Hydraulic Energy Research Articles

열역학법을 이용한 중규모급 수력플랜트 현장 효율 시험

The field efficiency test for a hydropower plant where a Franics hydraulic turbine is installed has been carried out by thermodynamic method usually used for the high head hydraulic turbine over 100 m. During the testing, the loss of hydraulic energy converted to thermal energy is measured by a precise thermometers with accuracy of 0.001K to estimate the efficiency. In order to measure the water temperatures on the low-pressure measuring section in the draft tube, two perforated pipes were used per draft tue outlet. Three thermometers were installed in these perforated pipes in each draft tube outlet. On the high-pressure measuring section at the casing inlet, 2 opposite thermometers were installed to obtain the inflowing water temperature. The field test was conducted for total 39 cases while adjusting the power output from max. 52.0MW to min. 19.2 MW. Error analysis of the test results confirmed that the max. absolute uncertainty of turbine efficiency is 0.73% and repeatability is estimated to be less than 0.4%. Based on the measuring data, the best efficiency point for the turbine efficiency without aeration is estimated at 93.21% for a specified flow rate of 50.91 m³/s and a specified turbine power of 52.53MW. In addition, plant efficiency is evaluated by considering generator and water way efficiencies in addition to turbine efficiency which has the main effect in order to seek optimal operation condition of the hydropower plant.

Modelling of the circular edge-clamped interface of a hydraulic pressure energy harvester to determine power, efficiency and bandwidth

There is an increasing desire to monitor and control hydraulic systems in an autonomous and battery-free manner. One solution to this challenge is to harvest hydraulic pressure ripples and noise by exploiting the piezoelectric effect. This paper develops a new generalized model of a hydraulic piezoelectric harvester based on a circular edge-clamped flat plate interface with a central piezoelectric stack. Such a model allows the relationships between harvesting performance and structure to be assessed in detail. It is demonstrated that the force-deflection relationship of a circular edge-clamped plate with a central lumped mass follows a cubic hardening Duffing equation. A single degree of freedom (SDOF) lumped-parameter model of the system is established where the nonlinear frequency response resulting from hardening nonlinearities are explored. The input mechanical energy and the output electrical energy both exhibit a quadratic nonlinear relationship with vibration amplitude. The maximum output occurs at the jump-down frequency and the overall energy conversion efficiency of the system is determined. The optimum resistance load for maximum output energy and energy efficiency are obtained as non-dimensional excitation frequency. Experimental validation is performed and good agreement is observed between model results and experimental measurements. The developed model provides important insights into the optimization of power output and response of future hydraulic energy harvesting devices.

Morpho-sedimentary and stratigraphic characteristics of the 2000 Yigong River landslide dam outburst flood deposits, eastern Tibetan Plateau

Sedimentary characteristics of landslide dam outburst flood deposits are distinct from those of rainfall flood deposits due to their very high hydraulic energy and sediment concentration. While they have been studied well in geological record, investigations of modern outburst flood deposits are relatively rare. Well-preserved flood deposits and landforms caused by the June 2000 landslide dam outburst flood in the Yigong River, eastern Tibet provide an opportunity to evaluate such sedimentological response to a high energy modern event. The sedimentary characteristics of boulder bars and channel evolution over c. 17 km downstream of the breach were investigated by field survey and remote sensing interpretation. The results show that the post-flood channel migrated downstream and increased in curvature. The bar shape is very little changed toward downstream, but the bar area shows a fluctuating decrease. Poorly sorted accumulations composed of massive granular gravels and boulders near the breach indicate sediment-rich bedload depositing processes occurred during rapid rising stage flows. In contrast, there are eddy bars and deposition of fine gravel with horizontally bedded laminations 17 km downstream of the dam, suggesting suspended sediment dominated deposition with a rapid loss of transport capacity. Comparison with previous hydrodynamic simulations indicates that the rates of the rising stage and the falling stage strongly affect the sedimentary characteristics of boulder bars and slackwater deposits.

