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This paper proposes a high-speed brushless doubly-fed machine for aviation turboelectric distributed propulsion. The electromagnetic performance of the designed machine, including power ratio, voltage capability, power factor, and efficiency is analyzed. A customized rotor mechanical design is introduced, which allows for 4 times increase in speed than legacy designs. A simple TeDP system with one generator and one motor is simulated using FEA-circuit co-simulation in certain operating conditions. The losses and efficiency of the system are investigated for a better understanding of the machine.

Modular Multilevel Converters have been proposed to be a viable topology for medium voltage and high power motor drives due to the stackable structure of the topology. This allows for a transformer-less drive, better output current THD and reduces input and output filter sizes compared to traditional topologies. Replacing the traditional Si IGBT based submodules with SiC MOSFETs has been shown to improve the overall efficiency of the MMC. However, the lower switching losses of SiC MOSFETs have not been fully utilized to realize further system level improvements in the MMC. In this paper, the impact of the SiC MOSFETs on the efficiency, power density and output current THD of the drive is compared against Si IGBTs using analytical and simulation. A 7 kV dc bus, 4.16 kV ac, 1 MVA, 0-1,000 Hz medium voltage variable speed drive based on 1.7 kV devices based is used for the comparison.

With a growing number of silicon carbide (SiC) devices used in the modular multilevel converter (MMC) based medium voltage motor drive systems, the reflected wave phenomenon (RWP) under high dv/dt needs to be studied. In this paper, the voltage reflection in the MMC based motor drives is analyzed with a focus on the impact of the leakage inductance of the arm inductors. A seven-level MMC built with 1.7 kV SiC MOSFETs is modeled and simulated. The simulation results show that the leakage inductance of the arm inductors helps reduce the dv/dt at the MMC output but increases the voltage stress on the arm inductor windings and the load. A simple method is proposed to mitigate dv/dt and voltage overshoots applied to the machine windings. Presented simulation and experimental results validate the proposed method.

It may be an important route to improve the alkylation performance of MCM-22 zeolite by regulating the Al siting during the synthesis, as the liquid alkylation of benzene with ethylene mainly occur on the acid sites in the surface pockets and supercages of MCM-22. Here, the Al siting has been successfully adjusted by introducing additional anion in the hydrothermal synthesis of MCM-22 using piperidine as the structure directing agent. The effect of the additional anion in the synthesis precursor on the physiochemical property, especially the Al siting, and alkylation performance of MCM-22 zeolite was investigated. The morphology of products tends to be irregular lamellar structure when Cl−, PO43−, or SO42− are present in the synthesis gel. Although H-MCM-22-PO43− and H-MCM-22-SO42− show less acid site concentration than H-MCM-22, they exhibit obviously higher conversion of ethylene than H-MCM-22. This can be attributed to that more Al species are oriented to T2 sites located in the pockets or supercages by virtue of the presence of PO43− or SO42− in the synthesis gel. The novel synthesis strategy may provide an alternative way to modify the performances of MCM-22 and even other zeolites.

IM-5 series zeolites (I-xat-0.05TPABr) were prepared by treating the pristine IM-5 zeolites in a mixed solution of NaOH and TPABr (tetrapropylammonium bromide) with different NaOH concentrations (CNaOH). It was found the porosity and acidity of modified IM-5 zeolite changed obviously with CNaOH. When used for alkylation of benzene with ethanol, the modified I-xat-0.05TPABr exhibited better reaction stability than the unmodified IM-5 zeolite, and I-0.5at-0.05TPABr showed the best stability. Typically, the reaction stabilities of I-xat-0.05TPABr catalysts were directly related to the hierarchical factor, besides the carbon deposition rate.

The DFT investigation of methanol and dimethyl ether (DME) carbonylation at different sites of FER zeolite is carried out in an attempt to explore whether some specific acid sites are present to selectively catalyze the desired reaction. It is shown that the surface methoxy groups (SMG), generated by the reaction of methanol or DME with the Bronsted acid sites of zeolites, preferentially forms in the 8-membered ring (8MR) and 10-membered ring (10MR) channels. Further study of the CO attack on the SMG shows that, the carbonylation reaction occurs selectively at the 6MR zone of 8MR channel of FER zeolites. This result not only provides a theoretical perspective for the experimentally observed higher carbonylation reactivity of SMG located inside the 8MR channels, but also makes the location of the reaction more accurate.

