Extra Loss Research Articles

Multidimensional Design of DC-Link for Two-Stage Solid-State Transformer Cell Considering Second-Order Harmonic Current Distribution

In a two-stage solid-state transformer (SST) cell, the grid power pulsates at the double-line frequency, yielding second-order harmonic current (SHC) across the unit. SHC into the DC/DC stage causes extra losses in the semiconductors and magnetics, resulting in reduced efficiency and lifetime at the gain of lower DC-link requirement. This paper investigates how the DC-link design affects the SHC distribution using a proposed impedance model, which in turn impacts losses, volume and overall reliability. Particularly, the overall lifetime is evaluated considering the reliability interactions between components resulting from varied DC-link design. The newly introduced reliability dimension provides further insight into the DC-link design, in addition to the voltage ripple requirement and efficiency-power density tradeoff. The model and design concept are verified by the simulation and experiment.

All-Solid-State Nanosecond Pulse Power Supply Based on BLTs and Pulse Transformer for DBD Application

Nanosecond(ns) pulses have been proven to drive DBD more efficiently. However, since the DBD device is a capacitive load, which will cause distortions in the pulse waveform of the power supply. To maintain the ns pulse waveform, a parallel resistor is normally set to overcome the influence of DBD loads in the traditional methods, which will cause extra energy loss. This paper proposed a bipolar ns pulse power supply for DBD based on Blumlein transmission lines (BLTs) and pulse transformer. It does not need to set a parallel resistor and can adapt well to the load characteristics of DBD. This topology can output bipolar ns pulses on DBD loads with a rise time of 100 ns, a pulse width of 300 ns, an adjustable amplitude of 0-5 kV, and a maximum repetition frequency of 20 kHz. In this context, the operating characteristics of the circuit are derived based on the lossless transmission line model and Laplace transform, and then the correctness of the theoretical derivation is verified by the prototype. The results showed that the proposed ns power supply can drive DBD loads with adjustable output voltage amplitude and frequency.

Manipulating near-wall flow instability and transport characteristics by the airfoil probe: Investigation on a transonic compressor cascade

The flow field exhibits complex features, such as shock waves, wakes, and end wall vortices in a transonic cascade. Installation of airfoil probes exacerbates the multi-scale and unsteady behavior of the internal passage flow. Apart from inducing measurement errors, it also generates extra flow loss inevitably and further affects the measuring accuracy. This paper investigates the impact of airfoil probes on a transonic compressor cascade's unsteady behavior and transport characteristics. Using high-fidelity numerical simulations, the influence of pipe layouts on the flow field of instrumented blades is visualized, revealing highly radial asymmetry. Loss analysis uncovers entropy transport induced by the streamwise vortices, primarily manifested by large-scale angular deformation at the outlet. The vortex structures in the wake region are dominated by momentum transport, displaying regional evolution and momentary equilibrium. The vortex expansion plays a leading role in the global vortex transport process, which is strengthened by the presence of the probes. Spatiotemporal analysis of the unsteady flow field can reveal some features overlooked by conventional fluid mechanics analysis. Using proper orthogonal decomposition, wake vortex pairs' high-frequency oscillations and shedding behaviors are captured in adjacent modes for the first time. The proposed approach can provide a theoretical basis for in-depth investigations of instrumented blade flow fields at the transonic regime. Furthermore, corresponding research can promote the refinement of instrument design by enabling experimentalists to understand the effects of intrusive instruments on transonic flow fields.

Evaluation of additional electricity losses in electric networks using a meter

In this article, additional electricity losses are calculated using the voltage imbalance factor. There is also a method for predicting extra losses in the case of longitudinal and transverse asymmetry, as well as information on how to measure power quality indicators. It is suggested that home appliances be used to monitor a separate power system's power quality indicators. The findings of investigations on the condition of asymmetry conducted in operational low voltage electrical networks are presented, along with an illustration of how to calculate additional electricity losses in low-voltage networks. In this article for this purpose, the author developed a Malika device, which is fully capable to measure, store, analyze, and draw conclusions from the results of all electrical quality indicators.

