Electro-hydraulicactuator (EHA) systems have grown to be one of the most popular actuators in modern applications for several decades. EHA systems can be found easily in production assembly lines, robotics, automotive, aircraft, submarine operations, mining processes, etc. This is due to the fact that EHA systems have fast and smooth response characteristics and high power density. EHA systems also have excellent capability in positioning that gives a significant influence to the above applications especially in position tracking control issues. However, as introduced in Yao et al. (2000), EHA systems exhibit highly nonlinear behaviours, such as nonlinear servo valve flow-pressure characteristics, variations in control volumes, dead-band, stiffness, internal leakage, and associated friction. Apart from the nonlinear natures, parametric uncertainties, uncertain nonlinearities and disturbances also become large extent of EHA systems. Hence, consideration on these issues to obtain more accurate model in the modelling of EHA systems is essential.
systems with both packet dropouts and channel noises in the networked scenario. Literature  developed a distributed state estimation method based on MHE for a class of two- time-scale nonlinear systems. These works have contributed to the teleoperation system based on network communication which enhanced robustness of the networked controlsystem. Advanced controllers, including slidingmode con- trollers (SMCs) and adaptive controllers, have recently been developed for teleoperation systems in order to obtain accu- rate trajectory tracking and faithful force feedback. One slidingmode approach, the three-modecontrol scheme, can implehent a position–position, force–force, or force–position scheme, and the results show good trajectory tracking per- forhance . However, it does not consider time delay. To solve the problem of the adverse effects of parametric uncertainties, an adaptiveslidingmodecontrol scheme was proposed by Motamedi et al. . The algorithm has been verified on a teleoperation system with a single degree of free- dom (DOF). Yang and Hua  proposed a novel nonsingular fast integral terminal slidingmode (NFITSM) for a teleoper- ation system, and practical experiments on one-DOF motion tracking have now been completed. A nonsingular terminal slidingmode and adaptive finite-time control method was proposed by Zhang et al. , and simulation results have verified the effectiveness of this method. These methods are useful attempts to design feedback controllers that improve the performance and stability of a teleoperation system.
In that regards Poley (Poley, 2005) in his work developed a digital controller for an electro-hydraulic using the digital signal processor (DSP) C2000 series which was new at that time and has a distinguishing feature that it has assisted structures for programming. Hence, the advantage of using digital systems was harnessed with relative ease, and it entailed improved performance and flexibility. In another contribution in control of the electro-hydraulic systems Bonchis (Bonchis, 2001) proposed a position controller using variable structure algorithm for such systems with the aim of eradicating errors caused by frictional disturbances which are nonlinear in nature. In the research the load on the system and the disturbances were regarded as external perturbations, and results showed that the control scheme was effective. Zhong and He in 2008 (Zhong and He, 2008) proposed solution to arrest the time varying disturbances and nonlinearities associated with the electro- hydraulic systems by utilizing a combination of fuzzy logic and neural networks techniques. They also employed a method known as the hierarchical fuzzy error with the aim of improving the weight and convergence rate of the neuro-fuzzy system. Results showed that the developed system was able to improve on accuracy and robustness of the system (Zhong and He, 2008). In the work of Troung and Ahn (Troung and Ahn , 2009) a sandwich of grey predictor and fuzzy logic was utilized to improve on the overshoot and settling time response of a hydraulicactuatorsystem. The proposed method also showed ability to reduce disturbances both internal and external. In another development by Guan and Pan (Guan and Pan, 2008) an adaptiveslidingmodecontrol scheme was developed for the electro-hydraulic systems to curb the effects of both linear and nonlinear unknown parameter variations in such systems. Results show that the proposed method was effective with good system stability.