Research on energy-saving characteristics of battery-powered electric-hydrostatic hydraulic hybrid rail vehicles

With the advantages of no emission and low noise, battery rail vehicles (BRVs) are widely used in the construction of subway, high-speed railway and so on. However, the problems of low energy efficiency and peak power shock of traction motor have severely restricted the application and promotion of BRVs. To address these problems, an electric-hydrostatic hydraulic hybrid powertrain (EH3) is designed in this paper. Friction braking (FB) is replaced by hydraulic regenerative braking (HRB) and the mode of recovered hydraulic energy coupled at the inlet of pump (ECIP) to assist acceleration is proposed. The energy conservation characteristics of recovery and coupling of hydraulic energy in EH3 powertrain are verified by simulation and laboratory test bench. The energy recovery efficiency of HRB is up to 50% and the new coupling modes can greatly reduce the consumption of electric power. The control strategy is designed to coordinate different working modes which are established based on the high-pressure accumulator (HPA) and the driving state parameters of BRVs. The simulation result shows that the energy consumption of the battery can be reduced by 17.32%. The EH3 powertrain has broad application prospects in realizing energy conservation, reducing peak motor power shock and improving the braking performance of BRVs.

Investigation on Energy Loss in Centrifugal Pump Based on Entropy Generation and High-Order Spectrum Analysis

Abstract Full-open, straight-blade centrifugal pumps have the advantages of simple structure and high stability at high speeds. However, this type of centrifugal pump has a large internal energy loss and low efficiency. The flow loss caused by unstable flow accounts for most of the internal energy loss of a centrifugal pump, and this energy dissipates mainly to the surroundings of the pump in the form of pressure pulsation and vibration. In this study, to effectively understand the hydraulic behavior and energy loss in a centrifugal pump, the energy losses in the pump were numerically analyzed by the entropy generation method, the distribution of the energies of pressure pulsation and vibration was evaluated based on experimental results at different flowrates, and the correlation between flow and energy loss at 20% of the design flowrate (Qd) was investigated by high-order spectrum analysis. The energies of pressure pulsation and vibration in the experiment were evaluated by the root-mean-square (RMS) value. The distribution of the entropy generation rate (EGR) indicated large energy losses at the diffusion section of the volute, clearance, tongue, and blade inlet. At 20% of the design flowrate (Qd), the energy loss was caused by the backflow near the tongue, and the EGR at EP2 had a nonlinear fundamental characteristic frequency of 0.44fn. By bispectrum and coherence analysis, the nonlinear fundamental characteristic frequencies generated by the unforced flow were analyzed, and it was found that unforced flow was transmitted to one another in the near-tongue region.

Quantification of Energy Loss in Two Grated Inlets under Pressure

Grated inlets have the normal function of collecting the surface runoff into sewer networks, but when the flow exceeds the capacity of the sewer pipes and conduits get pressurized, an outflow from the sewer manholes and grates can occur. In this case, the grate produces an energy loss in the outflow from sewer to street that could be hydraulically quantified characterizing this kind of flow. Energy loss analysis in trash racks can be found in technical literature, but no specific studies on sewer grate inlets have been found. For this reason, some experiments in full scale were developed in the hydraulic laboratory of the Technical University of Catalonia (UPC) in order to quantify hydraulic energy losses associated with flow through grated inlets during surcharging conditions. The main goal of this research work was to experimentally quantify the values of the local loss coefficient k for two different surcharged real scale grated inlets existing in Barcelona. For the tested overflows between 20 and 50 L/s, a range from 0.25 to 3.41 was observed for k coefficients under different average velocities of reference and different flow conditions.

Simulation and Experimental Study of Hydraulic Cylinder in Oscillating Float-Type Wave Energy Converter

Abstract Hydraulic cylinders play a vital role in the energy output (PTO) system of an oscillating float-type wave energy converter, whose function is to convert the mechanical energy captured by the float from the waves into hydraulic energy. The performance of the hydraulic cylinder determines the conversion efficiency of mechanical energy to hydraulic energy in the system; therefore, it is necessary to study the working mechanism of the hydraulic cylinder. This paper takes a self-developed oscillating float-type wave energy converter as the research object, and studies the working mechanism of its hydraulic cylinder, and uses the linear analysis method to derive the critical self-excited vibration curve of the hydraulic cylinder. In addition, the effects of the external load, hydraulic cylinder load mass, stroke length, spring stiffness and piston area on the performance of the hydraulic cylinder were studied by AMESim simulation software. According to the simulation results, a physical model of the hydraulic cylinder is established. Finally, the physical model is tested in a hydrodynamic pool. The test results show that the hydraulic cylinder can stably and efficiently convert mechanical energy into hydraulic energy even under small waves, thus verifying the rationality of the hydraulic cylinder design.

