Electro-hydraulic Actuator System Research Articles

PID-based control strategies for enhancing stability and precision in electro-hydraulic actuation systems

Electro-hydraulic actuation systems are essential in industrial applications but often face challenges related to nonlinearity, leading to instability and reduced precision. This paper explores the application of Proportional-Integral-Derivative (PID) control strategies to enhance the stability and precision of these systems. A detailed system model is developed, and the PID controller is designed and tuned using optimization techniques. Simulation results demonstrate improvements in performance metrics, such as reduced overshoot, settling time, and steady-state error. The proposed control strategy is validated experimentally on a physical setup, confirming its effectiveness in real-world applications. The findings show that PID-based control significantly enhances both stability and precision in electro-hydraulic actuation systems, offering a practical solution for industrial control challenges.

Research on position tracking control of electro-hydraulic actuator system combining feedforward inverse model controller and exponential functional link network adaptive controller

The electro-hydraulic actuator system plays a crucial role in indoor high-frequency simulation experiments. Many components of the system exhibit unavoidable nonlinear characteristics, which reduce its dynamic position response capability. Additionally, most algorithms are unsuitable for practical high-frequency conditions due to either local instability or high computational complexity. To improve position tracking accuracy under high-frequency control, a novel combined control strategy is proposed, integrating an appropriate feedforward inverse model controller (FFIMC) with an exponential functional link network adaptive controller (EFLNAC). Initially, the system has reached a stable state under the action of the PID controller. Subsequently, the FFIMC estimates both the model and the inverse model of the PID system by applying the AIC technique developed through the DCT-VSSNLMS adaptive algorithm, which extends the system’s bandwidth. Following this, the EFLNAC, as the outermost loop, acquires the inverse model of the FFIMC system and updates internal parameters in real-time, thereby enhancing the system’s resistance to nonlinear disturbances. Finally, the combined controller is validated through simulations and experiments under various working conditions. The results show a significant increase in the PID system’s bandwidth and demonstrate that the tracking error of the signal is maintained within 0.079 mm. Therefore, the combined controller proves to be an effective solution for high-precision, high-frequency displacement tracking, offering the advantages of low computational complexity, high accuracy, and strong effectiveness.

Enhanced Hybrid Robust Fuzzy-PID Controller for Precise Trajectory Tracking Electro-Hydraulic Actuator System

The Electro-Hydraulic Actuator (EHA) system integrates electrical and hydraulic elements, enabling it to generate a rapid reaction, a high power-to-weight ratio, and significant stiffness. Nevertheless, EHA systems demonstrate non-linear characteristics and modeling uncertainties, such as friction and parametric uncertainty. Designing a controller for accurate trajectory tracking is greatly challenging due to these limitations. This paper introduces a hybrid robust fuzzy proportional-integral-derivative (HFPID) and (HF+PID) controller. The controller is designed to effectively control a third-order model of an EHA system for trajectory tracking. It is a significant contribution to the development of an intelligent robust controller that can perform well in different environments. Initially, a mathematical model for the EHA system was created using a first-principle approach. Subsequently, the Ziegler-Nichols method was employed to fine-tune the PID controller, while a conventional Fuzzy Logic Controller (FLC) was constructed in MATLAB Simulink utilizing linguistic variables and rule-based control. Without further tuning, the FL and PID controller are combined as a hybrid controller with different structures: Hybrid Fuzzy-PID (HFPID) and Hybrid Fuzzy+PID (HF+PID) controller. The Mean Square Error (MSE) and Root Mean Square Error (RMSE) are utilized as indices to assess the tracking accuracy and robustness of the four controllers. A greater value of MSE and RMSE indicates poorer performance of the controller. The results demonstrate that the HF+PID controller surpasses the other controllers by reaching the lowest MSE and RMSE values. It showcases the efficacy and accuracy in monitoring sinusoidal, multi-sinusoidal, and point-to-point trajectory tracking. Future work should focus on implementing the designed controller on hardware for real-time performance and experimenting with various types of FLC or Hybrid controllers, such as self-tuning fuzzy-PID, to further explore their potential.

Model-Assisted Muti-source Fusion Hypergraph Convolutional Neural Networks for intelligent few-shot fault diagnosis to Electro-Hydrostatic Actuator

Electro-Hydrostatic Actuator (EHA) is a critical electro-hydraulic actuator system widely used in aerospace equipment. To ensure its normal operation, the intelligent fault diagnosis of the EHA system has gained increasing attention. However, the EHA exhibits strong nonlinearity, high structural complexity, and difficulty obtaining fault samples. A Model-Assisted Multi-source Fusion Hypergraph Convolutional Neural Network (MAMF-HGCN) is proposed to address the few-shot intelligent fault diagnosis of EHA. Specifically, the fault data obtained from the hydraulic simulation model is used to establish the relationship among each channel signal. This assists in constructing a hypergraph structure for actual multi-source fault data under limited samples. Each node in the hypergraph employs message transmission to fuse signals from different channels. Subsequently, the hypergraph data are input into the constructed hypergraph convolutional neural network to perform fault classification. Finally, validating the EHA hydraulic system test rig from Nanjing University of Science and Technology illustrates the method’s effectiveness in diagnosing hydraulic system problems under limited fault samples.

