Showing papers by "Beihang University published in 2022"

Modeling and Advanced Control of Dual-Active-Bridge DC–DC Converters: A Review

Abstract: This article classifies, describes, and critically compares different modeling techniques and control methods for dual-active-bridge (DAB) dc–dc converters and provides explicit guidance about the DAB controller design to practicing engineers and researchers. First, available modeling methods for DAB including reduced-order model, generalized average model, and discrete-time model are classified and quantitatively compared using simulation results. Based on this comparison, recommendations for suitable DAB modeling method are given. Then, we comprehensively review the available control methods including feedback-only control, linearization control, feedforward plus feedback, disturbance-observer-based control, feedforward current control, model predictive current control, sliding mode control, and moving discretized control set model predictive control. Frequency responses of the closed-loop control-to-output and output impedance are selected as the metrics of the ability in voltage tracking and the load disturbance rejection performance. The frequency response plots of the closed-loop control-to-output transfer function and output impedance of each control method are theoretically derived or swept using simulation software PLECS and MATLAB. Based on these plots, remarks on each control method are drawn. Some practical control issues for DAB including dead-time effect, phase drift, and dc magnetic flux bias are also reviewed. This article is accompanied by PLECS simulation files of the reviewed control methods.

Engineering Metallic Heterostructure Based on Ni ₃ N and 2M‐MoS ₂ for Alkaline Water Electrolysis with Industry‐Compatible Current Density and Stability

Abstract: Alkaline water electrolysis is commercially desirable to realize large-scale hydrogen production. Although nonprecious catalysts exhibit high electrocatalytic activity at low current density (10-50 mA cm-2 ), it is still challenging to achieve industrially required current density over 500 mA cm-2 due to inefficient electron transport and competitive adsorption between hydroxyl and water. Herein, the authors design a novel metallic heterostructure based on nickel nitride and monoclinic molybdenum disulfide (Ni3 N@2M-MoS2 ) for extraordinary water electrolysis. The Ni3 N@2M-MoS2 composite with heterointerface provides two kinds of separated reaction sites to overcome the steric hindrance of competitive hydroxyl/water adsorption. The kinetically decoupled hydroxyl/water adsorption/dissociation and metallic conductivity of Ni3 N@2M-MoS2 enable hydrogen production from Ni3 N and oxygen evolution from the heterointerface at large current density. The metallic heterostructure is proved to be imperative for the stabilization and activation of Ni3 N@2M-MoS2 , which can efficiently regulate the active electronic states of Ni/N atoms around the Fermi-level through the charge transfer between the active atoms of Ni3 N and MoMo bonds of 2M-MoS2 to boost overall water splitting. The Ni3 N@2M-MoS2 incorporated water electrolyzer requires ultralow cell voltage of 1.644 V@1000 mA cm-2 with ≈100% retention over 300 h, far exceeding the commercial Pt/C║RuO2 (2.41 V@1000 mA cm-2 , 100 h, 58.2%).

Influences of joint action of natural and social factors on atmospheric process of hydrological cycle in Inner Mongolia, China

Abstract: The atmospheric process of a hydrological cycle is an important factor in the regional hydrological cycle, which determines dry-wet conditions in the region. In recent years, droughts have occurred frequently and covered a wide area in Inner Mongolia Autonomous Region, China, so the study of the atmospheric hydrological cycle in this region is vitally important for drought control. Drivers of different factors were identified by utilizing a geographical detector, especially influences of human activities in the region. Finally, mechanisms of mutual feedback between a nature-society coupling system and the atmospheric hydrological cycle were analyzed. The results demonstrate that 1) The characteristics of atmospheric water resources in Inner Mongolia have high spatial differences and their distribution are uneven. 2) The precipitation conversion efficiency in the region is dominated by the natural system, and the driving action of the nature-society coupling system formed after combining with the social system is stronger. The dominant drivers of the precipitation conversion efficiency in each subregion after partition are related to the ecological stability thereof. This study provides a scientific basis for identifying driving mechanisms of and preventing disasters in the atmospheric process of the water vapor cycle in Inner Mongolia Autonomous Region.

Influences of joint action of natural and social factors on atmospheric process of hydrological cycle in Inner Mongolia, China

Abstract: The atmospheric process of a hydrological cycle is an important factor in the regional hydrological cycle, which determines dry-wet conditions in the region. In recent years, droughts have occurred frequently and covered a wide area in Inner Mongolia Autonomous Region, China, so the study of the atmospheric hydrological cycle in this region is vitally important for drought control. Drivers of different factors were identified by utilizing a geographical detector, especially influences of human activities in the region. Finally, mechanisms of mutual feedback between a nature-society coupling system and the atmospheric hydrological cycle were analyzed. The results demonstrate that 1) The characteristics of atmospheric water resources in Inner Mongolia have high spatial differences and their distribution are uneven. 2) The precipitation conversion efficiency in the region is dominated by the natural system, and the driving action of the nature-society coupling system formed after combining with the social system is stronger. The dominant drivers of the precipitation conversion efficiency in each subregion after partition are related to the ecological stability thereof. This study provides a scientific basis for identifying driving mechanisms of and preventing disasters in the atmospheric process of the water vapor cycle in Inner Mongolia Autonomous Region.

