Showing papers on "Hydraulic machinery published in 2020"
TL;DR: This paper proposes a new control design method for high-order servo systems with hydraulic actuator dynamics, where the backstepping scheme is avoided and only the system output is required for the control implementation.
Abstract: Most of the existing control methods for servo systems driven by hydraulic actuators have been developed by using a backstepping scheme and assuming that all system states (including internal hydraulic signals) are measurable. In this paper, we propose a new control design method for high-order servo systems with hydraulic actuator dynamics, where the backstepping scheme is avoided and only the system output (e.g., motion displacement) is required for the control implementation. For this purpose, the system model is first transformed into a canonical form, where the unknown dynamics in the system are lumped as one term. Then, we introduce a simple robust unknown dynamics estimator (UDE) that has only one tuning parameter but achieves exponential error convergence to accommodate the lumped uncertainties. Therefore, the function approximators (e.g., neural network and fuzzy systems) can be avoided, leading to reduced computational costs, simpler parameter tuning, and improved convergence as compared to backstepping methods. Extensive simulations and experiments based on a realistic test rig are conducted to show the efficacy of the proposed control.
105 citations
TL;DR: To achieve precision motion control, an adaptive robust control with a backstepping design is proposed for an electrohydraulic system, where the cylinder actuator is direct-driven by a servomotor pump.
Abstract: Pump control hydraulic systems can achieve high efficiency by the advantages of no throttling loss and high power-to-volume ratio. However, low tracking accuracy and slow frequency response are main drawbacks for the applications of pump control hydraulic systems, because of the existing high-order dynamics, uncertainties, and highly nonlinear dynamics. Recently, the advent of servomotor-pump direct-drive electrohydraulic systems shows a good prospect for this issue, and the design of the control algorithm is the key to achieve high motion accuracy. In this article, to achieve precision motion control, an adaptive robust control with a backstepping design is proposed for an electrohydraulic system, where the cylinder actuator is direct-driven by a servomotor pump. Considering the high-order dynamics and nonlinearities of hydraulic systems, the controller is processed in two steps: position tracking step and pressure step. Besides, the pump flow deviation under low speed is another important limitation for good control performance. Thus, a nonlinear pump flow rate mapping is proposed by practical fitting and used into the controller design by the proper nonlinearity compensation of the desired pump flow. Comparative experiment results show that the proposed control strategy achieves high motion control performances in spite of the nonlinearities and uncertainties.
63 citations
TL;DR: In this paper, a basic introduction to the civil aircraft piston pump is presented, including the classification, structure, working principle, design features, and achievements by some research groups, and the future directions of the aircraft pump are reported from various perspectives.
62 citations
TL;DR: The energy regulation response mechanism of the hydrolic-transmission system in the wave energy power-generation system is proved and the energy output curve under different parameter regulations is drawn.
Abstract: This paper develops the dynamic response of a hydrolic-transmission system of wave-power devices under random wave conditions. Through theoretical calculation and experiment analysis, the mathematical model of the hydrolic-transmission system was built to make clear which parameters are related to electric-energy output. The working characteristics of the main parameters are developed through the designed experimental platform. The charging pressure of the accumulator, which affects the rigidity of the hydrolic-transmission system, is analyzed. The throttle valve opening and symmetrical electric loads, which affect the stability and efficiency of the electric energy output, are analyzed. Thus, the energy output curve under different parameter regulations is drawn. Through the orthogonal experimental method, the law curve is further modified, the design principle of hydraulic system parameters under the sea level condition is established, and the optimal design scheme and regulation strategy to the hydraulic conversion system of the power generation device is obtained, to solve the problem that the multiparameter coupling cannot be adjusted quickly and effectively. The energy regulation response mechanism of the hydrolic-transmission system in the wave energy power-generation system is proved.
57 citations
TL;DR: An adaptive neural network (NN) controller is proposed for a class of nonlinear active suspension systems (ASSs) with hydraulic actuator to eliminate the problem of “explosion of complexity” inherently in the traditional backstepping design.
Abstract: In this paper, an adaptive neural network (NN) controller is proposed for a class of nonlinear active suspension systems (ASSs) with hydraulic actuator. To eliminate the problem of “explosion of complexity” inherently in the traditional backstepping design for the hydraulic actuator, a dynamic surface control technique is developed to stabilize the attitude of the vehicle by introducing a first-order filter. Meanwhile, the presented scheme improves the ride comfort even when the uncertain parameter exists. Due to the existence of uncertain terms, the NNs are used to approximate unknown functions in the ASSs. Finally, a simulation for a servo system with hydraulic actuator is shown to verify the effectiveness and reliability of the proposed approach.