A 30-kVA SiC inverter has been developed for investigating challenges in harsh environment power electronics. In this design, operating temperature of both gate driver and power circuit is targeted at 180 °C ambient temperature. Specifically, the design is to achieve outstanding high-temperature (HT) performance at an affordable cost by taking full advantage of commercial components and applying the latest HT gate drive and protection circuit. The inverter has been evaluated at full power for hours in a thermal chamber. Experimental results of HT operation are provided to support the exciting success of the prototype and the promising future of HT power electronics. Meanwhile, comprehensive reviews on the challenges are presented along with the development process. The reviews cover the HT components in this design and the latest research on HT device characterization and packaging technique. At the end, the achievements and remaining challenges are summarized.

A series of FER/MOR composite zeolites were synthesized through seed-assisted organic template free route. And the FER/MOR composite zeolites exhibited specific catalytic performance in the dimethyl ether carbonylation to methyl acetate reaction. SEM images revealed that the FER circle plates grew along the surface of MOR bundle aggregates. Good pore connectivity and high adsorption capacity were observed on FER/MOR on basis of the hyperpolarized (HP) 129Xe NMR spectra and propane adsorption results, which was different from its corresponding mechanical mixture. Quantitative analysis of 1H MAS NMR spectra using pyridine as probe revealed that the total Brϕnsted acid density in FER/MOR, especially that in 8 MR channel, was higher than that of single zeolites. High Brϕnsted acid density and good pore connectivity guaranteed the superior performance of FER/MOR in DME carbonylation reaction.

Sliding-Mode Control (SMC) has been widely utilised to control nonlinear systems with uncertain dynamics. This is due to its order reduction properties, low sensitivity to disturbances, great dynam...

A novel route involving self-metathesis of 1-butene under mild conditions that gave high yields of ethene and hexene was proposed. The results of thermodynamic analysis revealed that the Gibbs energy of the target Metathesis I reaction (1-butene → ethene + 3-hexene) was much higher than that of the main side Metathesis II (1-butene + 2-butene → propene + 2-pentene). Suppression of 1-butene double-bond isomerization was the key step to increase the selectivity for the target olefin in the reaction network. The relationship between the catalytic performance and support nature was investigated in detail. On basis of H2-TPR, UV-Vis spectra and HRTEM results, an alumina (Al2O3) support with large surface area was beneficial for the dispersion of molybdenum (Mo) species. Both suitable acidity and sufficient Mo dispersion were important to selectively promote the self-metathesis reaction of 1-butene. On the optimal 6Mo/Al2O3 catalyst, 1-butene conversion reached 47% and ethene selectivity was as high as 42% on the premise of good catalytic stability (80 °C, 1.0 MPa, 3 h−1).

Zeolite beta, an important catalytic material widely applied in the petrochemical field, is typically prepared under hydrothermal conditions. However, it usually suffers from the drawback of relatively long crystallization time. Herein, we show that the crystallization rate of zeolite beta can be accelerated by a factor of as much as about nine via the addition of the low-toxic and cost-effective pentacyclic lactam N-methyl-2-pyrrolidone (NMP) as a ‘promoter’. Using characterization techniques, we demonstrate that the pentacyclic lactam induces the fast formation of secondary building units (SBUs) and enhances the formation rate of the activated TEA+ species responsible for the nucleation of beta crystals. More importantly, the as-synthesized beta exhibited high product yield (above 85 wt%) and good performance in the direct amination of isobutene (i-C4H8) to tert-butylamine reaction.

MCM-49 zeolite with a three-dimensional MWW framework was directly synthesized using low-toxicity and cost-effective cyclohexylamine (CHA) as an organic structure-directing agent under hydrothermal conditions. Compared with the traditional hexamethyleneimine template, the interaction between CHA with the framework was weaker and more CHA molecules occupied the surface pockets and supercages of as-synthesized MCM-49 zeolite. The obtained sample showed good catalytic performance in the liquid phase alkylation reaction of benzene with ethylene.