Atomic physics-inspired atom search optimization heuristics integrated with chaotic maps for identification of electro-hydraulic actuator systems

Electro-hydraulic actuator system (EHAS) has imposed a challenge in the research community for accurate mathematical modeling and identification due to non-linearities. In this paper, autoregressive exogenous (ARX) structure is used for EHAS modeling and identification is performed by exploiting the competency of atomic physics-based chaotic atom search optimization (CASO) that adapts ten chaotic maps (Chebyshev, Circle, Gauss, Iterative, Logistic, Piecewise, Sine, Singer, Sinusoidal and Tent) in position update of atom search optimization (ASO). The fitness/merit function of the EHAS model is developed in mean-square error (MSE) sense between desired and approximated values. Simulations and analysis show that ASO with a chaotic logistic map (CASO5) performs better than the ASO and its other chaotic variants, as well as other recently introduced metaheuristics for diverse variations in the system model. Statistics based on MSE, learning plots, results of autonomous trials and average fitness analyses verify the consistency and reliability of the CASO5 for the identification of the EHAS model.

Modeling and Development of Predictive Controller for Positioning Control of Electro-Hydraulic Actuator (EHA) System

Modeling and Development of Predictive Controller for Positioning Control of Electro-Hydraulic Actuator (EHA) System

Position control performance analysis of linear actuator in swashplate-controlled electro hydrostatic actuation system

The position control of an energy efficient electrohydraulic actuation system is a decisive characteristic of its performance. In position control applications, a servo valve and/or variable displacement pump are vital to control the position of the linear actuator. In this open-loop control experimental work, the position of a linear actuator having a stroke length of 0.2 m is controlled by a swashplate-controlled electro hydrostatic actuation system. LabVIEW is used to create the control algorithm, and the National Instrument compact-RIO controller is used to control the voltage supply. The National Instruments controller processes sinusoidal and square demand signals at frequencies of 1/16, 1/12, 1/8, and 1/4 Hz. Open-loop control performance is predominantly dependent on the appropriate tuning of the voltage supply. Control performance is evaluated using the parameters integrated absolute error, integrated square error, integrated time absolute error, and integrated time square error. In comparison to square demand, it has been found that sinusoidal demand offers better position control accuracy, and square demand also offers appropriate control accuracy only at lower frequencies (1/16 Hz).

State-observer-based asymptotic tracking control for electro-hydraulic actuator systems with uncertainties and unmeasurable velocity

In this paper, a velocity estimation-based adaptive dynamic surface asymptotic tracking control strategy for electro-hydraulic actuator (EHA) systems subjected to uncertainties and unmeasurable velocity is proposed. Firstly, an accurate velocity signal is estimated by constructing a new state observer, reducing the influence of measurement noise, system cost, and installation complexity. Moreover, the observer's robust gain is updated by an adaptive law, reducing the conservativeness of its selection. Then, a continuous friction model based on the desired velocity signal is used for feedforward compensation to alleviate the negative effect of estimation noise. Moreover, the adaptive dynamic surface control (ADSC) technique is incorporated to avoid “complexity explosion” and eliminate filtering errors via adaptive terms. Finally, the asymptotical stability of the closed-loop system is theoretically proved via Lyapunov analysis, while the efficacy of the proposed control strategy is experimentally validated and numerically verified.

A power-sharing electro-hydraulic actuator system to downsize electric motors for electric mobile machines

Hydraulic drives are popular in multiple industries due to their high-power density, robust operation, and low cost. However, they often suffer from low energy efficiencies, particularly in mobile applications where multiple functions are powered by a single pump. Decentralized hydraulic solutions, such as electro-hydraulic actuators, have emerged as a more efficient alternative. Nevertheless, the oversized electric motors compared to centralized solutions prevent it from penetrating the market. Therefore, in this paper, a power-sharing electro-hydraulic actuator system with planetary gearsets is proposed. This system allows for high-level system efficiency and downsized electric drive system, making it applicable to a wide range of applications. A minimum power loss strategy and system parameter optimization are proposed. The system operation and energy comparison between proposed system and baseline system is presented. Result shows the total installed motor power of proposed system is reduced by 37.0 % (from 138 kW to 87 kW) with a slightly lower overall efficiency.

