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The problem of submodule switching frequency reduction in half‐bridge modular multilevel converters (HB‐MMCs) with capacitor voltage self‐balancing control is considered and explored in this paper. A selection principle of submodule switching state vectors is proposed based on the voltage self‐balancing switching state matrix, aiming to lower submodule switching frequency and device losses. The relationship between system stability and submodule switching signals is revealed according to the capacitor voltage self‐balancing characteristics, and the full‐rank constraints on the voltage self‐balancing switching state matrix are proposed. Considering the tradeoff between switching loss and capacitor voltage fluctuation, the evaluation indexes of voltage self‐balancing control effect are determined. The selection principle of submodule switching state vectors and the optimized construction method of switching state matrix are presented. Voltage self‐balancing HB‐MMC models are built in MATLAB/Simulink, and it is verified that the submodule switching state vector selection principle proposed in this study can effectively reduce switching frequency while meeting the evaluation requirements of practical engineering projects, so as to achieve the balance between switching loss and steady‐state capacitor voltage fluctuation. [ABSTRACT FROM AUTHOR]

With the increasing proportion of renewable power generations in the power system, the power grid impedance may fluctuate greatly, and it is difficult for the virtual synchronous generator (VSG) with a single control structure to meet the stability requirements. Thus, the control principles of the two types of VSGs are compared to conclude that there are similarities in the control structure of the two VSGs. And the small signal models of the two types of VSGs are established to analyze the stability boundaries, coming to the conclusion that the stability region is complementary. Based on the conclusions, the paper puts forward the idea of switching operation modes: switch to the U‐VSG mode when the grid strength weakens and switch to the PQ‐VSG mode when greater, so that the inverter can keep stable in a wider range of grid strength. Therefore, the characterization method of the switching boundary with hysteresis properties is proposed. Then the improved recursive least squares (RLS) algorithm is introduced to identify the power grid impedance online without additional injected disturbance, based on which the adaptive multi‐mode smooth switching control strategy is proposed. Finally, the effectiveness of the analysis and the control strategy are verified by simulations. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Ammonia (NH3) is one of the most important industrial feedstocks in the fields of fertilizers, drugs, explosives, ordnance, commercial cleanings, and so on. However, the features of ammonia such as high toxicity and corrosivity, and difficulty in handling would inevitably increase the risk of environmental damage and the deterioration of natural/public lands. Although sorts of solid adsorbents such as metal oxides, zeolites, organic polymers, activated carbons, and metal organic frameworks have been applied in NH3 capture, they still show low uptake capacity, low affinities, and instability. Herein, we developed the first case of a highly stable sulfuric acid covalent organic framework (COF), namely TpBD‐(SO3H)2, as NH3 capturer, in which sulfonic acid sites can strongly interact with NH3 molecules, and enhance the performance of NH3 sorption. As a result, TpBD‐(SO3H)2 shows high chemical stability under strong acid and water conditions, an important merit for the potential application in harsh environment. And it also exhibits high ammonia capacity of 11.5 mmol·g−1 at 298 K and 1.0 bar, making it one of the best in all chemically stable NH3 adsorbents up to date. This work thus develops sulfuric acid COF materials as a new platform for ammonia capture and storage. [ABSTRACT FROM AUTHOR]

Traditional fermented foods and beverages (TFFB) are an important dietary component consumed in large quantities worldwide. Currently, much attention has been focused on the health benefits of TFFB. Melanoidins, a class of bioactive substance produced in the final stage of the Maillard reaction, not only have a significant impact on sensory properties of TFFB but also contribute to the health effects. Melanoidins formed in the fermentation system with a long reaction time at low temperature could be different from those obtained from high‐temperature, short‐duration roasted systems due to the multiple formative stages and involvement of microorganisms and enzymes. In this paper, the current state of knowledge regarding the formation, distribution, extraction and purification, physicochemical properties, structure characteristics, and biological activities of TFFB melanoidins are comprehensively reviewed, with predominant focus on TFFB that are typically brown like douchi, miso, cheonggukjang, soy sauce, huangjiu (Chinese rice wine), beer, vinegar, and sweet wine. The current challenges and prospective recommendations for the research of melanoidins in fermented systems are also presented. In future, people should pay more attention to the basic research on TFFB melanoidins, especially purification methods and formation mechanisms, further substantiation of health properties of TFFB melanoidins in vivo, and development of specific melanoidins to fulfill technological, productive, or health needs of consumers. [ABSTRACT FROM AUTHOR]

