Digital Hydraulic System Research Articles

Performance optimization and testing of a novel energy coupled actuated high-speed valve based on peak-and-hold driving strategy

High-speed on/off valve acts as critical enabling component of digital hydraulics, which has been challenging the traditional hydraulic system by providing efficient and effective hydraulic control solutions. The high-speed on/off valve that ideally fits the digital hydraulic system is expected to achieve fast response and long stroke with affordable energy consumption. This not only requires developing advanced actuation mechanism but also demands extensive study on the driving strategy. This study focuses on investigating the Peak-and-hold driving strategy applied to a novel high speed on/off valve-energy coupling actuated valve (ECAV), in order to achieve target performance with optimized energy consumptions. This work has developed an electro-mechanical coupled physics model based on commercial finite element solver COMSOL. This model helps to investigate the performance of ECAV under different peak-and-hold driving parameters and thereby recommend the optimal peak-and-hold driving strategy. Then, the experimental testing on the prototype ECAV has been conducted to validate the simulated performances. The measurement results showed that the prototype ECA using the optimal peak & hold solution demonstrated significant advantage in energy saving targeting at response of 10 ms for 1.5 mm stroke, especially compared to a typical step input signal.

Characteristics analysis and nonlinear control of a digital hydraulic pressure tracking system for high-speed helicopter wet friction clutch

The reliability and control precision of the engagement and disengagement of wet friction clutch are crucial to the transmission of high-speed helicopters. In contrast to the traditional proportional hydraulic system, the digital hydraulic system provides a viable solution due to the use of several fast switching valves (FSVs). In this research, a digital hydraulic pressure tracking system using two fast switching valve arrays (DHPTS-FSVA) is proposed and its nonlinear model is established. First, the static and dynamic characteristics of the DHPTS-FSVA are deeply analyzed by virtue of the half-bridge resistance theory. Moreover, a novel pressure control strategy is proposed, which consists of nonlinear adaptive control method, differential pulse width modulation (PWM) with pressure compensation, and logic allocation strategy of PWM duty ratio. Finally, comparative simulation and experimental results indicate that the maximum, average, and standard deviation of the errors are reduced by at least 16.1%, 45.1%, and 39.5%, respectively, at the tracking frequencies of 1 and 2 Hz, which proves that the proposed controller exhibits better tracking performance at low frequencies.

Study on the Digital Hydraulic Driving System of the Belt Conveyor

The electrohydraulic equipment of the coal gangue belt conveyor has been widely studied in recent years, but studies have been limited to the traditional hydraulic system with proportional valve and servo valve as control elements. Because of their own structural characteristics, proportional valves and servo valves have inherent defects such as low reliability, high cost and a long debugging cycle. It is necessary to carry out technological innovation and upgrading. This paper presents a hydraulic system scheme which uses digital valves instead of proportional valves and servo valves to control the belt conveyor propulsion system. Firstly, the system scheme is described in detail. Secondly, the simulation model of the control element digital valve is established, and its dynamic characteristics are analyzed in detail. Finally, the displacement tracking control of the new system is carried out to verify the feasibility of the proposed control scheme. The results show that the new digital hydraulic control system can effectively achieve the displacement control function of the belt conveyor propulsion system.

Real-Time testing of novel robust digital pitch controller for digital hydraulic pitch system in wind turbine

ABSTRACT This research work draws insight on developing a novel digital hydraulic pitch system for a large-scale wind turbine. Digital hydraulic pitching can be appropriate for wind turbine application due to its high response, high power-to-weight ratio, and robustness. To perform digital pitch control, a machine learning-based robust digital pitch controller was designed and implemented in the developed real-time test setup. The proposed real-time test setup consist of sub-systems such as digital hydraulic system hardware, real-time interface, robust digital pitch controller, and 5 MW benchmark wind turbine model. Real-time testing was conducted on proposed controller using the developed test setup. Robustness test exhibited robust pitch control tracking when subjected to high wind gusts/fluctuations. In this test, the proposed controller reduced the pitch control error (mean absolute) by 68.10% and 51.75% when compared to feed forward and Elman controller, respectively. Subsequently, a power regulation test was performed on the proposed controller under real-time turbulence wind speed. Relative to the feed-forward and Elman controller, the proposed controller regulates power close to the rated value and improved the mean generator power by 3.39%, and 3.72%, respectively. A comparative study conducted with existing controllers (in the literature) demonstrate the superior performance of the proposed controller. This study reports that intelligent digital pitching action of proposed controller generates power close to rated power when compared to existing controllers in the literature.

