Hydraulic Subsystems Research Articles

Balancing operational efficiency and regulation performance, for guiding pumped-storage day-ahead scheduling

Pumped-storage plants (PSPs) have significant potential to regulate intermittent energy sources. However, achieving coordinated optimization of regulation stability and operational efficiency has been a long-standing challenge. This study proposes a new soft linking model to address the limitation that current scheduling methods fail to account for both efficiency and second-level stability simultaneously, aiming to improve the day-ahead scheduling strategies for PSP. Firstly, a Pumped-Storage Hydroelectric System (PSHS) model is developed to reflect the regulation stability of PSP, considering the transient characteristics of hydraulic, mechanical, and electrical subsystems. Then, by analyzing transient responses under various operating working conditions, the study integrates the transient variation laws of the power plant into a regulation stability dataset (RSD). Finally, using RSD as the coupling interface, with regulation stability and operational efficiency as the objective functions, a Pumped-Storage Power Day-ahead Scheduling (PSPDS) model is established. An actual PSP is used as a case study to evaluate the effects of four operational scenes with varying optimization objectives on operational efficiency and subsystem performance. The results indicate that controlling load change magnitude and increasing the load decrease working conditions effectively enhance the stability of PSP subsystems. In addition, although the proposed scheduling scheme increases water consumption by 0.0213% compared to traditional scheduling method, it improves regulation stability by at least 15.14%. The findings suggest that a minor compromise in operational efficiency can lead to a significant improvement in regulation stability. This study provides new perspectives and methods for the management and optimization of PSPs.

Adaptive robust disturbance rejection backstepping control of a novel friction electro-hydraulic load simulator

This paper introduces a novel frictional electro-hydraulic load simulator that avoids the problem of force-motion coupling disturbances in traditional electro-hydraulic load simulators. An adaptive robust disturbance rejection backstepping control (ARDRBC) is proposed to address the challenges posed by parameter uncertainty, external disturbances, and unmodeled behavior, thereby enhancing the system’s tracking capability. A new adaptive rule has been designed to address the uncertainty of mechanical subsystems through virtual control adjustments. A sliding mode control scheme based on immersion and invariance has been integrated into the practical control design of hydraulic subsystem to address the neglected dynamics. The stability of the entire system was analyzed using the Lyapunov stability. Comparative experiments were conducted to confirm the practicality and robustness of the proposed method.

Bursting oscillation behaviors of a multi-time scales pumped storage power station with governor subsystem nonlinearity

Pumped-storage power station (PSPS) play a crucial role in supporting the grid integration of intermittent energy and require frequent regulation to balance fluctuations. Eliminating potential stability risks under the strong nonlinear and complex multi-scale coupling characteristics to ensure the stability of PSPS is crucial for new power systems. Although governor nonlinear elements have been studied in previous studies, the effects and potential risks of their non-smooth characteristics on the stability of different subsystems have not been reported. In this study, a mathematical model of PSPS considering the non-smooth characteristics of governor is established by introducing a segmentation function. Then the influence laws of their effect on important variables in different subsystems are studied through the time waveforms and phase trajectories. Additionally, sensitivity analysis is employed to identify key parameters affecting stability at various stages. Finally, the risk of bursting oscillation caused by the nonlinear elements is revealed. The results show that the nonlinear elements have less effect on the hydraulic subsystem, but their non-smooth characteristic induces state switching in mechanical subsystems, which poses a risk for frequency oscillations. Adjusting the deadband has an inhibiting effect on both oscillations caused by nonlinear elements and improves stability in hydraulic and mechanical subsystems. This work provides fresh perspectives and theoretical basis for minimizing the risk of bursting oscillations while improving Pumped-storage plant stability.

