Hydrostatic Transmission Research Articles

Steady-state Characteristics Study of a Power Split Hydraulic Transmission

The steady-state characteristics of a power split hydraulic transmission were carefully studied in this article. The hydraulic transmission is an alternative power split device for power split hydraulic hybrid drivetrain. It was built from a balanced vane pump, where an output shaft is added and coupled to its floating ring. The internal friction torques due to the relative motion between floating ring and vanes help to drive the output shaft. This improves the mechanical transfer efficiency from input to output shaft, making it more competitive than conventional hydrostatic transmission. The steady-state characteristics of the hydraulic transmission were investigated through both theoretical analysis and experimental studies. Mathematical models of the input and output shaft torques, and the outlet flow rate of the hydraulic transmission were developed. Studies show that the input and output shaft torques are not only dependent on outlet pressure, but also dependent on differential shaft speed. The outlet flow rate is proportional to the differential shaft speed. Finally, a hydro-mechanical transmission based on power split hydraulic transmission was introduced. The characteristics and system application of the hydro-mechanical transmission were given.

Hydrostatic Actuation for Remote Operations in MR Environment

This article presents a novel design and experiment of a system of hydrostatic actuation, transmission network, and control as a research platform for investigating magnetic resonance image (MRI) based tracking and intervention of a moving target. Based on novel double-acting piston-cylinder type rolling diaphragm fluid actuators, the system comprises two remotely controlled modules, an instrument manipulation module and a target motion module. The instrument manipulation module controls an instrument to access a target and it features a fluid network of multiple actuators and several modes of the instrument intervention of a stationary or moving target. The target motion module generates emulated target motions, such as breathing profiles, in the interventions. It also serves as truth motion for developing and testing MRI scanning and tracking algorithms. An iterative learning control is employed to create precise target motion profiles without needing real-time feedback from an MR-safe/conditional sensor. Integrating the two modules, the system enables closed-loop actuated intervention study with real-time MRI.

Electric Hydraulic Hybrid Acceleration Strategy Based on Hydrostatic Transmission for Battery Rail Engineering Vehicle

Electric Hydraulic Hybrid Acceleration Strategy Based on Hydrostatic Transmission for Battery Rail Engineering Vehicle

ADV Preview Based Nonlinear Predictive Control for Maximizing Power Generation of a Tidal Turbine With Hydrostatic Transmission

As the development of tidal turbines attracts more and more attention in recent years, reliable design and efficient control of tidal turbines are becoming increasingly important. However, the majority of existing tidal turbines still utilize traditional fixed ratio geared transmissions and the associated control designs focus on simple feedback controllers that use measurements or possibly estimates of the turbine itself or current local tidal profile. Therefore, the measurement and control are inevitably affected by the inherent delay with respect to the current tidal speeds. This paper proposes a novel tidal turbine with continuously variable speed hydrostatic transmissions and a nonlinear predictive controller that uses short-term predictions of the approaching tidal speed field to enhance the maximum tidal power generations when the tidal speed is below the rated value. The controller is designed based on an offline finite-horizon continuous time minimization of a cost function, and an integral action is incorporated into the control loop to increase the robustness against parameter variations and uncertainties. A smooth second order sliding mode observer is also designed for parameter estimations in the control loop. A 150 kW tidal turbine with hydrostatic transmission is designed and implemented. The results demonstrate that the averaged generator power increases by 6.76% with this preview based nonlinear predictive controller compared with a classical non-predictive controller.

Design and feasibility analysis of a novel auto hold system in hydrostatic transmission wheeled vehicle

Auto hold refers to vehicle’s function of automatic braking under shutdown condition and automatic relieving braking force when vehicle starts. This paper presents a concrete structure of the novel auto hold system of hydrostatic transmission wheeled vehicle, and deeply analyses the working mechanism and control method. To validate its feasibility, AMESim software is adopted to establish the simulation model of the auto hold system based on mathematical theories. By using the data of a certain comprehensive operation mode as input, the curve of braking force of the auto hold system is obtained through simulation. It can be known through analysis that the proposed auto hold system can realize rapid response and provides stable braking force under different road conditions. Finally, the feasibility of the proposed auto hold system is validated by comparing the simulation data with actual braking force required and the electronic vehicle parking technology. It turns out that the auto hold system can meet the requirements of all road conditions. Besides, it also can provide a fault tolerance range for real vehicle experiments, and it will not cause adverse impacts due to excessive parking brake force.