UNITATE DIGITALĂ DE POMPARE CU POMPE CU ROŢI DINŢATE UTILIZATĂ PENTRU FURNIZAREA DEBITULUI NECESAR ECHIPAMENTELOR MOBILE CU EFICIENŢĂ ENERGETICĂ MARE

In this article, the authors want to present the benefits of digital hydraulics, by presenting a Digital Hydraulic Pumping System (DHPS), consisting of 4 fixed flow pumps, driven by a biaxial electric motor, 4 3/2 on/off electrohydraulic directional valve, 4/2 types electrohydraulic directional valve and a bidirectional hydraulic motor. With the help of a micro-controller, the 4 3/2 electrohydraulic directional valve, which independently control the output of each pump, are operated in a certain sequence, so that a regulation of the flow provided in the system in 15 discrete points is obtained. Due to the construction of the 3/2 electrohydraulic directional valve (electrohydraulic directional valve with port P to T), but also of the microcontroller, a variation of the flow supplied in the system with low energy losses is obtained. This system is designed within the digital hydraulics laboratory of the INOE 2000-IHP Research Institute, in order to obtain preliminary results, which will also lead to its physical realization. The article contains the results obtained by numerical simulation of using Digital fluid power technology in the field of hydraulic drives, systems which have advantages such as: the use of simple, robust components with a high degree of flexibility and programmability.

Analysis of Dynamic Characteristics and Power Losses of High Speed on/off Valve with Pre-Existing Control Algorithm

A high-speed on/off valve (HSV) is generally the core component of a digital hydraulic transmission system. Therefore, its dynamic characteristics often restrict the overall performance of the digital hydraulic system. Most of the current studies focus on the optimization on the dynamic characteristics or the energy characteristics, few studies have comprehensively considered the two characteristics of the valve together. In this paper, a pre-existing control algorithm (PECA) is proposed to improve the dynamic characteristics of the HSV, and simultaneously optimize the power losses of the HSV to improve its energy conversion efficiency. The results show that, compared with the traditional single-voltage driven strategy, the opening time of the PECA decreases by 29.4%, the closing time decreases by 59.6%, and the energy conversion rate increases by 7.9%.

Optimization of Multi-Way Valve Structure in Digital Hydraulic System of Loader

In this paper, a digital hydraulic variable control method based on multi-way valve spool displacement feedback is proposed, which combines the advantages of low cost and high reliability of the loader fixed displacement pump hydraulic system, and the distinguished energy saving effect of the loader variable pump hydraulic system. Based on the principle of hydraulic resistance, the mathematical model of flow-pressure of multi-way valve was established. Meanwhile, the theoretical structure of a valve spool suitable for digital hydraulic system was deduced. On this basis, an improvement scheme of the valve spool was proposed in combination with machining feasibility. The simulation model of multi-way valve was established, the correctness of which was verified by experiment with the significance test method, and the valve port parameters of the multi-way valve were optimized by genetic algorithm. The simulation model before and after optimization was analyzed by AMESim software. The simulation results showed that the digital hydraulic system can basically realize the function of a variable system, and the energy consumption was significantly reduced compared with the fixed displacement pump hydraulic system. The optimized valve spool structure of the digital hydraulic system had more stable load characteristics than the fixed displacement pump system and a larger speed range. The increase range accounts for about 27% of the total stroke.

Pitch Control of a Digital Hydraulics Pitch System for Wind Turbine Based on Neuro-Fuzzy Digital Pitch Controller

Digital Hydraulics has been implemented in the hydraulic pitch system of Wind Turbine (WT) which aids in uniform power generation at above-rated wind speeds. A novel Digital Hydraulic Pitch System (DHPS) model which uses a hydraulic motor as the end actuator was established and a wind generator system model was developed. Further, a Neuro-Fuzzy Digital Pitch Controller (NFDPC) with two distinct neuro-fuzzy controllers was employed in the developed models. Two comparative studies are conducted and in these studies, the proposed NFDPC was compared with Proportional Integral Derivative Cascade Controller (PIDCC) where PID is implemented in inner and outer loop. In the first comparative study (considering custom wind speed), results revealed that the proposed controller maintains rated generator speed than PIDCC. The Root Mean Square Error (RMSE) (between rated speed and generated speed) of the generator was 1.23 and 3.73 for the proposed and PIDCC, respectively. Thus, uniform power was generated. Consequently, in the second case study (real-time effective wind speed), the proposed controller maintains optimal generator speed with a minimal RMSE of 0.66 when compared to PIDCC with an RMSE of 3.55. Thus, uniform power was developed by the proposed controller. Therefore from these results, the proposed controller generates uniform power at above-rated wind speed with large wind fluctuations.

