Entire Load Range Research Articles

Temperature optimization for improving polymer electrolyte membrane-water electrolysis system efficiency

Most of the hydrogen produced today is made using fossil fuels, making a significant contribution to global CO2 emissions. Although polymer electrolyte membrane water-electrolyzers can produce green hydrogen by means of excess electricity generated from renewable energy sources, their operation is still not economical. According to industry experts, the necessary cost reductions can be achieved by 2030 if system efficiency can be improved. The commonly stated idea is to improve efficiency by increasing the stack temperature, which requires the development of more resistant materials. This study investigates not only the efficiency of an electrolysis cell, but of the entire electrolysis process, including gas compression of hydrogen. The results indicate that an optimal stack temperature exists for every operating point. It is shown that the optimal temperature depends solely on the electrode pressure and cell voltage and can be analytically calculated. In addition, the temperature optimization leads to significantly reduced hydrogen permeation at low current densities. In combination with the pressure optimization, the challenging safety issues of pressurized electrolysis can be eliminated for the entire load range and, at the same time, the efficiency of the overall system be maximized.

Synchronous Push–Pull Class E Rectifiers With Load-Independent Operation for Megahertz Wireless Power Transfer

This article presents the analytical modeling of synchronous class E rectifiers with the load-independent operation, which achieves zero-phase-angle input impedance, soft-switching over the entire load range with a constant voltage gain. The optimal design of the synchronous class E rectifier is proposed to realize both zero-voltage-switching turn-ON and zero-current-switching turn-OFF at the expected output power. An LCC-S compensated MHz-WPT topology, which comprises the push-pull class E inverter and rectifier with the load-independent operation, is proposed to achieve the fully soft-switching and a nearly constant voltage gain over the entire load range. The efficiency improvement of the compensation network is also investigated to provide a design methodology for the proposed topology. A 6.78-MHz WPT prototype, along with an alternative phase detector using an auxiliary coil to realize phase detection, is built to validate the analytical model and the proposed methodology. The system efficiency reaches 86.7% at 214-W output. The synchronous push-pull class E rectifier maintains soft-switching over the load range, and the rectification efficiency reaches 94.6%.

Assessment of the influence of variable loads on the strength of welded joints of metal structures of bridge cranes

The article considers the assessment of the influence of dynamic effects on the calculation of welded joints of metal structures of bridge cranes operating under the influence of variable loads. Requirements for the dynamic characteristics of load-bearing elements of cranes are determined by the specifics of operation, design features and operating conditions of cranes operating under variable loads. Thus, it is proposed to perform calculations of welded joints of bridge cranes for endurance, operating under non-stationary variable load, based on the principle of linear summation of damages, which allows calculating in terms of load equivalent to the entire range of operational loads.

Experimental investigation of performance and emission characteristics of a miniature gas turbine supplied by blends of kerosene and waste tyre pyrolysis oil

Fossil fuels are non-renewable sources of energy that could be depleted in the near future, giving rise to a major energy crisis. Scientists from all over the world are working on new technologies to produce fuel not only from renewable sources but also from waste. This article is concerned with: (i) waste tyre management by means of the pyrolysis process, (ii) investigation of physico-chemical parameters of waste tyre pyrolysis oil (TPO), and (iii) investigation of performance and emission characteristics of a miniature GTM-140 turbine engine supplied by blends of kerosene and waste tyre pyrolysis oil. The final aim of the research is to determine the influence of the applied blend composition (between 10 and 50% of TPO in the blends) on the performance and emission parameters of a small gas turbine. Turbine inlet and outlet temperatures, fuel flow, static thrust, thrust specific fuel consumption (TSFC) and emissions index of NOx, CO, SO2 are measured in a wide range of turbine load. The differences are the largest for the highest rotational speeds, where the temperatures, TSFC and emissions of NOx especially tend to increase with the increasing fraction of pyrolytic oil in the blends, as compared to those of kerosene. However, emissions of SO2 are lower for the all blends in the entire range of load.

