 0.2%. The overshoot and undershoot are 1.5% and 1%, respectively. Moreover, when the input voltage is changed by 26%, there is approximately no overshoot and undershoot. Also, some experimental results are presented to further illustrate the effectiveness of the proposed system. Experimental studies have been performed using a Spartan-6 field programmable gate array platform by Xilinx for the implementation of the digital control and relevant logic. [ABSTRACT FROM AUTHOR]

• The mechanical system consists of a wheel, a brake shoe, and a pusher. • The flexibility of the points of contact is modeled using viscoelastic springs. • Dynamical system is a variable structure system. • Existence of limit cycles of the brake shoe accompanying the "rattling" of the wheel is shown. The applicability of the dry friction model to modeling of mechanical systems was questioned in the late 19th century. In the 20th century, several studies were devoted to some classical problems with dry friction, including the problem of contact between a brake shoe and a rotating wheel. An important methodological aspect in solving this problem was the modeling of the flexibility of the contact area. In this work, the classical problem of the contact of a shoe with a wheel is solved by basic methods of theoretical mechanics. In addition to the element with elastic and viscous properties, which simulates the compliance of material in the area of contact between the wheel and the brake shoe, an elastic force acts on the shoe from the side of the pusher pressing the shoe against the wheel. The equations of motion of the system are compiled, which are a dynamic system of variable structure. This required critical points to be identified for each structure element. Particular attention is paid to the interaction between the friction force and elastic forces. The solutions of the linearized and complete systems are discussed for the cases of small, critical, and supercritical friction. Numerical simulation of dynamic systems was carried out in order to identify the features of the behavior of the mechanical system. In the presence of damping, the existence of limit cycles for the linearized and complete equation of the shoe is shown, accompanying the "rattling" of the wheel with constant amplitude and frequency. The initial conditions leading to the damping of the shoe oscillations and the complete stop of the wheel are found. [ABSTRACT FROM AUTHOR]

An exact analysis of sliding mode boost converter dynamics based on the locus of a perturbed relay system (LPRS) method is presented in this article. An LPRS representation of the dc–dc boost converter based on a full nonlinear model is developed. This is a first known attempt to apply the LPRS concept to an industrial process having a nonlinear model. The frequency and amplitude of the self-excited oscillations (chattering/ripple) are analyzed through the LPRS method. The LPRS is also used to analyze the effect of the propagation of an external disturbance (fluctuations in the source voltage). It is found that the effect of source voltage fluctuations on the system dynamics can be attributed to a combination of the effects of amplitude modulation and input signal propagation. Further, LPRS is used in the design problem of the dc–dc boost converter prototype to determine the required controller hysteresis value which ensures the desired operating switching frequency. Simulation and experimental results are presented to validate and illustrate the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a simple new design method of the sliding mode control based on the integral compensation of an output error is described. The key to this method is to obtain a control with a switching function. The proposed linear control input is robust against plant parameter deviations and external disturbances. We confirmed the effectiveness of the proposed method through simulation of a second and a third order plant. [ABSTRACT FROM AUTHOR]

This paper describes a novel modeling approach for self-oscillating resonant power converters operating under a control method based on the variable structure of the system (VSS). Using a fundamental harmonic approximation, the link between control and switching frequency in steady state is found to be accurately described by an affine function that depends on the load. Besides, this link has been extended in order to characterize the control-to-switching frequency dynamics, resulting in a novel small-signal continuous-time model. The resulting control-to-switching frequency transfer function can be appended to the well-known models for frequency modulation, in order to obtain a complete control-to-output system. The new model exposes that the dynamics of the converter under the VSS-based control approach presents advantages with respect to the conventional methods as frequency modulation: 1) reduced dc gain variation for uncertain loads and 2) improved phase margin at high frequencies. The dynamic modeling is complemented with the design of a controller for regulating the output voltage of a parallel resonant converter, whose performance and robustness are compared with the standard frequency modulation. Numerical simulations and experimental results confirm and verify the analytical derivations. [ABSTRACT FROM AUTHOR]

In this paper, a multirate output feedback (MROF) based discrete-time sliding mode control for the stochastic system with slowly varying bounded uncertainty is proposed. The states are estimated by the multirate Kalman filter and are used for designing the stochastic sliding mode controller which guarantee the stability under the bounded uncertainty and the uncertain noise covariance. The proposed algorithm has advantage of computational and implementation simplicity as it requires only the past output and input information. The stochastic sliding band (SSB) is also calculated which is found to be wider as compared to the state feedback case. Finally, the design procedure for stochastic sliding mode controller is demonstrated with an illustrative example. [ABSTRACT FROM AUTHOR]

