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Records with Subject: Other
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A Feedback Passivation Design for DC Microgrid and Its DC/DC Converters
Feifan Ji, Ji Xiang, Wuhua Li, Quanming Yue
March 15, 2019 (v1)
Subject: Other
Keywords: DC microgrid, distributed control, feedback passivation
There are difficulties in analyzing the stability of microgrids since they are located on various network structures. However, considering that the network often consists of passive elements, the passivity theory is applied in this paper to solve the above-mentioned problem. It has been formerly shown that when the network is weakly strictly positive real (WSPR), the DC microgrid is stable if all interfaces between the microgrid and converters are made to be passive, which is called interface passivity. Then, the feedback passivation method is proposed for the controller design of various DC⁻DC converters to achieve the interface passivity. The interface passivity is different from the passivity of closed-loop systems on which the passivity based control (PBC) concentrates. The feedback passivation design is detailed for typical buck converters and boost converters in terms of conditions that the controller parameters should satisfy. The theoretical results are verified by a hardware-i... [more]
A New Dynamic Injection System of Urea-Water Solution for a Vehicular Select Catalyst Reduction System
Long Li, Wei Lin, Youtong Zhang
March 15, 2019 (v1)
Subject: Other
Keywords: dynamic correction, NH3 slip, select catalyst reduction (SCR), urea water solution (UWS)
Since the Euro-ІІІ standard was adopted, the main methods to inhibit NOx production in diesel engines are exhaust gas recirculation (EGR) and select catalyst reduction (SCR). On these methods SCR offers great fuel economy, so it has received wide attention. However, there also exists a trade-off law between NOx conversion efficiency and NH₃ slip under dynamic conditions. To inhibit NH₃ slip with high NOx conversion efficiency, a dynamic control method for a urea water solution (UWS) injection was investigated. The variation phenomena of SCR conversion efficiency with respect to the cross-sensitivity characteristics of the NOx sensor to NH₃ have been thoroughly analyzed. The methodology of “uncertain conversion efficiency curve tangent analysis” has been applied to estimate the concentration of the slipped NH₃. The correction factor “φ” of UWS injection is obtained by a comparative calculation of the NOx conversion ability and subsequent NH₃ slip. It also includes methods of flow compen... [more]
Performance Study on a Single-Screw Expander for a Small-Scale Pressure Recovery System
Guoqiang Li, Yuting Wu, Yeqiang Zhang, Ruiping Zhi, Jingfu Wang, Chongfang Ma
March 15, 2019 (v1)
Subject: Other
Keywords: Natural Gas, pressure energy recovery, single-screw expander
A single-screw expander with 195 mm diameter is developed to recover pressure energy in letdown stations. An experiment system is established using compressed air as a working fluid instead of natural gas. Experiments are conducted via measurements for important parameters, such as inlet and outlet temperature and pressure, volume flow rate and power output. The influence of inlet pressure and rotational speed on the performance are also analyzed. Results indicate that the single-screw expander achieved good output characteristics, in which 2800 rpm is considered the best working speed. The maximum volumetric efficiency, isentropic efficiency, overall efficiency, and the lowest air-consumption are 51.1 kW, 83.5%, 66.4%, 62.2%, and 44.1 kg/(kW·h), respectively. If a single-screw expander is adopted in a pressure energy recovery system applied in a certain domestic natural gas letdown station, the isentropic efficiency of the single-screw expander and overall efficiency of the system are... [more]
Torque Distribution Characteristics of a Novel Double-Stator Permanent Magnet Generator Integrated with a Magnetic Gear
Shehu Salihu Mustafa, Norhisam Misron, Norman Mariun, Mohammad Lutfi Othman, Tsuyoshi Hanamoto
March 15, 2019 (v1)
Subject: Other
Keywords: cogging torque, double-stator magnetic geared machine (DS-MGM), field magnet, finite element method, flux density, harmonic analysis, magnetic gear (MG), permanent-magnet (PM), prime magnet, torque distribution, transmission torque
This paper presents a novel double-stator permanent-magnet machine integrated with a triple rotor magnetic gear structure, which is proposed to address problems of mechanical geared generators for low-speed applications. Torque transmission is based on three rotors consisting of prime permanent-magnet (PM) poles in the middle rotor and field PM poles in the inner and outer rotors. The proposed machine combines the functions of magnetic gearing and electrical power generation. The operating principles of the magnetic gear and generator are discussed and the torque distribution characteristics of the integrated machine are analysed using the 2D finite-element method (2D FEM). Also the power, torque, and speed characteristics are reported. A prototype is fabricated and tested experimentally. The predicted and measured results validate the proposed machine design.