Modeling of dynamic modes of a generalized pumping station with an asynchronous electric drive of centrifugal pumps

Transportation of large volumes of liquid to distribution pipelines is provided by transit facilities - main pipelines and pumping stations, which consume significant amounts of electricity and are of strategic importance. The requirements for continuity, reliability, safety, fault finding, and diagnosis of existing, as well as requirements for the design of new strategic objects, are usually regulated by national legislation. The possibility of conducting physical experiments to analyze the modes of operation of such complexes is significantly limited by the inadmissibility of interrupting their functioning, as well as technical and financial risks. The use of a hybrid model consisting of a digital model of the power equipment and a physical model of the control system makes it possible to solve this problem. In this work, attention is focused on the digital model of power equipment. Based on the system approach and the principle of electrohydrodynamic analogy, a formalized mathematical model of the generalized system of asynchronous centrifugal pump units of a multi-unit pumping station with asynchronous electric drive of centrifugal pumps was created. The use of the principle of electrohydraulic analogy made it possible to apply the basic principles of the theory of electric circuits to form the equations of the hydraulic subsystem. The achieved formalization makes it possible to automate the formation of equations to obtain a model of an object of a specific configuration. The use of pump parameters in the model, which depend on the geometry of the internal elements, the speed of the impeller, and the physical properties of the liquid, makes it possible to investigate the impact of emergency and operational deviations of the equipment characteristics on the operating modes both at the level of individual modules and at the level of the pumping station as a whole. The obtained mathematical model was verified by adapting it to the pumping station of the given configuration. A computer simulation of several operational and emergency modes of operation of a pumping station with four hydraulically connected pumps was carried out. The scope of use and ways of improving the developed model are proposed, as well as the direction of further research

Adaptive backstepping-extended state observer control for electrohydraulic position servo systems with multiple disturbances using the compound friction compensation

Multiple disturbances coming from friction, matched, and mismatched uncertainties make it difficult for electrohydraulic servosystems to obtain the satisfactory position-tracking performance. The existing adaptive backstepping controllers fail to effectively distinguish the difference of disturbance between the mechanical subsystem and the hydraulic subsystem, which limits the compensation effect of multiple disturbances, especially for friction nonlinearity. Therefore, the adaptive backstepping-extended state observer position-tracking controller combined with compound friction compensation is proposed to simultaneously compensate for the fast-varying friction disturbance of a mechanical subsystem and the slow-varying matched disturbance of a hydraulic subsystem. The extended state observer algorithm is integrated into the adaptive backstepping controller to suppress the null bias of the average tracking error. The compound friction compensation includes a LuGre model-based compensation and a high-order disturbance observer, which can improve the tracking performance of system and avoids the excessive gain of observer. A large number of comparative experiments are conducted to verify the effective of the proposed controller.

Experimental study and comprehensive analysis of leakage characteristics of the casing flange of an aero-engine

Leakage at the casing flange in aero-engines can reduce the engine performance and endanger the normal operation of the whole aircraft. An experimental system is designed in this paper to investigate the influence of loaded parameters and structural parameters on the sealing characteristics of the casing flange in aero-engines. The system includes an experimental table subsystem, a hydraulic subsystem, an inflation and leakage measurement subsystem and an experimental data acquisition subsystem. The results show that the gas pressure has a greater influence compared to the axial force. When the gas pressure rises from 0.2 MPa to 0.5 MPa, the leakage volume increases from about 9 L/min to about 34 L/min. Among the structural parameters, the number of bolts has the greatest influence, followed by the number of layers, and the surface roughness has the least influence, with the three influencing parameters not being mutually exclusive. The benefits of improving the structural parameters to reduce the leakage volume all increase with the rise of gas pressure. The leakage volume of experiment parts with 48 bolts arranged on the 2-layer casing flange with surface roughness 1.6 and 3.2 are taken as two sets of the contract type data and fitted by the nested Genetic Algorithm. The fitted results indicate that increase of surface roughness from 1.6 to 3.2 will result in an increase of 26 L/min in the leakage volume. The conclusions from the paper can provide guidance suggestions for the sealing design of the aero-engine casing.