This paper views the classical Chiu-Jain algorithm, originally proposed for congestion control of network links, as a decentralized algorithm for the fair allocation of a total of c units of a shared resource among n users. A new analysis is given of the general case of additive increase and multiplicative decrease (AIMD) dynamics, from the perspective of virtual equilibria and variable structure systems, leading to a better understanding of the Chiu-Jain algorithm, which is one example of AIMD dynamics. It is shown that the variable structure discrete dynamical system that describes the evolution of the share of each individual, starting from an arbitrary initial allocation, always attains a neighbourhood of the fair share ( c/ n) for each user, under the assumption that the latter is known. Subsequently, a new adaptive version of the algorithm, called adaptive AIMD, is described, with the same property of converging to the fair share, without assuming that it is known. Simulations that show the behaviour and advantages of the proposed adaptive AIMD adaptive algorithm are given. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An improved tracking technique of the reference current waveform in a shunt type active power filter is proposed in this paper using sliding mode control and feedback linearization. Feedback linearization approach helps to reduce the complexity of the controller. Excellent tracking is achieved in both for steady state and dynamic performance. A three-phase four-wire system is considered. The proposed algorithm is simulated first in MATLAB/SIMULINK. An experimental prototype using a dspace1104 based controller is also produced in the laboratory. Results from simulation match well with the corresponding results from experimental prototype confirming the usefulness of the proposed technique. [ABSTRACT FROM AUTHOR]

An all-digital sliding-mode (ADSM) controlled dc-dc converter, utilizing single-bit oversampled frequency domain digitizers in its feedback path is proposed. Sliding-mode control provides several benefits over the traditional PID control in terms of fast transient response, robustness to parameter and component variations, and low sensitivity to loop disturbances. However, analog implementations of sliding-mode control require several amplifiers in the controller and suffer from process, voltage, and temperature variations. In the proposed approach, the sliding-mode controller (SMC) is implemented digitally; utilizing a first order single-bit ΣΔ frequency to digital converter (ΣΔFDC)-based feedback and reference digitizing ADCs, running at 32-MHz sampling rate. The ADSM regulator achieves 1% settling time in less than 5 μs for a load variation of 600 mA. The SMC uses a high-bandwidth hysteretic differentiator and an integrator to perform the sliding control law in digital domain. The proposed approach overcomes the steady-state error (or dc offset), and band limits the switching frequency, which are the two common problems associated with SMCs. The IC is designed and fabricated on a 0.35-μm CMOS process occupying an active area of 2.72 mm2. [ABSTRACT FROM AUTHOR]

SUMMARY In order to discretize continuous dynamics with variable structures, Euler integrators are often used. However, Euler integrators include large discretization errors, so that they reduce the performance in the discretized dynamics. The use of Richardson extrapolation (RE) and fractional delay (FD) can reduce the discretization errors. However, Euler integrators using RE and FD directly have infinite gains at the Nyquist frequencies, and they are unsuitable for integrations of dynamics with variable structures. In this paper, we propose an improved integrator that is suitable for the integration of dynamics with variable structures. The proposed method consists of a high forward gain and a feedback structure with a high-precision differentiator. To realize the high-precision differentiator, RE and a high sampling rate (HSR) are used instead of FD, and these are implemented using a field programmable gate array (FPGA). The effectiveness is verified through software simulations, hardware in the loop (HIL) simulations, and experiments. [ABSTRACT FROM AUTHOR]

A novel control for a nonlinear two-dimensional (2-D) overhead crane is proposed. Instead of the complex design procedures used in classic methods, the proposed scheme combines the principles of neural networks (NNs) and variable structure systems (VSS) to derive control signals needed to drive the cart smoothly, rapidly and with limited payload swing. The merits include the robustness and model-free properties of the sliding mode and neural based controllers, respectively. Simulations performed using a scaled 2-D mathematical model of the crane confirm the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, a variable structure adaptive controller is proposed for redundant robot manipulators constrained by moving obstacles. The main objective of the controller is to force the model states of the robot to track those of a chosen reference model. In addition, the controller is designed directly in Cartesian space and no knowledge on the dynamic model is needed, except its structure. The parameters of the controller are adapted using adaptive laws obtained via Lyapunov stability analysis of the closed loop. The performances of the proposed controller are evaluated using a 3 DOF robot manipulator evolving in a vertical plane constrained by a mobile obstacle. The obtained results show its effectiveness compared to other tested variable structure controllers. [Copyright &y& Elsevier]

Abstract: This paper presents a robust output feedback controller based on sliding modes and indirect adaptive control applied to the angular shaft speed control of a three-phase induction motor. This approach has remarkable stability properties and offers a straightforward and intuitive tuning of its parameters. Moreover, a simplified version of the algorithm, named compact indirect variable structure model reference adaptive control (CIVS-MRAC), provides not only an easy design procedure, but also a computational implementation of low complexity, thus motivating its application in industrial environments. [Copyright &y& Elsevier]

This paper presents a new three-phase rectifier that allows the operation as rectifier or as inverter, with the use of three conventional switching cells. This reversion of power flow can be obtained simply by the inverting two reference currents. The system is analyzed as a connection of three independent lower order subsystems, controlled by sliding regime with decentralized switching scheme. The output voltage can be lower, equal, or greater than the peak of the input voltage. The operation stages, equations, control strategy, and design of the converter are presented. Finally, experimental results are shown for operation as inverter and as rectifier. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we give an LMI-based method for designing an output feedback variable structure control (VSC) system with an constraint. The uncertain system model under consideration may have nonmatching disturbance input signals. Nonmatching disturbance input signal reduction is performed via norm minimization. In terms of a constrained Riccati inequality we give a sufficient condition for the existence of a linear sliding surface and a compensator guaranteeing an constraint, and we show that the control parameters can be characterized by using the solution to the given inequality condition. We also give a simple LMI-based design algorithm of an output feedback VSC law guaranteeing an constraint. Finally, by using a design example we show that our method can supplement the existing results. [Copyright &y& Elsevier]