Given that many of the inherent nonlinearities are omitted in EHAs, the system dynamics can be well char- acterized by a linear model . Hence, complicated con- trollers such as adaptive controllers , slidingmode controllers , and fuzzy controllers  are not neces- sary, while those are often implemented in hydraulic systems. However, actuator efficiencies still introduce nonlinear effects. Figure 3 shows the volume and torque efficiencies for the S-380 actuator made by Eaton Indus- tries Ltd., and used in this study . Note that actuator efficiencies are dependent on the angular velocity. Fur- thermore, efficiencies in the low speed domain are not given; high oil leakage in the low-speed domain poses a challenge in the accurate estimation of efficiencies. The effects of oil leakage are characterized as static friction because the applied force decreases in the low speed
will be generated probably in the steady state and there will be chattering when there is strong disturbance in the system. A novel slidingmode controller based on extended disturbanceobserver is studied for a class of underactuated systems in reference, aiming to cut down the chattering effect in . But small oscillation still exists in the system state when disturbance is added. Document  proposes an adaptive hierarchical slidingmodecontrol method based on extended state observer for the practical application of spherical robots. The designed closed-loop controlsystem of the spherical robot possesses robust and adaptive capabilities to overcome the uncertain rolling resistance but the response time of the system is slow and chattering exists. The proposed controller strategy that the integral slidingmodecontrol and the optimal feedback control law is composed in . The main advantages of the proposed approach are ensuring the robustness throughout the whole system response against the uncertainties, decrease the chattering effect and eliminate the reaching phase. But the simulation experiment system is linearized. A unified adaptive second order slidingmodecontrol method is devised. By using the proposed control structure, the upper bounds of uncertainties are not required, the over-estimation of the control gains are avoided, and the chattering of the conventional slidingmode controllers can be attenuated in . But only simple disturbance phenomena are analyzed, and complex disturbance factors are not analyzed.
Other control techniques in active suspension designs include nonlinearity nature of the system. Back stepping control techniques has been considered by .  proposed a work on fuzzy control design technique using full vehicle model for nonlinear active suspension system with hydraulicactuator.  proposed a designed controller using slidingmodecontrol method; also adaptiveslidingmodecontrol was looked into by . All the results found in the literatures bring about some improvement into the system.
In most of the considered research, the boundaries of the perturbations are directly employed in the design of the TSMC law [22,23]. To estimate the disturbances, various design procedures based on the disturbanceobserver have been planned in the recent years . In , SMC has been established for the control and stabilization of uncertain and nonlinear dynamical systems using the disturbance observers. In , a novel multiple-surface SMC is recommended for the uncertain nonlinear systems and a disturbance- observer-based approach is dened to estimate the mismatched uncertainties of the system. In , the design procedure of the adaptive nite reaching time controllers for the rst- and second-order dynamical systems with perturbations is investigated, where the suggested controllers are continuous and retain robust- ness to the disturbances. The combination of FTSMC and Global Sliding-Mode (GSM) surface for the robust tracking control of nonlinear second-order systems with time-varying uncertainties is investigated in . A recursive FTSMC technique for tracking control of non- holonomic systems in the chained form is proposed in , where the tracking errors are allowed to decay to the origin in the nite time with an exponential decay rate. A disturbance-observer-based recursive TSMC tracker is presented in  for the nite-time tracking control of third-order non-holonomic systems with unknown external disturbances. An adaptive FTSMC technique combined with GSM scheme is
It is well known that hydraulic pitch systems play a signiﬁ- cant role in limiting the output power of wind turbines and reducing unbalanced blade loads by IPC system under high wind conditions (Lan et al. (2018)). Nevertheless, pitch systems often suﬀer from low pressure faults caused by oil leakage in the hydraulic supply system, resulting in slow pitch dynamics and further negative eﬀects on operational stability and even accelerating the blade vibrations. Fault tolerant control (FTC) can compensate fault eﬀects and maintain satisfactory system performance under faulty cases (Patton (2015)). There has been a few papers focus- ing on the detection and compensation of faults occurred in the pitch system. The fault detection and fault isolation (FDI) is used in the work of Sloth et al. (2011) to detect the occurrence of the actuator faults. Fault estimation (FE) observer-based FTC design has been demonstrated to be competent at obtaining the pitch actuator fault reconstruction compared with FDI (Chen et al. (2013), Shi and Patton (2015)). However, very little work has been reported to consider IPC cases, this can be a disadvantage. The remainder of this paper is organized as follows.