This paper proposes a double-end sourced layout for multichip SiC MOSFET power module adopting conventional wire-bonded packaging technology. The unique design provides each MOSFET with two parallel commutation loops by incorporating a symmetrical pair of dc-bus terminals into the power module. This new layout provides symmetrical equivalent power loops to each paralleled MOSFET and thus enables consistent switching performances and equal dynamic current sharing for the paralleled MOSFETs. Compared to the conventional design, the proposed design reduces the equivalent power-loop stray inductance by more than 50% and achieves improved dynamic current sharing among devices. By mitigating the imbalance of the switching current, the new module design demonstrated reduced temperature differences among devices and decreased near-field radiation noise level compared to the conventional layout. These features can further help to improve the power module density by shrinking the heat sink and integrating the gate driver board with the power modules. In this paper, an analytic model has been proposed for fast prediction of the near-field radiation from the power module. Detailed design procedures and experimental validations are also included in this paper.

The synthesis of ferrierite (FER) zeolite using piperidine as an organic structure-directing agent was investigated. X-ray diffraction, X-ray fluorescence, N2-adsorption, and scanning electron microscopy were used to characterize the crystal phases, textural properties, and particle morphologies of the zeolite samples. The crystallization behavior of the FER zeolite was found to be directly related to crystallization temperature. At 150 °C, pure FER phase was observed throughout crystallization. At 160–170 °C, MWW phase appeared first and gradually transformed into FER phase over time, indicating that the FER phase was thermodynamically favored. In the piperidine-Na2O-H2O synthetic system, alkalinity proved to be the crucial factor determining the size and textural properties of FER zeolite. Furthermore, the obtained FER samples exhibited good catalytic performance in the skeletal isomerization of 1-butene.

Asymmetries in permanent magnet synchronous machines (PMSM) can result from manufacturing tolerances or optimization techniques that deliberately introduce them on rotor, stator, or both. This paper analyzes the impact of such unbalance on the air gap pressure, that is radial and tangential to the direction of motion, by means of Maxwell Stress Tensor; also, their consequences on torque pulsations and unbalanced magnetic pulling. Neglecting the manufacturing variations in the analysis of high power density PMSMs underestimates the resultant torque ripple. Additionally, new vibration modes occur due to unbalanced radial pressure. On the other hand, a geometry optimized to minimize torque ripple through controlled asymmetry is investigated, the approach compensates harmonics in torque effectively, but such compensation does not have the same effect on radial forces. Finite element analysis and experimentation are used to support the analysis and it is found that an asymmetric PMSM with low torque ripple will not necessarily produce lower vibrations and noise.

The adsorption behavior of dimethyl ether (DME) and carbon dioxide (CO) on FER zeolite with different Si/Al ratios and Al positions was calculated. For pure CO or DME gas, the CO adsorption quantity rises near linearly with pressure, while the DME adsorption quantity firstly rises rapidly but then rises much moderately at higher pressure. For the CO-DME gas mixture, both CO and DME adsorption quantity rises rapidly but then rises much moderately at higher pressure. Further investigation reveals that CO and DME molecules are preferentially located in the 6-MR zone of the 8-MR channel.

The rational design of zeolite-based catalysts calls for flexible tailoring of porosity and acidity beyond micropore dimension. To date, dealumination has been applied extensively as an industrial technology for the tailoring of zeolite in micropore dimension, whereas desilication has separately shown its potentials in the creation of mesoporosities. The free coupling of dealumination with desilication will bridge the tailoring at micro/mesopore dimensions; however, such coupling has been prevailingly confirmed as an impossible mission. In this work, a consecutive dealumination-desilication process enables the introduction of uniform intracrystalline mesopores (4-6 nm) into the microporous Al-rich zeolites. The decisive impacts of steaming step have been firstly discovered. These findings revitalize the functions of dealumination in porosity tailoring, and stimulate the pursuit of new methods for the tailoring of industrially relevant Al-rich zeolites.