Materials, physics and systems for multicaloric cooling

Abstract: Calls to minimize greenhouse gas emissions and demands for higher energy efficiency continue to drive research into alternative cooling and refrigeration technologies. The caloric effect is the reversible change in temperature and entropic states of a solid material subjected to one or more fields and can be exploited to achieve cooling. The field of caloric cooling has undergone a series of transformations over the past 50 years, bolstered by the advent of new materials and devices, and these developments have contributed to the emergence of multicalorics in the past decade. Multicaloric materials display one or more types of ferroic order that can give rise to multiple field-induced phase transitions that can enhance various aspects of caloric effects. These materials could open up new avenues for extracting heat and spearhead hitherto unknown technological applications. In this Review, we survey the emerging field of multicaloric cooling and explore state-of-the-art caloric materials and systems (devices) that are responsive to multiple fields. We present our vision of the future applications of multicaloric and caloric cooling and examine key factors that govern the overall system efficiency of the cooling devices. Multicaloric cooling promises environmentally friendly and high-efficiency refrigeration. In this Review, the authors discuss emerging multicaloric materials and their physics involving coexisting ferroic order parameters, examine key factors that govern the overall system efficiency of potential multicaloric devices and envision future applications.

Enhanced Internal Electric Field in S-doped BiOBr for Intercalation, Adsorption and Degradation of Ciprofloxacin by Photoinitiation

Abstract: A photocatalyst of layered structural BiOBr doped with sulfur (S-BiOBr) was synthesized using a facile hydrothermal method. X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and density functional theory calculation revealed that S-BiOBr consisted of covalent [Bi2O2S]2+ layer and exchangeable bromide ions [Br2]2-. The specific layered structure of S-BiOBr exhibited excellent performance for the intercalation, adsorption and photocatalytic degradation of ciprofloxacin (CIP) by forming interlayer [Bi2O2S]2+--OOC-R complexes. Furthermore, the internal electric field enhanced by polarization effects in the [Bi2O2S]2+ layer was conducive to a lasting electron transfer in the dark condition after photoactivation. The electron of R• radical derived from oxidizing [Bi2O2S]-OOC-R persistently migrated to the S-BiOBr surface and was trapped by O2 to form O2•-, facilitating the degradation of CIP in the dark. Hence, the degradation of CIP could be realized by utilizing the R• radical triggered through transient photoinitiation with low optical energy consumption.

Artificial tactile perception smart finger for material identification based on triboelectric sensing

Abstract: Tactile perception includes the direct response of tactile corpuscles to environmental stimuli and psychological parameters associated with brain recognition. To date, several artificial haptic-based sensing techniques can accurately measure physical stimuli. However, quantifying the psychological parameters of tactile perception to achieve texture and roughness identification remains challenging. Here, we developed a smart finger with surpassed human tactile perception, which enabled accurate identification of material type and roughness through the integration of triboelectric sensing and machine learning. In principle, as each material has different capabilities to gain or lose electrons, a unique triboelectric fingerprint output will be generated when the triboelectric sensor is in contact with the measured object. The construction of a triboelectric sensor array could further eliminate interference from the environment, and the accuracy rate of material identification was as high as 96.8%. The proposed smart finger provides the possibility to impart artificial tactile perception to manipulators or prosthetics.

Synergistic effect in ultrafine PtNiP nanowires for highly efficient electrochemical hydrogen evolution in alkaline electrolyte

Abstract: Platinum-based catalysts play an important role in electrochemical hydrogen evolution reaction, which is a renewable and clean way to produce H2. Herein, we have successfully synthesized the ultrafine PtNiP NWs with diameter less than 5 nm via a simple two-step hydrothermal reaction method. Impressively, the PtNiP NWs exhibit one of the best electrocatalytic activity toward HER under alkaline conditions, which can reach current density of 500 mA cm−2 only at the −0.153 V vs RHE with Tafel slop of only 30 mV dec−1. The DFT calculation results show synergistic effect of Pt, Ni and P atoms, where Ni atoms are conducive to the adsorption of H2O and P atoms are helpful for the dissociation of H2O, significantly improving kinetic processes of hydrogen evolution reaction. This work could be instructive and meaningful to design highly efficient and stable HER catalyst in alkaline condition for practical applications.