Hydraulic cylinder is an indispensable linear actuator in high power applications like construction machinery. In order to reduce the energy consumption, the noise and the waste oil disposal pollution of the hydraulic cylinder control system, the most direct method is adopting the direct pump control technology which eliminates the throttle losses in the main power line. In such system, by changing the speed or the displacement of the pump, the pressure and volume flow will be matched with the need of loads. To date, research works in this field have been reported in many articles, but they are scattered and written in different languages. An overview which can summarize the latest development of this technology appears to be necessary. This paper provides a comprehensive review on this technology, aiming at clarifying recent advances and outlining potential challenges in the research and application of this technology. The review mainly covers three parts: system structure, control, and derived energy recovery system. Also the evolvement of the electro-hydraulic cylinder control system is introduced. The review indicates that attentions should be paid to the control and energy recovery plan of the direct pump controlled cylinder system, and to the newly proposed asymmetric pump controlled differential cylinder technology. It is envisaged that the information gathered in this paper will be a valuable one-stop source of information for researchers, as well as providing a direction for future research in this area.

Review of energy efficient direct pump controlled cylinder electro-hydraulic technology

Mobile hydraulic systems are developed toward better control performance and higher energy efficiency. Pressure compensators, which govern the pressure drops over the control orifices, are widely used in multiactuator systems to improve their operability. However, additional energy is also dissipated in the compensators especially under the overrunning load conditions. This paper presents a novel energy-saving system, where the compensator is designed as a regeneration device consisting of a hydraulic motor and an electric generator. Then, hydraulic energy can be regenerated and pressure compensation function is realized by adapting the electromagnetic torque of the generator to the load as well. The close-loop control of the generator is designed by effective pressure drop estimation. The proposed energy-saving system and controller are implemented on an experimental platform of hybrid excavators which is equipped with an electric energy storage device. The experimental results show both good control performance and significant energy-saving effect.

An Energy-Saving Pressure-Compensated Hydraulic System With Electrical Approach

This paper presents a very fast dc-bus voltage controller for a single-phase grid-connected voltage-source inverter (VSI) with an LCL output filter used in renewable energy applications. In single-phase grid-connected inverters, the design of the dc-bus voltage control scheme is very challenging due to the presence of a second harmonic ripple across the dc-bus voltage. The proposed dc-bus voltage control scheme is able to address the difficulties introduced by the second-harmonic ripple. The dc-bus voltage controller is based on an adaptive droop control technique, which is able to provide a very fast transient response for the closed-loop system and ensures the optimal operation of the VSI during steady-state conditions. Also, the simple structure of the controller makes it very practical for grid-connected VSIs used in renewable energy power conditioning systems. Theoretical analysis and experimental results demonstrate the superior performance of the proposed control approach compared to conventional dc-bus voltage control schemes.

An Adaptive Droop DC-Bus Voltage Controller for a Grid-Connected Voltage Source Inverter With LCL Filter

In this paper, a flatness-based nonlinear controller is proposed to improve the position-tracking performance and to reduce the current input ripple in electrohydraulic systems (EHSs). The proposed method consists of feedforward control using a flatness concept and feedback control to yield a stable control system. This paper presents an analysis on the problem of tracking a reference position, conditions for open-loop stability, as well as an analysis on the flatness of EHS. These results are used for a nonlinear feedforward control design. To further improve the position-tracking performance, feedforward control is augmented with a nonlinear feedback control, which is designed based on the flatness property of EHSs. Moreover, the state variable derivatives are not used so that the measurement noise and structural vibration are not amplified, which in turn can increase the machinery's life expectancy because the current inputs' ripples are reduced.

Flatness-Based Nonlinear Control for Position Tracking of Electrohydraulic Systems

In this paper, we use singular perturbation theory to simplify control designs for hydraulic systems and to make designs more feasible for engineering practice. The paper presents the derivations, simulations and experimental tests of control laws for a hydraulic displacement-controlled actuator. Analyses of applied conditions and stability proofs are provided. The developed control design procedure is simplified and is robust to variations in the bulk modulus. The proposed design is simulated with cases of different control input models. Experiments are conducted on a novel hydraulic circuit. The results show that position tracking error exponentially decays and control efforts are dominated by low-frequency signals.

Application of Singular Perturbation Theory to Hydraulic Pump Controlled Systems

| Introduction | The Flow Control Circuit With Dynamical Compensations | Stationary Stability Analysis | Dynamic Stability Analysis | Compensation Algorithms for the Flow Control Valves | Simulations and Experiments | Conclusion | Acknowledgements | References Abstract < > FIGURES IN THIS ARTICLE Related Content Customize your page view by dragging and repositioning the boxes below. Related Journal Articles

A Hydraulic Circuit for Single Rod Cylinders

Pump controlled hydraulic actuators offer higher energy efficiency than valve controlled actuators. However, there exists mode switching in pump controlled systems and instability may arise when a single rod cylinder is implemented. This paper examines the problem of system stability in a pump controlled system with single rod cylinders. It is shown that the system dynamics have a stable tendency or an instable tendency corresponding to different cylinder movements. The paper shows system instability can be avoided by controlling fluid leakage, and two applicable methods are presented: physical leakage compensation and virtual leakage compensation, which can be applied depending on applications. Experiments and numerical simulations are presented. Results show that the proposed solutions can maintain circuit stability: physical leakage compensation can be a general approach while virtual leakage compensation offers higher energy efficiency and lower cost, but its applications are limited by some factors.

Using Leakage to Stabilize a Hydraulic Circuit for Pump Controlled Actuators

In this paper, we aim to use singular perturbation theory to simplify control designs for hydraulic systems and to make the designs more feasible for engineering practice. The paper presents the derivations and simulations of a control law for a hydraulic displacement controlled actuator. Analysis of applied conditions and stability proofs are provided. The developed control design procedure is simplified and is robust to variations in the bulk modulus. The proposed design is simulated and applied to cases of different control input models. Position tracking error exponentially decays and control efforts are dominated by low frequency signals.

A control approach with application to variable displacement pumps

This paper proposes a robot control approach using a discrete recursive least square algorithm. The scheme shows robustness when the system suffers from measurement noise and has a fast parameter convergence rate. The control algorithm is computationally efficient and numerically stable. Guaranteed trajectory tracking can be achieved by simple parameter design if disturbances are bounded.Copyright © 2009 by ASME

Longke Wang

Papers

Application of Singular Perturbation Theory to Hydraulic Pump Controlled Systems

A Hydraulic Circuit for Single Rod Cylinders

Using Leakage to Stabilize a Hydraulic Circuit for Pump Controlled Actuators

A control approach with application to variable displacement pumps

Adaptive Robust Control of Hydraulic Robots With Recursive Least Squares