The atomically economic and green chemical reaction of direct amination of isobutylene to tert-butylamine, particularly under the relative mild reaction conditions available for future industrial use, was carried out over zeolite catalysts possessing different topological structures, from one dimensional to three dimensional pore system, and from small 8-member ring pore (MRP) to medium 10 MRP and further to large 12 MRP zeolites, to disclose the relationship between the zeolite properties/topologies and their amination performance systematically under the mild reaction conditions. It was discovered that the pore structure and the acidities of zeolite catalysts played crucial roles in the isobutylene amination process, and suitable pore diameter (larger than 0.5 nm or with large side pockets/cups in the outside surface) and a certain number of mid-strong acid sites are indispensable to catalyze the amination reaction, while too strong acid strength was not conducive to the process of isobutylene amination. Among them, zeolites with topologies of BEA, MFI, MEL, MWW and EUO exhibited good amination performance, with which the isobutylene conversion was higher than 12.61% (>46.42% of the equilibrium conversion) under the studied mild reaction conditions. Due to the good amination performance and the large adjustable Si/Al2 ratio range, ZSM-5 was selected to further study the effect of acidity on the amination performance systematically under the mild reaction conditions, and the activity-acidity relationship in the amination process was disclosed: the amination activity (isobutylene conversion) had a linear correlation with the amount of mid-strong B acidity under the studied conditions over ZSM-5 catalyst, which can provide guidance for further developing high-efficient amination catalyst under mild reaction conditions available for future industrial use.

Shaped binderless ZSM-11 zeolite catalysts were synthesized via a dry-gel conversion technique from 70ZSM-11/30SiO2mix extrudates. 1,6-hexanediamine combined with tetrabutylammonium bromide was proved to be the best structure directing agent for the synthesis of the binderless ZSM-11 catalyst, without adding other alkaline materials. The 70HZSM-11/30SiO2mix serials materials crystallized for different times were detected by X-ray diffraction (XRD), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy–energy dispersive spectroscopy (STEM–EDS) techniques, and so on. In order to investigate the possible crystallization mechanism, the textural and structural properties of 70HZSM-11/30SiO2mix serials samples were further characterized by N2 adsorption–desorption. Acid properties were determined by temperature-programed desorption of NH3 (NH3-TPD) and pyridine adsorption-infrared (Py-IR) measurements. In the alkylation of benzene with dimethyl ether, the serials catalysts exhibited different benzene conversions. 70HZSM-11/30SiO2mix showed the lowest benzene conversion while sample 70HZSM-11/30SiO2mix-6.5h synthesized only for 6.5h displayed a higher benzene conversion, even higher than the value over 70HZSM-11/30Al2O3mix. Extending the crystallization time, the obtained samples displayed the increased benzene conversion in general under the same reaction conditions. In the end, the relation of physicochemical properties with the reaction performance was investigated.

In recent years, a lot of research efforts have been devoted to the application of sliding mode control (SMC) techniques to power electronic equipment and electrical drives. Hundreds of technical papers have been published in this research field. The tendency stems from the nature of sliding mode with discontinuous control actions and due to its potential for circumventing parameter variation effects along with low implementation complexity. This paper presents a control design procedure for DC/DC power converters. It develops SMC algorithms for several types of DC/DC converters with different control objectives, complete and incomplete information about system states. A chattering reduction approach for power converters based on the idea of multi-phase converters is also proposed. A wide range of MATLAB/SIMULINK computer simulations along with experimental results are provided to demonstrate the effectiveness of the proposed control design.

This paper presents a high-temperature (HT) gate drive and protection circuit for Silicon-Carbide (SiC) power mosfets entirely built from commercial off-the-shelf HT discrete components. To estimate cost reduction, a brief comparison was made between the proposed circuit and a commercial circuit using silicon-on-insulator integrated circuits. To evaluate performance, power tests were conducted up to 180°C in a thermal chamber. Eventually, the proposed circuit achieved a 90% cost reduction, and all functions were validated by experiments at 180°C. This demonstrated that the proposed circuit is a cost-effective solution for contemporary HT applications.

Nano-ferrierite zeolite aggregates with hierarchical porosity were successfully prepared by using pyrrolidine as sole organic structure-directing agent. SEM and TEM images revealed that nano-sized crystals (40–60 nm) stacked together loosely to form irregular clusters. Influence of crystallization temperature and initial gel compositions (pyrrolidine content, alkalinity, water content) on the synthesis of ferrierite zeolite were investigated in detail. Low crystallization temperature and high alkalinity were beneficial to form nano-ferrierite zeolite aggregates with high hierarchical porosity (total pore volume: 0.461 cm 3 /g). Compared with commercialized ferrierite zeolite, hierarchical nano-ferrierite aggregates showed better catalytic stability and product selectivity in the 1-butene skeletal isomerization reaction.