Use environmentally friendly hydraulic power to design a hydraulic rapid mixing basin in the drinking water treatment plant

Most cities in Iraq provide drinking water by purifying river water of physical and chemical contaminants. It uses energy from petroleum (electricity). As it seeks to get drinking water from the rivers with clean and renewable technologies and energy, the State of Iraq plans to use one of its most abundant resources to address the shortage of fresh water, namely hydropower. This study is based on the use of hydraulic energy (environmentally friendly) in the purification of water instead of the use of electricity. The use of electrical energy in water purification has a lot of problems, including the continuous interruption of the current and therefore stop the station from work and that it needs periodic maintenance and need to staff specialized for operation and maintenance, so it is expensive while the use of hydraulic energy will help to solve most of these problems. The possibility of replacing the rapid-mechanical mixing basin to the rapid hydraulic mixing, which operates according to the principle of forced forexes, where the study of the performance of the drinking water treatment plant in the eastern district of Al-Hamzah On the ADiwaniyah River in the southern province of ADiwaniyah, where concentrations of pollutants in the river are high in the study area. Where samples were taken from different locations for water in the drinking water treatment plant of Al-Hamzah for different treatment stages. Where the pollutants were examined in the laboratories of the Environment Directorate of ADiwaniyah and the laboratories of the Faculty of Engineering. All concentrations of physical and chemical contaminants were higher than the standards of Iraqi standards and the efficiency of treatment was not as low as 83%. This is due to the continuous interruption of electrical current and the failure of the mechanical equipment of the rapid mechanical mixing basin, which requires periodic maintenance and the continuation of the addition of high coagulant doses which cause high processing costs as well as the high concentration of aluminum used for coagulation. Therefore, a hydraulic mixing basin was used by conducting experiments in the fluid laboratory In the Faculty of Engineering using the Free and Forced Vortex, which has been developed and adjust suit the requirements of the study. There have been various experiments to obtain the best dimension of hydraulic mixer and best amount of coagulant to remove the turbidity and the best mixing speed and the best value of the pH, which achieved processing efficiency of up to 98.0%.

Design and performance analysis of human walking induced energy recovery system by means of hydraulic energy conversion and storage

Human walking induces a lot of mechanical energy available for harvesting. It is promising to use such energy to reduce the energy supply of wearable electronics and robotic equipment such as exoskeleton. This paper mainly deals with the design and performance analysis of the energy recovery system based on fluid power transmission principle. Firstly, modeling and simulation of single foot walking motion were carried out to investigate the human walking dynamics to explore the variation of energy produced by human walking within a gait cycle. Together with gait characteristics measurement, the foot-ground interaction force in the horizontal and vertical directions is obtained. Then, the energy recovery system based on the working principle of volumetric pump was designed to convert the human walking induced mechanical energy into hydraulic energy directly and achieve energy storage with accumulator in the meantime. The energy recovery results obtained under different conditions of walking speed and load carrying are considered by numerical simulation and experimental verification. It is shown that the output power in average of the recovery mechanism by single foot walking at 5.56 km/h is around 3.2 W, and the captured power can be increased with higher precharge pressure of accumulator. Comparisons indicate that power and its density of the system proposed in this paper are far greater than that achieved by electric generation, providing a potential solution for hydraulically actuated walking mechatronic systems.

