The rapid industrial development in the fields, such as robotics and high-tech manufacturing, has put forward much higher requirements for the application of high-performance electrohydraulic system, which should not only achieve high control accuracy but also work in a highly energy-efficient way. As we know, a valve control method could achieve good accuracy, but the low energy efficiency is its essential drawback. Conversely, a pump control method could achieve good energy efficiency, but the achievable accuracy is the drawback. Since neither individual valve control nor individual pump control method can meet the dual requirements, a novel idea of advanced valves and pump coordinated hydraulic control design is developed in this article. Within the control details, the high-performance adaptive robust control law is synthesized to handle the nonlinearities and uncertainties of the electrohydraulic system, and the optimized command generation approach for the valves and the pump is developed to attain the high level of energy efficiency while considering the control performance. Essentially, the control command of the pump is based on the desired model compensation to provide the majority amount of flow in an energy-efficient way, and control commands of the valves are generated directly by tracking errors to guarantee the control accuracy. The theoretical performance of the overall system control design is analyzed. Comparative experiments are conducted, and impressive results are obtained, showing that the proposed system could achieve even better tracking accuracy than the typical valve-controlled system, while the energy efficiency reached a high level. The advantages of the advanced system control design can be verified both in theory and experiments.

Advanced Valves and Pump Coordinated Hydraulic Control Design to Simultaneously Achieve High Accuracy and High Efficiency

The electrohydraulic flow matching system is one of the most promising fluid power technologies for the improvement of the control performance and system efficiency of mobile machinery. However, pressure impacts and low efficiencies caused by flow excess are significant drawbacks that hinder its development. To solve this problem, this paper proposes a hybrid displacement/pressure control scheme by utilizing a switching rule according to the pressure margin and the candidate Lyapunov function. The mathematical model of an electrohydraulic flow matching system with primary pressure compensators was established, and the energy efficiency performance was analyzed. Experimental tests in single-actuator and dual-actuator systems were carried out on a test rig with a hydraulic excavator. The experimental results indicated that the pump pressure could be reduced when the supplied flow was excessive, and also the system efficiency was improved. The proposed controller is simple and pragmatic so that it can be easily implemented in the current mobile machinery.

A Hybrid Displacement/Pressure Control Scheme for an Electrohydraulic Flow Matching System

Large energy loss caused by mismatching between the installed power and demanded power, as well as the wasted potential energy, is a serious problem for a hydraulic press. In order to reduce the energy loss, an energy-saving method by balancing the load of operations of presses was proposed based on the analysis of energy flow characteristics of the hydraulic system. In the method, the motor pumps in the drive system are shared in different time by a unit composed of two hydraulic presses so that the energy loss caused by unloading operations can be reduced. Furthermore, these two presses are combined, and the excessive energy from one press can serve as the input energy to the other one during some operations to improve the energy efficiency of the drive system, and the potential energy can be utilized directly. Meanwhile, operation durations of these combined presses are optimized for coordination of working processes. The method was applied to two hydraulic presses in a tandem line, and the energy consumption was obtained by quantifying the characteristics of conversion components. Results indicate that for a single press, 36% of electrical energy can be saved in the investigated forming processes.

An Energy-Saving Method by Balancing the Load of Operations for Hydraulic Press

In mobile machinery, the existing load sensing system is featured by low response and oscillation tendency. As a promising alternative, the Electrohydraulic Flow Matching (EFM) system has the controllability advantages of fast response and good damping, but suffers from the flow mismatch problem leading to pressure impacts and low efficiency. To retain the controllability advantages and reduce flow mismatches of the EFM system, this paper proposes an Electrohydraulic Load Sensing (ELS) system via flow/pressure switched control, in which the pump displacement is controlled by the smaller output of the flow controller and the pressure controller. The actual flow requirement is calculated by the flow feedforward controller, while the pressure margin is kept as a desired value by the pressure feedback controller. The system linearization model is firstly established, and then the theoretical analysis was carried out to investigate the stability performance in the flow or pressure control mode. More importantly, the stability is analyzed under the condition of switching between flow/pressure controls. Using a converted hydraulic excavator, a test rig was constructed to verify the effectiveness of the switched controller. The performance of the existing EFM controller is studied as a comparison The result indicates that the pressure impacts caused by flow mismatches were avoided, and then the energy consumption was reduced. Meanwhile, the velocity performance is consistent with the EFM controller without loss of controllability.

An Electrohydraulic Load Sensing System based on flow/pressure switched control for mobile machinery.

The disturbance suppression is one of the most common control problems in electro-hydraulic systems. especially largely an unknown disturbance often obviously degrades the dynamic performance by biasing the desired actuator outputs (e.g., load forces or torques). In order to reject the dynamic disturbances in some multi-degree-of-freedom manipulators driven by electro-hydraulic actuators, this paper proposes a state feedback control of the cascade electro-hydraulic system based on a coupled disturbance observer with backstepping. The coupled disturbance observer is designed to estimate both the independent element and the coupled element of the external loads on each electro-hydraulic actuator. The cascade controller has the ability to compensate for the disturbance estimating, as well as guarantees the system state error convergence to a prescribed steady state level. The effectiveness of the proposed controller for the suppression of largely unknown disturbances has been demonstrated by comparative study, which implies the proposed approach can achieve better dynamic performance on the motion control of Two-Degree-of-Freedom robotic arm.

Coupled-disturbance-observer-based position tracking control for a cascade electro-hydraulic system

https://purehost.bath.ac.uk/ws/files/141809732/Can_Du_Journal.pdf

Performance analysis of a new energy-efficient variable supply pressure electro-hydraulic motion control method★

RETRACTED: Performance analysis of an energy-efficient variable supply pressure electro-hydraulic motion control system

The subject of this paper is a VPVC (variable pressure valve-controlled) hydraulic actuation system, which is a hydraulic plant with variable supply pressure. The concept is similar to a load sensing system but it is implemented using an electronic controller, instead of a hydraulic one, and the flow is provided using a servo pump, instead of a variable displacement pump. The intention is to maintain a high dynamic response but substantially improve efficiency compared to a conventional system with fixed supply pressure. FPVC (fixed pressure valve-controlled) systems are unable to completely modulate the input energy due to the constant supply pressure. However, since the ability to control the energy flow is usually needed, a proportional valve for each actuator is used to dissipate the extra input energy. This leads to a simple but inefficient way to control, for example, the velocity of a piston. The idea of a VPVC system is that, instead of dissipating energy by throttling flow, it is better to generate less fluid power in the first place: this is achieved by adjusting the speed of the servo pump as well as the spool positions. In this paper, a controller for a VPVC system is presented along with numerical simulations showing a comparison with a fixed pressure system. Up to 70% energy saving is predicted.Copyright © 2011 by ASME

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Performance analysis of a new energy-efficient variable supply pressure electro-hydraulic motion control method★

RETRACTED: Performance analysis of an energy-efficient variable supply pressure electro-hydraulic motion control system

Energy Efficient Variable Pressure Valve-Controlled Hydraulic Actuation