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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Application of electric machines in the traction and transmission systems of hybrid/electric vehicles has been studied for many years. The hybrid vehicle based on dual mechanical port (DMP) electric machine has gained more and more attention, because it eliminates the need for planetary gear and combines the motor and the generator into a compact electric machine. The DMP machine with a squirrel-cage outer rotor (SCDMP) is investigated in this paper. Due to its unique electromagnetic characteristics, control algorithms for conventional machines cannot be applied to the SCDMP machine. The methods to calculate the correct current commands and estimate the outer rotor flux position are proposed. Based on these two methods, a control algorithm for the SCDMP machine is proposed and estimated by simulation. The results show that the proposed control algorithm is able to independently control the torque productions and the flux levels of the two rotors of the SCDMP machine. [ABSTRACT FROM AUTHOR]

A new type of electric machine with two free rotating rotors [dual mechanical port (DMP)] is investigated in this paper. Since this DMP machine has a squirrel-cage outer rotor, it is named as SCDMP machine. First, the electromagnetic characteristic of the SCDMP machine is analyzed. Then, the transient model and steady-state model of the SCDMP machine are derived. The proposed machine models are verified by finite element method and simulation. The results show that the proposed models accurately represent the unique electromagnetic characteristics of the SCDMP machine. [ABSTRACT FROM AUTHOR]

With the proposed dual-current-loop control algorithm, the torque and air-gap flux of a doubly fed induction motor are controlled directly. Compared to the singly fed permanent magnet and induction motors, the torque–speed operation region for electric vehicle/hybrid electric vehicle applications is nearly doubled with the proposed dual-current-loop control algorithm for a given battery voltage. Computer simulations and experimental results are provided to verify the proposed control algorithm. [ABSTRACT FROM PUBLISHER]

A 1000 kW/19 200 rpm wound-rotor synchronous machine has been designed as a draft based on 2-D transient finite-element method (FEM). The magnetic fields distribution, the iron losses, the electromagnetic torque and the terminal characteristics of the prototype machine are investigated in this paper by using 2-D finite element analysis. The d-axis inductance Ld and the q-axis inductance Lq of the sample machine are predicted in analytical models. All studies indicate that the wound-rotor synchronous machine is potential to apply in high speed generator or motor application. [ABSTRACT FROM PUBLISHER]

This paper introduces a new method to solve the sensorless control problem for a grid-connected doubly fed induction machine (DFIM). The proposed method is based on high-frequency signal injection and the fact that the rotor of a DFIM can be seen as the rotating secondary of an induction transformer. The commonly used sensorless technique based on stator-flux linkage, aside from being parameter sensitive, does not work during fault ride through (FRT) conditions. Nevertheless, the proposed method is parameter independent and remains fully functional during FRT conditions. Moreover, as opposed to other high-frequency injection methods, the proposed method does not require rotor saliency. The mathematical principle of the proposed technique and its implementation are presented. Computer simulations and initial experimental results are also included for verification. [ABSTRACT FROM PUBLISHER]

Indirect field-oriented control, direct field-oriented control, and direct torque control are the most widely used instantaneous torque control techniques for the drive system of alternative energy vehicles (AEVs). This paper evaluates three candidate alternating-current machines and investigates the suitability of different control techniques for the drive systems of battery-powered electric vehicles, hybrid electric vehicles, and integrated starter alternators. Accurate flux and torque estimation is the core of any opted control technique for all types of AEV drive systems. Therefore, an accurate closed-loop voltage model flux and torque estimator that is insensitive to stator resistance variation has been designed. This paper also analyzes loss model control and search control (SC) techniques for the drive system's efficiency optimization and proposes an offline SC efficiency optimization technique. Experimental results are presented to demonstrate the performance of the proposed flux and torque estimator and efficiency optimizer. [ABSTRACT FROM PUBLISHER]