Design and implementation of an intelligent digital pitch controller for digital hydraulic pitch system hardware-in-the-loop simulator of wind turbine

ABSTRACT Digital hydraulics is a potential technology for the Hydraulic Pitch System (HPS) in Wind Turbine (WT). Digital Hydraulics Pitch System (DHPS) uses Digital Flow Control Units (DFCU) to develop the precise pitching action. In this paper, a novel Intelligent Digital Pitch Controller (IDPC) is proposed. The proposed controller is designed and implemented on a developed lab-scale DHPS Hardware-in-the-Loop (HIL) simulator. The various parameters of DHPS-hardware were designed using the bottom-up design methodology. The IDPC comprises Machine Learning (ML)-based WECS and DHPS controllers in the outer and inner loop respectively. HIL simulations were conducted with the implemented IDPC. The ML-based WECS controller predicts the reference pitch angle close to its desired value. The ML-based DHPS controller predicts the states of DFCU to develop real-time pitching action in DHPS-hardware. Several case studies were conducted to validate the effectiveness of the proposed IDPC. A study shows that IDPC controlled DHPS exhibits better performance than an ML-Proportional Integral (PI) controlled HPS with proportional flow control valve. Subsequently, the performance of the IDPC is compared with PI-ML cascade controller. This study shows that the Maximum Absolute Error (MAE) between the generator speed and its rated speed is 0.87% and 19.29% for the proposed controller and PI-ML cascade controller, respectively. Similarly, MAE (error between generator torque and its rated torque) of torque is 0.85% and 5.46% for the proposed controller and PI-ML cascade controller, respectively. Thus, the implementation of the IDPC develops optimal power with minimal speed/torque fluctuations.

Digital hydraulic single-link trajectory tracking control through flow-based control

Recent advancement in controllability of digital hydraulic is similar to the performance of a proportional/servo hydraulic system, and several studies show that digital hydraulic will be an alternative for proportional/servo hydraulic. In this paper, tip point tracking of a single-link arm is taken as the subject of the study. Here, the single-link arm is controlled by a digital hydraulic system, which is established with parallel-connected on/off valves. In order to attain stepwise flow control, the pulse code modulation technique is used. By referring to the previous work, the control signal for the trajectory tracking is calculated by taking account of cylinder chamber pressure and velocity. But in this study, the required volume flow rate for trajectory tracing is taken into account for generating control signal. This approach improves the performance of the digital hydraulic system at lower velocity tracking and also reduces the computational complexity. The analysis is conducted with the proposed algorithm for 4-bit and 5-bit digital flow control units and tip point response of single link is presented. The results show that the 5-bit system has significantly better performance than the 4-bit system. In addition, the analysis is conducted with different stroke lengths such as 200, 100 and 50 mm for studying the behaviour of the system at lower velocity tracking. Better controllability is achieved at lower velocity tracking, and the results obtained with the proposed algorithm have nearly 2% tracking error.

Design and Experimental Research of a Miniature Digital Hydraulic Valve.

A digital hydraulic valve is an important component of the digital hydraulic system, and its performance is directly related to the system function. In order to make the valve system more competitive in dimension, digital valve miniaturization is an important research point. A new micro digital valve is designed, which is analyzed from the mechanical structure and magnetic circuit mechanism, and the design difficulties are also expounded. The four subsystems and switching characteristics of the valve are theoretically analyzed and simulated. In order to test the performance of the valve, a test system is designed, and performance of the new micro valve is tested. The test results show that the switch characteristic analysis of the valve is correct. The comparison between the test curve and the simulation curve is carried out, which demonstrates that the accuracy of the simulation model is reasonable. The theoretical analysis of the new micro digital valve is consistent with experiments.

High-linear digital hydraulic valve control by an equal coded valve system and novel switching schemes

This study proposes a novel digital hydraulic valve system using multiple equal size on/off valves and a circulating switching control, with an aim to increase the resolution and the linearity of t...

Selective Laser Melted Digital Hydraulic Valve System

Abstract The purpose of this article is to investigate the possibility of manufacturing a digital hydraulic valve system using additive manufacturing and to identify the challenges and benefits of doing so. In this study, an existing hydraulic valve manifold, operating at pressures up to 25 MPa, was redesigned for selective laser melting (SLM) and further optimized with computational fluid dynamics. Certain dimensioning challenges were encountered because laser melting is not yet accurate enough for some features, but these challenges were circumvented. The manifold was successfully manufactured from tool steel and tested for maximum operating pressure and flow capacity. Due to the improved flow channels, the selective laser melted manifold provided up to 49% reduction in the energy losses caused by flow resistance. This article demonstrates that SLM can be used to improve the performance of hydraulic valves and that the cost of SLM manifolds is feasible for high-end valve assemblies.