Synergistic effect of transpassive film and gamma double prime phase on the electrochemical dissolution behavior of Inconel 718 manufactured by laser directed energy deposition

This study investigated the synergistic effect of transpassive film and γ″ phase on the electrochemical dissolution behavior of Inconel 718 manufactured by laser directed energy deposition. The investigation was based on samples after homogenization and aging with (γ + γ″) phases and homogenization with γ phase. The compositions of the transpassive films for two kinds of heat-treated samples were similar, mainly comprising porous Ni hydroxides. The incompact transpassive film induced the local preferential dissolution of the γ matrix and generated multiple dispersive pits on the surface. Compared with the sample after homogenization, the spatial distribution of the γ″ phase in the sample after homogenization and aging restricted the expansion of pits in the γ matrix, leading to superior surface quality. The detachment of the γ″ phase during electrochemical dissolution provided extra mass loss and higher current efficiency. A qualitative model was proposed to demonstrate the synergistic effect of the transpassive film and γ″ phase on the dynamic electrochemical dissolution process.

Numerical study on the dynamic process of reciprocating liquid hydrogen pumps for hydrogen refueling stations

Reciprocating liquid hydrogen pump operates under alternating pressure, temperature, and flowrate with dramatic changes in the thermodynamic states of liquid hydrogen. The thermodynamic state in the pump is influenced by the dynamic interactions between fluid flow, heat transfer, piston motion, and valve dynamics. This paper presents a numerical study for reciprocating liquid hydrogen pumps based on a coupled simulation of the dynamic processes between the alternating flow, unsteady heat transfer, and valve dynamics with a given piston motion as the input. A pump for hydrogen refueling stations with a nominal flowrate and delivery pressure of 50 kg/h and 87.6 MPa is selected as the research object. The appropriate design parameters of the pump and its valves are determined to avoid cavitation in the cylinder and oscillation of the valves. The effects of the frequency and delivery pressure on the valve motion and pump performance are further analyzed. Finally, the in-cylinder heat transfer leads to an extra evaporation loss of 0.012 kg/day, and the isentropic and volumetric efficiencies of the liquid hydrogen pump are 97.30% and 90.76% respectively. The work presented here would be beneficial for the design and optimization of reciprocating liquid hydrogen pumps.

Improved Loss Minimization Control Based on Time-Harmonic Equivalent Circuit for Linear Induction Motors Adopted to Linear Metro

By the supply of two-level voltage source converter with low switching frequency, the linear induction motor (LIM) adopted to linear metro suffers from time harmonics greatly, which would aggravate the airgap flux density, cause extra harmonic loss, and reduce working efficiency for the LIM and drive. In order to quantitatively analyze and reduce the neglective influence of time harmonics, one loss minimization control (LMC) scheme based on improved loss model is proposed in this paper. First, the traditional loss model under sinusoidal excitation is introduced. Second, after analyzing the main harmonic components of converter, one improved loss model based on the equivalent circuit under harmonic excitation is innovatively proposed in this work. Third, one novel LMC scheme with loss minimization cost function is developed, which can find out the optimal flux linkage to get the minimal loss for the LIM. Finally, the proposed loss model considering harmonic and LMC scheme have been fully validated by comprehensive simulation and experiments in terms of one 3 kW prototype.

A comprehensive study on transient thermal behaviors and performances of the modular pipe-embedded energy wall system under intermittent operation conditions

The active thermal insulation technology based on utilizing low-grade thermal energy makes the opaque envelopes gradually be treated as multifunctional components with structural and energy properties. In this study, the dynamic thermal behaviors of modular pipe-embedded energy (MPE) walls integrated with pipe installation cavity and backfilling material are numerically studied, and then the impacts of key variables on MPE walls are explored. Results show that the thermal behaviors of MPE walls can be significantly improved under all intermittent charging modes, while the maximum extra heat loss caused by applying filler cavity and backfilling material is only 2.4%. When the injection time is kept constant, MPE walls operated in multi-pulse modes, especially those with higher heat injection frequency (e.g., 3On3Off mode), can achieve a better performance enhancement and operating energy reduction effect. Besides, a reasonable increase in λf-value or a:b-value can effectively alleviate the heat accumulation around water pipes. In addition, the energy consumption of heat charging systems can be significantly reduced when performance indicators can be slightly sacrificed. Results highlight the effectiveness of adding pipe cavity and backfilling materials in enhancing the performance of MPE walls, which can provide theoretical guidance and data support for such walls in the future.

