Throttling Energy Research Articles

An Improved Zero-Flowrate Switching Control Method to Reduce Switching Losses in a Hydraulic Actuator

Hydraulic switching actuators are high-efficiency, fast response, and low-cost solutions for hydraulic control systems. One of the challenging problems is throttling losses during valve transitions. Previously, the authors proposed a zero-flowrate switching method to reduce the throttling energy loss of the switching valve, where a hydraulic resonator is applied to make the flowrates through the lines approaching zero before the valves are switched off. The major challenge of this approach is fast switching valves whose transition times are less than 2 ms. In this paper, an improved zero-flowrate switching method is presented. It utilizes the capacity with independent inlet/outlet ports to regulate flowrates through the lines. Models of capacity applied in a simple line with different pressure signals are developed to explore characteristics of the capacity, based on which a complete actuation system is developed. In the complete model, resistance and inductance are optimized to achieve the desired flowrate response. The improved zero-flowrate switching method reduces throttling energy losses by 99.945% compared to a hard switching system. The simulation results demonstrated that the improved zero-flowrate switching method performs as expected in the design condition. A capacity with proper volume is able to regulate flowrates through all the lines to zero, with the help of appropriate resistance and inductance. Compared to the previous zero-flowrate switching method, the novel strategy allows slower switching valves applied in hydraulic actuation systems and achieves better efficiency performance. This research paves a new avenue for reducing throttling energy losses and improves system efficiency in hydraulic switching actuators, as well as most of the hydraulic switch-mode circuits.

Constrained Motion Control of an Independent Metering System with Uncertain Loads

Independent metering systems (IMSs) have been applied and researched in mobile machinery due to their advantages of reduced throttling energy losses and remarkable advances under negative load through decoupling actuator throttling control. Although IMSs have the control flexibility to deal with negative workloads, the control performance of the IMSs is challenged by uncertain loads in mobile operations, limiting the control accuracy. In addition, if the motion reference is improperly specified and exceeds the constraints, the pressure of the actuator may oscillate significantly and potentially result in control instability. In this study, a constrained adaptive robust control strategy is proposed for an IMS. An adaptive robust control strategy is designed for the meter-in and meter-out throttling to achieve precision motion control despite the nonlinearities and uncertainties of the electro-hydraulic IMS. The value of the uncertain workload is estimated in real-time and utilized in the model-based controller to improve control accuracy. In addition, a constrained trajectory planning approach is presented to handle out-of-constraint references and ensure motion tracking performance. This effectively prevents pressure fluctuations caused by the inappropriate reference.

Selection, control and techno-economic feasibility of Pumps as Turbines in Water Distribution Networks

Abstract Water Distribution Networks (WDNs) are becoming an attractive area of application for small hydropower, which can contribute to the development of distributed energy generation from renewable sources. Indeed, WDNs experience considerable water leakages due to their age and water management authorities often divide the WDNs by inserting Pressure Reducing Valves (PRVs), which waste a potentially recoverable hydraulic head. The replacement of PRVs with Pump as Turbines (PaTs) can be considered as an economically feasible solution to achieve both an effective pressure control and a throttling energy recovery. The selection, installation and control strategy of a PaT in a WDN must consider the variability of the pressure and the flow rate demand. Starting from the evaluation of the available head and the water demand, in this work, we describe a methodology to select from pump catalogues the most suitable PaT and the best control criteria for a specific WDN. Then, knowing the pump geometry, it is possible to predict the characteristic curve of the pump operating as a turbine by using a 1-D performance prediction model. The WDN of a town in the Apulia region (Southern Italy) has been used as a case study. Finally, a techno-economic evaluation has been carried out by considering both economic and environmental benefits.

An Overview of Energy Savings Approaches on Hydraulic Drive Systems

Different procedures to improve the energy efficiency of a hydraulic drive system have been surveyed in this article. The energy-saving approaches are classified into four categories: hybridization, control algorithms, waste energy recovery and reduction of energy losses. Also, the sub-categories of each strategy are discussed individually in brief. The energy efficiency can go up to 69% using a hybridization strategy, whereas using a fuel-saving strategy is within the range of 20–40%. Another strategy, i.e., control algorithms, yields 40% of fuel savings on the displacement-controlled excavator system. Similarly, the maximum potential to recover the braking energy is about 78% in the case of the Constant Pressure System (CPS) system using flywheel under the category of waste energy recovery. Moreover, 56–66.1% throttling energy saving potential is observed on an On/Off high-speed valve-controlled hydraulic system under the reduction of energy loss strategy. Different energy saving potentials of the hydraulic system have been presented in tabular form for a clear understanding of the historical development in this field.

Design and Validation of a Soft Switch for a Virtually Variable Displacement Pump

Switch-mode hydraulic control is a compact and theoretically efficient alternative to throttling valve control or variable displacement pump control. However, a significant source of energy loss in switch-mode circuits is due to throttling during valve transitions. Hydraulic soft switching was previously proposed as a method of reducing the throttling energy loss, by absorbing, in a small variable volume chamber, the flow that would normally be throttled across the transitioning high-speed valve. An active locking mechanism was previously proposed that overcomes the main challenge with soft switching, which is a lock mechanism that releases quickly and with precise timing. This prior work demonstrated a reduction in energy losses by 66% compared to a control circuit. In this paper, a numerical model is developed for a switch-mode virtually variable displacement pump (VVDP) circuit, utilizing the proposed soft switch. The model is then used as a means of designing a proof of concept prototype to validate the model. The prototype design includes methods for controlling the soft switch spring preload, travel distance, piston displacement required to unlock the soft switch, valve command duty cycle, switching cycle period, and load pressure. Testing demonstrated that the soft switch circuit performed as expected in a baseline condition. The operating region for this prototype was found to be quite narrow. However, the model does a good job of predicting the displacement of the soft switch.