Mechatronic Design of Digital Hydraulic Micro Valve Package

Digital hydraulic valve system is a new kind of hydraulic control valve assembly, which has potential to save energy and improve performance of valve controlled actuators. The typical digital valve system has 4-6 parallel connected on/off valves per control edge totaling 16-24 valves in the four-way valve configuration. The flow capacities of the parallel connected valves are set according to the powers of two such that it is possible to achieve 2N different flow rates with N valves. An alternative approach is to use equally sized valves, which means that N parallel connected valves give only N+1 different flow rates. This approach has several benefits, but the number of valves becomes very large. This paper shows that it is possible to implement valve assembly having 128 miniaturized valves, such that it can be installed instead of traditional CETOP3 servo or proportional valve. Careful electromagnetic optimization and mechatronic design are used together with novel manufacturing methods and new type of power electronics. The prototype is build and experimentally studied and results show that the performance of this kind of digital valve system is superior to traditional four-way control valves in terms of response time and fault tolerance.

Equal Coded Digital Hydraulic Valve System – Improving Tracking Control with Pulse Frequency Modulation

Previous research on digital fluid power indicates down-scaling to be beneficial to the characteristics of digital valves. This theoretical aspect yields to use equal size on/off valves in digital hydraulic valve systems. A simple miniaturized on/off valve, having orifice diameter of 0.7mm, have been developed to study the feasibility of this approach. A manifold manufacturing technology also has been developed to facilitate a compact framework for the valve system containing dozens of the miniature valves. The first equal coded valve system prototype contains 16 miniature valve prototypes. A natural modulation method for an equal coded valve system is Pulse Number Modulation (PNM), where the output depends on the number of activated valves. With this modulation method, resolution of the output is equivalent to the number of the valves in the control edge. Limited resolution hampers the tracking control performance especially at low velocity where small steps in flow rate are required. The main purpose of this paper is to study the feasibility of Pulse Frequency Modulation (PFM) to improve the controllability of the equal coded valve system at the velocities below the minimum velocity of PNM control. Poor controllability at low velocities is one of the main challenges of the digital hydraulic valve systems. Characteristics of the PFM method are analysed and an experimental study is carried out to measure the improvement of the PFM method on the tracking control performance. The study indicates that the PFM method is an effective way to improve tracking control performance at low velocity.

Analysis by Simulation of Different Control Algorithms of A Digital Hydraulic Two-Actuator System

Many hydraulic systems have losses, which could be avoided with new technology. Because component efficiency can be optimized to a certain operation point, hydraulic machines are no worse than other machines. More important than the peak efficiency values of each individual component in a system is the efficiency of the whole power transfer line. In a system where the amount of required power and the velocity/force ratio are variables, components may but seldom operate at their optimal design points. A typical approach to mobile work hydraulics is to use a load-sensing pump for a hydraulic multi-actuator system. This approach is efficient but seldom, if many actuators are used simultaneously. Our recent prototype of an improved hydraulic power supply system is the Digital Hydraulic Power Management System (DHPMS), which can serve many actuators at optimised supply pressure but is also capable of motoring and transforming. This functionality holistically reduces losses in the system. Losses can be further ...

Dynamic analysis of a bistable actuator for digital hydraulics

A fast and small electromagnetic actuator, which requires a small amount of work to switch between two stable positions, for the use in digital hydraulics, is presented. A dynamic study of the bistable actuator as part of a new kind of hydraulic on/off valve is carried out. A prototype is built and measured to verify the analysis. The results show that with careful elaboration the design is feasible. Furthermore, the response times depend on driving frequencies and an optimal current density for minimal energy consumption in cyclic action can be found. A single on/off valve is a critical part of a digital hydraulic system.

A Design of Two-Degree-of-Freedom Digital Controller for Hydraulic Servo Systems. Continued Report. A Countermeasure for Deterioration of Stability Caused by a Saturation Characteristic.

This paper is concerned with the application of a two-degree-of-freedom (2DOF) digital controller to a hydraulic servo system. For suppression of a disturbance effect, the controller has an integral term and this causes instabilities by interacting with a saturation characteristic included in the actual hydraulic plant. To avoid the instabilities, a supplementary feedback loop is added to the 2DOF control system so as to suppress the input signal into the integral term under saturation conditions. A stability analysis is made for the system with that feedback loop and a nonlinear saturation element. Experiments are conducted under various conditions and from the results it has been clarified that the 2DOF digital hydraulic servo system has the prescribed desired input and disturbance response characteristics and that, even under saturation conditions, there occur no instabilities if the gain of the supplementary feedback loop is determined in the absolutely stable region obtained analytically.