Current Shaping Research Articles

Analysis of Acceleration Characteristics of a Railgun

To accelerate a launch mass with a low level of pressure as possible in a railgun, it is required to hold supplied current nearly constant during launch phase. We obtained the discharging conditions for required current shaping by modeling and analysis of circuit equations coupled to acceleration equation of the launch mass. The acceleration characteristics of the railgun in the conditions were analyzed by comparing experimental and theoretical results.

Freeform optical design of beam shaping systems with variable illumination properties.

Freeform optics constitutes a new technology that is currently driving substantial changes in beam shaping. Most of the current beam shaping systems are elaborately tailored for fixed optical properties, which means the output light distribution of a beam shaping system usually cannot be changed. What we present here is a class of beam shaping systems, the optical properties of which can be changed to meet the requirements for different applications. The proposed beam shaping system is composed of a freeform lens and a non-classical zoom system which is designed by ray aiming and the conservation of energy instead of aberration control. The freeform lens includes two elaborately designed freeform optical surfaces, by which both the intensity distribution and wave-front of an incident light beam are manipulated in a desired manner. The light beam after propagating through the non-classical zoom system produces an illumination pattern on a fixed observation plane with a variable pattern size and an unchanged irradiance distribution at different zoom positions. Two design examples are presented to demonstrate the effectiveness of the proposed beam shaping systems.

The promotion of leasing in oilfield services as a mechanism for the innovative development of the oil and gas industry

Subject. This article focuses on the oilfield service market and innovative development mechanisms for Oil & Gas in particular. Objectives. The study provides the rationale for leasing as a practical mechanism for encouraging the innovative activity of Oil & Gas companies. Methods. The study is based on methods of the analysis, systematization, comparison and matching. Results. We report on the analysis of the development of the oilfield service market as a crucial constituent of the oil and gas industry. The article presents indicators and trends in the development of the oil and gas market worldwide and in Russia. We describe distinctions of the oilfield service market, classify key lines of activities in the industry. The article spotlights key issues of the oilfield service market and displays the current factors shaping trends in the oilfield market development. We analyzed innovation indicators in the industry, the applicable lease schemes, and classified lease companies operating in the oil and gas market. Conclusions and Relevance. The predominance of short-term contracts turns to be a key issue of the oil and gas industry, since companies cannot be assured that technical retrofitting costs be repaid and justified. There should be further research into the practical potential, expanded development and practical guidelines for leasing schemes in the oilfield service market, which will push the innovative activity of companies operating in the industry.

A Cuk Converter and Resonant LLC Converter Based E-Bike Charger for Wide Output Voltage Variations

In this article, an e-bike charging solution for two wheelers, is presented. This e-bike charger is realized by a Cuk converter followed by a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter with an improved power quality (PQ) input current indices. The pulsewidth modulated Cuk converter is operated in discontinuous conduction mode of its output side inductor, which leads to a voltage follower approach for input current shaping. Thus, the control loop is greatly simplified as it consists of a single voltage loop. The e-bike battery charging algorithm is implemented in variable frequency controlled HB <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter followed by a diode rectification at its output stage. Furthermore, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{550}\;\text{W}$</tex-math></inline-formula> , constant current/constant voltage charger with a maximum current rating of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{10}\;\text{A}$</tex-math></inline-formula> is developed to charge a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$20AH$</tex-math></inline-formula> e-bike battery. A variable dc link reference voltage estimator is presented, which varies the dc link voltage and extends the output voltage range for charging e-bike battery of varying voltage rating from 42– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{80}\;\text{V}$</tex-math></inline-formula> . Moreover, a resonant frequency optimizer loop is also proposed, which reduces the turn-off losses during charging a deeply discharged battery. The behavior of this charger is exhaustively analyzed under steady state and transient conditions and the PQ at the input, is found to comply the international standard of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$IEC-61\,000-3-2$</tex-math></inline-formula> .