Choice of truck for installation of concrete pump and distribution boom

Numerous mechanisms (up to 10) have hydrostatic transmissions, working from the energy, coming from several hydraulic pumps, driven by the engine of the truck. The selection of engine power is always different for different types of attachments installed on the chassis of the truck. Therefore, when choosing a truck, it is necessary to take into account that both the concrete pump and the boom work simultaneously. The use of concrete pump and placing boom on the chassis of the truck requires increased power up to 300 kW and even more, On the other hand, it is required that the chassis of the truck be able to withstand both static and dynamic loads of equipment, taking into account its size, especially in length. Despite many years of experience in design and production, the issues of choosing a truck for these machines remain little investigated. In this article on the basis of the constructive and statistical analysis the method of the choice of the truck for a concrete pump and a placing boom is offered.

A Testbed for Haptic and Magnetic Resonance Imaging-Guided Percutaneous Needle Biopsy

Magnetic resonance imaging (MRI) is used for soft tissue pathology diagnosis and assistance with targeted lesion procedures. However, limited physician access to patients in the magnetic resonance scanner bore requires iterative positioning and imaging, which extends the procedure time and increases patient risk. We present a teleoperated system and instrumented testbed for robotic MRI-guided needle biopsy, particularly targeting transperineal prostate biopsies. The device has a 1:1 kinematic mapping and uses a low-friction hydrostatic transmission based on antagonistic pairs of rolling diaphragms. It has three degrees of freedom (DOFs) and a passive two-DOF swivel, which holds a biopsy needle at the end-effector. Measured force hysteresis is 0.085 N (single DOF) and 0.44 N (full three-DOF manipulator) at the needle driving point. To quantitatively assess the system's haptic qualities, impulse modal testing for one DOF ( $>$ 300 Hz bandwidth) and three DOFs ( $>$ 40 Hz bandwidth) was conducted. Task performance was also assessed through membrane puncture testing with tissue phantoms; puncture events as low as 0.1 N are reliably detectable from transmission hydraulic pressure sensors.

Influence of variable inertia flywheel and soft switching on a power hydraulic system

In this work a variable inertia flywheel and a soft switch are incorporated into an on/off valve-controlled power hydraulic system to analyze the influences of those in energy saving and vibration isolation of the system. Four different configurations of hydrostatic transmission systems, i.e. Hydrostatic Transmission with Constant Inertia Flywheel (HSTCIF), Hydrostatic Transmission with Variable Inertia Flywheel (HSTVIF), Hydrostatic Transmission with Constant Inertia Flywheel and Soft Switch (HSTCIFSW) and Hydrostatic Transmission with Variable Inertia Flywheel and Soft Switch (HSTVIFSW) have been modeled and simulated. The Lagrange’s approach is used to obtain the mathematical model of the variable inertia flywheel. The main objective of the study is to reduce the transient peak of the system response by using the variable inertia flywheel and the soft switch individually or collectively. It is observed that the incorporation of these two components together provides benefits from two different perspectives, i.e. energy savings and vibration reduction of the system.

Improving the reliability and energy production of large wind turbine with a digital hydrostatic drivetrain

Gearbox failure is one of the major factors causing the increased downtime in modern wind turbines. This increases the turbine maintenance cost and therefore the turbine cost of energy. A hydrostatic transmission not only improves the turbine reliability through its “soft” transmission, but also eliminates the use of power converter through its continuous variable transmission function. A hydrostatic wind turbine usually employs a fixed displacement pump to drive a variable displacement motor. The variable displacement motor runs at partial displacement when the wind speed is below the rated wind speed, leading to low drivetrain efficiency. Moreover, large variable displacement motors for large utility wind turbine are not commercially available. Therefore in this paper a digital hydrostatic transmission solution for large utility wind turbine has been proposed. The large variable displacement motor was replaced by combining several fixed displacement motors and a small variable displacement motor with some digital encoding scheme. Two encoding schemes have been proposed for digital hydrostatic transmission. The modeling and design of the digital hydrostatic wind turbine were presented. A hydrostatic wind turbine control based on kw2 control law has been proposed. A dynamic simulation model of the digital hydrostatic wind turbine has been developed. The proposed digital hydrostatic drive solution has been compared with a conventional hydrostatic solution in a commercial 2.5 MW wind turbine. Simulation studies verified the feasibility and the engineering practice of the proposed digital hydrostatic drive solution.

