This paper proposes the switching strategy based on finite control set model predictive control (FCS-MPC) method, to reduce switching losses and obtain balanced loss distribution of the ...voltage-source inverters (VSIs). Unlike the conventional FCS-MPC method with no explicit information of the reference voltage, the developed voltage-based FCS-MPC scheme produces the future reference voltage vector with the Lyapunov function every sampling period. With information of both the future reference voltage and the future load current vectors, the proposed switching strategy instantaneously determines one optimum clamped phase among the three legs in the VSI every sampling period. By optimally determining the clamping phase and its duration on the basis of every sampling period, the proposed switching strategy can successfully reduce the VSI switching losses. In addition, the proposed switching method can yield a balanced loss distribution among the switches in the VSI, contrary to the conventional FCS-MPC. The balanced loss generation as well as the switching loss reduction by the proposed method, which is optimal at the sampling period scale, is directly incorporated with the platform of the FCS-MPC algorithm, since the FCS-MPC operates on the basis of the sampling period. Thus, the proposed switching operation based on the voltage-based FCS-MPC algorithm enables the future VSI output currents to track the future reference current vector, as well as results in the reduced switching losses and the balanced loss performance.
This paper proposes predictive-control-based direct power control (DPC) with an adaptive online parameter identification technique for ac-dc active front ends (AFEs) to overcome model mismatch and ...parameter uncertainty. Based on least-squares estimation, the input inductance and input resistance of the AFE are calculated every sampling period using sampled input currents and input voltages. Because the online-tuned input inductance and resistance are updated for the controller, the proposed predictive-control-based DPC with the adaptive parameter identification technique can mitigate performance degradation resulting from the model uncertainty of the model predictive controller without any additional sensors. Therefore, the AFE generates sinusoidal input currents with a unity power factor despite parameter uncertainty.
This paper proposes a novel method to reduce switching losses on the basis of a model-predictive direct power control (MPDPC) method for ac-dc active rectifiers. The main idea is to preselect voltage ...vectors to decrease switching losses at the next sampling period, and then select one optimum voltage vector among only the preselected voltage vectors to perform direct power control (DPC). The proposed vector preselection scheme enables a predefined cost function to consider only four vectors to control the real and the reactive power at every sampling period. The proposed MPDPC method using only the four preselected vectors stops switching operation of one leg exposed to the largest input current at every sampling period. On the basis of the preselected vectors at each sampling period, the proposed method can effectively reduce the switching losses, as well as accurately perform power control of the active rectifier.
2D layered materials with sensitive surfaces are promising materials for use in chemical sensing devices, owing to their extremely large surface‐to‐volume ratios. However, most chemical sensors based ...on 2D materials are used in the form of laterally defined active channels, in which the active area is limited to the actual device dimensions. Therefore, a novel approach for fabricating self‐formed active‐channel devices is proposed based on 2D semiconductor materials with very large surface areas, and their potential gas sensing ability is examined. First, the vertical growth phenomenon of SnS2 nanocrystals is investigated with large surface area via metal‐assisted growth using prepatterned metal electrodes, and then self‐formed active‐channel devices are suggested without additional pattering through the selective synthesis of SnS2 nanosheets on prepatterned metal electrodes. The self‐formed active‐channel device exhibits extremely high response values (>2000% at 10 ppm) for NO2 along with excellent NO2 selectivity. Moreover, the NO2 gas response of the gas sensing device with vertically self‐formed SnS2 nanosheets is more than two orders of magnitude higher than that of a similar exfoliated SnS2‐based device. These results indicate that the facile device fabrication method would be applicable to various systems in which surface area plays an important role.
A novel approach for fabricating self‐formed active‐channel devices based on 2D semiconductor materials with very large surface areas is proposed and their potential gas sensing ability is examined. The device exhibits extremely high response values and this novel fabrication method is expected to find use in various applications where surface area plays an important role in function.
This paper proposes a predictive control method with zero-sequence voltage injection to efficiently reduce the switching losses of three-phase voltage source inverters (VSIs). In the proposed ...predictive control method, three-phase future voltage references modified by a zero-sequence voltage injection are generated to clamp one of the three legs with the largest load current. Furthermore, the future zero-sequence voltage, which is produced online with the future voltage and current references in every sampling period, optimally adjusts the clamping duration on each leg, depending on the load angle. In addition, the proposed method selects the zero vector on the basis of the polarity of the future zero-sequence voltage to reduce the switching losses. Using a predefined cost function, the proposed predictive control scheme chooses one optimal voltage state closest to the future voltage references modified by the zero-sequence voltage injection. Therefore, the proposed predictive control method can perform load current control and minimize the switching losses of the VSI under any load condition regardless of the load angle.