Harris hawks optimization tuned exponential reaching law based integral SMC for pitch control of linear hydraulic actuated wind turbines

In the present study 5MW NREL horizontal axis wind turbine (HAWT) has been considered for pitch control to reduce fatigue loads and maintain rated power in region III of operation, that is, above rated wind condition. An electrohydraulic linear actuation system has been considered for blade-pitch revolve-motion of the rotor blade, based upon available wind speed. An augmented state improved exponential reaching law integral sliding mode controller (ASIERL-ISMC) has been designed for the HAWT pitch control application. In contrast to the previously reported improved exponential reaching law based controllers, in our ASIERL-ISMC, all state variables and the sliding variable have been considered together to define an augmented reaching law that can enhance the degree of freedom of the controller. Further, hyperparameters of the proposed ASIERL-ISMC have been optimized using Harris hawks optimization (HHO), to achieve superior control performance. The performances of this proposed HHO-ASIERL-ISMC have been compared with existing dynamic exponential term reaching law integral sliding mode controller (DETRL-ISMC) and improved exponential reaching law integral sliding mode controller (IERL-ISMC). The robustness and sensitivity of the proposed ASIERL-ISMC and HHO-ASIERL-ISMC have also been tested with three different available wind data. The proposed HHO-ASIERL-ISMC has been found to provide the most superior performance, in terms of both blade-pitch angle error (computed using integral absolute error (IAE)) and control energy (CE).

Progress in Redundant Electromechanical Actuators for Aerospace Applications

The power to move aircraft control surfaces has advanced from being manually generated (by the pilot and transmitted via rods and links) to electrically transmitted (via wires) to operate control surface actuators. Various hydraulic, electromagnetic, and electromechanical architectures have been developed to provide the necessary power and to maintain the expected redundancy. Numerous aircraft actuator system designs have been proposed in the past decades, but a comprehensive review has yet to be undertaken. This review paper aims to fill this gap by providing a critical review of the actuation system designs developed for a variety of aircraft. The review focuses on aircraft actuator system designs, namely: electrohydraulic actuator systems, electromechanical actuator systems, and the force-fighting effect in redundant actuation systems. The significance and operational principle of each actuator system are critically analysed and discussed in the review. The paper also evaluates the solution proposed to address force-fight equalization (or force-fight cancelation) in force or torqued-summed architectures. Future trends in redundant actuation system development with reduced force-fighting effect in aircraft actuator systems are also addressed.

A novel ESO-based adaptive RISE control for asymptotic position tracking of electro-hydraulic actuator systems

This paper is focused on asymptotic tracking control of electro-hydraulic actuator (EHA) systems subject to matched and mismatched time-varying disturbances. To counteract the matched disturbance, a novel extended state observer (ESO) is proposed to achieve asymptotic convergence of the estimation error, by incorporating the strictly positive real (SPR) Lyapunov design method and a Nussbaum function. To further suppress the mismatched disturbance, an adaptive robust integral of the sign of the error (RISE) controller is formulated in the backstepping framework based on the proposed ESO. Asymptotic tracking performance is theoretically achieved via closed-loop system stability analysis. The efficacy of the proposed control scheme is verified through comparative experiments executed on an EHA test rig. In this study, a priori bounds of the disturbances and their higher-order derivatives are no longer needed, and only one auxiliary error signal is introduced. This approach loosens the restrictions on the disturbances and reduces the design conservativeness, thus making it promising in practice.

Experimental Verification of An Electro-Hydraulic Actuation System Driven by An Integrated Electro-Hydraulic Unit

This paper proposes an electro-hydraulic actuator (EHA) system, and a novel-designed electro-hydraulic unit (EHU) consisting of a fixed-displacement hydraulic gear machine and a variable-speed electric machine. The novel EHU design integrates an electric machine and a hydraulic machine in a single housing, targeting optimal compactness, power density, and component reduction. The EHA system features an open circuit design, where hydraulic hoses connect the EHU with a tank, a valve manifold, and the hydraulic cylinder. In this way, the proposed EHA technology can be used to implement distributed hydraulic actuation in a vehicle without requiring changes to the hydraulic actuators or at the overall layout of the hydraulic components with respect to the original vehicle design. A dedicated test rig is developed to verify the performance of the proposed EHA system. The efficiency of the EHA is measured in a steady state and under a realistic duty cycle of a commercial compact loader. The efficiency of the EHA system based on the measurements on the test rig can reach 54% with up to 20 kN load and 6 kW power level. Furthermore, the EHU is implemented on the reference machine to drive the boom function. Preliminary results on the performance of the EHU show an efficiency of up to 68% under different loading conditions.