Disturbance observer–based backstepping sliding mode cascade control of 2–degrees of freedom hydraulic tunneling robot

For the 2–degrees of freedom position tracking problem of the robotized hydraulic-driven roadheader with high nonlinearities and strong uncertainties, a practical disturbance observer–based backstepping sliding cascade control method together with an adaptive compensator is proposed and investigated. The presented methodology mainly includes a continuous nonsingular fast terminal sliding mode with the backstepping technique and the power reaching law with time-varying coefficients used to achieve satisfactory performance against the multi-source disturbances, two disturbance observers used to approximately estimate the unknown dynamics in the mechanical and hydraulic subsystem, respectively. Simultaneously, a continuous robustifying term is also utilized to compensate for the residual disturbances and enhance the robustness. The presented control method doesn’t need the precise model thanks to the auxiliary disturbance observer, and can ensure fast convergence and small tracking error thanks to the backstepping sliding cascade control and the adaptive robust compensator. Based on Lyapunov theory, stability of the overall closed-loop system is proved rigorously, and asymptotically bounded tracking performance of the robotic manipulator is guaranteed. Finally, 2–degrees of freedom trajectory tracking experiments are conducted, and comparative results effectively verify the superiorities of the proposed method.

Mixed Reality: A Tool for Investigating the Complex Design and Mechanisms of a Mechanically Actuated Digital Pump

Digital hydraulics is a discrete technology that integrates advanced dynamic system controls, digital electronics, and machine learning to enhance fluid power systems’ performance, overall efficiency, and controllability. A mechanically actuated inline three-piston variable displacement digital pump was previously proposed and designed. The inline three-piston pump incorporates complex mechanical and hydraulic subsystems and highly coupled mechanisms. The complexity of the utilized subsystems poses challenges when assessing the viability of the conceptual design. Therefore, this work focuses on designing, developing, and implementing a collaborative virtual platform involving a digitized module showcasing the internal mechanical structure of the digital pump utilizing mixed reality (MR) technology. MR technology is acknowledged as the forthcoming evolution of the human–machine interface in the real–virtual environment utilizing computers and wearables. This technology permits running simulations that examine the complexity of highly coupled systems, like the digital pump, where understanding the physical phenomenon is far too intricate. The developed MR platform permits multiple users to collaborate in a synchronized immersive MR environment to study and analyze the applicability of the pump’s design and the adequacy of the operated mechanisms. The collaborative MR platform was designed and developed on the Unity game engine, employing Microsoft Azure and Photon Unity Networking to set up the synchronized MR environment. The platform involves a fully interactive virtual module on the digital pump design, developed in multiple stages using Microsoft’s Mixed Reality Tool Kit (MRTK) for Unity and deployed in the synchronized MR environment through a HoloLens 2 MR headset. A research study involving 71 participants was carried out at Purdue University. The study’s objective was to explore the impact of the collaborative MR environment on understanding the complexity and operation of the digital pump. It also sought to assess the effectiveness of MR in facilitating collaboration among fluid power stakeholders in a synchronized digital reality setting to study, diagnose, and control their complex systems. Surveys were designed and completed by all 71 participants after experiencing the MR platform. The results indicate that approximately 75% of the participants expressed positive attitudes toward their overall MR platform experience, with particular appreciation for its immersive nature and the synchronized collaborative environment it provided. More than 70% of the participants agreed that the pump’s collaborative MR platform was essential for studying and understanding the complexity and intricacy of the digital pump’s mechanical structure. Overall, the results demonstrate that the MR platform effectively facilitates the visualization of the complex pump’s internal structure, inspection of the assembly of each of the involved subsystems, and testing the applicability of the complicated mechanisms.

Modeling and Transient Response Analysis of Doubly-Fed Variable Speed Pumped Storage Unit in Pumping Mode

Doubly-fed variable speed pumped storage (VSPS) unit is an advanced hydropower system. In pumping mode, its input power can continuously be adjusted within a certain range via changing speed. Thus, it overcomes the major defect that the pumped storage unit cannot provide frequency regulation services to the power grid in pumping mode. However, for the pumping mode VSPS, how to establish its model is still a problem. In this article, an electromagnetic-electromechanical transient multi-time scale model of pumping mode VSPS is presented. This model depicts the intrinsic speed-power regulation characteristics and the extrinsic power-frequency coupling characteristics of pumping mode VSPS, which can be used for the power grid frequency regulation analysis. Firstly, the hydraulic subsystem model of VSPS is established within the electromechanical transient time scale. The model is built based on the variable speed characteristics of the reversible pump-turbine (RPT) in pumping mode and considers the hydrodynamics and additional friction effects of the wicket gate in the water conveyance system. Secondly, the electric subsystem model of VSPS is established within the electromagnetic transient time scale. The model mainly describes the operation characteristics of a doubly-fed induction machine (DFIM) and the control properties of the inner and outer loops of the back-to-back (BTB) converter system. Finally, comprehensive simulation and experimental results have fully verified the established model and theoretical analysis.