Modeling and Optimal Dimensioning of a Pumped Hydro Energy Storage System for the Exploitation of the Rejected Wind Energy in the Non-Interconnected Electrical Power System of the Crete Island, Greece

The aim of the present paper is to investigate the use of the site “Potamon” Dam in the Prefecture of Rethymnon, Crete island, Greece, as a “virtual” renewable electricity supply of a pumped storage plant (PSP) in order to save and exploit the maximum possible part of the rejected wind energy of the autonomous power system of the Crete island. Taking into account the annual time series of the rejected power of the Crete power grid, the present research work targets the optimal configuration of the proposed PSP power station, including the sizing of its individual components as well as the determination of the capacity it could guarantee in order to be economically viable. The rejected electric energy from the actually operating wind farm production, which is not possible to be absorbed by the grid of Crete due to its stable operation limitations, could be absorbed by the here proposed pump storage plant (PSP) and converted to hydraulic energy. This can be achieved by pumping the water from the lower reservoir, which is the existing reservoir of the site “Potamon” Dam, with a storage capacity of about 22.5 million m3, up to the upper reservoir, which must be constructed accordingly. For the proposed PSP’s optimal size determination, established financial indices are used as an evaluation criterion for an investment life cycle of 25 years. The proposed PSP optimization is based on the dynamic mathematical model of the simulation results of the PSP’s hourly operation when incorporated in the Crete power grid for a whole year, performed in the Matlab 2016b computational environment (The MathWorks, Inc., Natick, MA, USA). The results of this research demonstrate the PSP’s technical feasibility and determine the PSP’s optimal CAPEX and the PSP’s whole life-time financial indicators in order that the whole investment be viable. Furthermore, the appropriate selling prices of the electricity produced from the proposed PSP were determined to achieve the PSP’s financial viability. The results comprise the key elements to prove the necessity for the establishment a.s.a.p. of the appropriate legal framework in order to have authorization to exploit the rejected RES (renewable energy sources) electric energy or the major part of it through PSPs, in priority in both the non-interconnected, as well as the interconnected power systems.

Conduit arterial wave reflection promotes pressure transmission but impedes hydraulic energy transmission to the microvasculature.

Current thinking suggests that wave reflection in arteries limits pulse pressure and hydraulic energy (HE) transmission to the microvasculature and that this protective effect reduces with advancing age. However, according to transmission line theory, pressure transmission (Tp) and reflection (R) coefficients are proportional (Tp = 1 + R), implying that wave reflection would promote rather than limit pressure transmission. We hypothesized that increasing distal pulse pressure (PPd) with age is instead related to increased proximal pulse pressure (PPp) and its forward component and that these are modulated by arterial compliance. A one-dimensional model of a fractal arterial tree containing 21 generations was constructed. Wave speed in each vessel was prescribed to achieve a uniform R at every junction, with changes in R achieved by progressively stiffening proximal or distal vessels. For both stiffening scenarios, decreasing reflection led to a decrease or no change in PPd when forward pressure or compliance were held constant, respectively, suggesting that wave reflection per se does not limit pressure transmission. Proximal pulse pressure, its forward component, and PPd increased with decreasing compliance; furthermore, proximal and distal pulse pressures were approximately proportional. With fixed compliance but decreasing reflection, HE transmission increased, whereas pressure transmission decreased, consistent with transmission line theory. In conclusion, wave reflection does not protect the microvasculature from high PPd; rather, PPp and PPd are modulated by arterial compliance, which reduces with age. Wave reflection has opposing effects on pressure and HE transmission; hence, the relative importance of pressure versus HE in contributing to microvascular damage warrants investigation.NEW & NOTEWORTHY With aging, a reduction in the stiffness gradient between elastic and muscular arteries is thought to reduce wave reflection in conduit arteries, leading to increased pulsatile pressure transmission into the microvasculature. This assumes that wave reflection limits pressure transmission in arteries. However, using a computational model, we showed that wave reflection promotes pulsatile pressure transmission, although it does limit hydraulic energy transmission. Increased microvascular pulse pressure with aging is instead related to decreasing arterial compliance.