The 2021 Veblen-Commons Award Recipient: Deborah M. Figart: Good Work

: COVID-19 has exposed underlying weaknesses in the economy, including the political economic institutions structuring work. The labor market has moved toward more precarious work, negatively affecting job quality and well-being. After a summary of the current context shaping work, I discuss a new, 2021 Top Ten list of policy proposals aimed at institutionalizing good work. This list revises ten public policies I proposed in 2003, and reconsiders how they might be updated given evolving economic structures and context. Theoretically, the article draws upon major concepts in institutional and heterodox economics: progressive institutional change, invidious distinctions, countervailing power, social balance, capabilities, caring labor, and social provisioning.

Advanced and Innovative Optimization Techniques in Controllers: A Comprehensive Review

New commercial power electronic controllers come to the market almost every day to help improve electronic circuit and system performance and efficiency. In DC–DC switching-mode converters, a simple and elegant hysteretic controller is used to regulate the basic buck, boost and buck–boost converters under slightly different configurations. In AC–DC converters, the input current shaping for power factor correction posts a constraint. But, several brilliant commercial controllers are demonstrated for boost and fly back converters to achieve almost perfect power factor correction. In this paper a comprehensive review of the various advanced optimization techniques used in power electronic controllers is presented.

The Role of Education in Shaping Attitudes of Academic Youth Towards Sustainable Development

Purpose: The purpose of the article is an attempt to answer the question about the current shaping of attitudes of European academic youth towards the idea of sustainable development. Design/Methodology/Approach: The C&RT classification tree model was used, which allowed systematizing the factors differentiating attitudes towards the idea of sustainable development of 1175 students from over 30 European countries. Findings: The work focuses on the role of education in understanding and perceiving the idea of sustainable development. It was not only a factor in the first division of the tree but also one of the more important predictors in the ranking generated by the C&RT model. The tree structure showed that school education and family’s influence were the overriding criteria for differentiating students' attitudes towards the idea of sustainable development. Practical Implications: In the conducted analysis of education, it appeared both as an indirect and direct factor - through meetings with sustainable everyday life and proper understanding of this concept. Also, some respondents indicated that in comparison to other actors and stakeholders addressed to recipients and implementers of the idea of development is precisely the idea of school. Originality/value: The value of the research is extensive statistical material that enabled the use of an innovative research method - the classification model of C&RT trees.

A high voltage pulse generator using avalanche‐mode thyristors

AbstractA high voltage and high current pulse switch using avalanche mode thyristor has been developed for the high voltage pulse generator. When the break‐over voltage is applied to a thyristor, the thyristor turns on without the gate input current. We call avalanche mode thyristor (AMT) which operates such a switch mode. AMT has many advantages, for example, turn on function without trigger input circuit in the series connection, high speed switching characteristics, etc. A magnetic switch (MS) using the saturation of the core is adopted for the high current pulse shaping. Twelve stages of AMTs generate 11 kV and 1.36 kA with 260 nanoseconds pulse width. A high voltage pulse has been produced up to 65 kV, 43A by using the AMT pulse generator and a pulse trans. The behavior of AMT and the performance of the circuit are discussed.

Effectiveness of Power Electronic Controllers in Mitigating Acoustic Noise and Vibration in High-Rotor Pole SRMs

This paper presents a comparative evaluation of power electronic control approaches for vibro-acoustic noise reduction in High Rotor-Pole Switched Reluctance Machines (HR-SRM). It carries out a fundamental analysis of approaches that can be used to target acoustic noise and vibration reduction. Based on the comprehensive study, four candidates for control have been identified and applied to the HR-SRM drive to evaluate their effectiveness and identify challenges. These four methods include phase advancing, current shaping based on field reconstruction, and random hysteresis band with and without spectrum shaping. The theoretical background, implementation, and vibro-acoustic noise reduction performance of each method are presented in detail. Comparative studies from simulation and experimental measurements have been used to identify the most effective solution to acoustic noise and vibration reduction in HR-SRM configuration.