Transient vibration of shafting in coupled hydraulic-mechanical-electrical- structural system for hydropower station during start-up process

The operating parameters of hydroelectric generating system vary constantly in the course of transition, meanwhile, the coupled correlations among hydraulic, mechanical, electrical and structural subsystems are convoluted, which makes the vibration of shafting system prominent, as well as affects the safe and stable operation for hydropower station. In this paper, a coupled hydraulic-mechanical-electrical-structural model for hydroelectric generating system is proposed, while the start-up transient process is incorporated into the investigation system, and the dynamic response from shafting system at different stages attached to start-up process is scrutinized numerically, making allowance for the effect of unbalanced magnetic pull with static and dynamic eccentricity. The kinetic property of structure over the start-up process is illuminated, by means of the comparison with motion trait for system under steady-state operating condition. The results indicate that the dynamic feature of rotor and runner is significantly contrasting in different stages affiliated to the start-up scenario, especially for the voltage building-up subdivision. In addition, the response peculiarity from rotor covering the trajectory, vibration amplitude and frequency components, etc., is markedly altered, due to the participation of static, dynamic eccentricity as well as the matching variation on electromagnetic excitation. The trajectory of rotor evolves from a regular circle to a butterfly-shaped curve, and the associated transient displacement intensifies immensely, besides, the 2x frequency component emerges and corresponding dominant role gradually strengthens, accompanied by a developmental amplitude of 1x frequency in spectrum diagram. Relevant research results can provide profitable reference for the analysis of dynamic characteristic on hydropower station through transient conditions.

Testing and performance analysis of an integrated electromagnetic and hydraulic retarder for heavy-duty vehicles

Hydraulic retarder and eddy current retarder are important auxiliary braking component, which installed on heavy-duty vehicles. However, the hydraulic retarder has poor braking performance at low speeds, while the eddy-current retarder presents serious thermal recession at high speed. To overcome these issues and ensure safe driving during downhill conditions, a novel Integrated Electromagnetic and Hydraulic Retarder (IEHR) is proposed. The design includes a rotor with blades, double salient poles, and a coil built in a C-type stator. The electromagnetic field model of the IEHR is established and analyzed using the Finite Element Method. Moreover, the nonlinear eddy viscosity model of the flow field is generated and analyzed using the Computational Fluid Dynamics. The Blend braking control strategy is adopted to distribute the braking torque at high speed and low speed The IEHR performance was tested at a test bench. The test results show that the calculated braking characteristics of the electromagnetic and hydraulic subsystems were reasonable agreement with the measured results. The road test was carried out on a vehicle with a total mass of 49 tons. The deceleration and torque peaked at 0.75 m/s2 and 3620 N m, respectively. These results indicated that the IEHR has better performance than conventional hydraulic retarders and eddy current retarder, and is more suitable for heavy vehicles.

Simulation Study of Aircraft Active-Active Hydroelectric Hybrid Power Drive Unit

The Power Drive Unit (PDU) is the power source of the aircraft high-lift system (HLS), which converts hydraulic or electric energy into mechanical energy for output, and deflects the flap/slat through the transmission lines to increase the wing area to improve lift. Two sets of hydraulic motor subsystems working simultaneously are used in the Active-Active PDU of traditional aircraft to improve the reliability of the system. In this paper, an Active-Active Hydroelectric Hybrid Power Drive Unit (HPDU) is designed with a fixed-displacement hydraulic motor and a permanent magnet synchronous motor, the fundamental composition of the HPDU is introduced, the mathematical model of main components is analyzed, the HPDU is modeled based on AMESim, and the function and operation performance are investigated by simulation. The results show that the HPDU can realize the functional design requirements such as forward and reverse rotation and the performance design requirements such as withstanding sudden load within the rated load range during running.