Various power transmission strategies in wind turbine: an overview

A wind power system integrates different engineering domains, i.e. aerodynamic, mechanical, hydraulic and electrical. The power transmission from the turbine rotor to the generator is an important and integral part of the wind turbine system. Generally, the power transmission unit is of two types, e.g., mechanical transmission system and hydrostatic power transmission system (HST). Normally, the mechanical transmission system (gear train) is used to transmit the power in wind turbine. But this transmission is not suitable in large scale power production. Currently, hydraulic power system has drawn an attention as a power transmission system in the wind turbine field. It provides some advantages over the mechanical transmission system, such as it is capable to transmit high power in compact size, it has an ability to vary the speed infinitely, convenient installation, flexibility and high reliability. Also, the HST system helps to obtain a stable power from wind turbine using an accumulator whenever the input wind velocity is of fluctuating nature. In this article, various schemes on the hybrid power transmission system in wind turbine system are addressed in a chronological order. However, the aerodynamics and the electrical transmission of the wind turbine are excluded from the discussion.

Components Sizing and Performance Analysis of Hydro-Mechanical Power Split Transmission Applied to a Wheel Loader

The powertrain efficiency deeply affects the performance of off-road vehicles like wheel loaders in terms of fuel economy, load capability, smooth control, etc. The hydrostatic transmission (HST) systems have been widely adopted in off-road vehicles for providing large power density and continuous variable control, yet using relatively low efficiency hydraulic components. This paper presents a hydrostatic-mechanical power split transmission (PST) solution for a 10-ton wheel loader for improving the fuel economy of a wheel loader. A directly-engine-coupled HST solution for the same wheel loader is also presented for comparison. This work introduced a sizing approach for both PST and HST, which helps to make proper selections of key powertrain components. Furthermore, this work also presented a multi-domain modeling approach for the powertrain of a wheel loader, that integrates the modeling of internal combustion (IC) engine, hydraulic systems, mechanical transmission, vehicle(wheel) dynamics, and relevant control systems. In this modeling, an engine torque evaluation method with a throttle position control system was developed to describe the engine dynamics; a method to express the hydraulic loss of the axial piston hydraulic pump/motor was developed for modeling the hydraulic transmission; and a vehicle velocity control system was developed based on altering the displacement of a hydraulic unit. Two powertrain models were developed, respectively, for the PST and HST systems of a wheel loader using MATLAB/Simulink. The simulation on a predefined wheel loader drive cycle was conducted on both powertrain models to evaluate and compare the performance of wheel loader using different systems, including vehicle velocity, hydraulic displacement control, hydraulic torque, powertrain efficiency, and engine power consumption. The simulation results indicate that the vehicle velocity controller developed functions well for both the PST and HST systems; a wheel loader using the proposed PST solution can overall save about 8% energy consumption compared using an HST solution in one drive cycle. The sizing method and simulation models developed in this work should facilitate the development of the powertrains for wheel loaders and other wheeled heavy vehicles.

Sensorless Maximum Power Extraction Control of a Hydrostatic Tidal Turbine Based on Adaptive Extreme Learning Machine

In this paper, a hydrostatic tidal turbine (HTT) is designed and modeled, which uses more reliable hydrostatic transmission to replace existing fixed ratio gearbox transmission. The HTT dynamic model is derived by integrating governing equations of all the components of the hydraulic machine. A nonlinear observer is proposed to predict the turbine torque and tidal speeds in real time based on extreme learning machine (ELM). A sensorless double integral sliding mode controller is then designed for the HTT to achieve the maximum power extraction in the presence of large parametric uncertainties and nonlinearities. Simscape design experiments are conducted to verify the proposed design, model, and control system, which show that the proposed control system can efficiently achieve the maximum power extraction and has much better performance than conventional control. Unlike the existing works on ELM, the weights and biases in the ELM are updated online continuously. Furthermore, the overall stability of the controlled HTT system including the ELM is proved and the selection criteria for ELM learning rates are derived. The proposed sensorless control system has prominent advantages in robustness and accuracy, and is also easy to implement in practice.