57 citations
TL;DR: In this article, the authors employed a high-speed imaging method to explore the spatial patterns and time evolutions of cavitation structures and utilized a hydroacoustic pressure transducer to record and analyze local pressure pulsations due to the collapse of the cavities in the hydrofoil wake region.
Abstract: Cavitation is a process of liquid evaporation, bubble or vapor sheet formation, and further collapse of vapor structures, which plays a destructive role in many industrial applications. In marine transport and hydraulic machinery, cavitation usually occurs nearby the surface of a ship propeller and rudder, impeller blades in a pump, and distributor vanes and runner blades in a hydroturbine and causes various undesirable effects such as vibrations of frameworks and/or moving parts, material erosion, and noise enhancement. Based on an extensive literature review, this research is aimed at an experimental investigation of a passive approach to control cavitation on a benchmark hydrofoil using a wedge-type vortex generator in different flow regimes with a high Reynolds number. In this study, we employed a high-speed imaging method to explore the spatial patterns and time evolutions of cavitation structures and utilized a hydroacoustic pressure transducer to record and analyze local pressure pulsations due to the collapse of the cavities in the hydrofoil wake region. The results show that the examined control technique is quite effective and capable of hindering the formation of cloud cavities and reducing the amplitude of pressure pulsations associated with unsteady cavitation dynamics. This study provides important experimental information, which can be useful for improving industrial technologies and for promoting new developments in this particular research field.
56 citations
TL;DR: The results suggest that Amazonian trees, both small and large, have limited capacity to acclimate their hydraulic systems to future droughts, potentially making them more at risk of drought-induced mortality.
Abstract: The fate of tropical forests under future climate change is dependent on the capacity of their trees to adjust to drier conditions. The capacity of trees to withstand drought is likely to be determined by traits associated with their hydraulic systems. However, data on whether tropical trees can adjust hydraulic traits when experiencing drought remain rare. We measured plant hydraulic traits (e.g. hydraulic conductivity and embolism resistance) and plant hydraulic system status (e.g. leaf water potential, native embolism and safety margin) on >150 trees from 12 genera (36 species) and spanning a stem size range from 14 to 68 cm diameter at breast height at the world's only long-running tropical forest drought experiment. Hydraulic traits showed no adjustment following 15 years of experimentally imposed moisture deficit. This failure to adjust resulted in these drought-stressed trees experiencing significantly lower leaf water potentials, and higher, but variable, levels of native embolism in the branches. This result suggests that hydraulic damage caused by elevated levels of embolism is likely to be one of the key drivers of drought-induced mortality following long-term soil moisture deficit. We demonstrate that some hydraulic traits changed with tree size, however, the direction and magnitude of the change was controlled by taxonomic identity. Our results suggest that Amazonian trees, both small and large, have limited capacity to acclimate their hydraulic systems to future droughts, potentially making them more at risk of drought-induced mortality.
51 citations
TL;DR: An advanced position controller incorporated with effective disturbance observers (DOs) applied for a pump-controlled hydraulic system is proposed in this article and uncertainties are considered as certainties (nominal terms) and their deviations.
Abstract: Researches for improving the control performance of hydraulic systems in both control accuracy and energy efficiency have never stopped in aerospace and industrial applications. The existence of nonlinearities, uncertainties, and unknown terms in the system dynamics, however, significantly limits the desired performance. To realize improvements by dealing with these problems, an advanced position controller incorporated with effective disturbance observers (DOs) applied for a pump-controlled hydraulic system is proposed in this article. Here, uncertainties are considered as certainties (nominal terms) and their deviations. To eliminate certain nonlinearities in the system dynamics, the proposed controller is designed based on a simplified robust sliding-mode-backstepping scheme. The lumped unknown terms, which mainly degrade the performance of the controller, in pressure dynamics and force dynamics are expanded by using equivalent nonautonomous models. To effectively approximate the terms and to ensure usability of the estimated results inside the control framework, two different high-order DOs are developed. Asymptotic convergences of these observers are achieved by adopting nonlinear combinations of the estimation errors. Effectiveness and feasibility of the designed observers and the closed-loop system for an asymptotically tracking performance in the presence of bounded time-varying disturbances are then confirmed by Lyapunov-based proofs and extensive experiments.