The Effect of Distributed Parameters on Conducted EMI from DC-Fed Motor Drive Systems in Electric Vehicles
Li Zhai, Liwen Lin, Xinyu Zhang, Chao Song
March 15, 2019 (v1)
Subject: Other
Keywords: conducted electromagnetic interference (EMI), DC-fed, distributed parameter, electric vehicle, motor drive system
The large dv/dt and di/dt outputs of power devices in DC-fed motor drive systems in electric vehicles (EVs) always introduce conducted electromagnetic interference (EMI) emissions and may lead to motor drive system energy transmission losses. The effect of distributed parameters on conducted EMI from the DC-fed high voltage motor drive systems in EVs is studied. A complete test for conducted EMI from the direct current fed(DC-fed) alternating current (AC) motor drive system in an electric vehicle (EV) under load conditions is set up to measure the conducted EMI of high voltage DC cables and the EMI noise peaks due to resonances in a frequency range of 150 kHz⁻108 MHz. The distributed parameters of the motor can induce bearing currents under low frequency sine wave operation. However the impedance of the distributed parameters of the motor is very high at resonance frequencies of 500 kHz and 30 MHz, and the effect of the bearing current can be ignored, so the research mainly focuses on... [more]
HVDC-System-Interaction Assessment through Line-Flow Change-Distribution Factor and Transient-Stability Analysis at Planning Stage
Sungchul Hwang, Jaegul Lee, Gilsoo Jang
February 27, 2019 (v1)
Subject: Other
Keywords: high-voltage direct current (HVDC), interaction, Planning, transient stability
Many of the recent projects for new transmission line have considered the high-voltage direct current (HVDC) system, owing to the many advantages of the direct current (DC) system. The most noteworthy advantage is that a cable can serve as a substitute for the overhead transmission line in residential areas; therefore, the HVDC system application is increasing, and as the number of DC systems in the power system increases, the interaction assessment regarding the HVDC system gains importance. An index named multi-infeed interaction factor (MIIF) is commonly used to estimate the interaction between power converters; however, the HVDC system is composed of two converters and a transmission line. The MIIF represents the interaction between the rectifiers and inverters, but not for the whole system. In this work, a method to assess the interaction of the whole system was therefore studied. To decide on the location of the new HVDC transmission system at the planning stage, in consideration... [more]
Development of Seismic Demand for Chang-Bin Offshore Wind Farm in Taiwan Strait
Yu-Kai Wang, Juin-Fu Chai, Yu-Wen Chang, Ti-Ying Huang, Yu-Shu Kuo
February 27, 2019 (v1)
Subject: Other
Keywords: design earthquake, offshore wind, response spectrum, seismic hazard analysis, supporting structures
Taiwan is located on the Pacific seismic belt, and the soil conditions of Taiwan’s offshore wind farms are softer than those in Europe. To ensure safety and stability of the offshore wind turbine supporting structures, it is important to assess the offshore wind farms seismic forces reasonably. In this paper, the relevant seismic and geological data are obtained for Chang-Bin offshore wind farm in Taiwan Strait, the probabilistic seismic hazard analysis (PSHA) is carried out, and the first uniform hazard response spectrum for Chang-Bin offshore wind farm is achieved. Compared with existing design response spectrum in the local regulation, this site-specific seismic hazard analysis has influence on the seismic force considered in the design of supporting structures and therefore affects the cost of the supporting structures. The results show that a site-specific seismic hazard analysis is required for high seismic area. The paper highlights the importance of seismic hazard analysis to a... [more]