End-to-End Mispronunciation Detection and Diagnosis Using Transfer Learning

As an indispensable module of computer-aided pronunciation training (CAPT) systems, mispronunciation detection and diagnosis (MDD) techniques have attracted a lot of attention from academia and industry over the past decade. To train robust MDD models, this technique requires massive human-annotated speech recordings which are usually expensive and even hard to acquire. In this study, we propose to use transfer learning to tackle the problem of data scarcity from two aspects. First, from audio modality, we explore the use of the pretrained model wav2vec2.0 for MDD tasks by learning robust general acoustic representation. Second, from text modality, we explore transferring prior texts into MDD by learning associations between acoustic and textual modalities. We propose textual modulation gates that assign more importance to the relevant text information while suppressing irrelevant text information. Moreover, given the transcriptions, we propose an extra contrastive loss to reduce the difference of learning objectives between the phoneme recognition and MDD tasks. Conducting experiments on the L2-Arctic dataset showed that our wav2vec2.0 based models outperformed the conventional methods. The proposed textual modulation gate and contrastive loss further improved the F1-score by more than 2.88% and our best model achieved an F1-score of 61.75%.

Modeling and analysis of oil frictional loss in wet-type permanent magnet synchronous motor for aerospace electro-hydrostatic actuator

To improve the power density and simplify the seal structure, the Wet-Type Permanent Magnet Synchronous Motor (WTPMSM) technique has been applied to aerospace Electro-Hydrostatic Actuators (EHA). In a WTPMSM, the stator and the rotor are both immersed in the aviation hydraulic oil. Although the heat dissipation performance of the WTPMSM can be enhanced, the aviation hydraulic oil will cost an extra oil frictional loss in the narrow airgap of the WTPMSM. This paper proposes an accurate oil frictional loss model for the WTPMSM, in which the wide speed range (0–20 kr/min) and the narrowness of the airgap (0.5–1.5 mm) are its features. Firstly, the mechanism of the oil frictional loss in the airgap of the WTPMSM is revealed. Then an accurate oil frictional loss model is proposed considering the nonlinear influence caused by the Taylor vortex. Furthermore, the influence of motor dimensions on oil frictional loss is analyzed. Finally, the proposed oil frictional loss model is verified by experiments, which provides a guideline for engineers to follow in the WTPMSM design.

Modular Multilevel Converter With Parallel Branch Providing Integrated Partially Rated Energy Storage

In the line of research on inclusion of Energy Storage Systems (ESS) into HVDC stations, this paper presents the integration of partially rated ESS into Modular Multilevel Converter (MMC) substations using parallel branches to the arm inductors. The proposed ESS-MMC topology keeps the design of the original MMC unmodified, as it just adds partially rated ESS with electrical connections outside the valve hall. The system utilizes another frequency component in the arm circulating current to exchange power between the energy storage branches and the original MMC stacks. This third frequency component allows decoupling to some extent the power on the dc and ac sides of the substation. Analysis of the circuit performance led to the development of control algorithms to maximize the power flow capabilities from the ESS within the operational limits of the existing MMC design. This allows the addition of up to 37% power from the ESS considering similarly rated power semiconductors in a simulated 1 GW MMC substation. Analysis shows that extra device losses are kept under 1% for an addition of 10% of ESS power to the nominal substation power. Therefore, the proposal is suitable for adding services such as fast frequency response or black start capability to existing MMC designs.

Effect of cryogenic laser surface modification on the microstructure evolution and corrosion resistance of accident-tolerant FeCrAl alloys

Accident-tolerant FeCrAl alloys require a thinner cladding wall than zirconium cladding to overcome the extra neutron loss, thus requiring enhanced corrosion resistance. Surface treatment was used in this study to address this issue via cryogenic laser surface modification. A finite element model based on heat-transfer theory was raised to reveal the temperature field change during cryogenic laser treatment. The relationship between the laser processing parameters and surface morphology was studied with various characterizations to better understand the process mechanism and verify the correctness of the model. Hydrothermal corrosion test was proceeded in an autoclave at 290 °C and 7.5 MPa for 150 h to examine the enhancing corrosion resistance. STEM observations were used to study the microstructure evolution by cryogenic laser processing and corrosion. Electrochemical tests were performed to analyze the relationship between processing parameters and corrosion resistance before and after corrosion. The oxide film thickness and corrosion rate of the cryogenic laser-modified sample were 66 % and 80 % smaller than the as-received sample. The enhanced corrosion resistance was attributed to the microcrystalline layer and the thin duplex passive film that formed during the cryogenic laser process.