Various models have been utilized to investigate the Bronsted acidity (BA) of zeolites which affects the acid strength and the catalytic performance of zeolite catalysts. They sometimes yield confusing results in literature. To understand this phenomenon, the zeolite ferrierite as a typical example was investigated in this study by using calculation parameters similar to, if not more accurate than, the previous ones. The tradeoff between the calculation precision and the costs indicates that relaxing all atomic coordinates through lower k-point meshes would be a better choice to study the acidic ferrierite. Our results demonstrated that it would be better to determine the preferred T sites for the Al substitution and the proton siting of zeolites in a statistical view. This study is expected to shed light on the methodology validity in the practical application to solve the acidic zeolites.

On basis of thermodynamic empirical equations, the thermodynamic parameters for the direct amination of isobutylene to tert-butylamine, an atomically economic and green chemical reaction, were calculated. In particular, the equilibrium conversion of isobutylene under various reaction conditions close to those used in industry was calculated and discussed. Isobutylene amination is a temperature sensitive reaction due to its exothermic nature and isobutylene equilibrium conver-sion decreases with temperature. However, kinetically, the amination reaction will be faster at a higher temperature. Thus, there must be an optimum temperature for the reaction. A high pressure and n (NH 3 )/ n (i-C 4 H 8 ) molar ratio promote the transformation of isobutylene to tert-butylamine. Developing a highly efficient catalyst under mild reaction conditions is preferred for the amination process. The reaction was investigated over a series of acidic zeolites. ZSM-11 zeolite exhibited the best performance with 14.2% isobutylene conversion (52.2% of the equilibrium conversion) and > 99.0% tert-butylamine selectivity. The effect of reaction conditions on the performance of the ZSM-11 catalyst agreed with the thermodynamic results, which provides guidance for further cata-lyst development and reaction condition optimization.

A shaped binderless and two binder-containing ZSM-11 zeolite catalysts were prepared and char-acterized by powder X-ray diffraction, N 2 adsorption-desorption, and pyridine adsorption-infrared measurements. The binderless catalyst was synthesized using a dry-gel conversion technique, in which 1,6-hexanediamine and tetrabutylammonium bromide were used as structure-directing agents and no other alkaline materials were added. The catalytic performance of the zeolites in the direct amination of isobutene to tert -butylamine was evaluated in a fixed-bed reactor. By virtue of its high crystallinity as well as its good mechanical strength, the shaped binderless ZSM-11 catalyst showed a higher rate of formation of tert -butylamine than did the binder-containing catalysts.

In the production of surface-mounted permanent magnet machines, manufacturing tolerances also contribute to torque ripple. Additional harmonics of low electrical orders are created in the torque spectrum. Slight manufacturing variations develop asymmetry conditions in the rotor as well as in the stator. Finite element models can be used to analyze the magnitude of pulsating torque generated due to these asymmetries. However, due to its random nature, lack of periodicity, and symmetry, it is time consuming to study the problem with numerical methods for its uneven geometry that does not allow reduced geometrical models. Moreover, the experimental verification of all possible variations would be very challenging as it would require part dimensioning and part sorting a large quantity of motor builds and finally testing of all samples. Therefore, in this paper an analytical model is presented to study the effect of such imbalance on the torque ripple. The model shows an agreement against finite element models and also with experimental results when predicting torque harmonics that come from asymmetries.

Medium-voltage motor systems with adjustable- speed drives are employed in a wide range of applications. The adoption of medium-voltage Silicon Carbide (SiC) devices in motor drives can improve motor system’s efficiency, power density, and dynamic response. But the high switching dv/dt (short rise time) produced by SiC devices increases the stress on the motor winding insulation and leads to partial discharges. This paper studies the partial discharge in the medium-voltage motor winding subjected to two-level PWM waveforms produced by medium-voltage SiC devices. Partial discharge inception voltages (PDIVs) and repetitive partial discharge inception voltages (RPDIVs) of the motor winding at various rise time, switching frequencies and modulation index are tested. Statements on PD behaviors are analyzed based on the test results.