Effect of Wind Turbine Blade Rotation on Triggering Lightning: An Experimental Study
Xishan Wen, Lu Qu, Yu Wang, Xiaoyue Chen, Lei Lan, Tianjun Si, Jianwei Xu
February 27, 2019 (v1)
Subject: Other
Keywords: blade, rotation, scaled test, up-and-down method, wind turbine
Compared with other lightning targets on the ground, the most notable feature of a wind turbine is that the blades are usually in a rotating state when lightning strikes. To study the mechanism of blade rotation influencing wind turbine on triggering lightning, lightning discharge comparison tests based on a typical 2-MW 1:30-scaled wind turbine model with an arching high-voltage electrode were conducted under different modes of stationary and rotating blades. Negative polarity switching impulses of 250/2500 μs were applied to the arching electrode. The up-and-down method was adopted for 50% discharge voltage and the discharge process was observed. The experimental results showed that under the condition of a 4 m gap, the breakdown voltage decreases and the connection point of the leaders approaches the high-voltage electrode with increasing blade speed, indicating that the wind turbine’s blade rotation enhances the triggering of lightning. The analysis showed that the blade rotation c... [more]
Energy Optimization and Fuel Economy Investigation of a Series Hybrid Electric Vehicle Integrated with Diesel/RCCI Engines
Ali Solouk, Mahdi Shahbakhti
February 27, 2019 (v1)
Subject: Other
Keywords: Diesel, emissions, fuel economy, hybrid electric vehicle, low temperature combustion (LTC), model predictive control (MPC), optimal energy management, reactively controlled compression ignition (RCCI), time horizon
Among different types of low temperature combustion (LTC) regimes, eactively controlled compression ignition (RCCI) has received a lot of attention as a promising advanced combustion engine technology with high indicated thermal efficiency and low nitrogen oxides ( NO x ) and particulate matter (PM) emissions. In this study, an RCCI engine for the purpose of fuel economy investigation is incorporated in series hybrid electric vehicle (SHEV) architecture, which allows the engine to run completely in the narrow RCCI mode for common driving cycles. Three different types of energy management control (EMC) strategies are designed and implemented to achieve the best fuel economy. The EMC strategies encompass rule-based control (RBC), offline, and online optimal controllers, including dynamic programing (DP) and model predictive control (MPC), respectively. The simulation results show a 13.1% to 14.2% fuel economy saving by using an RCCI engine over a modern spark ignition (SI) engine i... [more]
Numerical Investigation on the Effect of Cementing Properties on the Thermal and Mechanical Stability of Geothermal Wells
Jongmuk Won, Hyun-Jun Choi, Hyobum Lee, Hangseok Choi
February 27, 2019 (v1)
Subject: Other
Keywords: G-class cement, geothermal well cementing, numerical analysis, thermal conductivity, Young’s modulus
In this paper, a two-dimensional (2-D) Finite Element (FE) analysis of a geothermal well was performed with respect to five different cross-sections corresponding to the design specifications for the geothermal well that is currently constructed in Pohang, South Korea. Among the essential components (such as ground formation, casing, and cementing) of a geothermal well, the thermal and mechanical stability of the cementing component was discussed based on a series of parametric studies with consideration of the thermal conductivity and Young’s modulus of the cementing component. With increasing number of casing layers, the cementing component experiences less stress concentration. In addition, the lower thermal conductivity of the cementing material is advantageous for effectively controlling radial displacement. Consequently, it should be noted in geothermal well cementing construction that long-term strength degradation of the cementing might cause the severe structural instability o... [more]