A DC-DC Center-Tapped Resonant Dual-Active Bridge with Two Modulation Techniques

Power converters with higher efficiency in a wide load range are important for reducing the overall energy consumption of renewable energy generation systems. A center-tapped LC series resonant dual-active bridge (LC-DAB) converter for DC-DC conversion is proposed in this paper. The proposed converter utilizes a center-tapped bridge to block reverse current and eliminate back flow power to reduce conduction losses. Two modulation methods for the proposed topology (i.e., fixed frequency modulation (FFM), and variable frequency modulation (VFM)) are proposed and analyzed. Both modulation methods can realize soft switch over the entire load range to reduce switching losses. In addition, the proposed modulation techniques guarantee soft switching for all devices and synchronous rectifier is realized by the center-tapped bridge to further reduce the conduction losses. Furthermore, a comprehensive comparison in terms of conduction losses and switching losses has been carried out to highlight the superiority of the proposed converter over the existing LC resonant converters. Finally, simulated and experimental results for a 1.5 kW prototype are presented to validate the theoretical analysis and performance of the proposed converter.

Novel strategies to overcome the limitations of a low compression ratio light duty diesel engine

Low compression ratio (LCR) approach in diesel engines can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously owing to lower temperatures and longer fuel-air premixing time. The present work investigates the effects of lowering the geometric compression ratio (CR) from 18:1 to 14:1 in a naturally aspirated (NA) single cylinder common rail direct injection (CRDI) diesel engine. Based on the investigations done across the entire speed and load range, significant benefits were observed in the NOx and soot emissions. However, lowering the compression ratio had adverse effects on brake specific fuel consumption (BSFC), unburned hydrocarbon (HC) and carbon monoxide (CO) emissions, especially at low-load and high-speed operating points. To overcome these limitations, novel strategies including split-cooling system (SCS) and secondary exhaust valve opening (SEVO) are proposed in the present work. While the fuel injection parameters optimization specific to LCR could help to improve the BSFC, HC and CO emissions penalty to a reasonable extent, the SCS concept can provide further benefits by reducing the heat loss to coolant and improving the engine component temperatures. Increasing the residual gas fraction using the optimized SEVO concept could further improve the charge temperature leading to a further reduction in the BSFC, HC and CO emissions. The net benefits of the optimized LCR approach are quantified for the modified Indian drive cycle (MIDC) using a one-dimensional simulation tool. The results obtained show a signification reduction of 22% and 74% in NOx and soot emissions respectively as compared to the base 18 CR engine results. Moreover, the penalty in HC and CO emissions could be contained to a large extent resulting in only a slight penalty of 23% and 20% respectively. Furthermore, the higher BSFC with the LCR approach could be successfully addressed and the final values were found to be better than the stock compression ratio by 1.5%. Overall, the strategies proposed in the present work are found to be beneficial to develop modern diesel engines in compliance with the future emission regulations which demand extreme control on NOx and soot emissions.

Identification of plasticity-controlled creep and fatigue failure mechanisms in transversely loaded unidirectional thermoplastic composites

In continuous fiber-reinforced thermoplastics, the macroscopic failure mode in transverse long-term failure is dominated by a brittle crack-growth mechanism. Neat thermoplastic matrices, on the other hand, generally display also a plasticity-controlled mechanism in long-term loading at elevated stress levels and/or temperature. This failure mechanism requires a different approach to lifetime prediction than crack growth; hence, it is important to identify it in the long-term performance of composites. In this study, we demonstrate the presence of the plasticity-controlled failure mechanism in long-term failure of transversely loaded unidirectional (UD) thermoplastic composites made of glass/iPP, carbon/PEEK and carbon/PEKK. The main method used is to compare the lifetime in cyclic loading to that in static loading at the same level of maximum stress, where an increase in lifetime is characteristic for plasticity controlled failure, and, vice versa, a decrease is indicative for fatigue crack growth. In addition, the applicability of a lifetime prediction method common to plasticity-controlled failure of neat thermoplastics is evaluated for the composites investigated. The results of this study indicate that the plasticity-controlled failure was present in composites, although the extent to which the effects are present varied depending on the materials investigated. Glass/iPP showed the most explicit evidence of the plasticity-controlled failure over the entire load range experimentally covered. Its long-term failure was delayed with a decrease in the stress ratio and lifetime was predicted well using the principles of plasticity-controlled failure.