PMSM Current Shaping for Minimum Joule Losses While Reducing Torque Ripple and Vibrations

This paper presents a current shaping method for torque ripple and mean air-gap radial force-shape harmonics reduction, under minimum Joule losses, used for air-born and structure-born vibration reduction in 3-phase PMSM electric drives. The main source for structure-born noise in electric powertrains is the torque ripple, while the main source for air-born noise are the radial air-gap forces. The proposed method uses a Fourier-decomposed LUT model obtained from updating the 2D electromagnetic FE model using test-bench results. Modal testing is used to update the structural model, and the vibration response on the machine full RPM range is determined using the vibration-synthesis method. The proposed current shaping algorithm is deterministic and can be used on any topology of 3-phase PMSMs. The torque and mean air-gap force harmonics that are intended for reduction can be arbitrary selected and their minimization can be fully completed if the maximum current and voltage constraint are respected. On the machine under test, vibration reduction is accomplished, especially for the mechanical orders that interact with the second mode-shape.

Dental Public Health Education in Europe: a survey of European Dental Schools to determine current practice and inform a core undergraduate programme.

Describe current Dental Public Health [DPH] curricula content and delivery across European dental schools and ascertain views on a core undergraduate curriculum for dental students. Survey of European dental schools, informed by professional and academic literature and European Association for Dental Public Health [EADPH] Special Interest Working Group discussions. Questionnaires were distributed electronically, by post, and via EADPH network members, to the Deans of 252 dental schools in Europe. E-mail reminders were sent to non-responders. European Dental Schools. Around half (n=124, 49%) out of a possible 252 schools responded, all of which reported having some DPH education. Two-thirds reported having a dedicated DPH department. Education was delivered by a variety of staff including those trained in paediatric and preventive dentistry. There were differing degrees of integration within the undergraduate programme and substantial variability in topics, teaching methods and approaches to assessment. Key components of the curriculum supported by respondents were: DPH philosophy and approach, population demography and health, health promotion and disease prevention, health care systems, the dental workforce and planning for health and oral health. Respondents were generally in favour of improving current teaching and shaping a core DPH curriculum for Europe. Amongst those who completed the questionnaire, there was a general agreement on the need for a core Dental Public Health curriculum for European dentists. Given the variation across Europe, increased awareness and prioritisation of the subject is required, facilitated by collaborative support.

Low power and low phase noise VCO with dual current shaping for IoT applications

In this paper, two low phase noise and power consumption VCO circuits, which are suitable for Internet of things (IoT) applications, are proposed. In the first structure, in order to have more control of the current consumption, the current shaping technique is used in the PMOS and NMOS biasing circuit. In the second structure, for increasing the oscillation amplitude and reducing the phase noise, independent biasing for the NMOS section is used. In both structures, to increase the frequency tuning range (FTR), without using a capacitor bank, the varactor is used in the biasing structure. In the first structure the supply voltage, output frequency, power consumption, and phase noise are 0.8 V, 2.44 GHz, 0.37 mW, and -117.5 dBc/Hz, respectively, but in the second structure, the supply voltage, output frequency, power consumption, and phase noise are 0.8 V, 2.44 GHz, 0.62 mW, and -120 dBc/Hz, respectively. It should be noted that the two structures are designed and simulated in 65-nm CMOS technology. Finally, the results show that the figure-of-merit for the first and second structures is --190 dBc/Hz and --190.2 dBc/Hz, respectively.

PFC‐SEPIC converter‐fed half‐bridge LLC resonant converter for e‐bike charging applications

In today's market, electric bikes (e-bikes) are becoming exceedingly popular due to their smaller size, ease of domestic charging and cost-friendly alternative in the category of electric vehicles. So, there is a need for the development of a power factor corrected (PFC) private off-board charger (OBC) to cater to the need of the domestic charging of e-bikes. Traditionally, e-bike chargers powered by a domestic meter are realised by a non-PFC OBC with a power rating of 500–700 W. Such converters draw harmonic currents at very high crest factor and affect the life and performance of other domestic appliances. A private OBC which derives its power from the domestic supply for charging the battery of an e-bike is proposed. The charger has two stages, i.e. the PFC stage for input current shaping and the DC–DC stage for regulating the battery charging voltage and charging current. The PFC stage is based on the single-ended primary inductance converter and the DC–DC stage is based on the inductor inductor capacitor (LLC) resonant converter. A 570 W, 57.6V, 10 A prototype is built using digital signal processor (TMS320F28035) to evaluate and validate its performance for charging a lithium-ion battery pack.

