Embarking in an educational research paper is one of the daunting processes any scholar can go through. And the process is even harder for novice education students who wander through the plethora of ...terminology, styles and paradigms trying to figure out their way in that jungle called educational research. The following of the review presents the constructs and basic theoretical components needed. By illustrating the differences between, strengths, weaknesses and research methods attached to each paradigm, this paper aims at introducing the first step in the thousand mile journey for novice education researchers and graduate students. Moreover, the paper is aiming at extending a departure point for the novice educational researchers, and strives to supplement the work of professors and supervisors who are engaged in training future educational researchers.
Staircase modulation is a switching strategy widely used for multilevel inverters employing high number of output voltage levels. With tens of levels, a staircase modulated multilevel inverter ...produces a stepped, sinewave-like output voltage without requiring inductive or capacitive switching harmonics filters. Among the several multilevel inverter topologies, the modular multilevel converter (MMC) has proven its superiority due to its modular and easily scalable structure. However, voltage balancing of the submodule (SM) capacitors is a major challenge associated with MMC operation. In this paper, a staircase matrix modulation (SMM) technique, achieving sensor-less capacitor voltage balancing, is proposed for the switched - capacitor MMC (SCMMC), which has no discrete arm inductor. The proposed SMM utilizes a symmetric switching matrix, where rotation between specific switching patterns of a certain voltage level keeps capacitor voltages balanced every switching cycle. The structure of the proposed symmetric matrix is described, and the proper choice of the pattern rotation frequency is quantified, both from the voltage balancing perspective. Time-domain simulations for an 11-level SCMMC under SMM are provided to illustrate the voltage balancing capability of the proposed SMM under steady state and transient conditions.
Staircase modulation is a switching technique ubiquitous in multilevel inverters utilizing large number of output voltage levels. With tens of levels, the output of a multilevel inverter employing ...staircase modulation approaches a sinusoid without requiring switching harmonics filters. Out of various multilevel inverter topologies, the modular multilevel converter (MMC) became prominent due to its modularity, scalability, and efficiency. However, balancing the submodule (SM) capacitor voltages poses a significant challenge in MMC operation. In this work, a staircase matrix modulation (SMM) strategy, which achieves sensor-less capacitor voltage balancing, is proposed for the switched - capacitor MMC (SCMMC), an MMC topology with a very small arm inductor. The proposed SMM utilizes a full rank, symmetric switching matrix, where specific switching patterns are assigned for each voltage level. The structure of the proposed matrix, its unique features, and the process of populating its entries for any converter voltage level are described. Theoretical analysis on the operation of the proposed SMM, simulations for an 11-level SCMMC, and experimental results on a single-phase, 2kW, 425V, 4-level SCMMC prototype are presented to illustrate the voltage balancing capability of the proposed SMM. The resulting switching frequency of the SCMMC under SMM is also analyzed.
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Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high ...temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (
s
N
N
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2.7--4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (
μ
B
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500
MeV), effects of chiral symmetry, and the equation of state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2024, in the context of the worldwide efforts to explore high-density QCD matter.
The literature abounds with many researches and articles that are written in a way that portray the Kingdom of Saudi Arabia as the poster child of hegemony, essentialism and women oppression. In ...recent years, no aspect of Saudi Arabian society has been subject to more scrutiny and debate than the women’s domain. Women’s rights and responsibilities have been controversial issues among both conservatives and progressives in Saudi Arabia; nevertheless, Saudi women remain among the least studied population. This study draws on the academic and professional experiences of the author dealing with Saudi women in Canada, the UK, the USA and inside Saudi Arabia to further the critical scholarship on Saudi Arabia and Saudi women as site and population of academic research to avoid the essentialist, orientalist and Westernized understanding of Saudi Arabia and Saudi women. This article is a springboard to any researcher interested in studying – critically- Saudi women’s issues.
Among several multilevel converter topologies, the modular multilevel converter (MMC) has received increasing interest due to its modularity, efficiency, and voltage and power scalability features. ...However, before the MMC can run in normal steady-state conditions, its submodule (SM) capacitors have to be pre-charged to their nominal voltage value. In this paper, we describe an ac-side and a de-side pre-charging strategy, both utilizing Y-matrix modulation (YMM), to startup the switched-capacitor modular multilevel converter (SCMMC) with middle SM. This topology employs a SM between the upper and lower arms, and has no discrete arm inductors. The proposed startup methods do not require any extra hardware besides the current-limiting (charging) resistors, which are bypassed after pre-charging is completed. It is shown that achieving a soft-startup requires balancing the SM voltages at their nominal values during the active charging stage, which necessitates actively controlling the middle SM voltage using the ac line current. Theoretical analysis is presented to quantify the capacitor voltages during the different pre-charging stages, and a time-domain simulation of a 6-level SCMMC with middle SM under YMM is provided to validate the results.
Power electronic applications that demand ratings exceeding 250kW require medium voltage (MV) converters to handle the high power (HP) levels. MV HP converters are widely used in motor drive ...applications such as in heavy-duty electric and hybrid-electric propulsion/traction drives, as well as in other industrial applications including refiners, fans, pumps, and rolling mills. In addition to drives applications, the increased grid integration of renewable energy resources to achieve a more sustainable and cleaner energy has led to the proliferation of MV HP converters in utility applications. MV converters have played a major role in modernizing traditional transmission and distribution networks and facilitating the smart-grid transition. They can provide active control of power quality, provide shunt and series compensation, and achieve self-healing, islanding operation, fault handling, and other functionalities.To achieve low common mode voltages (CMV), low dv/dt stresses, low electromagnetic interference (EMI), and better harmonic performance, MV HP converters are often implemented with multi-level topologies. Among the several multilevel converter topologies, the modular multilevel converter (MMC) has received increasing interest due to its modularity, efficiency, and voltage and power scalability features.However, some challenges still exist for utilizing MV converters in general, and MMCs in particular, whether in motor drives or grid applications. These challenges are mainly driven by the high power density requirements. Along with cost, reliability, and efficiency, power density has recently become among the fundamental figures of merit when characterizing a power electronic conversion system performance. Nevertheless, many barriers exist that hinder achieving high power densities in MV applications. These power density barriers include the magnetic components such as transformers, harmonic filters, and the arm inductors of MMC-based MV conversion systems. As a result, any advancement along the power density trajectory would not be possible without a substantial reduction in the volume and weight of the aforementioned magnetic components.This research proposes the switched-capacitor modular multilevel converter (SCMMC) as a high power density converter, which can achieve inductor-less, filter-less, and transformer-less MV conversion. The dissertation is divided into six parts. In the first part, the power density challenges of MV converters are highlighted in grid and drives applications. In the second part, the switching frequency and the modulation technique choice of the multilevel inverters are presented. The importance of using the lowest frequency modulation with high number of levels to achieve the lowest harmonic distortion is demonstrated as the approach to make a filter-less and transformer-less operation possible. In the third part, the SCMMC topology is introduced as a solution towards high power density MV power conversion through its arm inductor-less topology. In the fourth part, the control of the SCMMC is presented; a low output frequency modulation technique is proposed for the SCMMC, and a startup control strategy is proposed for the SCMMC with middle submodule. In the fifth part, a 2kW, 425Vrms single phase SCMMC prototype built in our lab is showcased, and its modulation techniques are verified. In the final part, the scope of future research is presented.
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