48 citations
TL;DR: A robust constrained output feedback approach employing sliding mode controllers is proposed for the nonlinear active suspension system equipped with hydraulic actuators, establishing robust control performance with high-performance improvements for ride comfort in the presence of parametric uncertainties, sensor noise, and over variable driving velocities for different road conditions.
Abstract: The nonlinear active suspension control design can be analyzed as a multiobjective control problem that caters to the enhancement in ride comfort levels while ensuring that road holding is maintained with the constrained suspension displacement movement. In this article, a robust constrained output feedback approach employing sliding mode controllers is proposed for the nonlinear active suspension system equipped with hydraulic actuators. Adhering to mechanical design limitations, the suspension displacement and the corresponding displacement rate are constrained using asymmetric barrier Lyapunov functions. Consequently, a nonlinear control law that incorporates the first-order sliding mode control is then formulated to regulate the hydraulic valve and thereby provide an active control effort. The robust control performance with high-performance improvements for ride comfort in the presence of parametric uncertainties, sensor noise, and over variable driving velocities for different road conditions is established using simulation studies.
35 citations
TL;DR: An intelligent fault diagnosis approach based on Dempster-Shafer (DS) theory is proposed specifically for detecting several faults occurred in hydraulic valves using a novel ensemble approach which introduces information fusion theory.
32 citations
TL;DR: The validation results demonstrate that the hybrid wind turbine achieves better performance in both the maximum wind power extraction and power quality than the hydrostatic wind turbine, and the proposed H∞ loop-shaping pressure controller has better tracking performance than the traditional proportional integral controller.
Abstract: This paper presents the design, modeling, and optimal power generation control of a large hybrid wind turbine transmission system that seamlessly integrates planetary/parallel gear sets with a hydraulic transmission to improve the turbine's reliability and efficiency. The hybrid wind turbine has power splitting flows including both mechanical and hydraulic power transmissions. The turbine transmission ratio can be controlled to continuously vary for the maximum wind power extraction and grid integration. Dynamics of the hybrid wind turbine is modeled as an incremental disturbed state space model based on the dynamic equations of each mechanical/hydraulic element. To achieve good tracking and robustness performance, an optimal H∞ loop-shaping pressure controller is designed, which accurately tracks the optimal load pressure in the hydraulic transmission for maximizing wind power generations. The validations of the proposed hybrid wind turbine and the H∞ loop-shaping pressure controller are performed based on a detailed aero-hydro-servo-elastic hybrid type wind turbine simulation platform with both mechanical geared transmission and hydraulic transmission, which is adapted from the National Renewable Energy Laboratory 5 MW monopile wind turbine model within fatigue, aerodynamics, structures, and turbulence code. The validation results demonstrate that the hybrid wind turbine achieves better performance in both the maximum wind power extraction and power quality than the hydrostatic wind turbine. In addition, the proposed H∞ loop-shaping pressure controller has better tracking performance than the traditional proportional integral controller.
TL;DR: Experimental results show that MVIPC can significantly improve the performance of traditional position-based impedance control, and have an excellent adaptability under different working conditions.
Abstract: In this paper, aimed at the problem of control accuracy when the traditional position-based impedance control is applied in the hydraulic drive unit (HDU) of legged robot, a kind of nonlinear model-based variable impedance parameters controller (MVIPC) is designed. First, the mathematical model of position-based impedance control for HDU is given. Second, the performance of traditional position-based impedance control is tested on the HDU performance test platform under different working conditions, and the experimental results show that the control accuracy of this control method needs to be improved greatly. Thirdly, the control idea of MVIPC is described, and the theoretical derivation is deduced. MVIPC considers the high-order dynamic characteristics of servo valve, pressure-flow nonlinearity of servo valve, oil compressibility and load characteristics. Finally, the control performance of MVIPC is verified on the HDU performance test platform. The experimental results show that MVIPC can significantly improve the performance of traditional position-based impedance control, and have an excellent adaptability under different working conditions. This research can provide an underlying control method of hydraulic systems during the robot locomotion.
TL;DR: The result reveals that the deep neural network model can be effectively used to predict the health of hydraulic cooling circuit.
TL;DR: In this paper, two cooling concepts using fuel as a heat sink are investigated for a hybrid electric aircraft platform with entry into service of year 2035+, 180 PAX and a design range of 1300nm.
TL;DR: A novel RISE term with NN-based feedforward component is developed for the first time to enable the incorporation of model reference adaptive control structure where acceleration signal is not employed and guarantees controlled hydraulic system a semi-global asymptotic stability.