This paper analyzes critical control issues associated with the deep field weakening operation of interior permanent magnet (IPM) synchronous machines. The singlecurrent-regulator control algorithm is reviewed, which controls the d-axis current actively and gives a fixed q-axis voltage command. To achieve better operational efficiency and performance, improvements are made to choose an optimal q-axis voltage for variable-speed and variable-load conditions. The control algorithm is implemented on a 50-kW IPM machine. Test results, including 7:1 constant power speed ratio operation, are presented to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper discusses the problems of current decoupling control and controller tuning associated with sensorless vector-controlled induction-motor (IM) drives. In field-oriented control, the d-q synchronous-frame currents should be regulated to have independent dynamics such that the torque production of the IM resembles that of a separately excited dc motor. However, these currents are not naturally decoupled, and decoupling compensators should be used. Current loop tuning is an additional problem, since controller gains obtained by theoretical methods or simulation, quite often, do not work well on the real system. This paper proposes a new approach for current control that uses integral-sliding-mode (ISM) controllers to achieve decoupling. The synchronous-frame control voltages are synthesized as the sum of two controller outputs: a traditional one (PI) that acts on an ideal plant model and an ISM controller. The ISM controller decouples the d-q currents and compensates the parameter variations in the current loops of the machine. Simulations and experimental tests on a 0.25-hp three-phase induction machine show satisfactory results. [ABSTRACT FROM AUTHOR]

This paper presents two novel sliding mode (SM) model reference adaptive system (MRAS) observers for speed estimation in a sensorless-vector-controlled induction-machine drive. Both methods use the flux estimated by the voltage model observer as the reference and construct SM flux observers that allow speed estimation. Stability and dynamics of the two proposed SM flux observers are discussed. The observers are compared with the classical MRAS observer. The proposed estimators seem very robust and easy to tune. Unlike the classical MRAS, the speed-estimation process is based on algebraic calculations that do not exhibit underdamped poles or zeros on the right-hand plane. Simulations and experimental results on a 1/4-hp three-phase induction machine confirm the validity of the approaches. [ABSTRACT FROM AUTHOR]

This paper presents an improved method of flux estimation for sensorless vector control of induction motors based on a phase locked loop (PLL) programmable low-pass filter (LPF) and a vector rotator. A PLL synchronized with the voltage vector is used for stator frequency estimation. The pure integration of the stator voltage equations is difficult to implement and LPFs with a fixed cutoff provide good estimates only in the relatively high frequency range—at low frequencies, the estimates fail in both magnitude and phase. The method proposed corrects the above problem for a wide range of speeds. Simulations and experimental results on a 0.25-hp three-phase induction machine verify the validity of the approach. [ABSTRACT FROM AUTHOR]

A novel approach is developed in this paper for sensorless control of permanent magnet (PM) machines down to zero speed without signal injection or special pulsewidth modulation (PWM) techniques. Taking advantage of the low inductance in a PM machine, the phase current ripples under a Conventional PWM excitation are measured to derive the rotor position and speed. The new approach can also be used to estimate the rotor position at standstill if a minor rotor saliency exists. Neither prior knowledge of machine parameters, nor any special signal injection, is needed for the rotor position detection. Sensorless control of a PM machine based on the proposed scheme has been investigated by comprehensive computer simulations. Experimental results are presented to verify the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

The production of ethylbenzene from the alkylation of dilute ethylene in fcc off-gases with benzene has been commercialized in China over a newly developed catalyst composed of ZSM-5/ZSM-11 co-crystallized zeolite. The duration of an operation cycle of the commercial catalyst could be as long as 180 days. The conversion of ethylene could attain higher than 95%, while the amount of coke deposited on the catalyst was only about 10 wt.%. Thermogravimetry (TG) was used to study the coking behavior of the catalyst during the alkylation of fcc off-gas with benzene to ethylbenzene. Based on effects of reaction time, reaction temperature, reactants and products on coking during the alkylation process, it is found that the coking rate during the alkylation procedure follows the order: ethylbenzene>ethylene>propylene>benzene for single component, and benzene–ethylene>benzene–propylene for bi-components under the same reaction condition. Furthermore, the coking kinetic equations for benzene–ethylene, benzene–propylene and ethylbenzene were established. [Copyright &y& Elsevier]

Proposes a method of detecting rotor position for sensorless control of switched reluctance machine (SRM) in super-high speed operation. Popularity of SRM; Establishment of general nonlinear magnetizing model (GNMM); Rotor position detection based on GNMM.