Experimental Investigation of Crack Extension Patterns in Hydraulic Fracturing with Shale, Sandstone and Granite Cores
Jianming He, Chong Lin, Xiao Li, Xiaole Wan
February 27, 2019 (v1)
Subject: Other
Keywords: anisotropy, crack extension, fracture distribution, heterogeneity, hydraulic fracture
Hydraulic fracturing is an important method of reservoir stimulation in the exploitation of geothermal resources, and conventional and unconventional oil and gas resources. In this article, hydraulic fracturing experiments with shale, sandstone cores (from southern Sichuan Basin), and granite cores (from Inner Mongolia) were conducted to investigate the different hydraulic fracture extension patterns in these three reservoir rocks. The different reactions between reservoir lithology and pump pressure can be reflected by the pump pressure monitoring curves of hydraulic fracture experiments. An X-ray computer tomography (CT) scanner was employed to obtain the spatial distribution of hydraulic fractures in fractured shale, sandstone, and granite cores. From the microscopic and macroscopic observation of hydraulic fractures, different extension patterns of the hydraulic fracture can be analyzed. In fractured sandstone, symmetrical hydraulic fracture morphology could be formed, while some m... [more]
Soiling and Cleaning of Polymer Film Solar Reflectors
Christopher Sansom, Aránzazu Fernández-García, Florian Sutter, Heather Almond, Peter King, Lucía Martínez-Arcos
February 27, 2019 (v1)
Subject: Other
Keywords: concentrating solar power (CSP), mirror cleaning, polymer film, reflectance, soiling, solar collector
This paper describes the accelerated ageing of commercially available silvered polymer film by contact cleaning using brushes and water in the presence of soiling created by dust and sand particles. These conditions represent cleaning regimes in real concentrating solar power (CSP) solar fields in arid environments, where contact cleaning using brushes and water is often required to clean the reflecting surfaces. Whilst suitable for glass reflectors, this paper discusses the effects of these established cleaning processes on the optical and visual characteristics of polymer film surfaces, and then describes the development of a more benign but effective contact cleaning process for cleaning polymer reflectors. The effects of a range of cleaning brushes are discussed, with and without the presence of water, in the presence of sand and dust particles from selected representative locations. The experiments were repeated using different experimental equipment at Plataforma Solar de Almería... [more]
A Novel Boil-Off Gas Re-Liquefaction Using a Spray Recondenser for Liquefied Natural-Gas Bunkering Operations
Jiheon Ryu, Chihun Lee, Yutaek Seo, Juneyoung Kim, Suwon Seo, Daejun Chang
February 27, 2019 (v1)
Subject: Other
Keywords: boil-off gas, bunkering, liquefied natural gas, re-liquefaction, recondenser
This study presents the design of a novel boil-off gas (BOG) re-liquefaction technology using a BOG recondenser system. The BOG recondenser system targets the liquefied natural gas (LNG) bunkering operation, in which the BOG phase transition occurs in a pressure vessel instead of a heat exchanger. The BOG that is generated during LNG bunkering operation is characterized as an intermittent flow with various peak loads. The system was designed to temporarily store the transient BOG inflow, condense it with subcooled LNG and store the condensed liquid. The superiority of the system was verified by comparing it with the most extensively employed conventional re-liquefaction system in terms of consumption energy and via an exergy analysis. Static simulations were conducted for three compositions; the results indicated that the proposed system provided 0 to 6.9% higher efficiencies. The exergy analysis indicates that the useful work of the conventional system is 24.9%, and the useful work of... [more]