Entire Magnetic Integration Method of Multi-Transformers and Resonant Inductors for CLTLC Resonant Converter

An entire magnetic integration methodology of high efficiency printed circuit board (PCB) winding transformer for CLTLC (capacitor-inductor-transformer-inductor-capacitor) resonant converter is presented. All magnetic components in the converter, including two resonant inductors and two transformers, are integrated into an improved EIE (E-type and I-type and E-type) core structure. According to the matrix transformer concept and uneven winding distribution, the novel structure can be obtained by introducing an air gap to the center core leg. Thus, the magnetizing inductance and leakage inductance of the transformer can be controlled easily through adjusting the air gap reluctances. In addition, both the detailed mathematical analysis and the reluctance model of the transformer have been studied. Furthermore, a four-layer printed circuit board winding structure is chosen. The related winding arrangement is also discussed in depth. Finally, a 1 kW prototype with the presented structure is implemented to verify the validity of the theoretical analysis. Experimental results demonstrate that the proposed structure guarantees high efficiency within the entire load range. Peak efficiency of 96.62% can be ensured.

Non‐isolated LLC resonant converter with suppressed circulating current and automatic resonant frequency matching capability

This study proposed a novel non-isolated half-bridge Inductor-Inductor-Capacitor (HB LLC) resonant converter with automatic resonant frequency adjustment ability and a circulating current suppression auxiliary circuit. The proposed converter employs a hybrid modulation technique based on frequency modulation (FM) and pulse width modulation (PWM) to regulate the output voltage. At the nominal operating point, all the excellent attributes of a conventional LLC converter over the entire load range are maintained and output voltage control is achieved with FM. However, when the input voltage decreased to a level that LLC output voltage cannot be maintained with FM, the primary switches will operate at the minimum switching frequency and the auxiliary switch will be turned ON with PWM. The auxiliary switch is turned ON with zero-voltage switching and automatically matching the circuit resonant frequency with the switching frequency for optimal operation. The effective resonant inductor is energised directly from the dc bus storing more energy which is later released to the load to achieving high gain while maintaining the desired output voltage with a narrow frequency span. In addition, the converter exhibits low circulating current under an enhanced gain condition. Experimental results are presented on a 60 W prototype to validate the theoretical prediction. The proposed converter has a peak efficiency of 97%.

Analysis, design, and optimisation of an LCC/S compensated WPT system featured with wide operation range

Wireless power transfer (WPT) offers the advantages of convenience, safety, low-maintenance, high reliability, and strong adaptability to the environment. This study proposes a design method to help LCC/S compensation topology achieve zero voltage switching (ZVS), which helps improve the efficiency of the system. The optimisation design of the magnetic coupling structure is conducted first via the finite element simulation software, ANSYS Maxwell. Planar circular coil offers superior comprehensive performance over other structures and is thus utilised in this study, which theoretically analyses the primary characteristics of LCC/S (primary inductor-capacitor-capacitor, secondary series) compensation topology. The study makes an in-depth comparison of two methods for achieving ZVS, adjusting secondary series compensation capacitance, and making a primary T-type network asymmetric. The conclusions of the theoretical analysis indicate that making a primary T-type network asymmetric is the most suitable method for the proposed WPT system. A 400 W prototype was built, and it consistently achieved ZVS operation within the entire load range (5–50 Ω). The highest power transfer efficiency (PTE) achieved by the prototype was 92.9%, and the PTE was consistently above 88% within the entire power range (50–400 W).