A new process has been suggested for converting natural gas to ethylene by combining oxidative coupling of methane with ethane dehydrogenation to provide an efficient method for the utilization of thermicity and CO2. From their thermodynamics, it is clear that the exothermicity from CH4 oxidative coupling reaction (ΔH800 °C=−174.3 kJ mol−1) can support C2H6 dehydrogenation by CO2 (ΔH800 °C=+180.2 kJ mol−1). Meanwhile, the two reactions can be conducted under the same reaction conditions, such as the reaction temperature and reaction pressure as well as space velocity. In addition, the CO2 yielded from CH4 oxidative coupling reaction can be directly used for C2H6 dehydrogenation. Two kinds of catalyst are developed for this combined process with an achievement, from which C2H4 content in tail gas can reach attractively 16.4%, which can be used directly to produce ethylbenzene by the alkylation of benzene. [Copyright &y& Elsevier]

Discusses the use of novel methods for rotor position estimation both at standstill and during running conditions for a switched reluctance motor starting free of position sensor and hesitation. Analysis of switched reluctance machine starting hesitation; Model selection for rotor position estimation; Computer simulation.

Presents a comparison study of the rotor structures for the nonsine five-phase synchronous reluctance machines (SynRM) with a detailed examination of different reluctance rotor structures. Advantages of SynRM with a higher number of phases; Harmonic magnetomotive force interaction due to reluctance motor; Linear model analysis of rotor structures; Nonlinear analysis by finite-element method.

[Display omitted] Constructing hollow structure into microporous zeolites can improve the accessibility of acid sites located at the inner part and the diffusion property. Hence, the development of an efficient synthesis strategy to acquire zeolites with tunable hollow structures and acidity has attracted much attention. In this work, an innovative tandem synthesis route was proposed to prepare MFI zeolites with diverse hollow structure while maintaining solid yields exceeding 90 %. The substitution of ethanol molecules, which previously occupied the micropores, with tetrapropylammonium cations was proved to be the key factor to construct hollow structure. And a crystallization-driven particle dissolution mechanism was proposed. The dimension of the hollow cavity, particle size, and Si/Al ratio can be flexibly regulated. Interestingly, hollow MFI samples featuring the common cavity structure, "eye-like" cavity structure, or double-cavity structure can be directly synthesized by controlling the dissolution of core parts. In the 1-butene catalytic cracking reactions, a much higher conversion of 67.2 % was acquired over hollow ZSM-5 compared with that over conventional ZSM-5 (35.8 %) after 64 h of reaction. This improvement can be attributed to the eightfold increase of diffusivity in hollow ZSM-5. This facile and efficient synthesis method endows accurate regulation of the hollow structure, which is meaningful for both fundamental research and industrial applications of hollow zeolites. [ABSTRACT FROM AUTHOR]

Proposes a mutual model reference adaptive system (MRAS) containing two models for the use in industrial electronics. Why position sensorless vector control approaches have been well accepted in industrial electronics; Implementation of a position sensorless field-orientation control of an induction machine; In-depth look at the mutual MRAS scheme for speed estimation.

Presents the concept and implementation of field-orientation control (FOC) of a doubly excited brushless reluctance machine (DEBRM) for variable-speed drives and generating systems. Reason why a stator-flux-orientation scheme was employed; Types of controller and converter used to verify the theoretical analysis.

Presents a methodology for steady-state performance analysis and design of the doubly fed reluctance motor. Linear model; Stator movements; Prototype design; AC line current waveform.

Presents a novel adaptive algorithm used for the one-line estimation of variable parameters of synchronous machines, through the estimation and experimental verification process. Expression of the variable parameters.

Presents an on-line estimation variable parameter of synchronous machines by using the principles and procedures of a novel adaptive algorithm. Details on a Synthesized Information Factor (SIF) used as a novel adaptive algorithm; Procedures associated with adaptive estimation.