A Singular Perturbation Theory-Based Composite Control Design for a Pump-Controlled Hydraulic Actuator with Position Tracking Error Constraint

Pump-controlled hydraulic actuators (PHAs) contain slow mechanical and fast hydraulic dynamics, and thus singular perturbation theory can be adopted in the control strategies of PHAs. In this article, we develop a singular perturbation theory-based composite control approach for a PHA with position tracking error constraint. Disturbance observers (DOBs) are used to estimate the matched and mismatched uncertainties for online compensation. A sliding surface-like error variable is proposed to transform the second-order mechanical subsystem into a first-order error subsystem. Consequently, the position tracking error constraint of the PHA is decomposed into the output constraint of the first-order error subsystem and the stabilizing of the first-order hydraulic subsystem. Slow and fast control laws can be easily designed without using the backstepping technique, thus simplifying the control design and reducing the computational burden to a large extent. Theoretical analysis verifies that desired stability properties can be achieved by an appropriate selection of the control parameters. Simulations and experiments are performed to confirm the efficacy and practicability of the proposed control strategy.

An efficient and accurate linearization approach for hydraulically actuated multibody systems with holonomic and nonholonomic constraints

Hydraulics is often used to actuate mechanisms in the applications of heavy machinery. In this work, a linearization approach for hydraulically driven multibody systems is presented. The approach allows linearizing the equations of motion of general multibody systems with holonomic and nonholonomic constraints, augmented with the hydraulic equations of the hydraulic subsystem. The derivation of this linearization approach is of interest in many applications, such as the performance of linear stability analyses. The procedure is tested with a three-dimensional multibody model of a hydraulically actuated four-bar mechanism. The validation of the approach is performed by means of the forward dynamics simulation of the linear and nonlinear systems. The results show the power of the approach, obtaining the linearized equations of motion around the equilibrium position of the four-bar mechanism multibody model in terms of the mechanical and hydraulic parameters. A comparison of the proposed procedure with a conventional counterpart approach is included, demonstrating the great accuracy and computational efficiency of the approach developed in this work.

Small-Signal System Frequency Stability Analysis of the Power Grid Integrated With Type-II Doubly-Fed Variable Speed Pumped Storage

This article proposes a structurally distinctive doubly-fed variable speed pumped storage (VSPS), denoted as the Type-II VSPS. Where, the speed is controlled by a back-to-back (BTB) converter while the power is controlled by a speed governor, which is the exact opposite of the control method for conventional VSPS. The small-signal frequency stability analysis of a power grid integrated with the Type-II VSPS is carried out to investigate the influence of this type of VSPS on power grid stability. Firstly, the transfer function models of hydraulic and electric subsystems of the Type-II VSPS are established, and the system small-signal stability analysis is carried out based on the obtained models and Nyquist stability criterion. Secondly, an improved system frequency response (SFR) model for the power grid integrated with Type-II VSPS is presented. Such a model is applied to investigate the frequency response of the modern power grid integrated with a large-scale VSPS (the current single unit capacity has reached 450 MW). Furthermore, the small-signal stability of the modern power grid is analyzed based on the Nyquist stability criterion. Finally, time-domain simulations and experiments are conducted to validate the effectiveness of the small-signal stability analysis.

Operation reliability monitoring towards fault diagnosis of airplane hydraulic system using Quick Access Recorder flight data

Hydraulic system operation reliability (HSOR) can evaluate time series state reliability for hydraulic system fault diagnosis and provide condition based maintenance decisions. The quick access recorder (QAR) flight data and normal values of the hydraulic system are utilized to analyze time series HSOR by calculating the operation reliability index. Considering the relationship of the hydraulic subsystem among the components, hydraulic components Bayesian Network is constructed to analyze time series HSOR. Furthermore, the sensitivity of HSOR features to fault location is assessed using categorical boosting (CatBoost) and Shapley Additive ex-Planations values. Through the analysis of two flights hydraulic system QAR datasets, it is revealed that (a) HSOR can accurately monitor the time series operating states of the hydraulic system; and (b) with demonstrating two illustrative case, the HSOR values and features sensitivity analysis can be a useful reference for the fault diagnosis and location of the airplane hydraulic system. The study intends to develop a practical reference approach for hydraulic system fault diagnosis and location using QAR data.