Li‐ion hybrid supercapacitors (LHSCs) are intensely studied due to their favorable power densities. However, combined higher energy density materials, particularly anodes, are desirably sought. Herein, a defect‐dominating structure protocol is reported. Specifically, two visible structural defects, i.e., crystal vacancy and lattice distortion have been introduced in situ in ultrafine niobium nitride (NbN) monocrystals that are integrated into a carbon (C) framework. Highly reversible Li‐ion storage capacities up to 540 mAh g−1 are demonstrated in such a NbN@C composite anode, together with excellent rate capability and cycling stability. An extra vacancy‐induced capacity contribution of the defective NbN component is evidenced by first‐principles density functional theory (DFT) simulations in contrast to perfect modeling. Coupling with an activated carbon (AC) cathode, the NbN@C//AC cell can deliver balanced energy and power densities of 53.8 Wh kg−1 and 7818 W kg−1 at 4 A g−1, and retain a desired energy density of 56.1 Wh kg−1 after 10 000 cycles at 1 A g−1. Findings from this study, particularly the demonstrated defects‐induced extra capacity of pseudocapacitive materials, may inspire new structural material designs of LHSCs. [ABSTRACT FROM AUTHOR]

Element doping/alloying is a common strategy to tune the electrical and thermal transports of thermoelectric (TE) materials, but the doping/alloying limit of foreign elements in many TE materials is usually very low, bringing a great challenge to improve the TE performance. In this work, beyond the classic principle of “like dissolves like,” it is found that choosing the compound with a severely distorted lattice and diversified chemical bonding as the matrix also facilitates achieving a high doping/alloying limit. Taking ductile semiconductors as an example, this work shows that gold (Au) element is nearly immiscible in Ag2S and Ag2Te, but has a relatively high alloying limit in complex Ag2S0.5Te0.5 meta‐phase. Au in Ag2S0.5Te0.5 significantly decreases the carrier concentration and improves the TE performance, but scarcely changes the mechanical properties. Consequently, Ag1.99Au0.01S0.5Te0.5 demonstrates both a high figure‐or‐merit of 0.95 at 550 K and extraordinary room‐temperature ductility. This work offers an effective and general strategy to develop stabilized doped/alloyed TE materials. [ABSTRACT FROM AUTHOR]

Herein, we firstly develop porous organic cage (POC) as an efficient platform for highly effective radioactive iodine capture under industrial operating conditions (typically ≥150 °C), ≤150 ppmv of I2). Due to the highly dispersed and readily accessible binding sites as well as sufficient accommodating space, the constructed NKPOC‐DT‐(I−) (NKPOC=Nankai porous organic cage) demonstrates a record‐high I2 uptake capacity of 48.35 wt % and extraordinary adsorption capacity of unit ionic site (~1.62) at 150 °C and 150 ppmv of I2. The I2 capacity is 3.5, 1.6, and 1.3 times higher than industrial silver‐based adsorbents Ag@MOR and benchmark materials of TGDM and 4F‐iCOF‐TpBpy‐I− under the same conditions. Furthermore, NKPOC‐DT‐(I−)Me exhibits remarkable adsorption kinetics (k1=0.013 min−1), which is 1.2 and 1.6 times higher than TGDM and 4F‐iCOF‐TpBpy‐I− under the identical conditions. NKPOC‐DT‐(I−)Me thus sets a new benchmark for industrial radioactive I2 adsorbents. This work not only provides a new insight for effectively enhancing the adsorption capacity of unit functional sites, but also advances POC as an efficient platform for radioiodine capture in industry. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Ammonia (NH3) is one of the most important industrial feedstocks in the fields of fertilizers, drugs, explosives, ordnance, commercial cleanings, and so on. However, the features of ammonia such as high toxicity and corrosivity, and difficulty in handling would inevitably increase the risk of environmental damage and the deterioration of natural/public lands. Although sorts of solid adsorbents such as metal oxides, zeolites, organic polymers, activated carbons, and metal organic frameworks have been applied in NH3 capture, they still show low uptake capacity, low affinities, and instability. Herein, we developed the first case of a highly stable sulfuric acid covalent organic framework (COF), namely TpBD‐(SO3H)2, as NH3 capturer, in which sulfonic acid sites can strongly interact with NH3 molecules, and enhance the performance of NH3 sorption. As a result, TpBD‐(SO3H)2 shows high chemical stability under strong acid and water conditions, an important merit for the potential application in harsh environment. And it also exhibits high ammonia capacity of 11.5 mmol·g−1 at 298 K and 1.0 bar, making it one of the best in all chemically stable NH3 adsorbents up to date. This work thus develops sulfuric acid COF materials as a new platform for ammonia capture and storage. [ABSTRACT FROM AUTHOR]