Presents an on-line fuzzy tuning scheme for indirect field-orientation (IFO)-controlled induction machine drives. Detuning of IFO drive systems; Enhancing of the efficiency and torque/ampere capability; Correction of the detuning effects of the IFO induction machine drives.

Presents a fuzzy logic design approach which can meet the speed tracking control of an indirect field-oriented induction machine drive, while discussing the field orientation (FOC) method. Detailed information on fuzzy control; What the FOC method entails; Discussion on the demand for the effects of a detuned FOC machine.

[Display omitted] Inferior diffusion capacity and insufficient acid density hinder the practical application of ZSM-48 zeolite. Finding a simple and practical strategy to simultaneously address these two defects remains a challenge. In response to this dilemma, we developed an unconventional seed-assisted synthesis strategy for Al-rich hierarchical ZSM-48 zeolite. This approach allows for achieving a broader range of silica to alumina ratio and accelerates the entire crystallization process through the selection of unconventional seeds. The synergy between the seed and organic template was demonstrated to play a pivotal role in facilitating nucleation. Direct evidence from 1H-29Si CP MAS NMR, TG, and IR results demonstrates that hexamethonium ions (HM2+) electrostatically adsorb at the defect sites on the seed, thereby promoting nucleation sites formation. Smaller seed crystals undergo more etching during the induction period, resulting in additional defects and enhanced nucleation ability. The obtained catalyst exhibits a diffusion time constant (Deff/L2) nine times that of conventional ZSM-48 zeolite when using p -xylene as a probe molecule. In m -xylene isomerization reaction, Al-rich hierarchical ZSM-48 demonstrates excellent stability along with higher selectivity and yield for p -xylene compared to typical ZSM-5 catalysts. Remarkably, long-term testing of 1000 h yields over 22.5 % of p -xylene, indicating the potential of this catalyst as an alternative for xylene isomerization reaction. This work not only advances the practical application process of ZSM-48 catalyst but also provides valuable insights for optimizing other zeolites. [ABSTRACT FROM AUTHOR]

A procedure to calculate maximum torque operating conditions for the inverter-fed induction machine is proposed in this paper. The proposed procedure minimizes the finite-element analysis computation load by identifying the variation range of stator current and slip frequency for the entire torque-speed map. Thus, the total calculation time for machine steady-state performance estimation can be significantly reduced. The effectiveness of the proposed procedure is validated by an experiment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

This article proposes a fixed switching frequency (FSF)-based improved model predictive control (MPC) for a five-level active neutral-point clamped (5L-ANPC) converter. Compared to the conventional MPC for 5L-ANPC converter, the proposed MPC significantly reduces the computational burden while ensuring the balance of dc-link and flying capacitor voltages. The proposed MPC optimally selects the control voltage vectors to reduce common mode voltage (CMV), leading to a small CMV of the converter. Using three voltage vectors action per control cycle in MPC, FSF is achieved. Steady-state and dynamic performances of the proposed MPC have been evaluated by experiments. The results verify the feasibility and effectiveness of the proposed MPC method. [ABSTRACT FROM AUTHOR]

The morphology control of zeolite has attracted extensive attention because of its close relationship with catalytic performance. How to control the crystal morphology of EUO zeolite on premise of low silica to alumina ratio is a challenging task. This study provides a novel route for controlling the morphology of Al-rich EUO zeolite via inter-zeolite transformation from Si-rich *MRE zeolite within 24 h. The morphology change from nanocrystals to coffin-like single crystal exhibits the merits of inter-zeolite transformation strategy in morphology control. Characterization tracking reveals that the deposition of aluminum species on parent *MRE zeolite is not uniform and migration between different precursors happens during the crystallization. No obvious mass transfer is observed between the liquid and solids after 2 h indicating it may follow a solid phase crystallization mechanism. Compared with conventional EUO samples, the EUO zeolite obtained by inter-zeolite transformation exhibits higher p-xylene selectivity. This approach not only provides a novel morphology control strategy for Al-rich EUO zeolite, but also promotes the understanding of the zeolite crystallization through inter-zeolite transformation route. A strategy for synthesis of coffin-like Al-rich EUO zeolite via inter-zeolite transformation route. [Display omitted] • Coffin-like Al-rich EUO crystals were obtained via inter-zeolite transformation route. • The whole crystallization could be completed within 24 h. • No obvious mass transfer was observed between the liquid and solids after 2 h. • The micro-sized EUO zeolite exhibited high p-xylene selectivity in the m-xylene isomerization reaction. [ABSTRACT FROM AUTHOR]