Abstract: In this paper, the control of a ratio-dependent predator–prey system is considered. This system, in its equivalent nondimensional form, is subjected to an on–off control, also known as a threshold policy. The control, applied only to the predator, is of the “constant effort removal” type. It is shown that such a control can be designed by a suitable choice of so called virtual equilibrium points. The analysis of the global stability of a specific nondimensional model is carried out. It shows that, in the nondimensional model, the on–off control changes the original equilibrium points on the axes to a globally stable positive equilibrium point, attained through a sliding mode, thus avoiding extinction, and achieving coexistence of both species. [Copyright &y& Elsevier]

Abstract: In some industrial batch reactors the accuracy in tracking desired temperature profiles is significantly influenced by the characteristics of the actuation system that regulates the thermal exchange. In these plants it may not be structurally possible to switch promptly between the heating and the cooling configurations; this implies that, for long time periods, the sign of the actuating signal is constrained to be either positive or negative. This fact, as long as spontaneous evaporation of the coolant, limits the possibility of tracking the desired temperature profile. Under the constraints that the actuation system can only subtract heat from the reactor, a new scheme is proposed to improve the controllability of the reactor temperature. The strategy alternates phases of coolant injection and phases of forced draining of the jacket. The proposed scheme has been worked out on the basis of the numerical analysis of a detailed thermodynamic model of an industrial reactor. The scheme has been extensively tested with remarkable results and is now in use in some industrial reactors of the CIBA Specialty Chemicals at Pontecchio Marconi, Italy. [Copyright &y& Elsevier]

Abstract: A highly robust position controller for brushless direct drive servo motors (BLDDSM) is presented using a new improved variable structure system with an integral-augmented sliding surface. With the proposed technique, the reaching phase is completely removed by the integral sliding surface. The dynamics of its ideal sliding mode is analytically obtained from a given initial condition to the origin without any reaching phase. In order to choose a suitable integral sliding surface, the optimal regulator theory is effectively applied. Moreover, the suggested control technique can exhibit the output response identical to that previously designed in the integral sliding surface for all the load variations and parameter uncertainties. The usefulness of the proposed algorithm is illustrated through the comparative experiment studies on the position controls of BLDDSM under load variations. [Copyright &y& Elsevier]

Abstract: The stability of predator–prey models, in the context of exploitation of renewable resources, subject to threshold policies (TP) is studied in this paper using the idea of backstepping and control Liapunov functions (CLF) well known in control theory, as well as the concept of virtual equilibria. TPs are defined and analysed for different types of one and two species predator–prey models. The models studied are the single species Noy-Meir herbivore-vegetation model, in a grazing management context, as well as the Rosenzweig–MacArthur two species predator–prey model, in a fishery management context. TPs are shown to be versatile and useful in managing renewable resources, being simple to design and implement, and also yielding advantages in situations of overexploitation. [Copyright &y& Elsevier]

In this article, the secure transmission of data is being realized on the basis of the synchronization of two chaotic systems. The transmitted signal is only the sign of a projection of the state. This has the advantage of making the transmission not very sensitive to the noises of transmission and the attenuation of the transmitted signal without using a VCO (Voltage Control Oscillatory) into the transmitter and the receiver. It should be noted that for the considered type of chaotic system, the traditional conditions of observability and linearization by injection of outputs are not checked. Here, we can only carry out an estimator. [ABSTRACT FROM AUTHOR]

A new improved robust variable structure controller is presented to provide an accurately prescribed tracking performance for brushless direct drive (BLDD) servo motors (SM) under uncertainties and load variations. A special integral sliding surface suggested for removing the reaching phase problems can define its ideal sliding mode and virtual ideal sliding trajectory from an initial position of SM. The tracking error caused by the nonzero value of the sliding surface is derived. A corresponding continuous control input with the disturbance observer is suggested to track a predetermined virtual ideal sliding trajectory within a prescribed value under all the uncertainties and load variations. The usefulness of the proposed algorithm is demonstrated through the comparative simulations for a BLDD SM under load variations. [Copyright &y& Elsevier]

DC/DC converters require a controller that ensures high performance under the variations of load and source voltage, ensuring stability and a fast transient response at all operating points. This paper provides a detailed analysis of the dynamics of sliding mode boost converter using the locus of a perturbed relay system (LPRS) method. LPRS allows for an exact determination of the amplitude and the frequency of the output voltage oscillations as well as the equivalent gain. Furthermore, it describes the external signal propagation through the system. Analysis of the effect of the source voltage fluctuations on the output voltage waveform is presented in the paper as analysis of exogenous disturbance propagation. The mathematical analysis is verified through simulations and hardware experiments. [ABSTRACT FROM AUTHOR]