Ice loads on hydraulic engineering structures: enhancement of analysis methods

Introduction. It is very important to properly analyze ice loads when selecting architectural and structural solutions for hydraulic engineering structures (HS), as this analysis has a significant impact on the economic efficiency of a construction project as a whole. Since this discipline is relatively new and relevant for certain areas only, the use of the finite-element method is not common for the modeling of ice as compared to other materials, such as concrete and steel, and it is rarely used in design.
 Materials and methods. Ice loads are classified into types subject to the availability of sufficient regulatory requirements ensuring safe and cost-effective design of offshore HS; the co-authors believe that FEM should be applied if there are no sufficient regulatory requirements in place.
 Results. Based on the performed analysis the authors make a conclusion that FEM can be applied to certain types of ice loads to increase the accuracy of results. It is possible to cover the entire range of HS ice loads provided that the extended finite element method (X-FEM) is adapted to them, which is an ambitious task.
 Conclusions. Different types of ice loads require specific approaches to be adopted whenever FEM is used for modeling purposes. Since proven modeling methods cannot be applied to all types of ice loads, it is impossible to make ice load calculations for all loading options. To convert empirical estimates, made in design engineering, to comprehensive analyses of ice loads using FEM one should revise methods of ice field cracking analysis to be able to analyze the loading produced by hummocks and flat ice and perceived by multi-column structures, so that one could take a better account of the architectural parameters of HS basements within the framework of the ice load perception analysis.

Omnicoupled Inductors (OCI) Applied in a Resonant Cross-Commutated Buck Converter

All input and output inductors of a resonant cross-commutated buck (rccBuck) converter are coupled to shrink the core size while maintaining efficiency. The steady-state current ripples of the omnicoupled Inductors (OCI) are modeled by separating common-mode and differential-mode voltages. The coupling coefficients are derived to minimize inductance and energy. In this article, the twisted E-E cores with one-turn printed circuit board (PCB) windings are proposed to realize the recommended coupling coefficients. The magnetic flux paths and reluctances are analyzed. A prototype was fabricated to demonstrate the OCI in a 2-MHz rccBuck converter with 12-V input and 3.3-V output. Magnetic volume was 57% smaller and efficiency was 0.5% higher (over the entire load range) than those of the reference rccBuck converter with discrete inductors.

A Scalable Soft-Switching Photovoltaic Inverter With Full-Range ZVS and Galvanic Isolation

Modular converters with stacked cells have an advantage of achieving higher voltage or current levels by using standard low-voltage or low-current switches. This study presents a galvanically isolated and scalable three-phase photovoltaic inverter with stacked output cells. Instead of a dc link with electrolytic capacitors, a distributed ac link composed of small ac capacitors and transformer magnetizing inductances is proposed. Due to nonappearance of a dc link, a fast dynamic response is achievable. The oscillation of the ac link provides soft-switching for all switches in the entire load range without using auxiliary snubbing switches. The transformer core is utilized symmetrically in positive and negative half cycles and the inverter operation is not affected by unequal winding leakage inductances, which makes the transformer design simple. Current symmetry among the windings and voltage symmetry among the ac capacitors is provided naturally. Analytical study, design, and experimental validation of a 750 W prototype is presented.

Phase-Shifted Full-Bridge Converter for a Half-Current-Multiplier Rectifier Using an Autotransformer-Based Filter

A half-current-multiplier rectifier (HCMR) is proposed, which is capable of increasing the output filter current of phase-shifted full-bridge (PS-FB) by 1.5 times. The HCMR filter is based on an autotransformer structure and improves the valid duty cycle of the PS-FB converter by using the induced current from the common winding. The primary current will decrease rapidly during the dead time period, effectively reducing the transition current level and the transition period. Accordingly, the new valid duty period is almost close to the terminal v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AR</sub> period, over the entire load range, and the power delivery goes nearly in the entire v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AR</sub> period. Experiments have shown that although the zero-voltage switching (ZVS) of all switches can usually implement in continuous-conduction mode (CCM) and most discontinuous-conduction modes (DCMs), it still performs excellently at light loads. Maintenance of 89%-94% high efficiency over a wide load range is like the performance of current-doubler rectifier (CDR) filter.