This article discusses a high-speed brushless doubly-fed machine (BDFM) for aviation turboelectric distributed propulsion application. After a brief overview of the machine fundamentals and propulsion architecture, the electromagnetic properties of the newly designed BDFM are analyzed. An innovative rotor mechanical design is introduced, which allows for a significant increase of speed compared to legacy rotor designs. Experiments were conducted to verify the 12 000-r/min high-speed operation. The findings in this article will give prominence to the feasibility of applying BDFMs for aviation applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical siliceous MFI zeolite was obtained by Al3+-assisted alkali-treatment route. • Inorganic B3+ and Al3+ directed the construction of suitable hierarchical structure. • Acid washing process preserved intrinsic micropores and enhanced VOC diffusion. • BHZ-AT2-AW2 showed high adsorption capacities for VOCs with different molecular sizes. • Construction of new silanol groups was found to contribute to the ethanol adsorption. Efficient removal of volatile organic compounds (VOCs) with different molecular sizes over a single zeolite remains a great challenge, especially under humid conditions. Here, we introduced an innovative base leaching strategy to construct hierarchical pores within high-silica MFI zeolite on premise of maintaining a similar high micropore volume. The key points were the introduction of Al3+ and B3+ as pore directing agents into the base solution and meticulous regulation of the acid washing process. Because of the introduction of mesopores, the adsorption capacities for m-xylene increased by 16.1 times compared to that on conventional MFI adsorbent. Meanwhile, it exhibited comparable adsorption capacities for smaller VOCs, including dichloromethane and toluene. The adsorption capacities for ethanol showed a notable increase, accompanied by a decrease in the desorption temperature. This was attributed to the generation of additional silanol adsorption sites, as confirmed by 1H MAS NMR and in situ FT-IR spectra. Moreover, the optimal adsorbent presented good regeneration performance throughout the four dynamic adsorption–desorption cycling tests for all VOCs. [ABSTRACT FROM AUTHOR]

This paper focuses on a novel modeling method for interior permanent-magnet (IPM) synchronous machines. This modeling method is based on a stator winding flux linkage table that is obtained from experimental testing. As indicated by the comparison between computer simulation and dyno testing, this modeling approach can model the nonlinear behavior of IPM synchronous machines with high fidelity without adding significant computational loads. [ABSTRACT FROM PUBLISHER]

An optimally designed ferrite permanent magnet (PM)-assisted synchronous reluctance machine (PMaSynRM) is presented to demonstrate its feasibility in electric vehicle applications. The Prius rare-earth interior PM machine is used as the benchmark, and through theoretical study and experimental testing, it is verified that the optimally designed PMaSynRM can achieve performance very close to that of the benchmark PM machine with much lower costs. [ABSTRACT FROM PUBLISHER]

[Display omitted] • ZSM-12 with various morphologies and acidity were synthesized. • Acid distribution of ZSM-12 is crucial to the alkylation performance. • More Brønsted acid sites in channel are beneficial to the high selectivity to p -TBEB. Para - tert -butyl ethylbenzene (p -TBEB) is an important polymer monomer raw material to produce poly (tert -butylstyrene). Achieving relatively high selectivity to p -TBEB (S p -TBEB) by shape selective alkylation of ethylbenzene with isobutylene is highly attractive, and it is crucial to clarify the major factors affecting S p -TBEB. Herein, ZSM-12 zeolites with various morphology or acid distribution were synthesized by altering alkalinity or structure directing agent (SDA). Despite different morphology of MTW(70)-M- x series samples using MTEACl as the SDA, they show similar catalytic performance in alkylation of ethylbenzene with isobutylene due to their similar acid distribution. On the other hand, MTW(1 0 0)-M-0.06 and MTW(1 0 0)-T with various morphology, synthesized with MTEACl and TEAOH as the SDA, respectively, exhibit quite different selectivity to the target product in this reaction. MTW(1 0 0)-M-0.06 has much higher S TBEB (87 % vs. 70 %) and S p -TBEB (95 % vs. < 60 %) than MTW(1 0 0)-T, which is attributed to that MTW(1 0 0)-M-0.06 possesses much more Brønsted acid sites distributed in the micropore channel. This provides a route to improve the selectivity to main product (TBEB, especially p -TBEB) of alkylation of ethylbenzene with isobutylene over ZSM-12 zeolite even other zeolites. [ABSTRACT FROM AUTHOR]