Abstract: It is well known that hydraulic systems typically suffer from heavy disturbances including parametric uncertainties and unknown disturbances. In order to attain high performance tracking control, this paper proposes a composite design of nonlinear neural-networks (NN) and continuous robust integral of the sign of the error (RISE) feedback controller. The control development incorporates a NN feedforward component to have a compensation for unknown state-dependent disturbances and to further improve the accuracy of feedforward compensation, meanwhile input parameter is updated online. To achieve asymptotic stability, a novel RISE term with NN-based feedforward component is developed for the first time to enable the incorporation of model reference adaptive control structure where acceleration signal is not employed. The proposed controller guarantees controlled hydraulic system a semi-global asymptotic stability. For the experimental results, the prescribed transient performance is tested under rectangular trajectory and the steady state performance is tested under sinusoidal trajectory.
TL;DR: It turns out that heat transfer coefficients and pipe diameter are of less importance than accumulator volume and displacement of the hydraulic unit, and their influence on the energy saving potential of the system is discussed.
Abstract: Hybrid drive systems able to recover and reuse braking energy of the vehicle can reduce fuel consumption, air pollution and operating costs. Among them, hydraulic recuperation systems are particularly suitable for commercial vehicles, especially if they are already equipped with a hydraulic system. Thus far, the investigation of such systems has been limited to individual components or optimizing their control. In this paper, we focus on thermodynamic effects and their impact on the overall systems energy saving potential using endoreversible thermodynamics as the ideal framework for modeling. The dynamical behavior of the hydraulic recuperation system as well as energy savings are estimated using real data of a vehicle suitable for application. Here, energy savings accelerating the vehicle around 10% and a reduction in energy transferred to the conventional disc brakes around 58% are predicted. We further vary certain design and loss parameters—such as accumulator volume, displacement of the hydraulic unit, heat transfer coefficients or pipe diameter—and discuss their influence on the energy saving potential of the system. It turns out that heat transfer coefficients and pipe diameter are of less importance than accumulator volume and displacement of the hydraulic unit.
TL;DR: A variable speed hydropower (VSHP) model is developed that can aid the design of controllers that maximize the utilization of power plant for the provision of ancillary services, considering the limitations given by the hydraulic system.
Abstract: The objective of this paper is to develop and analyse a variable speed hydropower (VSHP) model that can aid the design of controllers that maximize the utilization of power plant for the provision of ancillary services, considering the limitations given by the hydraulic system. The model is tested and analysed with more or less conventional controllers to identify critical modes, adverse interactions or other limitations that must be taken into account in the future design of potentially multivariable or more advanced controllers for VSHP. Dynamic tests are performed by simulating step responses in power demand and by comparing responses of the model with the VSHP and with a conventional hydropower plant. A participation factor-based interaction analysis shows that there are no strong dynamic couplings between the hydraulic system of the VSHP and the rest of the grid. This simplifies the tuning of the control system. However, the analysis concludes that some oscillatory modes associated with the hydraulic system become significantly more excited when operating at variable speed; which is due to the larger deviation in turbine rotational speed. Extra awareness when designing the control system is therefore needed to keep the hydraulic system variables within their limits.
TL;DR: A new mechanical–electric–hydraulic dynamic coupling drive system (MEH-DCDS), which integrates the traditional motor and the swashplate hydraulic pump/motor into one, which can realize the mutual conversion between the mechanical energy, electrical energy, and hydraulic energy.
Abstract: To simplify the layout of a purely electric vehicle transmission system and improve the acceleration performance of the vehicle, this paper utilizes the characteristics of the large torque of a hydraulic transmission system and proposes a new mechanical–electric–hydraulic dynamic coupling drive system (MEH-DCDS). It integrates the traditional motor and the swashplate hydraulic pump/motor into one, which can realize the mutual conversion between the mechanical energy, electrical energy, and hydraulic energy. This article explains its working principle and structural characteristics. At the same time, the mathematical model for the key components is established and the operation mode is divided into various types. Based on AMESim software, the article studies the dynamic characteristics of the MEH-DCDS, and finally proposes a method that combines real-time feedback of the accumulator output torque with PID control to complete the system simulation. The results show that the MEH-DCDS vehicle has a starting time of 4.52 s at ignition, and the starting performance is improved by 40.37% compared to that of a pure motor drive system vehicle; after a PID adjustment, the MEH-DCDS vehicle’s starting time is shortened by 1.04 s, and the acceleration performance is improved by 23.01%. The results indicated the feasibility of the system and the power performance was substantially improved. Finally, the system is integrated into the vehicle and the dynamic performance of the MEH-DCDS under cycle conditions is verified by joint simulation. The results show that the vehicle is able to follow the control speed well when the MEH-DCDS is loaded on the vehicle. The state-of-charge (SOC) consumption rate is reduced by 20.33% compared to an electric vehicle, while the MEH-DCDS has an increased range of 45.7 m compared to the EV. This improves the energy efficiency and increases the driving range.