Pulsation Test and Analysis of Internal Gear Pump Used in Electro-hydraulic Actuator

The linear conjugate internal gear pump is widely used in the Electro-hydraulic Actuator (EHA) system because of its high efficiency and low noise, especially in the ship domain where vibration and noise requirements are very strict. To find out the reason, the calculation method of flow fluctuation and pressure pulsation at the pump outlet is obtained theoretically. First, the method of obtaining the two characteristic values of pump source flow pulsation Qs and pump source impedance Zs, and the data calculation and processing program are compiled by Matlab. Then the test platform was built, as well as the computer simulation and data collection. According to the theoretical method, the actual flow fluctuation and pressure pulsation at the pump outlet under different working conditions are measured and calculated respectively. The data of each working condition can be summarized and analyzed as: the test platform is reasonable and the data obtained from the test and calculation are reasonable; under the same frequency spectrum, the amplitude corresponding to the fundamental frequency of the motor pump is much larger than that of the pump tooth; under different working conditions, the variation trend of flow fluctuation and pressure pulsation corresponding to the fundamental frequency and the frequency doubling of the internal gear pump is obtained by testing; the specific values are smaller and suitable for the use in a silent system.

Further results on the design of an observer for an electro-hydraulic actuation system with deadzone nonlinearity

In this paper we present further results on the design a non-linear observer for estimating the null current in an electro-hydraulic actuation system. In previous work it was shown that the observer achieves ultimate boundedness of the observation error based on results on the stability of control loops with slope restricted non-linearities. In this work we give a complete characterisation of the asymptotic convergence of the observation error considerably tightening the results obtained earlier.

Delay Estimation for Nonlinear Systems With Unknown Output Delay

In this letter, the problems of delay identifiability and delay estimation for a nonlinear systems subject to constant unknown output delay are studied. Usually, the estimation of such delay is based on a monotonic condition which is hard to satisfy in the case of nonlinear systems. To deal with this open and interesting problem, a change of coordinates is introduced in this letter to transform the nonlinear system to the triangular form. Then, a high order sliding mode observer is designed based on implicit Lyapunov function to estimate the state and delayed-input, based on these estimation, the delay estimator is proposed. The convergence of the proposed observer is proved and the effectiveness of the proposed method is illustrated through simulation results of an Electro-Hydraulic Actuator (EHA) system.

Design of an Optimal Tracking Controller with Unmeasured States for Electro-Hydraulic Actuation System using 4/3 Proportional DC Valve

Design of an Optimal Tracking Controller with Unmeasured States for Electro-Hydraulic Actuation System using 4/3 Proportional DC Valve

Design of an optimal tracking controller with unmeasured states for electro-hydraulic actuation system using 4/3 proportional DC valve

Design of an optimal tracking controller with unmeasured states for electro-hydraulic actuation system using 4/3 proportional DC valve

Design and experimental validation of an adaptive fast-finite-time observer on uncertain electro-hydraulic systems

This paper presents the design of an adaptive fast-finite-time extended state observer for electro-hydraulic actuator systems. First, the system model is divided into three parts, and fast-finite-time state observers are designed independently for each part. This guarantees the fast-finite-time uniform ultimate boundedness of the estimation errors. Then, based on the designed state observers and without neither any knowledge about the upper bounds of the uncertainties nor their derivative, supplementary observers are presented to estimate the unknown terms. Rigorous analyses of the proposed strategy are provided through the Lyapunov approach. The suggested adaptive framework can improve the convergence rate for zones both far from the equilibrium points and around them. The adaptive gains are computed based on the straightforward evaluation of the absolute value of the observation errors, thus their values are valid in real life applications, achieving finite-time estimate of both the full state variables as well as uncertainties. Comparative simulations are presented to analyze the effectiveness of the proposed observers with and without unknown measurement noise. Finally, the effectiveness of the proposed approach in real-life conditions is demonstrated through experimental studies.

Control Synchronization Design of a Multiple Electrohydraulic Actuator System with Linearization Dynamics and an External Disturbance Observer

The control synchronization of multiple electrohydraulic actuators (MEHAs) is initially discussed to ensure the consensus of every electrohydraulic actuator (EHA) with three-order isomorphic dynamics. First, the EHA model is linearized using the Lie derivative method to obtain the state-space model of MEHAs. Then, the disturbance observer is used to estimate and compensate for the unknown external load caused by the driving force of a motion plant. Via the Lyapunov technique, this protocol asymptotically achieves consensus to a zero neighborhood with the ultimate boundaries of the MEHAs’ state errors. The effectiveness of the synchronous control protocol is verified by both simulation and experimental benches with two-node EHAs.