The super-twisting control law (STW) is one of the most powerful second order continuous slidingmodecontrol algorithms that handles a relative degree equal to one. It generates the continuous control function that drives the sliding variable and its derivative to zero in finite time in the presence of the smooth matched disturbances with bounded gradient, when this boundary is known. Since STW algorithm contains a discontinuous function under the integral, chattering is not eliminated but reduced. The knowledge of the boundaries of the disturbance gradient are required in STW. In many practical cases this boundary cannot be easily estimated. The overestimating of the disturbance boundary yields to larger than necessary control gains, while designing the STW control law. The adaptive-gain STW (ASTW) control law, which handles the perturbed plant dynamics with the additive disturbance or uncertainty of certain class with the unknown boundary, was proposed in  to overcome this drawback.
The Electro-HydraulicActuator (EHA) system, due to its excessive strength to weight ratio and stiffness reaction being more precise, smooth and fast, is one of the crucial force systems in industrial sectors and most engineering practices around the world. Owing to such wide applications, the best overall performance of the electro-hydraulic actuators with regards to its position, force or pressure is necessary. It is however worthy of note that the system is tremendously nonlinear due to many elements, such as leakage, friction, and specifically, the fluid flow expression through the servo valve . Such characteristics, which are prevalent within the system have significantly contributed to the degradation of its overall performance. Upon closely looking into studies such as –, it was discovered that the slidingmodecontrol (SMC) as efficient and broadly implemented in comparison
In this paper a new method has been presented to modeling of doubly-fed induction generator (DFIG)based wind turbine, and a new scheme of slidingmodeobserver of Double Fed Induction Generator, based on theestimation of the value of the rotor resistance. The estimation of the rotor resistance is based on the use of theerror between real and estimated value of DFIG in faulty condition, this will have to improve the performances ofrobustness and stability and precision for the slidingmodeobserver. The results show that the proposed, even inpresence of rotor resistance variation. The FTC control strategy has been validated steady-state conditions byMatlab/simulink.
This paper relates to active steering system which is an integrated steering support system for cars. The system is close to the steering systems on conventional cars but with additional functionality to withstand with disturbances such µ-split which is a split adhesion coefficient between wheels, and wind gusts or decreased road adhesion conditions. Therefore, influenced by , the main purpose of this paper is to propose a slidingmodeobserver based controller (SMOC) for a single track model. The design of the slidingmodeobserver is based on the slidingmode controller in the paper mentioned. There are two main features of this paper:
In general indeed, due to sensor limitations (for cost reasons, technological constraints, etc.), the directly measured signals do not coincide with all signals characterizing the system behavior. Those signals of interest roughly include time-varying signals characterizing the system (state variables), constant ones (parameters), and unmeasured external ones (disturbances). This need for internal information can be motivated by various purposes: modeling (identification), monitoring (fault detection), or driving (control) the system, all these being required for keeping a system under control, as summarized by figure (Fig. 2) hereafter.
Similar results are observed for varying τ 2 , and d c . Fig. 15 summarizes the model predictions as a cross plot of contact velocity versus transition time. It also shows measured closed-loop results that will be discussed later. The model results demonstrate that, for a simple open-loop control scheme (varying τ 1 , τ 2 , and d c ), minimizing the contact velocity increases the transition time. Of course, the voltage command sequence used here is not optimal, but this simple control scheme is clearly limited because the results for contact velocity and transition time fall outside of the desired range. Similar behavior with "one-step- change" current trajectory has also been presented in . One can allow the voltage to switch on and off following an optimal pattern. The optimal number of switches can be determined numerically using a model and optimization techniques similar to the ones in .