Technical-economic analysis for a green ammonia production plant in Chile and its subsequent transport to Japan

Green ammonia can be produced using fossil fuels or any renewable energy source combined with heat or electricity. Chile has one of the highest rates of solar irradiation and also the environmental conditions that support the development of solar industry. Other renewable sources of energy are the wind and the hydraulic dams. These energies could be used to generate ammonia by a standard method such as the Haber-Bosch process, which transforms hydrogen and nitrogen using high temperatures and a catalyst. The ammonia has several desirable characteristics that suggest its use as a way to store hydrogen. Firstly, it can be liquified under mild conditions. Secondly, the ammonia has a high weight fraction of hydrogen. Thus, it is deemed necessary to study technical and economic variables that may support the use of green ammonia as an energy carrier for hydrogen. The aim of this work is to develop a technical-economic analysis about the production of ammonia using hydrogen by means of electrolysis (carried out with solar, wind, and hydraulic renewable energies). The aforementioned green ammonia would be produced in Chile and it would be necessary to transport it to Japan. Sensitivity analysis of main parameters (plant operating hours, size of the ammonia synthesis plant - related to the capacity of the electrolysis plant size in MW-, electricity price, electrolyzer cost, Haber-Bosch cycle cost, and ammonia sales price) was performed to report what factors are primordial at the moment of carried out techno-economic analyses. An optimization process that minimize the NPV was run in order to settle the most convenient size of the electrolyser stack. A net present value (NPV) of base case is €77,414,525 and 7.62 years of pay-back period were calculated for this green ammonia production plant, which considered hydrogen production via electrolysis, Haber-Bosch processes, and trade values of different operational units. The sensitivity analysis has determined that the main variables affecting the NPV are the size of the ammonia synthesis plant and the electricity price. Furthermore, by considering triangular probability distribution of specific variables, it was observed that with a 95% of confidence, the NPV would be positive with a 76.1% of occurrence. The optimization process defined that a stack of 164.21 MW would be the most convenient electrolyser stack dimension, which was estimated by considering all different effects over the operational expenditure (OPEX), capital expenditure (CAPEX), and investments risk. Therefore, the hydrogen production in Chile and its transportation to Japan using ammonia as an energy carrier would be a technically viable and profitable solution, which also has environmental benefits.

Energy-saving technologies for construction machinery: a review of electro-hydraulic pump-valve coordinated system

With the rapid development of the global economy, more and more attention has been paid to the energy conservation of construction machinery. The hydraulic system is the key component of construction machinery, and improving its energy utilization rate has become an important means to achieve energy conservation. In conventional valve-controlled or pump-controlled hydraulic systems of construction machinery, controllability and energy-saving performance typically cannot be considered at the same time. The pump-valve coordinated system combines the energy-saving characteristics of the pump-controlled system and the high-precision and high-frequency response of the valve-controlled system, which has the potential to become a primary research direction of electro-hydraulic systems. This review summarizes the recent research progress in energy-saving technologies based on pump-valve coordinated systems. Particularly, we discuss the structures of hydraulic systems in different categories of construction machinery, various control methods of the electro-hydraulic system, novel hydraulic hybrid energy regeneration systems, and key components. In addition, future directions and challenges of the pump-valve coordinated systems are described, such as independent metering system (IMS), common pressure rail (CPR), and hybrid power source (HPS).

The Effects of Different Shaped Baffle Blocks on the Energy Dissipation

Stilling basins can be defined as energy dissipaters constructed of the irrigation systems. This study aims at investigating the performance of the new seven baffle blocks design in terms of reducing the dimensions of stilling basins in irrigation systems. In order to assess the hydraulic efficiency of a new model for baffle block used in stilling basins, a Naval Research Laboratory (NRL) has conducted. The results of this study demonstrate that the performance of the new baffle block, in term of hydraulic jump length reduction and hydraulic energy dissipation, it's better than standard blocks. However, the ratios of the drag resistance attributed to the new baffles block (FB / F2) have been larger than that applied on the normal block. It was found that the new block dissipates the energy by 9.31% more than the concrete block, and decreases the length of the hydraulic jump by 38.6% in comparison with the standard blocks. However, the new block maximizes the drag force ratio by 98.6% in comparison with the standard baffle blocks. The findings indicated that in terms of energy reduction and dissipation in the length of the hydraulic jump, the new block is superior to the other kinds.