Mixed Tukey Exponentially Weighted Moving Average-Modified Exponentially Weighted Moving Average Control Chart for Process Monitoring

The goal of this study is to present the mixed Tukey exponentially weighted moving average-modified exponentially weighted moving average control chart (MEME-TCC) for monitoring process location with symmetric and skewed distributions in an attempt to significantly improve detection ability. With the benefits of nonparametric assumption robustness. The average and median run lengths are supporting measurements for assessing the performance of a monitoring scheme using Monte Carlo simulation. Furthermore, the average extra quadratic loss (AEQL), relative mean index (RMI), and performance comparison index (PCI) can all be used to evaluate overall performance criteria. The proposed chart is compared with existing charts such as; EWMA, MEWMA, TCC, MEME, MMEE, and MMEE-TCC. The comparison result shows that the proposed chart is the best control chart for detecting small to moderate shifts among all distributional settings. Nevertheless, the EWMA chart detects large shifts more effectively than other charts, except in the case of the gamma distribution, where MEWMA performs best. The results of adapting the proposed control chart to two sets of real data corresponded to the research findings. Doi: 10.28991/ESJ-2023-07-03-014 Full Text: PDF

Air pollution and associated health impact and economic loss embodied in inter-provincial electricity transfer in China

As the largest producer and consumer of coal in the world, China heavily relies on coal resources for thermal power generation. Owing to the unbalanced distribution of energy resources, electricity transfer among regions in China plays a key role in promoting economic growth and ensuring energy safety. However, little is known about air pollution and the related health impacts resulting from electricity transfer. This study assessed PM2.5 pollution and related health and economic losses attributable to the inter-provincial electricity transfer in mainland China in 2016. The results show that a large amount of virtual air pollutant emissions were transferred from energy-abundant northern, western and central China to well-developed and populated eastern coastal regions. Correspondingly, the inter-provincial electricity transfer dramatically reduced the atmospheric levels of PM2.5 and related health and economic losses in eastern and southern China, while increasing those in northern, western and central China. The health benefits attributable to inter-provincial electricity transfer were mainly found in Guangdong, Liaoning, Jiangsu and Shandong, whereas the extra health loss is concentrated in Hebei, Shanxi, Inner Mongolia, and Heilongjiang. Overall, the inter-provincial electricity transfer led to an extra increase of 3600 (95 % CI: 3200–4100) PM2.5-related deaths and 345 (95 % CI: 294–389) million USD of economic loss in China in 2016. The results could assist air pollution mitigation strategies for the thermal power sector in China by strengthening the cooperation between suppliers and consumers of electricity.

Tukey-EWMA control chart with variable sampling intervals for process monitoring

In this study, the Tukey-Exponential Weighted Moving Average control chart with variable sampling interval (VSI Tukey-EWMA) is proposed. The performance of the proposed control chart is investigated for several distributions and compared with Tukey-EWMA and VSI EWMA control charts. We show that the VSI Tukey-EWMA control chart outperforms the Tukey-EWMA control chart and it performs similarly to the VSI EWMA control chart. The average extra quadratic loss is calculated to examine the overall performance over the whole process shift range by using the Markov chain approach. Finally, the VSI Tukey-EWMA and Tukey-EWMA control charts are applied on real data.

Dynamic Galvanic Corrosion of Working Lithium Metal Anode Under Practical Conditions

AbstractThe practical deployment of lithium metal anodes in rechargeable batteries has been significantly restricted by poor electrochemical performance, which largely stemms from their high susceptibility to corrosion. Inan effort to complete the real picture of Li corrosion pathways, in this contribution, a dynamic galvanic corrosion mechanism under realistic working conditions is described, through which an extended solid electrolyte interphase (SEI) is progressively generated on the successively exposed copper substrate during the dynamic Li removal process. As determined by the titration gas chromatography method, the dynamic galvanic corrosion reaction is unveiled to induce an unfavorable extra Li loss and hence a reduced cell reversibility, especially at sluggish Li stripping rates. Systematic investigations reveal that three critical factors, including total step length of Li stripping, dynamic corrosion current (icorrosion) degradation speed, and SEI chemistry, are responsible form odulating the extent of dynamic galvanic corrosion in practical batteries. This work provides an important complement to current knowledge regarding the corrosion processes of working Li metal anodes, affording fresh insights into the design strategies toward high‐reversibility Li cycling.