To date, the in situ fabrication of the large‐scale van der Waals multi‐heterojunction transition metal dichalcogenides (multi‐TMDs) is significantly challenging using conventional deposition ...methods. In this study, vertically stacked centimeter‐scale multi‐TMD (MoS2/WS2/WSe2 and MoS2/WSe2) thin films are successfully fabricated via sequential pulsed laser deposition (PLD), which is an in situ growth process. The fabricated MoS2/WS2/WSe2 thin film on p‐type silicon (p‐Si) substrate is designed to form multistaggered gaps (type‐II band structure) with p‐Si, and this film exhibits excellent spatial and thickness uniformity, which is verified by Raman spectroscopy. Among various application fields, MoS2/WS2/WSe2 is applied to the thin‐film catalyst of a p‐Si photocathode, to effectively transfer the photogenerated electrons from p‐Si to the electrolyte in the photo‐electrochemical (PEC) hydrogen evolution. From a comparison between the PEC performances of the homostructure TMDs (homo‐TMDs)/p‐Si and multi‐TMDs/p‐Si, it is demonstrated that the multistaggered gap of multi‐TMDs/p‐Si improves the PEC performance significantly more than the homo‐TMDs/p‐Si and bare p‐Si by effective charge transfer. The new in situ growth process for the fabrication of multi‐TMD thin films offers a novel and innovative method for the application of multi‐TMD thin films to various fields.
A multihetero MoS2/WS2/WSe2 thin film with a multistaggered gap is directly fabricated on p‐Si by an in situ growth process using sequential pulsed laser deposition. The built‐in electric field generated by the multistaggered gap facilitates the effective transfer of the photogenerated electrons to the electrolyte in photo‐electrochemical hydrogen evolution.
Photoelectrochemical (PEC) biomass oxidation by the substitution of an oxygen evolution reaction is considered a promising strategy for efficient hydrogen production. Among the biomass derivatives, ...glycerol, which is a by-product of biodiesel, is an attractive alternative to water because it is easily oxidized at a potential lower than that of water. In this work, we report a novel CeO2-decorated Ce-doped ZnO nanowire (NW) photoanode, fabricated via hydrothermal and pulsed laser deposition processes, for efficient PEC glycerol oxidation and hydrogen production. The Ce dopant in the ZnO array improves the charge separation, light-harvesting, and adsorption of glycerol, by providing oxygen vacancies and active sites for PEC water splitting by glycerol. The operation stability of our CeO2-decorated Ce-doped ZnO NW photoanode is enhanced and its photocurrent density is retained even after 10 h. In addition, the amount of evolved hydrogen produced by the CeO2/Ce-doped ZnO photoelectrode is two times higher than that of a bare ZnO electrode. Through our results, we confirm the efficient hydrogen evolution via Ce utilization.
This paper proposes two model predictive current control (MPCC) methods utilizing two output voltages with variable application durations in one sampling period to control the output currents of ...single-phase voltage source inverters (VSIs). In the proposed methods, the application durations of the two voltages, as well as the selection of two output voltages used in the future sampling period, are determined by an optimization process to minimize current error inside the future sampling period and to eliminate current error at the end of the future sampling instant. By utilizing the two voltages with variable durations, the two proposed MPCC methods can reduce steady-state current errors and decrease output current ripples without increasing the sampling frequency in comparison with the conventional MPCC method, despite only three distinctive output voltages being allowed in the single-phase VSI. The two proposed methods along with the conventional MPCC method are compared in terms of current errors and total harmonic distortion. The effectiveness of the two proposed methods for the single-phase VSIs is verified with both simulation and experimental results.
Tin sulphide compounds have two different types of 2D layered crystal structures with different electrical conduction types. Tin disulphide with n-type semiconductor characteristics has a 2D crystal ...structure with hexagonal symmetry, while tin monosulphide (SnS) with p-type semiconductor characteristics has a 2D crystal structure with orthorhombic symmetry. These layered materials have many potential applications such as electronic and optoelectronic devices. Meanwhile, it is known that the growth products of tin sulphides are very sensitive to the process parameters. In this study, the authors investigated the growth phenomena of tin sulphides by the vapour transport method using SnS and sulphur powders because vapour transport reactions are relatively simple and facilitate the understanding of the effects of growth parameters. The growth behaviour of tin sulphides as a function of process temperature and pressure was observed, and the results can be explained in terms of the sulphurisation and reduction of SnS powder during the growth process.
Abstract
Antiferromagnetic-paraelectric SrMnO
3
(SMO) has aroused interest because of the theoretical strong coupling between the ferroelectric and ferromagnetic states with increasing epitaxial ...strain. In strained SMO films, the polarized state and polar distortions have been observed, although high leakage currents and air degradation have limited their experimental verification. We herein provide a conclusive demonstration of room-temperature ferroelectricity and a high dielectric constant (
ε
r
= 138.1) in tensile-strained SMO by securing samples with insulating properties and clean surfaces using selective oxygen annealing. Furthermore, a paraelectricity and low dielectric constant (
ε
r
= 6.7) in the strain-relaxed SMO film have been identified as properties of the bulk SMO, which directly proves that the ferroelectricity of the tensile-strained SMO film is due to strain-induced polarization. We believe that these findings not only provide a cornerstone for exploring the physical properties of multiferroic SMO but also inspire new directions for single-phase multiferroics.
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