Full-waveform-based characterization of acoustic emission activity in a mine-scale experiment: a comparison of conventional and advanced hydraulic fracturing schemes

SUMMARYUnderstanding fracturing processes and the hydromechanical relation to induced seismicity is a key question for enhanced geothermal systems (EGS). Commonly massive fluid injection, predominately causing hydroshearing, are used in large-scale EGS but also hydraulic fracturing approaches were discussed. To evaluate the applicability of hydraulic fracturing techniques in EGS, six in situ, multistage hydraulic fracturing experiments with three different injection schemes were performed under controlled conditions in crystalline rock at the Äspö Hard Rock Laboratory (Sweden). During the experiments the near-field ground motion was continuously recorded by 11 piezoelectric borehole sensors with a sampling rate of 1 MHz. The sensor network covered a volume of 30×30×30 m around a horizontal, 28-m-long injection borehole at a depth of 410 m. To extract and characterize massive, induced, high-frequency acoustic emission (AE) activity from continuous recordings, a semi-automated workflow was developed relying on full waveform based detection, classification and location procedures. The approach extended the AE catalogue from 196 triggered events in previous studies to more than 19 600 located AEs. The enhanced catalogue, for the first time, allows a detailed analysis of induced seismicity during single hydraulic fracturing experiments, including the individual fracturing stages and the comparison between injection schemes. Beside the detailed study of the spatio-temporal patterns, event clusters and the growth of seismic clouds, we estimate relative magnitudes and b-values of AEs for conventional, cyclic progressive and dynamic pulse injection schemes, the latter two being fatigue hydraulic fracturing techniques. While the conventional fracturing leads to AE patterns clustered in planar regions, indicating the generation of a single main fracture plane, the cyclic progressive injection scheme results in a more diffuse, cloud-like AE distribution, indicating the activation of a more complex fracture network. For a given amount of hydraulic energy (pressure multiplied by injected volume) pumped into the system, the cyclic progressive scheme is characterized by a lower rate of seismicity, lower maximum magnitudes and significantly larger b-values, implying an increased number of small events relative to the large ones. To our knowledge, this is the first direct comparison of high resolution seismicity in a mine-scale experiment induced by different hydraulic fracturing schemes.

Recuperation gain for a hydraulic energy storage in automotive applications

Vehicles with internal combustion engines waste a lot of energy during conventional braking. Therefore, energy recovery systems are needed to reduce the fuel consumption of these vehicles and improve sustianability. Here, a hydraulic energy storage system for such recuperation purposes in vehicles is considered. The complex processes inside such a system are mapped onto a simplified endoreversible model for the first time. Considering the different components of our system, we derive a differential equation system describing the recuperation process. Synthesizing these equations, we also derive an estimate for the full range operational behavior of the system for different driving cycles. Based on this data we calculate the recuperation gains which are 74% for a harmonic velocity profile, 18% for the Worldwide Harmonized Light Vehicles Test Procedure, and 9% for the New European Driving Cycle. Furthermore we discuss the recuperation gains for different parameter choices. The findings can be used to optimize design and process parameters of the powertrain.

Design of a Straight Bladed Vertical Axis Water Turbine Suitable for Deployment in River Like the Brahmaputra

Turbines are hydraulic machines which convert hydraulic energy into mechanical energy. This mechanical energy is used in running an electric generator that is directly coupled to the shaft of a turbine. These machines convert mechanical energy into electrical energy. The generation of hydro-electric power is the cheapest as compared to the power generated by other sources such as oil, coal, etc. Power generated by Small Hydro Power (SHP) station is not only cheap, but also environment friendly. Despite its dual advantage, the SHP has however remained untapped all over the world. Things are now changing surely but slowly, with more and more focus on SHP. Hydropower being the cleanest source of electrical energy from environmental considerations needs to be tapped as early as possible. The authors of this paper are motivated by the water current available in the river Brahmaputra, Assam, which may be suitable for establishing Small Hydro Power stations. A design of a prototype of a straight bladed vertical axis water turbine which is based on the theories of vertical axis wind turbine is proposed here. Encouraged by the existing theories of vertical axis wind turbine, the authors propose a mathematical analysis and design of a prototype of vertical axis water turbine which may be suitable for Small Hydro Power Station. Future scope of this work is also mentioned.