Hybrid Active Modulation Strategy for Three-Level Neutral-Point-Clamped Converters in High-Speed Aerospace Drives

In the aircraft electric starter/generator system, the three-level neutral-point-clamped converters play a crucial role in driving turbofan engines and delivering onboard electrical power. However, the conventional pulsewidth modulation (PWM) strategies face the challenge of capacitor voltage deviation, large common-mode voltage (CMV), and extra switching losses. Regarding the characteristics of the studied wide-speed range aerospace drives, the modulation scheme needs to be designed according to its operating conditions. To tackle the above demerits, a hybrid active modulation approach is, hence, proposed in this article. By the coordinate-based PWM, the nearest-three-vector is used in the startup process as the neutral-point (NP) voltage balance can be realized with fewer switching intervals; when the drives run in generation mode, an enhanced carrier-based virtual-space-vector modulation technique is involved, which aims to eliminate NP voltage fluctuation, suppress CMV, and simplify the modulation process. With the help of bias-offset injection in the time and voltage domain, capacitor voltages can be effectively kept at a balanced state even though the imbalance exists. The validity of the presented algorithm is proved by simulation and experimental results obtained from a 45 kW, 32 kr/min aircraft starter/generator test rig.

Coupling characteristic analysis and propagation direction control in hydrogen–air rotating detonation combustor with turbine

Two-dimensional numerical simulations are performed to investigate the interactions between a rotating detonation combustor (RDC) and turbine. The flowfield structure and coupling characteristics are analyzed under different equivalent ratios. Furthermore, the formation mechanism of the detonation wave direction is illustrated. Results show that although RDCs increase the average turbine work, they enhance the flowfield oscillation and maintain the quasi-periodic fluctuation in the turbine work. Compared to counter-clockwise propagation, the pressure oscillation attenuation and total pressure loss through the turbine guide vane increase when the detonation wave propagates clockwise. When the detonation wave height is low, RDCs are more prone to quenching due to the impact of reflected waves. After re-ignition, the detonation wave direction is unrelated to the initial ignition direction and is random. Introduction of deflecting wedges into RDCs enables the automatic control of the detonation wave direction but causes extra total pressure loss of at least 3.6%.

Application of erucyl dimethyl betaine sulfonate viscoelastic surfactant for optimization of acidizing operations in heterogeneous carbonate reservoirs

AbstractReservoir heterogeneity is an important factor which should be considered for each operation in oilfields. Acidizing operation is performed to eliminate or reduce the damages of reservoirs. The dissolution of the minerals and rock texture in damaged areas is the main goal of acidizing. However, the existence of high permeable zones through flowing paths results in extra damages and fluid loss. Some additives could be added to the injected acid to avoid these undesirable phenomena. In this research, we added a Zwitterionic sulfonate surfactant to hydrochloric acid (HCl) solution and evaluated the rheological behavior of several compositions of acid‐based viscoelastic surfactant (VES) solutions under various temperature and shear rates. The capability of optimum solution to plug the high permeable zone and divert the acid flow to low permeable zone is examined. The optimum solution was injected into a parallel sandpacked system with different permeabilities at various flow rates (1, 3 and 5 cc/min). It was observed that the injection rate of 3 cc/min has the most efficiency to reduce the heterogeneity. Besides the tendency of VES based solutions for altering wettability of rock to more water‐wet condition is observed. The findings of this study can help the better understanding of practical application of VES in acidizing through heterogeneous reservoirs. Besides, effective parameters for such application are determined.

An unbiased function‐based Poisson adaptive EWMA control chart for monitoring range of shifts

AbstractFor monitoring the number of nonconformities per unit in industrial processes during the inspection, Poisson control charts are most widely deployed. These charting structures are referred to as attribute control charts as the quality characteristic under study is based on a nominal scale other than a quantitative or measured scale. In this study, Poisson adaptive exponentially weighted moving average (PAEWMA) has been designed and the performance of the said chart under a steady‐state situation along with the zero‐state condition has been studied for detecting changes over an unknown range of shifts. The enactment of the proposed PAEWMA design with existing schemes has been evaluated and compared using run‐length (RL) profiles such as; average RL (ARL), the standard deviation of RL (SDRL), and some percentile points of the RL distribution. The extra quadratic loss and relative mean index measures have been used for comparing the range of shifts. The comparison reveals that the proposed PAEWMA chart under the steady‐state situations performs far better than the competitors. The effect of estimation of the process parameter is also a part of the study. The three applications of the proposal have been included; which are taken from the artificial dataset, from past study monitoring dataset, and the other from the aircraft accident monitoring data for the implementation of the proposal.