Core-shell ZSM-5@Silicalite-1 presents high para-selectivity in the alkylation reactions, however, its industrial application faces great challenges due to the lack of the efficient strategy for large-scale synthesis. In this work, we proposed a silicon twice-release synthesis route to prepare ZSM-5@Silicalite-1 and the corresponding H-type extruded catalyst can be acquired after sequential filtration, heating, extrusion, and calcination. Almost all aluminum (Al) sites were consumed after the initial hydrothermal crystallization with a partial silicon, hence, a further crystallization with remaining silicon led to a siliceous shell as evidenced by the TOF-SIMS characterization. Adding nano Silicalite-1 seed was demonstrated to be the key point for the crystal epitaxial growth during the silicon twice-release synthesis route. With the increase of silicon proportion in the second release, the selectivity of para -ethyltoluene presented a volcano-type variation trend with a maximum of 92.6 % and a minimum of 66.5 %; while the catalytic stability obviously decreased when the proportion was larger than 50 % ascribed to the poor accessibility of active sites. This work provides a facile protocol to prepare core-shell catalysts, which promotes their large-scale production and industrial application. [Display omitted] • A seed-directed silicon twice-release route was developed to prepare ZSM-5@Silicalite-1. • Adding minimal nano seed was the key role to avoid independence nucleation and growth. • The thickness of Silicalite-1 shell can be regulated by changing the Si feeding ratio. • A high para -ethyltoluene selectivity of 92.6 % can be acquired over the optimal catalyst. [ABSTRACT FROM AUTHOR]

High-frequency current responses of a permanent magnet synchronous machine (PMSM), with and without considering eddy current effects, are significantly different. This paper investigates the eddy current effects on rotor position estimation. A compensation method is developed to improve the high-frequency-injection-based rotor position estimation of a PMSM at zero and low speeds. The paper also contributes to an improved. magnetic pole identification based on space vector pulse width modulation for an arbitrary initial rotor position. The estimation and sensorless control method of PMSM, considering eddy current effects, has been verified by experimental results. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate the process of transformation of olefin into aromatics over HZSM-5, TPSR and pulse reaction were performed over HZSM-5, using alkenes, dienes and cycloolefins as reactants. The results illustrated that the initial step (i.e. the formation of diene or cycloolefin) in all hydrogen-transfer reactions during alkene aromatization could be carried out at temperatures lower than 200°C, while the further hydrogen-transfer reactions between dienes/cycloolefins and alkenes/cycloolefins, leading to the formation of aromatics required relatively higher temperatures. It is concluded that the formation of aromatics is a result of repeated adsorption–reaction–desorption of alkenes on various acid sites. Furthermore, the pathway of olefin aromatization was not by a single pathway. [Copyright &y& Elsevier]

Abstract: MCM-22 was employed as an effective adsorbent for removal of basic dyes including methylene blue, crystal violet, and rhodamine B from aqueous solution. The adsorption kinetics and isotherms were investigated. The adsorption capacity of MCM-22 for three dyes follows an order of MB>CV∼RB. Kinetic studies indicate that the adsorption follows the pseudo second-order kinetics and the adsorption is a two-step diffusion process with film diffusion dominating the process. The adsorption isotherm can be well fitted by both the Langmuir and the Freundlich models. Thermodynamic calculations suggest that the adsorption of basic dyes on MCM-22 is an endothermic reaction. [Copyright &y& Elsevier]