This paper describes a multi-scale thermal analysis approach for the design of an air-cooled 1.7-kV SiC MOSFET-based medium-voltage variable-speed motor drive. The scope of the models and required efficient and flexible thermal models to be developed. Two modeling techniques are described that significantly reduced model run time and enabled more complex models to be run faster while retaining needed accuracy. The first technique uses the effectiveness-NTU method to extract convection boundary conditions from a CFD model that can be applied to a fast-running FEA model. The second is a porous media technique that enables system-level CFD simulations that incorporate effects from heat exchangers (e.g., pin fin heat sinks) that run in a fraction of the time required for fully resolved CFD simulations. The multi-scale approach to the thermal analysis enabled fast and accurate simulation for the converter design ranging from the die level up to the full system with 36 submodules. The modeling results were validated against experimental data from system tests performed by OSU.

This paper proposes a simple control strategy for the dv/dt reduction in the modular multilevel converters (MMCs) based motor drives. In particular, the control strategy aims at the reduction of the MMC output voltage slew rate by coordinating the switching transients of several submodules. It is realized via utilizing extra submodules or simply applying a delay time to the switching transients. Both methods are implemented without affecting the switching speed of the power devices. Thus, the methods could mitigate the drawbacks caused by the high dv/dt while maintaining the advantages brought about by the fast switching speed of the silicon carbide (SiC) devices. The simulation results and test results based on a SiC MMC are provided. It is shown that the proposed control methods bring down the output dv/dt by around 50 %.

In this paper, a system-level analysis method is provided to evaluate the factors that affect the switching transients of modular multilevel converters (MMCs) based motor drives. In particular, the voltage transients at the device terminal are compared to the arm voltages as well as the MMC output voltage. The differences are identified and in detail evaluated via frequency domain approach and simulation. Experimental results based on a seven-level silicon carbide (SiC) MMC are provided to validate the mathematical analysis and the model-based simulation results. The study suggests that a dv/dt reduction is observed from the switching devices to the MMC output terminal, and both the system parameters and the operation principles affect the system transient performance.

As a learning step to gain experience in designing high specific power electric machines for demanding applications such as aircraft propulsion, this paper presents research results in the design, fabrication, and experimental testing of a scaled-down 300-kW electric machine. With advanced structure and materials, this machine achieves an active-material specific power of 14.4 kW/kg and an electromagnetic efficiency of 99.2% under full load condition using finite element analysis. The mechanical integrity of the rotor is fully validated at the rated speed of 17, 000 rpm in finite element analysis. The fabricated machine prototype is mounted onto a 350-hp dynamometer for comprehensive performance characterization. The efficiency of the machine prototype is mapped based on the experimental measurements under various operating conditions. In this paper, the electromagnetic analysis, trade-offs at the design stage, mechanical stability considerations, and experimental testing results are summarized and presented in detail.

This paper reviews popular methods for estimating damper currents in field-would salient rotor synchronous machines. Most research dealing with electric machine analysis tend to simplify multi-damper bar designs with two orthogonal dampers (commonly called D and Q). This paper uses an internally developed FEA (Finite Element Analysis) software to independently analyze the current in each damper bar using 3 popular methods.

This paper presents a high-speed and high-dynamic variable frequency drive (VFD) based on the modular multilevel converter (MMC) and silicon carbide (SiC) devices. A compact submodule design with the straightforward extension feature is introduced. An integrated control scheme including the low- and high- speed control is developed. Based on the designed prototype and the advanced control scheme, the dynamic response including speed acceleration and torque step-change capabilities are investigated. Besides, the steady-state performance in the high-speed range is also examined in terms of speed control accuracy and current distortion. Validated by the experimental results, the developed VFD prototype with the proposed control scheme can successfully reach the high speed (6000 rpm). It has accurate speed control (±1%) and low current distortion (THD%=2.54%) in high-speed operation, as well as the robust dynamic response.

Modular multi-level converters (MMCs) are one of the promising topologies in recent years for medium or high voltage applications. They are considered as the next generation DC/AC converters for medium/high voltage (MV/HV) motor drive applications due to their transform-less structures, high efficiency and modularity. Reliability is one of the most important challenges in MMCs, since a large number of power switching devices are used and each of these devices can be considered as a potential failure point. It is significant to detect and locate the fault accurately and apply appropriate protections in a timely manner. This paper investigates the behavior of the failure submodules and healthy submodules and use artificial neural network (ANN) classification algorithms for single-submodule open-circuit fault diagnosis. The ANN algorithm is implemented in field programmable gate array (FPGA) and the ANN parameters training is completed offline in Matlab. Experimental results of the proposed fault diagnosis for a single-module open-circuit fault are presented in this paper.