Reorientation of Magnetic Graphene Oxide Nanosheets in Crosslinked Quaternized Polyvinyl Alcohol as Effective Solid Electrolyte
Jia-Shuin Lin, Wei-Ting Ma, Chao-Ming Shih, Bor-Chern Yu, Li-Wei Teng, Yi-Chun Wang, Kong-Wei Cheng, Fang-Chyou Chiu, Shingjiang Jessie Lue
February 27, 2019 (v1)
Subject: Other
Keywords: crosslinked quaternized polyvinyl alcohol (CL-QPVA), direct methanol alkaline fuel cell (DMAFC), graphene oxide-iron oxide (GO-Fe3O4), magnetic field, reorientation
This work aims to clarify the effect of magnetic graphene oxide (GO) reorientation in a polymer matrix on the ionic conduction and methanol barrier properties of nanocomposite membrane electrolytes. Magnetic iron oxide (Fe₃O₄) nanoparticles were prepared and dispersed on GO nanosheets (GO-Fe₃O₄). The magnetic GO-Fe₃O₄ was imbedded into a quaternized polyvinyl alcohol (QPVA) matrix and crosslinked (CL-) with glutaraldehyde (GA) to obtain a polymeric nanocomposite. A magnetic field was applied in the through-plane direction during the drying and film formation steps. The CL-QPVA/GO-Fe₃O₄ nanocomposite membranes were doped with an alkali to obtain hydroxide-conducting electrolytes for direct methanol alkaline fuel cell (DMAFC) applications. The magnetic field-reoriented CL-QPVA/GO-Fe₃O₄ electrolyte demonstrated higher conductivity and lower methanol permeability than the unoriented CL-QPVA/GO-Fe₃O₄ membrane or the CL-QPVA film. The reoriented CL-QPVA/GO-Fe₃O₄ nanocomposite was used as the... [more]
Experimental Investigation of Thermal Behaviors in Window Systems by Monitoring of Surface Condensation Using Full-Scale Measurements and Simulation Tools
Goopyo Hong, Daeung Danny Kim, Byungseon Sean Kim
February 5, 2019 (v1)
Subject: Other
Keywords: chamber, condensation, spacer, window
The aim of the present study was to investigate the thermal performance of window systems using full-scale measurements and simulation tools. A chamber was installed on the balcony of an apartment to control the temperatures which can create condensation on the interior surfaces of window systems. The condensation process on the window was carefully scrutinized when outdoor and indoor temperature and indoor relative humidity ranged from −15 °C to −20 °C, 23 °C to 24 °C, and 50% to 65%, respectively. The results of these investigations were analyzed to determine how the moisture is influenced by changing temperatures. It appears that the glass-edge was highly susceptible to the temperature variations and the lowest temperature on the glass edge was caused by the heat transfer through the spacer, between the two glass panels of the window. The results from the simulation used in this study confirm that the thermal performance of window systems can be improved the use of super insulated o... [more]
Improving the Stability and Accuracy of Power Hardware-in-the-Loop Simulation Using Virtual Impedance Method
Xiaoming Zha, Chenxu Yin, Jianjun Sun, Meng Huang, Qionglin Li
February 5, 2019 (v1)
Subject: Other
Keywords: accuracy, impedance model, power hardware-in-the-loop, stability, virtual impedance
Power hardware-in-the-loop (PHIL) systems are advanced, real-time platforms for combined software and hardware testing. Two paramount issues in PHIL simulations are the closed-loop stability and simulation accuracy. This paper presents a virtual impedance (VI) method for PHIL simulations that improves the simulation’s stability and accuracy. Through the establishment of an impedance model for a PHIL simulation circuit, which is composed of a voltage-source converter and a simple network, the stability and accuracy of the PHIL system are analyzed. Then, the proposed VI method is implemented in a digital real-time simulator and used to correct the combined impedance in the impedance model, achieving higher stability and accuracy of the results. The validity of the VI method is verified through the PHIL simulation of two typical PHIL examples.