Optimization of the chamfering structures for ITER-like W/Cu monoblocks to avoid the leading edge-induced melting in EAST

EAST has installed a full ITER-like W divertor with W/Cu monoblocks for targets in the upper part of vacuum chamber since 2014. Although the dual chamfer shaping structure with 1 mm cutting in both toroidal and radial directions (1 mm × 1 mm) has been employed to mitigate the leading edge-induced thermal effect, severe leading edge-induced melting was widely observed on both inner and outer targets. All melting only occurred at the leading edges between neighboring cassette modules (inter-CMs), while it was not found at the leading edges between neighboring monoblocks within one cassette module (intra-CM). To optimize the chamfering structure for avoiding melting, thermal analysis of W/Cu monoblocks was performed by finite element method. It is identified that the current dual chamfer shaping structure (1 mm × 1 mm) does not work for inter-CMs due to the large radial misalignment which was hardly controlled and could even reached up to 3 mm. With such large misalignment, the maximum surface steady state heat load is only 1.2 MW m−2 for current structure. Thus, a symmetric structure of CMs which survive EAST operations requirement with two different toroidal magnetic fields has been proposed to improve the thermal performance and avoid melting. At inter-CMs, the optimized chamfering structure suitable for larger misalignments and heat fluxes has been suggested. And, the current dual chamfer shaping structure is remained at intra-CM after thermal evaluation. Such symmetric CMs should ensure EAST operate with heat flux up to 3 MW m−2 with 3 mm misalignment level. And, further improvement to withstand a higher heat flux is also proposed and discussed.

Interleaved Totem-Pole ZVS Converter Operating in CCM for Single-Stage Bidirectional AC–DC Conversion With High-Frequency Isolation

In this article, a new bidirectional single-stage interleaved totem-pole electrolytic capacitorless ac-dc converter with high-frequency isolation and low components count is proposed. The proposed converter is constructed using nonregulating two-phase interleaved totem-pole converter switched with a fixed 50% duty on the grid side and a full-bridge on the dc-side for active power and dc output regulation. This switching method results in a ripple-free grid current regardless of the magnitude of the input inductances. Consequently, a proper design of input inductance secures soft switching for all switches under wide voltage and load ranges without an auxiliary circuit or resonant tank. Hence, the proposed topology overcomes the reverse recovery issue, thereby enabling the use of Si devices in CCM. Moreover, the current spike around the ac main zero-crossing is avoided in the CCM operation due to small rectified voltage around zero-crossing. Furthermore, the instantaneous powers at the grid side and dc-side are identical since the proposed topology is electrolytic capacitorless with inherent second harmonic ripple current at the dc-side. PFC is inherently performed in the proposed converter without a current shaping control loop, and the phase-shift angle is the only control variable. Hence, the control system is simple and reliable. A 3.3 kW prototype of the proposed converter is built and tested in order to verify the performance and the theoretical claims.

Discontinuous Conduction Mode Operation of the Current-Shaping Modular Multilevel DC–DC Converter

The Current Shaping Modular Multilevel DC-DC Converter (CS-MMC) is a recently proposed class of modular multilevel dc-dc converters for dc distribution grid applications consisting of a single string of cascaded voltage source submodule cells (VSMs), a current source submodule (CSM) and notably no series inductor. In the CS-MMC, since it is the CSM that shapes the string current and there is no series inductor, this frequency can readily be in the medium-frequency range, enabling VSM cells to be realized with low cell capacitance. In the previous work, only continuous conduction mode (CCM) operation of the CS-MMC had been considered which led to several limitations including elevated switching losses and low utilization of the semiconductor devices in low output voltage applications. In this work, discontinuous conduction mode (DCM) operation is proposed for the CS-MMC which addresses these limitations. In traditional dc-dc converters, DCM is determined by the inductor current ripple. However, unique to the CS-MMC, DCM is determined by the VSM capacitor voltage ripple. In this work, the proposed DCM operational approach is presented along with its analysis and control. Both simulation and experimental results from a laboratory scale converter system are provided for validation.