In a mass production environment, due to the manufacturing tolerances, additional orders of cogging torque are created in addition to the fundamental components. The tolerances lead to asymmetry conditions both in the rotor as well as in the stator. Finite-element models can be used to analyze the cogging generated due to these asymmetries. However, it is extremely time consuming to study this uneven geometry numerically since periodicity and symmetry conditions cannot be used to reduce the model. Moreover, the experimental verification of all possible variations would be very challenging, as it would require part dimensioning, part sorting, a large quantity of motor builds, and finally testing of all samples. Therefore, in this paper, an analytical model is presented to study the effect of such imbalance on the cogging torque. The model is validated against finite-element models and also with experimental results.

Combination of the exothermic methanol aromatization with the endothermic n -butane aromatization provides a good way to meet the increasing demand for aromatics. Here, a series of Zn-ZSM-5/ZSM-11 catalysts were prepared with different introduction methods. The influence of location and state of Zn species on the coupling effects of cofeeding n -butane with methanol were investigated in detail. UV–vis, H 2 -TPR and XPS spectra were applied to reveal the state of the Zn species on different catalysts. Quantitative results of NH 3 -TPD and Pyridine-FTIR were provided to compare the acidity changes of the catalyst after Zn loading. Physical mixing method led to high portion of bulk ZnO particles outside the channel which could promote the formation of C 2 C 4 light alkane in cofeeding reaction. Ion exchange and impregnation modes were beneficial for the formation of Zn O Zn bridging species in the micropore channel. Zn O Zn bridging species was found to increase the promoting effect of cofeeding n -butane with methanol on aromatics selectivity.

This paper presents the effects on output voltage and current total harmonic distortion (THD) response with increasing the arm inductance (smooth reactor for HVDC) for the modular multilevel converter (MMC) behavior based on a closed loop-needless PID controller control. Also, it presents the effects on MMC quantities, such as a circulating current ripple, maximum output voltage, and submodule capacitor ripple responses with increasing the value of arm inductance. Because increasing arm inductor size could reduce the THD and circulating current ripple waveforms of the MMC, this effect will be investigated in this paper. The closed loop-needless PID controller control is presented first. Second, an examination of the effect of changing the arm inductor for MMC behavior is carried out based on many simulation results in this paper in order to analyze the change in THD for all MMC quantities, including circulating current, upper arm current and voltage, lower arm current and voltage, and AC output voltage and current. Third, arm inductance relationships with output voltage and current THD are shown. Also, arm inductance relationships with a circulating current ripple and submodule capacitor ripple are presented. As a part of this study, the relationship between arm inductance and maximum output voltage is explained. Finally, the hardware design and software design of the prototype are presented to verify the arm inductor value effect on MMC experimentally. The experimental results are also documented in this paper.

The adsorption behavior of methane in simulated coal-bed gas on several micropore zeolites is studied. Alkali and steaming treatments of ZSM-5 are carried out in order to adjust the pore structure ...

Power conversion from ultravoltage direct current (UVdc) to ultravoltage alternating current (UVac) is the biggest challenge facing industrial power application companies. Converting UVdc transmission systems with 2200 kV dc and distance up to 3000 km into UVac is the most challenging issue associated with transmitting power by UVdc transmission systems. This paper proposes an approximated arm energy control algorithm for a modular multilevel converter with a large scale of submodules per arm to convert UVdc of 2200 kV and more into UVac in order to achieve total harmonics distortion for UVac systems of $N$ ) is derived first. Second, the flooring switching pulsewidth modulation is explained in order to generate the number of inserted and bypassed submodules per arm. Third, submodules’ selections are proposed and verified by the simulations. Fourth, a set of simulation results for a dc bus of 2200 kV and 481 levels for the output voltage conducted in the MATLAB/Simulink environment are presented to verify the proposed algorithm. Finally, the proposed algorithm is experimentally verified by the hardware and software designs of the prototype.