TL;DR: The load-sharing based reliability model using survival signature to conduct system reliability assessment is proposed and the effectiveness and feasibility of the proposed methodology are demonstrated by the successful application on the hydraulic system of wind turbines.
TL;DR: In this article, the erosive behavior and influence of solid particles in hydraulic spool valve without notches were investigated and the exact calculation method of the orifice area under erosion was discussed and put forward.
TL;DR: This work proposes to model a small series hydraulic hybrid vehicle (SHHV) for the power demand of a real driving cycle with a low-cost Bluetooth Scanner.
Abstract: This work proposes to model a small series hydraulic hybrid vehicle (SHHV) for the power demand of a real driving cycle. The real driving cycle was measured with a low-cost Bluetooth Scanner connec...
TL;DR: The paper reviews the state of art hydraulic technologies and indicates the links between them and IM, and reviews the different types of hydraulic valves used when implementing IM.
Abstract: The subject of this paper is the review of advanced technology used in hydraulic systems. The technology in question is termed Independent Metering (IM); this is used in hydraulically driven mobile machinery, such as agricultural, construction, municipal, and forestry vehicles. The idea behind the concept is to modify the connection between the actuator, which could be a cylinder or a motor, and a flow control valve. Traditionally, spool hydraulic valves were used to control the fluid flow into and out of hydraulic actuators. This keeps the meter-in and the meter-out of the actuator mechanically connected due to the construction of these valves. This connection makes the control system blind to pressure changes in one of the hydraulic chambers in the actuator. This, in turn, reduces the overall system controllability. It also increases energy losses, especially under an overrunning load. These two main weaknesses led researchers to break this mechanical connection and get into a new technology with different characteristics. The proposed technology was called Independent Metering. New and more complex control techniques can now be applied to the hydraulic systems using this technology that were not possible before or could be applied to more conventional servo design. This paper reviews Independent Metering (IM) and the technologies used or developed in this field to date. The paper reviews the state of art hydraulic technologies and indicates the links between them and IM. It also reviews the different types of hydraulic valves used when implementing IM. This review also discusses some control algorithms, IM layouts, IM challenges, and identifies where further improvements may be achieved.
TL;DR: The eddy current-hydraulic hybrid retarder (EHR), a novel HER, both sides of the rotor are used for hydraulic braking, and the outer ring of theotor generates eddy currents, which simplifies the control system.
Abstract: Heavy-duty vehicles are generally equipped with non-contact hydraulic retarders or eddy current retarders to ensure safe driving during downhill conditions. The torque of the hydraulic retarder is large when the rotor rotates at a high speed, but the torque is small when the rotor rotates at a low speed. As another commonly used retarder, the eddy current retarder has a large torque at a low speed and a low power density at a high speed. High torque at full speed is the vehicles’ requirement for the auxiliary brake system, with no retarders can achieve this goal perfectly alone. Encouragingly, the braking performances of these two kinds of retarders are complementary. Based on the above properties, the eddy current-hydraulic hybrid retarder (EHR) is designed applying the principle of eddy current and the principle of hydraulic braking. In this novel HER, both sides of the rotor are used for hydraulic braking, and the outer ring of the rotor generates eddy currents. The finite element models of the flow field and the electromagnetic field are established separately and solved by computer to predict the braking torque of the EHR. The prototype was developed and the braking performance of the EHR was obtained through the bench tests. Comparing the theoretical calculation results and experimental data, the braking characteristics of the EHR are analyzed. At low speed, the EHR mainly relies on the eddy current braking, whereas at high speed, it relies on both eddy current and hydraulic braking. Moreover, the control of the EHR can be realized only by adjusting the braking torque of the eddy current part, which simplifies the control system.