Tribological characteristics of as-cast A356/10wt.% SiCp functionally graded composite dry sliding against EN-31 steel under unidirectional and oscillatory modes

A comparison in tribological response characteristics of as-cast Al-SiCp functionally graded composite material (FGM) dry sliding against hardened EN-31 steel under unidirectional and oscillatory sliding modes was investigated for a sliding/oscillating velocity of 0.4m/s slid through 500m utilizing a pin-on-disc configuration. The A356/10 wt.% SiCp FGM was prepared using vertical centrifugal casting technique. The microstructure characterization was done by Leica optical microscope, and the microstructural analysis revealed the presence of different zones due to the radial gradient distribution of SiCp reinforcement. The hardness variation was found to have a good correlation with its microstructural features at different zones of FGM. Wear loss against load curve indicated an increase in trend for both sliding modes, whereas the coefficient of friction versus load plot showed a decreasing trend for both cases under an identical set of operating parameters. Further, oscillatory wear loss of FGM/EN-31 steel tribopair was observed to be higher in comparison with unidirectional sliding mode for the entire load range, (30-150N) investigated. At the same time, the coefficient of friction of tribopair in oscillatory sliding mode was found to lower than the unidirectional mode.

Wide Voltage Resonant Converter Using a Variable Winding Turns Ratio

This paper presents a inductor–inductor–capacitor (LLC) resonant converter with variable winding turns to achieve wide voltage operation (100–400 V) and realize soft switching operation over the entire load range. Resonant converters have been developed for consumer power units in computers, power servers, medical equipment, and adaptors due to the advantages of less switching loss and better circuit efficiency. The main disadvantages of the LLC resonant converter are narrow voltage range operation owing to wide switching frequency variation and limited voltage gain. For computer power supplies with hold-up time function, electric vehicle battery chargers, and for power conversion in solar panels, wide input voltage or wide output voltage operation capability is normally demanded for powered electronics. To meet these requirements, the variable winding turns are used in the presented circuit to achieve high- or low-voltage gain when Vin is at low- or high-voltage, respectively. Therefore, the wide voltage operation capability can be implemented in the presented resonant circuit. The variable winding turns are controlled by an alternating current (AC) power switch with two back-to-back metal-oxide-semiconductor field-effect transistors (MOSFETs). A 500-W prototype is implemented and test results are presented to confirm the converter performance.

Quasi-resonant flyback PSR converter with adaptive frequency control

In this paper, a quasi-resonant (QR) flyback primary-side regulation (PSR) converter with adaptive frequency control is proposed. The converter adopts the PSR scheme to detect load information through the auxiliary winding. The converter employs the QR control scheme to switch in the valley mode either in CV or CC operation, which greatly reduces the switching loss. In addition, according to the load condition, the converter adaptively reduces the switching frequency and realize valley switching, which achieves better light-load efficiency in the CV mode. The proposed QR converter was implemented using the HHGRACE 0.35 μm BCD process and verified in a 5 V/1A circuit prototype. Experimental results show that the light-load power efficiency of the proposed converter is improved by up to 4.0% when compared to the conventional QR controller. In addition, the valley switching is realized under different load conditions, which improves the system efficiency in the entire range of output load.