A facile alkaline treatment with the addition of surfactant cetyltrimethylammonium bromide (CTAB) to prepare hierarchical ZSM-11 zeolite (Z-xat-yCTAB) is presented. The textural and structural properties of Z-xat-yCTAB were characterized by XRD and adsorption and desorption of N2 and benzene. By virtue of CTAB addition, uniform intracrystalline mesopore distribution centered at ca. 4.2 nm was introduced accompanied by well-protected microporosity. Based on characterization results such as TEM images and BJH curves as well as 29Si and 27Al MAS NMR spectra, the composite effects of NaOH and CTAB on mesoporosity production were proposed. Acidity was characterized thoroughly by FTIR of adsorbed pyridine (Py-IR) and pivalonitrile. Accordingly, the ratio and accessibility factor of Bronsted and Lewis acid sites are discussed systematically. In the alkylation of benzene with dimethyl ether, Z-xat-yCTAB series samples exhibited better reaction stability than ZSM-11 samples treated with NaOH solution. The catalytic promotion could be attributed to the dual effects of NaOH and CTAB on the porosity and acidity regulation. Moreover, based on the correlation between the reaction stability and the ratio of Bronsted to Lewis acid concentration with weak–medium strength, measured by Py-IR, it was revealed that the regulation of acidity could play a more important role for better reaction stability. In addition, the physicochemical properties and reaction activity were compared between ZSM-11 samples derived from alkaline treatment with CTAB addition and with tetrapropylammonium bromide (TPABr) addition under the same conditions.

A new synthetic protocol of hollow structured Beta zeolite via interzeolite conversion with the assistance of N-methyl-2-pyrrolidone (NMP) was reported in this work. The synthesis conditions were optimized to obtain the pure and hollow Beta zeolite from the USY zeolite. In comparison, the solid Beta zeolite with low yield was obtained in the absence of NMP. The important factors in successful synthesis of hollow Beta zeolite were the usage of USY zeolite and the addition of NMP. On the basis of the characterization data, such as XRD, SEM, TEM, and 29Si/27Al MAS NMR, a formation mechanism for the synthesis of hollow Beta zeolite from USY was proposed and discussed. The silicon species in the parent USY crystals dissolved firstly, afterwards the primary solid Beta crystals with high SiO2/Al2O3 molar ratio were generated at the earlier stage, finally, the hollow Beta zeolite was formed due to the dissolution-recrystallization of the crystalline nutriments located in the core of the primary solid Beta crystals as well as the consumption of USY. The catalytic performance of alkylation of benzene with isobutylene demonstrated that the obtained hollow Beta catalyst exhibited excellent isobutylene conversion and tert-butylbenzene selectivity against the solid Beta synthesized from an amorphous silica/alumina.

Power generation and grid stability have become key issues in the last decade. The high penetration of large capacity wind generation into the electric power grid has led to serious concerns about its influence on the dynamic behavior of power systems. The low-voltage ride-through (LVRT) capability of wind turbines during grid faults is one of the core requirements to ensure stability in the power grid during transient conditions. The doubly-fed induction generators (DFIGs) offer several advantages when utilized in wind turbines, but discussions about their LVRT capabilities are limited. This paper presents a comprehensive study of the LVRT of grid-connected DFIG-based wind turbines. It provides a detailed investigation of the transient characteristics and the dynamic behavior of DFIGs during symmetrical and asymmetrical grid voltage sags. A detailed theoretical study supported by computer simulations is provided. This paper also provides a new rotor-side control scheme for DFIG-based wind turbines to enhance its LVRT capability during severe grid voltage sags. The proposed control strategy focuses on mitigating the rotor-side voltage and current transients during abnormal grid conditions, without any additional cost or reliability issues. As a result, the DFIG performance is improved and utility company standards are fulfilled. Computer simulations are used to verify the expanded ride-through capability of the novel strategy and its effective performance compared to the conventional control schemes.

A novel discharging control strategy is proposed and implemented for submodules in modular multilevel converters (MMCs). By sequentially controlling the arm currents of a MMC to the arm resistors, all submodule capacitors are discharged safely and rapidly without adding additional devices and circuits, resulting in improved performance and reduced cost. Both open- and closed-loop control methods are evaluated for effectiveness of the new control strategy. Simulation and experimental results are provided to validate the new control strategy.