The role of acid strength of zeolites in liquid-phase alkylation of benzene with ethylene was studied over β, MCM-22, and USY zeolites by means of adsorbing NH3 at different temperatures. The strong acid sites are active centers, while the weak acid sites are inactive. The selectivity behavior of the strong acid sites varies with the relative acid strength as well as the types of the zeolites. [ABSTRACT FROM AUTHOR]

Solar photovoltaic (PV) energy sources are rapidly becoming more popular. The PV system output power relies on the applied current or voltage nonlinearity and there exist a unique point called the maximum power point (MPP). For effective energy extraction from the PV system, this paper presents a new controller design strategy to track the MPP of a PV system using a sliding mode control method of self-optimisation. The proposed controller design offers fast and accurate convergence to the MPP in steady state and during varying environmental conditions. A DC/DC boost converter is utilised as a control actuator for the MPP tracking using PWM control. Simulation and experimental results are provided to demonstrate the validity of the proposed controller design. [ABSTRACT FROM AUTHOR]

This article presents the design and development of a 7-kV dc bus, 1-MVA, 0–1000 Hz modular multilevel converter (MMC) prototype for high speed medium-voltage variable frequency drives. The system is designed based on 1.7-kV silicon carbide (SiC) mosfets. First, the full in-depth design of the prototype is provided, including the submodules, arm inductors, and system integration. Then, the unique control scheme and the control hardware design are presented to achieve the full-frequency range operation. The power loss based on Si and SiC devices is analyzed. Finally, experimental results are presented to demonstrate the performance of both the SiC-based submodule and the full-scale MMC system. Compared with the traditional Si-based solution, the established SiC MMC can reduce the drive system volume by 75% and achieve 325% power density, and the peak energy efficiency reaches around 99.35%. [ABSTRACT FROM AUTHOR]

When a four-level hybrid clamped converter (4L-HCC) operates at low frequencies, the high load current causes significant voltage fluctuations among the capacitors in the dc link. A mathematical model is developed to clarify the mechanism of excessive capacitor voltage fluctuations. An improved common-mode voltage injection algorithm is proposed and integrated to the overall control method. With the applied algorithm, the voltage fluctuation minimization of the dc-link capacitors and the dynamic voltage balancing capability are investigated. Both simulation and experimental results validate the effectiveness of the proposed algorithm, with a voltage fluctuation reduction over 50%. The 4L-HCC with the proposed algorithm achieves much faster dynamic response to converge the unbalanced capacitor voltages and the reduced output current harmonics compared with the conventional common-mode voltage injection algorithm. [ABSTRACT FROM AUTHOR]

An optimized model predictive control (MPC) method is proposed based on the selected switching states to control the four-level hybrid-clamped converter. The proposed method utilizes 64, instead of 512, switching states, compared with a conventional MPC, which greatly eases the calculation burden while achieving the high-quality regulation of output currents and the balance of capacitor voltages. The steady-state performance at both high and low frequencies is investigated, and results are compared with those by the traditional carrier phase-shifted pulsewidth modulation method. The dynamic response to the current or frequency step change is also evaluated. Both simulation and experimental results validate the feasibility and effectiveness of the optimized MPC method. [ABSTRACT FROM AUTHOR]

Without active control, the voltage fluctuations of the dc-link and flying capacitors in a 4-level hybrid-clamped converter (4L-HCC) become excessively large in low-frequency operation. This paper studies the switching state redundancy inherent in a 4L-HCC and proposes a new capacitor voltage balancing and stabilizing method to minimize the dc-link and flying capacitor voltage fluctuations. A straightforward algorithm is developed based on a logic table to select the suitable switching states. Verified by simulation and experimental testing results, the new method and algorithm virtually eliminate all the big voltage fluctuations of capacitors at low and zero frequencies, greatly enhancing the robustness and reliability of a 4L-HCC. The capacitor size can be reduced by more than 80% compared with the conventional method. [ABSTRACT FROM AUTHOR]