Performance analysis and control of NOx emissions in diesel engine using on-board acetylene gas from calcium carbide

The rise in fuel prices and strict regulations on exhaust emissions on one side and depletion of fossil fuels on the other side has demanded the usage of fuel-efficient and clean combustion engines by using alternative fuel. The selection of the most suitable and reliable alternative fuel to suit the existing engine without modifications is an energizing task. The features like the wide operating range in compression ratios and air–fuel mixture ratio encourages diesel engines more compatible as compared to petrol engines. In the present work, Acetylene gas was selected due to excellent combustion properties, high flame velocity, and has higher chemical energy in it. In addition to that, the Acetylene is produced from CaC2 (calcium carbide) and is acquired from CaCO3 (limestone) which is vastly available in nature. Several researchers have done extensive research with acetylene gas as an alternative fuel on both petrol engines and diesel engines with many modifications in the existing engines. In most of the cases, the high-pressure acetylene gas was used to improve power output, efficiency, and also to reduce exhaust emissions. The usage of C2H2 gas at higher pressure is not safe and backfiring is the most common phenomenon which influences the safety of operation. In the present investigation, the calcium carbide and water are mixed to produce the acetylene gas, and the same gas is mixed with air and this mixture will be as intake to the engine, and diesel is injected as usual. The acetylene gas at low pressure is used at various flow rates to explore the behavior of engine exhaust and efficiency and compare it with a pure diesel engine. The main focus is on brake thermal efficiency NOx emissions and the optimum flow rate of acetylene gas without a knock. With an optimum flow rate of acetylene, the brake thermal efficiency up to medium load is slightly reduced and at maximum load, it is very nearer to diesel fuel efficiency and even increased by 6.2%. The oxides of nitrogen emissions are escalated over the entire load range. The optimum EGR rate is investigated by considering the smoke, SFC, and temperature of the exhaust gases of the dual engines, and the same optimum EGR is applied to control NOx. The effects of hydrocarbons and carbon monoxide are not considerable. Hence, it is not covered in this study.

Switched-Capacitor LLC Resonant DC-DC Converter With Switch Peak Voltage of Vin/2

A DC-DC hybrid switched-capacitor LLC resonant converter integrating a ladder cell at the input of the LLC resonant converter using frequency modulation is proposed in this paper. This converter has six switches that are subjected to half the voltage of the input source. All switches commutate at zero voltage over the entire load range, and the diodes of the output rectifier bridge commutate at zero current. The proposed converter has the following characteristics: (a) symmetrical operation, (b) simple frequency modulation, (c) commutation of all switches at zero voltage, (d) all switches subjected to half the input voltage, and (e) static gain practically immune to load variations. Theoretical analysis, design, and experimental results in the laboratory for a prototype of 2 kW, 1000 VDC input, 48 VDC output, and 90 kHz switching frequency are included in this study. The maximum efficiency measured was 97.3%.

Experimental evaluation of the load capacity of the rollers of gravity conveyors for pallets

The main approaches to calculating the load capacity of the carrying rollers of gravity conveyors are presented. It is shown that in practice, in the designs of modern non-driven conveyors for pallets, the priority when choosing the pitch of the carrier rollers is the stability of the movement of the load, rather than minimizing the number of rollers. In connection with the urgent task of reducing the metal consumption and the cost of gravity roller conveyors for pallets, the purpose of the work is to experimentally determine the load capacity of the rollers of gravity conveyors for pallets with plastic bearing housings. The experimental studies were carried out in the laboratory of the Department of Applied Mechanics on a Galdabini Quasar 50 universal testing machine using a special roller support for two roller designs - with a solid axis and on half-axles. The test results showed that the stiffness of a roller with a solid axis in the load range up to 670 N is about 1358.4 N / mm, and in the load range from 670 to 1500 N - 2229.9 N / mm. The rigidity of the roller on the axle shafts in the entire load range is 2048.0 N / mm. The analysis of the obtained results showed that for loads over 670N the use of the axle slightly increases the stiffness coefficient, and, on the contrary, it decreases in the load range up to 670N. In order to reduce the cost of carrying rollers with plastic bearing housings, it is advisable to use a design on semi-axles.