Failure Criteria of Gas-Infiltrated Sandy Shale Based on the Effective Stress Principle
Wenpu Li, Dongming Zhang, Minghui Li
February 5, 2019 (v1)
Subject: Other
Keywords: effective stress, failure criterion, gas-infiltrated sandy shale, rock strength, triaxial compression test
Pore gas has a significant influence on rock strength. This study performed triaxial compression tests of gas-infiltrated sandy shale samples to investigate the strength characteristics under gas pressures of 0 and 2 MPa. The effective stress coefficient was evaluated while considering the gas and solid coupling effect, and was found to decrease with increasing confining pressure. The calculated and different assumed coefficient values (0 and 1) were applied to obtain the effective principal stress. The experimental results would serve as fundamental strength data for fitting analysis in failure criterion work. The Mohr-Coulomb, Hoek-Brown, Drucker-Prager, linear Mogi, and non-linear Mogi criteria were modified based on the effective stress principle of porous rock. In addition, the RMSE, cohesion, and internal friction angle were utilized for a quantitative criterion comparison. The results showed that the Mohr-Coulomb, Drucker-Prager, and linear Mogi failure criteria led to higher er... [more]
An Alternative to Conventional Rock Fragmentation Methods Using SCDA: A Review
Radhika Vidanage De Silva, Ranjith Pathegama Gamage, Mandadige Samintha Anne Perera
February 5, 2019 (v1)
Subject: Other
Keywords: expansive properties, fracture mechanisms, rock fracturing, soundless cracking demolition agents (SCDAs), volume expansion mechanism
Global energy and material consumption are expected to rise in exponential proportions during the next few decades, generating huge demands for deep earth energy (oil/gas) recovery and mineral processing. Under such circumstances, the continuation of existing methods in rock fragmentation in such applications is questionable due to the proven adverse environmental impacts associated with them. In this regard; the possibility of using more environmentally friendly options as Soundless Chemical Demolition Agents (SCDAs) play a vital role in replacing harmful conventional rock fragmentation techniques for gas; oil and mineral recovery. This study reviews up to date research on soundless cracking demolition agent (SCDA) application on rock fracturing including its limitations and strengths, possible applications in the petroleum industry and the possibility of using existing rock fragmentation models for SCDA-based rock fragmentation; also known as fracking. Though the expansive properties... [more]
Study on Insulator Flashover Voltage Gradient Correction Considering Soluble Pollution Constituents
Dongdong Zhang, Zhijin Zhang, Xingliang Jiang, Zhongyi Yang, Jiayao Zhao, Yongfu Li
February 5, 2019 (v1)
Subject: Other
Keywords: equivalent salt deposit density (ESDD), flashover voltage gradient, insulator, pollution flashover, soluble constituent
Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be deficient. In this paper, a systematic study on insulator flashover voltage gradient correction involving different types of soluble pollution constituents is presented. Using a typical type glass insulator as the sample, its flashover tests, polluted by typical soluble chemicals (NaCl, NaNO₃, KNO₃, NH₄NO₃, MgSO₄, Ca(NO₃)₂ and CaSO₄), were carried out. Then, the flashover gradient correction was made by combining the flashover performance of each soluble constituent, the equivalent salt deposit density (ESDD) contribution of the seven constituents, and the saturation performance of CaSO₄. The correction agreed with the flashover test results of insulator poll... [more]
Flow Induced Vibration and Energy Extraction of an Equilateral Triangle Prism at Different System Damping Ratios
Jun Zhang, Fang Liu, Jijian Lian, Xiang Yan, Quanchao Ren
February 5, 2019 (v1)
Subject: Other
Keywords: damping ratio, energy extraction, equilateral triangle prism, flow induced vibration, galloping, vortex induced vibration
The flow induced vibration and energy extraction of an equilateral triangle prism elastically mounted in a water channel are investigated experimentally at different system damping ratios ζtotal with the constant oscillating mass Mosc and system stiffness K. A power take-off system with a variable damping function is developed. The translation-rotation equation of the vibration system deduced in the study indicates that the total oscillating mass includes the material mass, and the equivalent mass due to the rotation of the gears and rotor. Besides, increasing load resistance can result in a decrease in ζtotal when K and Mosc remain unchanged. The prism experiences, in turn, soft galloping, hard galloping 1 and hard galloping 2 with increasing ζtotal. As ζtotal increases up to 0.335, only the vortex-induced vibration is observed because the extremely high ζtotal prevents the prism from galloping. The response amplitude decreases with the increasing ζtotal. In addition, higher ζtotal pr... [more]