Extended Operation Range of Photovoltaic Inverters by Current Waveform Shaping

The grid connection of photovoltaic voltage source inverters depends on the dc-link voltage level that can be supplied by the maximum power tracking of the photovoltaic system. The inverter disconnects from the grid, if the minimum required dc-link voltage level is violated, which leads to unwanted energy curtailments implying losses to the system owner. This article proposes to apply current waveform shaping to the inverter current in order to reduce the peak value of the voltage waveform at the point of common coupling by which the minimum required dc-link voltage level for power injection is reduced. This extended operation range of photovoltaic inverters is achieved through third harmonic current injection and can be applied to single-phase and three-phase, four-wire inverters without additional converter stages. A control structure for harmonic current injection and harmonic phase determination is presented and validated by simulations and the analysis is verified by experiments.

A revolution in biochemistry and molecular biology education informed by basic research to meet the demands of 21st century career paths

The National Science Foundation estimates that 80% of the jobs available during the next decade will require math and science skills, dictating that programs in biochemistry and molecular biology must be transformative and use new pedagogical approaches and experiential learning for careers in industry, research, education, engineering, health-care professions, and other interdisciplinary fields. These efforts require an environment that values the individual student and integrates recent advances from the primary literature in the discipline, experimentally directed research, data collection and analysis, and scientific writing. Current trends shaping these efforts must include critical thinking, experimental testing, computational modeling, and inferential logic. In essence, modern biochemistry and molecular biology education must be informed by, and integrated with, cutting-edge research. This environment relies on sustained research support, commitment to providing the requisite mentoring, access to instrumentation, and state-of-the-art facilities. The academic environment must establish a culture of excellence and faculty engagement, leading to innovation in the classroom and laboratory. These efforts must not lose sight of the importance of multidimensional programs that enrich science literacy in all facets of the population, students and teachers in K-12 schools, nonbiochemistry and molecular biology students, and other stakeholders. As biochemistry and molecular biology educators, we have an obligation to provide students with the skills that allow them to be innovative and self-reliant. The next generation of biochemistry and molecular biology students must be taught proficiencies in scientific and technological literacy, the importance of the scientific discourse, and skills required for problem solvers of the 21st century.

Psychology education and the neoliberal episteme in Australia

This article investigates some of the ways in which neoliberalism and mainstream psychology intersect to maintain a dominant episteme in psychology education within the Australian context. It is argued that the ubiquity and logic of neoliberalism and the philosophical inclination of mainstream psychology create a “culture of positivism” and epistemic deceit within psychology education. Some of the features of psychology as it has developed in Australia are offered to more clearly define what mainstream psychology is, before outlining the current regulatory, political, and economic forces shaping psychology education and the neoliberal university. The article concludes by proposing some of the consequences for a psychology education system that does not interrogate the origins of epistemic power and proposes that a greater focus on epistemological ethics and historical–hermeneutic elements in psychology education may offer some resistance to the neoliberal episteme.

A Low-THD Two-Switch PFC DCM Boost Rectifier for Aviation Applications

In this article, a new two-switch, single-phase, power-factor-correction, discontinuous-conduction-mode boost rectifier that features zero-voltage switching turn on and can achieve less than 5% input-current total harmonic distortion (THD) by injecting a simple feedforward signal obtained from input and output voltages to the output voltage feedback control is introduced. Since low THD is achieved without high- bandwidth active current shaping control, the proposed topology is suitable for modern aviation applications that require line frequency up to 800 Hz. The evaluation was performed on a 320-W prototype designed to operate from 94–134-V line input and deliver 220-V dc output. The prototype achieves 3.3% THD at full load over the line frequency range from 360 to 800 Hz and meets the required harmonic limits specified by the DO-160 standard that describes the environmental conditions and test procedures for airborne equipment.