Energy saving of a hydrostatic drive system by incorporating soft switch

A soft switching concept for the purpose of energy saving during on–off valve controlling of a hydrostatic drive system has been reported in this article. The soft switch has been incorporated in a state-of-the-art configuration in the drive circuit. Some identified soft switch parameters have been optimized with respect to minimum throttling energy loss using multi-run-simulation in bond graph. The bond graph technique has been used for the simulation study as it is based on power flow representation and guarantees energetic consistency in the model structure. Two different bond graph models, with and without the soft switch, have been simulated and validated experimentally; and the power and energy losses during spool movements of the directional control valve have been compared to quantify the energy savings. The study reveals that savings of more than 50% throttling energy can be possible using a soft switch in a switched mode hydrostatic drive system.

Influence of locking and passive soft switching on hydraulic circuit efficiency

Throttling and fluid compressibility losses are the major losses which occur during the valve transition in a switched mode hydraulic circuit. To minimize the throttling energy loss, a soft switch concept with lock and release mechanism was introduced by different researchers. In the literature, two different kinds of soft switches, one locking and another passive, were introduced in a hydraulic circuit. Thereafter, experimental validation was reported considering only a locking-type soft switch. But the influence of the passive soft switch on the performance of the hydraulic system was not reported. In this article, how the passive soft switch would affect the system efficiency has been investigated through bond graph model simulation. It has been shown both numerically and experimentally by other researchers that the use of a passive soft switch and a locking mechanism, depending upon configuration, can lead to more than 66.1% reduction in throttling energy loss. In this article, it has been further shown that an additional 3.25% throttling energy is saved when the passive soft switch is discarded from the system and only the locking mechanism is retained. The critical parameters of the locking soft switch have been optimized through multi-run simulation and, thereafter, a relationship between the critical parameters of the locking soft switch and the throttling energy loss of the valve has been obtained by using multiple regression analysis. Also, the variations of energy losses with respect to different valve orifice areas, duty cycles, and pulse width modulation frequencies are investigated through simulation.

Characterization of a supercharger as boosting & turbo-expansion device in sequential multi-stage systems

This paper proposes a detailed performance analysis and experimental characterization of a high-pressure supercharger in a multi-stage boosting system (turbo-super arrangement). Infact, besides the technical challenges associated with achieving adequate tuning, interoperability and driveability of multi-stage boosting systems, another challenge lies in their performance prediction during engine design. Indeed, performance maps of single boosting systems are usually provided by manufacturers and used as look-up tables in 1-D engine models. Tests are usually conducted in a standalone mode, with no information provided on the behaviour and performance of the combination of more than one boosting device.The supercharger was tested with varying inlet pressures and temperatures matching on-engine operating conditions and the results were then used to assess the effectiveness of 1-D engine models performance prediction when dealing with multi-stage boosting systems. An assessment on heat transfer in superchargers was also carried out together with the analysis on the nature of non-dimensional performance maps when dealing with a pressurized inlet. Finally, the analysis also looked into the opportunity to use the superchargers as expanders (‘expansion mode’) in order to cool the air charge entering the engine.The results showed that there is discrepancy between the efficiency values computed by 1-D engine models and those obtained experimentally under pressurized/heated inlet air conditions; the correction of the efficiency maps for heat transfer plays a significant role in the final measured efficiency and the correction of the maps for varying inlet temperatures must be carried out in order to avoid incurring in apparent efficiencies greater than unity. The experiments on the supercharger in ‘expansion mode’ showed that low isentropic efficiencies can be achieved; despite this, 1-D engine simulations showed that it is possible to achieve savings of a few percentage points in Brake Specific Fuel Consumption when the supercharger is used to recover some throttling energy by expanding the close-to-ambient pressure to the required intake pressure.

Soft Switch Lock-Release Mechanism for a Switch-Mode Hydraulic Pump Circuit

Switch-mode hydraulic circuits are a theoretically efficient, compact, fast responding, and inexpensive control option. Despite the many potential benefits of switch-mode hydraulic circuits, the control method suffers from large energy losses during transitions of the high-speed valve due to throttling and fluid compressibility. Rannow and Li previously proposed utilizing soft switching to minimize the throttling energy loss (Rannow and Li, “Soft Switching Approach to Reducing Transition Losses in On/Off Hydraulic Valve,” J. Dyn. Syst., Measure. Control (in press)). A major challenge of this approach is a locking soft switch that releases quickly and with precise timing, while under load. In this paper, a novel soft switch locking mechanism is presented that utilizes the pressure signal in the switched volume to trigger the release. A dynamic model is developed of three unique soft switch circuits and two control circuits that create a virtually variable displacement pump. The model is used to perform a grid search optimization of the soft switch parameters for the three circuits. The three soft switch circuits reduce the throttling and compressibility energy losses between 49% and 66% compared with the control circuit. The simulation results demonstrated that the soft switch circuits perform as expected for duty cycles and pressures below the design conditions. At higher duty cycles and pressures, the short time the circuit is connected to tank prevented the soft switches from resetting between cycles, preventing proper function. This novel lock and release soft switch mechanism enables soft switching in switch-mode hydraulic circuits, which significantly reduces throttling and compressibility energy losses during valve transitions. Lower losses during valve transition allow the use of slower switching valves, lowering energy consumption, and cost.