Coil Design for High Misalignment Tolerant Inductive Power Transfer System for EV Charging
Kafeel Ahmed Kalwar, Saad Mekhilef, Mehdi Seyedmahmoudian, Ben Horan
February 5, 2019 (v1)
Subject: Other
Keywords: electric vehicle (EV), inductive power transfer (IPT), misalignment tolerance
The inductive power transfer (IPT) system for electric vehicle (EV) charging has acquired more research interest in its different facets. However, the misalignment tolerance between the charging coil (installed in the ground) and pick-up coil (mounted on the car chassis), has been a challenge and fundamental interest in the future market of EVs. This paper proposes a new coil design QDQ (Quad D Quadrature) that maintains the high coupling coefficient and efficient power transfer during reasonable misalignment. The QDQ design makes the use of four adjacent circular coils and one square coil, for both charging and pick-up side, to capture the maximum flux at any position. The coil design has been modeled in JMAG software for calculation of inductive parameters using the finite element method (FEM), and its hardware has been tested experimentally at various misaligned positions. The QDQ coils are shown to be capable of achieving good coupling coefficient and high efficiency of the system... [more]
Analysis and Design of an Active Stabilizer for a Boost Power Converter System
Yigeng Huangfu, Shengzhao Pang, Babak Nahid-Mobarakeh, Akshay Rathore, Fei Gao, Dongdong Zhao
February 5, 2019 (v1)
Subject: Other
Keywords: boost power converter, input filter, stabilizer
In electrical power converter systems, the presence of an LC input filter can efficiently reduce the Electromagnetic Interference (EMI) effect, and at the same time protect the converter and the load from being impacted by sharp input impulse voltages. However, for transportation applications, the weight and size limitations of input LC filters for power converters have to be taken into consideration. The reduction of LC filter size may impair the system stability margin and dynamic response. In serve cases, the system may even become unstable. Thus, in order to ensure the system stability while minimizing the input LC filter size, the implementation of a stabilizer for the system control is needed. In this paper, a novel digital stabilizer design method is proposed for a boost power converter with a small input LC filter. The proposed method is based on input filter inductance current measurements and DSP (Digital Signal Processor) -based digital stabilizer design. Simulation and expe... [more]
Combustion and Emission Characteristics According to the Fuel Injection Ratio of an Ultra-Lean LPG Direct Injection Engine
Cheolwoong Park, Taeyoung Kim, Gyubaek Cho, Janghee Lee
February 5, 2019 (v1)
Subject: Other
Keywords: brake thermal efficiency, combustion stability, emissions, liquefied petroleum gas (LPG) direct injection, spray-guided type combustion system, ultra-lean combustion
The effect of the fuel injection ratio on the combustion and emission characteristics of stratified lean mixture combustion was investigated for a spray-guided liquefied petroleum gas (LPG) direct injection engine. Inter-injection spark-ignition combustion—a specially designed combustion strategy for LPG fuel derived from a two-staged injection—was employed to maximize the improvement in thermal efficiency when combustion stability is secured. When changing the fuel injection ratio, the optimum spark advance and fuel injection timings were experimentally determined to maximize the thermal efficiency based on sweeping timings. The optimum fuel injection ratio with the highest thermal efficiency (42.76%) and stable operation was 60%/40%, with the optimization of the spark advance and fuel injection timing, because of the locally rich mixture region in the recirculation zone. NOx emissions were at their highest level with a fuel injection ratio of 60%/40% because of the high combustion te... [more]
Minimization of Cogging Force in Fractional-Slot Permanent Magnet Linear Motors with Double-Layer Concentrated Windings
Qian Wang, Bo Zhao, Jibin Zou, Yong Li
February 5, 2019 (v1)
Subject: Other
Keywords: cogging force, concentrated winding, linear motor, permanent magnet motor
Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce the cogging force by adjusting the armature core dimensions in fractional-slot PMLMs with double-layer concentrated windings, together with magnet skewing. It is shown that the proposed technique is capable of reducing the cogging force of the motor in an effective way, with the peak value minimized to less than 0.4% of the rated thrust force in the case study. Such a technique can also be applicable to other linear motors with appropriate changes.
Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
Antoine Baudoin, Didier Saury, Bo Zhu, Cecilia Boström
February 5, 2019 (v1)
Subject: Other
Keywords: discrete heat sources, natural convection, Optimization, source array
Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two.
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