A decentralized multivariable controller for hydrostatic wind turbine drivetrain

AbstractA hydrostatic drivetrain transmits wind turbine energy to a generator. One hydrostatic transmission system (HTS) configuration utilizes a fixed displacement pump and a variable displacement motor. The system dynamics are captured in a nonlinear multi‐input multi‐output mathematical model. This paper introduces a decentralized control configuration based on this model to achieve two desired objectives: maximizing the harvested energy without direct measurement of wind and regulating the frequency of the generator without using power electronic converters. To accomplish these objectives, suitable pairing of control actuators and system responses are identified through nonlinear relative gain arrays (RGA) analysis. The pairing also provides a strong decoupling of control loops. So maximum power point tracking (MPPT) is achieved independently while the generator speed is regulated to maintain the frequency of generated power at 60 Hz. Simulation results demonstrate robust performance of MPPT and frequency regulation in the presence of uncertainties in the turbine and HTS model. We also demonstrate that the RGA paired input‐out control configuration offers superior performance over other possible input–output paired control configurations.

Research on the key problems of MPPT strategy based on active power control of hydraulic wind turbines

The constant displacement pump-variable motor hydrostatic transmission system is used as the main drive system in hydraulic wind turbines, and unlike traditional wind turbines using asynchronous generators and electronic converter devices, the synchronous generator is directly adopted for grid-connected generation. In this paper, the maximum power point tracking (MPPT) problem of hydraulic wind turbines is studied in depth. The energy transfer process of hydraulic wind turbines is introduced, and the key issues to be solved in MPPT are presented. A MPPT strategy based on active power control is proposed. The power transmission characteristics of hydraulic wind turbines and the nonlinear problems existing in active power control are analyzed. A small signal linearization method combined with variable gain proportional integral differentiation (PID) is used to solve the power response inconsistent problems that come from system nonlinearity. The MPPT strategy based on active power control is optimized by a speed control loop to insure the system stability in the process of MPPT. Finally, the power response consistency and the MPPT strategy are verified in the 30 kVA semi physical simulation platform.

Стенд для испытания бесступенчатого дифференциального механизма поворота со следящей системой управления движением гусеничного промышленного трактора

The curvilinear movement of tracked vehicles is controlled by the mismatch of track speeds. Appearance of sufficient installation power at an affordable price on the market of hydrostatic transmissions made it possible to organize stepless control of the turning radius both in the transport mode and when performing technological operations of bulldozing and loosening. External interference distorts the path defined by the joystick. To correct the trajectory, navigation systems are used, which also became available to manufacturers and consumers of industrial tractors. To test control algorithms for a tracked vehicle, bench test equipment is required. The article is devoted to the testing of tracked industrial tractors with modern navigation systems, in particular bench research tests of a stepless differential mechanism for turning machines with a tracking motion control system. The stand, which contains the test drive stepless differential rotation mechanism (BDM) with a motion tracking control system (CCM) motionlessly mounted on the base of a car frame with a drive, and is also equipped with guiding devices to provide a given spatial movement of a single gyrocompass with an accelerometer, entering -which is part of the SSU movement. The technical result is the expansion of the functionality of the stand, which allows to determine the operability and configure the control system by the motion, as well as to control the main parameters of the BDM by simulating in stationary bench conditions the input effects on the elements of the control system, which to the maximum extent correspond to the actual conditions of movement of the machine in the space , while reducing the complexity and cost of these works, by eliminating the need to use vehicles.

Power-Split Hydrostatic Transmissions for Wind Energy Systems

In a wind turbine, if a continuously variable transmission is placed between the turbine rotor and the generator, the speed ratio can be tuned to match the variable rotor speed to the constant speed of the electric generator, thus eliminating the need to adapt the frequency to the grid. In this paper, power-split hydrostatic transmission (PS-HTS) architecture is proposed as a suitable continuously variable transmission for application to wind turbine systems. The performance of PS-HTS is modelled and compared with that of previously proposed architectures in which the hydrostatic transmission is placed in-line with traditional drives (in-line HTS). It is shown here that the PS-HTS can improve the annual energy production of a 250 kW rated power wind turbine of about 10–11% by employing a hydrostatic transmission with one-seventh the size of the one requested by in-line HTS architecture.