Design, Manufacture, and Experimental Validation of a Hydraulic Semi-Active Knee Prosthesis.

In this article, a new hydraulic semi-active knee (HSAK) prosthesis is proposed. Compared with knee prostheses driven by hydraulic-mechanical coupling or electromechanical systems, we novelly combine independent active and passive hydraulic subsystems to solve the incompatibility between low passive friction and high transmission ratio of current semi-active knees. The HSAK not only has the low friction to follow the intentions of users, but also performs adequate torque output. Moreover, the rotary damping valve is meticulously designed to effectively control motion damping. The experimental results demonstrate the HSAK combines the advantages of both passive and active prostheses, including the flexibility of passive prostheses, as well as the stability and the sufficient active torque of active prostheses. The maximum flexion angle in level walking is about 60°, and the peak output torque in stair ascent is greater than 60Nm. Relative to the daily use of prosthetics, the HSAK improves gait symmetry on the affected side and contributes to the amputees better maintain daily activities.

A modal method for detection and exclusion of interactions

In structural dynamics or acoustics, one may wish to detect interactions with a system that is investigated by modal testing. Since the weighted modal assurance criterion (WMAC) constitutes an orthogonality check, the addition of an interacting system can influence the auto-WMAC matrices of the system under investigation. This applies for a structure interacting with an investigated fluid, a fluid interacting with an investigated structure, and for a substructure that is not included in the modal test. Decoupled mass matrices are assumed in the latter case, and the effect of interaction is considered for multi-degree-of-freedom models of undamped systems. Then, it is proved that for the above applications, the diagonality of a suitably weighted auto-WMAC matrix guarantees the absence of interacting systems. In case of an interaction, upper and lower limits are found for the number of coupled modes. The upper limit is given by the number of non-zero off-diagonal auto-WMAC matrix values. The lower limit is given by the number of modes associated with these values, and the associated modes are coupled. These results can be used in the search for system boundaries, in the extension of models, and in condition monitoring problems. In an experiment, they are applied to the hydraulic subsystem of a coupled hydraulic-mechanical system and verified by the calculation of hydraulic and mechanical energy contributions to overall coupled hydraulic-mechanical modes.

Dynamic Simulation of Starting and Emergency Conditions of a Hydraulic Unit Based on a Francis Turbine

The Francis hydro-turbine is a typical nonlinear system with coupled hydraulic, mechanical, and electrical subsystems. It is difficult to understand the reasons for its operational failures, since the main cause of failures is due to the complex interaction of the three subsystems. This paper presents an improved dynamic model of the Francis hydro-turbine. This study involves the development of a nonlinear dynamic model of a hydraulic unit, given start-up and emergency processes, and the consideration of the effect of water hammer during transients. To accomplish the objectives set, existing models used to model hydroelectric units are analyzed and a mathematical model is proposed, which takes into account the dynamics during abrupt changes in the conditions. Based on these mathematical models, a computer model was developed, and numerical simulation was carried out with an assessment of the results obtained. The mathematical model built was verified on an experimental model. As a result, a model of a hydraulic unit was produced, which factors in the main hydraulic processes in the hydro-turbine.

Bivariate active power control of energy storage hydraulic wind turbine

With the increasing proportion of wind turbines in power system, high-precision control of power generation directly affects the proportion of wind turbines connected to the grid. This paper takes the energy storage hydraulic wind turbines (ESHWTs) as the research object, the mathematical model of the hydraulic main transmission system and the hydraulic energy storage subsystem are established, and the energy transmission and control mechanism is obtained. The corresponding relationship between the output power of the hydraulic main drive system and the hydraulic energy storage subsystem and the variable motor speed is analyzed, based on the small signal linearization method, and the power transmission state is obtained with the variable motor speed fluctuation, and a double closed-loop power control strategy is proposed under the motor speed fluctuation, with the power control requirements after grid connection, Based on MATLAB software and 24 kW semi-physical simulation test platform of energy storage hydraulic wind turbine, the output power is accurately controlled and the power output problem is solved under the fluctuation of motor speed with the proposed control strategy.