System Characteristics Analysis for Energy Management of Power-Split Hydraulic Hybrids

Hydraulic hybrid powertrains provide an opportunity for specific applications, such as heavy-duty vehicles based on high-power density, which has not been included in other types of hybrid powertrains. Among the various architectures of hybrid vehicles, power-split hybrids have a greater possibility of producing better fuel efficiency than other hybrid architectures. This study analyzed the possible energy-saving characteristics of power-split hydraulic hybrid vehicles (HHVs); this has not been comprehensively described in previous studies. A typical configuration of power-split HHVs was modeled with the FTP-72 driving cycle using a novel simulation method that considered the dynamic and thermal behaviors together. The characteristics were analyzed in comparison to a power-split hydrostatic transmission (HST), which is designed with the same conditions except for hydraulic energy storage. The power-split HHV not only has a better fuel efficiency, but it also shows system energy-saving characteristics. The power-split HHV has more chances for engine idling, which is directly related to fuel consumption savings due to engine stop. Additionally, more engine idling time enables the system to operate in a more efficient area on the engine map by load leveling. The results for the system temperature show that the power-split HHV offers the possibility to deliver better thermal management because it prevents the waste of braking power, which is especially crucial for hydraulic systems in comparison to other power systems such as electric or mechanical power systems. The ease of thermal management results in less energy consumption for cooling down the system temperature by minimizing the cooling system, as well as in a better thermal stability for the hydraulic system. The power-split HHV characteristics analyzed in this study can be used to design and organize the system control logic while developing power-split HHVs.

Energy Efficiency Comparison of Hydraulic Accumulators and Ultracapacitors

Energy regeneration systems are a key factor for improving energy efficiency in electrohydraulic machinery. This paper is focused on the study of electric energy storage systems (EESS) and hydraulic energy storage systems (HESS) for energy regeneration applications. Two test benches were designed and implemented to compare the performance of the systems under similar operating conditions. The electrical system was configured with a set of ultracapacitors, and the hydraulic system used a hydraulic accumulator. Both systems were designed to have the same energy storage capacity. Charge and discharge cycle experiments were performed for the two systems in order to compare their power density, energy density, cost, and efficiency. According to the experimentally obtained results, the power density in the hydraulic accumulator was 21.7% higher when compared with the ultracapacitors. Moreover, the cost/power ($/Watt) ratio in the hydraulic accumulator was 2.9 times smaller than a set of ultracapacitors of the same energy storage capacity. On the other hand, the energy density in the set of ultracapacitors was 9.4 times higher, and the cost/energy ($/kWh) ratio was 2.9 times smaller when compared with the hydraulic accumulator. Under the tested conditions, the estimated overall energy efficiency for the hydraulic accumulator was 87.7%, and the overall energy efficiency for the ultracapacitor was 78.7%.

Hydraulic Potential Energy Model for Hydropower Operation in Mixed Reservoir Systems

AbstractThe forecast‐informed hydropower operation for mixed reservoir systems, which consist of parallel and cascade reservoirs, is of considerable importance in practice; however, this operation still lacks an analytical basis in theory. From the perspective of energy, this paper introduces the concept of “hydraulic potential energy” and mathematically derives the energy transformation formula for multi‐reservoir hydropower operation. Based on this formula and the rolling single‐period forecast, a maximum hydraulic potential energy model (E1 model) is proposed. The presented rigorous proofs demonstrate the deficiencies of the commonly considered objectives or principles of minimizing the outflow‐induced energy‐cost, while the objective function of the E1 model is demonstrated to be superior. If the constraints of power output and reservoir storage are nonbinding, the derived optimal spatial principle for hydropower operation is (1) to equalize the Relative Marginal Energy (RME) among reservoirs or (2) if this status is not feasible, to release water and generate hydropower first from the reservoirs that have the largest RME values. Considering the uncertainty of future inflow, the E1 model is extended to the two‐stage hydraulic potential energy model (E2 model). A case study of a hypothetical mixed three‐reservoir system demonstrates the superior performance of the E2 model compared with the conventional K‐value principle and the minimum energy‐cost model. This paper provides an innovative spatial principle and a practical model for the realization of forecast‐informed hydropower operation, which contributes to the optimization of the large‐scale energy market.