Study of Losses and Energy Efficiency of Hydrostatic Drives with Hydraulic Cylinder

Abstract Energy efficiency of hydrostatic transmissions, and especially efficiencies of drives with motor speed controlled by throttle, as well as efficiency of hydraulic servomechanisms can in fact be higher than the efficiency values most frequently given by the respective literature in this field. With the progress achieved in recent years in the development of hydraulic systems it is becoming necessary to develop methods for precise energy efficiency calculation of such systems. It is difficult to imagine that more and more, better and better machines and control elements could be used without the possibility of a mathematical tool at our disposal to enable an accurate analysis and assessment of behavior of the system in which such machines and control elements have been applied. The paper discusses energy savings using mathematical model of losses in elements, the energy efficiency of the system. There are possibilities to reduce energy losses in proportional control systems (in the pump, in the throttle control unit, especially in the cylinder), and thus to improve the energy efficiency of the throttling manifold. The considerations allow for comparison of the loss power resulting from the applied hydraulic control structure of the hydraulic cylinder and the power consumed by the pump from the electric motor that drives it, the power necessary to provide pump-driven hydraulic cylinder. The article shows the impact on the output (useful) power consumed in the considered systems, and the impact on the power consumed of the loss power in the individual elements. The paper presents also formulas of loss power, formulas of energy efficiency connected with investigated hydrostatic drives, two schematic diagrams of hydraulic systems, their principle of operation and problems of studying losses in elements and energy efficiency characteristics of systems consisting of a feed assembly, control set and cylinder. It also includes a subject matter connected with an energy loss power of hydrostatic systems with hydraulic cylinder controlled by proportional directional control valve. Diagrams of loss power of two hydraulic systems worked at the same parameters of speed and load of a cylinder, which were different due to structure and ability of energy saving, were presented and compared.

Dynamics and Control of a Shared Wind Turbine Drivetrain

This paper presents the dynamics and control of a new wind power plant configuration where multiple turbines are connected to a shared drivetrain. A hydrostatic transmission system is utilized to collect and transfer the harvested mechanical energy of individual turbines to the generator. The interconnected wind turbines are controlled individually to achieve maximum power point tracking (MPPT) while regulating the generator speed. In the first control loop, the pump displacement is adjusted accordingly to satisfy the MPPT. In the second control loop, the electrical load on the generator is controlled to balance the torque and reach a stable frequency operation. Simulation results show the performance of the control system operation. It also demonstrates an increase and improved smoothness of a power generation profile.

Power Generation Control of a Monopile Hydrostatic Wind Turbine Using an <inline-formula> <tex-math notation="LaTeX">$\mathcal{H}_{\infty}$ </tex-math> </inline-formula> Loop-Shaping Torque Controller and an LPV Pitch Controller

We transform the National Renewable Energy Laboratory (NREL) 5-MW geared equipped monopile wind turbine model into a hydrostatic wind turbine (HWT) by replacing its drivetrain with a hydrostatic transmission (HST) drivetrain. Then, we design an $\mathcal {H}_{\infty }$ loop-shaping torque controller (to regulate the motor displacement) and a linear parameter varying (LPV) blade pitch controller for the HWT. To enhance the performances of the pitch control system during the transition region around the rated wind speed, we add an antiwindup (AW) compensator to the LPV controller, which would otherwise have had undesirable system responses due to pitch saturation. The LPV AW pitch controller uses the steady rotor effective wind speed as the scheduling parameter, which is estimated by the light detection and ranging preview. The simulations based on the transformed NREL 5-MW HWT model show that our torque controller achieves a very good tracking behavior, while our pitch controller (no matter with or without AW) gets much improved overall performances over a gain-scheduled PI pitch controller.

Theoretical Study and Experimental Validation of a Hydrostatic Transmission Control for a City Bus Hybrid Driveline with Kinetic Energy Storage

A city bus with hybrid drive system was studied for its performance. The driveline under consideration consists of two alternative energy sources—an internal combustion engine (ICE) and kinetic energy storage (KES)—a hydrostatic transmission (HST), a drive axle and corresponding gears. A generalized law for HST control is obtained that satisfies kinematic and torque requirements for the alternative energy sources and the different modes of operation of the bus. A test stand was developed for validation of the chosen control strategy and for the energy flow simulations through the HST. The estimated maximum energy recovery potential is around 20–25%.