Electro-Hydraulicactuator is common tools used in the industries. This is due to accurate positioning toward the load and fast response make it as major instruments for the industries process. This paper presents experimental work on non-recursive identification of electro-hydraulicactuatorsystem that represented by a discrete-time model in open-loop configuration. A least square method is used to estimate the unknown parameters of the system based on auto regression with exogenous input (ARX) model. The plant mathematical model was approximated using system identification by aid of System Identification Toolbox of Matlab from open-loop input-output experimental data. These models have been validated by R 2 or best fitting criterion, root mean square error and correlation analysis to determine the adequate model for
The controller is an important component in the nonlinear controlsystem, especially for the s ys tem that needs a ccuracy i n position tra cking. El ectro-HydraulicActuator (EHA) s ys tem i s a popular nonlinear s ystem that is used by researchers. Proportional- Integral-Derivative (PID) controller is the most popular controller that is normally used i n the i ndustry. This i s mainly because of i ts simplicity i n the design process. However, there are three constants that need to be assigned in the PID controller, often we called thi s as the parameters s election process or the PID tuning process. In this paper, a compa rison s tudy for the s election process of the PID pa ra meters process will be conducted a mong Zi egler-Nichols tuni ng method, conventional Pa rti cle Swarm Opti mization (PSO) technique and Pri ority-based Fitness Pa rticle Swarm Optimization (PFPSO) technique. PFPSO is one of the i mproved versions of the conventional PSO technique. The s imulation study wi ll be conducted on a nonlinear Electro -Hydraulic Actua tor (EHA) system. A simple robustness test on the PID controller will be evaluated i n terms of actuator i nternal leakage. Results s howed that the PID performed better when its controller’s parameters are selected using PFPSO technique rather than the Zi egler-Nichols method and conventional PSO technique.
In , a good review on neutral point dc control is done and active, passive and hysteresis control methods are compared. Passive control, where the positive and negative small vectors are selected alternatively in each new switching cycle, is suggested for perfectly balanced loads. The hysteresis type control is the simplest method for NP control and requires the knowledge of current direction and then a suitable small vector is selected to compensate NP voltage. At last, the active control is a complicate method and requires measurements of NP voltage and phase currents to control current modulation indexes of small vectors. This method increases the switching losses due to additional switching states.
Nonlinear control is a field of control theory used when the system is time- variant and nonlinear. The nonlinear control widely used in many applications it deals with a wider type of systems that do not follow the superposition principle. The mathematical techniques of nonlinear become more accurate that used to handle all the real-time systems. The nonlinear controller design used in many applications to achieve the perfect performance of the system and used to dealing with the nonlinear electro- hydraulicsystem. Nonlinear control includes several feedback controllers employ for trajectory tracking control of nonlinear electro-hydraulicactuator such as slidingmodecontrol (SMC) .
Abstract—This paper studies the application of the slidingmodecontrol method to reduce the vibration of flexible structure with piezoelectric actuators and strain gage transducer in practical complex environment. The state- space dynamic model of the system was derived by using finite element method and experimental modal test. The structure is subjected to arbitrary, unmeasurable disturbance forces. Taking into account the uncertain random disturbance and measurement noise, Kalman filter is chosen as the state estimator to obtain the modal coordinates and modal velocities for the modal space control. A slidingmode controller is adopted due to its distinguished robustness property of insensitiveness to parameter uncertainties and external disturbances. The sliding surface is determined by using optimization method, and the sliding controller is designed by applying Lyapunov direct method. That is, along the switching surface, the cost function of the states is minimized. A real-time controlsystem was built using dSPACE DS1103 platform, and vibration control tests were performed to experimentally verify the performances of the proposed controller. The results of experiment show the controller can effectively attenuate elastic vibration of the structure.
The ability of EHA system such as high power to weight ratio, fast and smooth response characteristic, accurate positioning of heavy load, stiffness response and good power capabilities have increased the number use of EHA in industries. For an example injection molding machines as shown in Figure 2.3. Injection molding machines have several steps that needed to produce a product. The step is clamping, injection, dwelling, cooling, mold opening and removal of products. This method is suitable for production that produces with complicated shapes. Moreover, EHA system is the best way to implement in this method. This is because EHA produces high power to weight ratio and also accurate positioning for plastic processing. In addition, application of wind turbine also implement EHA system. The fundamentals and principles of hydraulicsystem used for wind turbines, such as for pitch control, yaw control, braking and cooling or filtration systems. For pitch controlsystem, the function is to adjust the pitch turbine blade angle based on Figure 2.4. Basically, the technical feature electrohydraulic pitch controlsystem is precision control, high level of integration, compact design, reliable fail-safe function, integrated safety function and high positioning forces.