TL;DR: In this paper, a power take-off oil-hydraulic system is designed for an oscillating wave surge converter, and the adaptation of the converter to the power takeoff is performed with genetic algorithms in order to find out the optimal geometrical and control parameters, while different power take off layout configurations are simulated to maximize their efficiency.
TL;DR: In this paper, a fracture initiated from the constrained (inlet) end as crack nucleated under the metallic sleeve on the pipe surface was observed during scanning electron microscopy (SEM).
09 Jun 2020
TL;DR: In this article, a methodology for designing hydraulic mechatronic systems with the elements of multi-criteria optimization has been developed, which allows designing a me-chatronic system with specified output characteristics.
Abstract: Current trends in expanding the scope of mechatronic systems with a hydraulic drive of active working bodies of self-propelled vehicles require the development of new approaches to solve the problem of improving the output characteristics of hydraulic drives of mechatronic systems with rotary hydraulic machines. It is established that for the drive of active working bodies and running systems of self-propelled equipment, the orbital and planetary hydraulic machines are mostly used. When designing mechatronic systems, much attention is paid to ensuring the specified output characteristics of the actuators of the designed system. A methodology for designing hydraulic mechatronic systems with the elements of multi-criteria optimization has been developed, which allows designing a mechatronic system with specified output characteristics. The optimization parameters of the controls of the mechatronic system with a hydraulic drive of the active working bodies of self-propelled vehicles have been substantiated. This technique involves five stages: the choice of the mechatronic system parameters; substantiation of optimized control parameters; development of a mechatronic system model; optimization of selected parameters of the mechatronic system; analysis of optimization results. The parameters of optimization of controls of a mechatronic system with a hydraulic drive for active working bodies and running systems of self-propelled vehicles have been substantiated. As a result of the studies, the optimal settings of the safety valve of the mechatronic system have been established, providing deviations of the pressure and angular velocity of the actuators from the set ones with an error of 0.17% and 0.67%, respectively.
TL;DR: This study shows that higher use of the hydraulic accumulator power indicates a higher degree of hydraulic hybrids, and shows that the series hydraulic hybrid wheel loader has a fuel saving of 18.9% compared to a hydrostatic wheel loader in the short loading cycle.
Abstract: A wheel loader is representative construction machinery that is designed to load material in off-road applications The vehicle moves back and forth in the loading process, showing great hydraulic hybridization potential The research target in this study is a compact wheel loader By adding hydraulic energy storage device – hydraulic accumulator, it is turned into a series hydraulic hybrid In this paper the system modeling and controllers design of series hydraulic hybrid wheel loader were illustrated A tunable energy management strategy has been proposed and studied By changing the hybrid weight factor in the strategy, the powertrain hybridization degree was adjusted without any additional hardware This study shows that higher use of the hydraulic accumulator power indicates a higher degree of hydraulic hybridization Results show that the series hydraulic hybrid wheel loader has a fuel saving of 189% compared to a hydrostatic wheel loader in the short loading cycle Studies had also been conducted to show the trade-off between the fuel consumption and the vehicle performance with different hybridization degrees
TL;DR: This review summarizes the recent research progress in energy-saving technologies based on pump-valve coordinated systems and discusses the structures of hydraulic systems in different categories of construction machinery, various control methods of the electro-hydraulic system, novel hydraulic hybrid energy regeneration systems, and key components.
Abstract: With the rapid development of the global economy, more and more attention has been paid to the energy conservation of construction machinery. The hydraulic system is the key component of construction machinery, and improving its energy utilization rate has become an important means to achieve energy conservation. In conventional valve-controlled or pump-controlled hydraulic systems of construction machinery, controllability and energy-saving performance typically cannot be considered at the same time. The pump-valve coordinated system combines the energy-saving characteristics of the pump-controlled system and the high-precision and high-frequency response of the valve-controlled system, which has the potential to become a primary research direction of electro-hydraulic systems. This review summarizes the recent research progress in energy-saving technologies based on pump-valve coordinated systems. Particularly, we discuss the structures of hydraulic systems in different categories of construction machinery, various control methods of the electro-hydraulic system, novel hydraulic hybrid energy regeneration systems, and key components. In addition, future directions and challenges of the pump-valve coordinated systems are described, such as independent metering system (IMS), common pressure rail (CPR), and hybrid power source (HPS).
TL;DR: In this paper, the authors proposed a hydraulic performance estimation method focusing on low-head turbine units, which is conducted by using CFD analysis and based on site test results, and introduced the concept of plant hydraulic efficiency, as regards the flow interaction between turbine unit, intake and tailrace.