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DC(Direct Current) droop control has the advantages of plug-and-play and the convenience of parallel operation of multiple converters. However, when the power changes drastically, the DC voltage may be too low. This paper proposes a converter control method based on schedulable variable droop coefficient to maintain voltage stability when the power changes drastically. The dual-machine parallel system is simulated on MATLAB/Simulink, and compared with the traditional DC droop control, the effectiveness of the proposed method is verified.

Due to the increases of renewable energy penetration and share of power electronic devices in the power system, Grid-forming (GFM) control methods have become one of the most important technology for the power systems with a high proportion of new energy resources. To improve the control performance of the VSC (Voltage Source Converter), a novel GFM control method based on negative imaginary theory is proposed in this paper. Firstly, the typical structure of distributed energy system is analyzed. Then, the negative imaginary characteristic of VSC’s mathematical model is proved and a negative imaginary controller (NIC) is designed. Finally, the effectiveness and feasibility of the proposed control method are verified by simulation results through MATLAB/Simulink.

Because of the rapid development of power electronics, DC loads, and distributed energy resources, the advantages of DC distribution systems are increasingly prominent. This paper provides a brief description of the concepts and functional advantages of DC distribution systems, introducing the main equipment of multi-terminal DC (MTDC) distribution system, the topologies, and the typical application scenarios of each topology. The coordinated control technology of MTDC distribution system is analysed and summarized in terms of control architecture, coordinated control, damping control, and operation mode. The existing MTDC distribution demonstration projects are summarized, and recent typical projects are introduced. Finally, the issues that can be studied regarding to the innovation and application of MTDC distribution system are pointed out.

Grid-forming (GFM) converters can provide inertia support for power grids through control technology, stabilize voltage and frequency, and improve system stability, unlike traditional grid-following (GFL) converters. Therefore, in future “double high” power systems, research on the control technology of GFM converters will become an urgent demand. In this paper, we first introduce the basic principle of GFM control and then present five currently used control strategies for GFM converters: droop control, power synchronization control (PSC), virtual synchronous machine control (VSM), direct power control (DPC), and virtual oscillator control (VOC). These five strategies can independently establish voltage phasors to provide inertia to the system. Among these, droop control is the most widely used strategy. PSC and VSM are strategies that simulate the mechanical characteristics of synchronous generators; thus, they are more accurate than droop control. DPC regulates the active power and reactive power directly, with no inner current controller, and VOC is a novel method under study using an oscillator circuit to realize synchronization. Finally, we highlight key technologies and research directions to be addressed in the future.

Fucoidan and laminarin are polymolecular compounds that extracted from seaweed. As functional polysaccharides, they possess various biological functions such as immunomodulatory, anti-inflammatory, antiviral and antioxidant bioactivities. Fucoidan and laminarin modulate host immune responses by activating immune cells (macrophages, neutrophils, T lymphocytes) and inducing the expression of cytokines (TNFα, IL-1β, IL-6, IL-8, NF-κB). Intelectin is a novel lectin that plays important roles in bacterial agglutination and bactericidal effects by recognizing the polysaccharide components on the cell surface of pathogens, which can also enhance the phagocytosis of macrophages. The present study intends to explore the immunomodulatory effects of fucoidan, laminarin and intelectin on the macrophages of Megalobrama amblycephala. The results showed that the incubation of both fucoidan and laminarin at the concentration of 100 μg/mL for 4 h could enhance the phagocytic capacity of M. amblycephala macrophages, which also showed remodeled cytoskeleton with extended pseudopodia. In addition, fucoidan and laminarin could induce the expression of M. amblycephala intelectin (MaINTL) in the primary hepatocytes and macrophages, and the recombinant MaINTL (rMaINTL) could bind with fucoidan and laminarin. Furthermore, fucoidan and laminarin induced the expression of cytoskeletal remodeling related genes in the primary M. amblycephala macrophages, such as Rac1 and WASP, which should contribute to the enhancement of seaweed polysaccharides (fucoidan and laminarin) and MaINTL on the phagocytosis of M. amblycephala macrophages. However, even though fucoidan and laminarin could induced the expression of CXCL8, while the chemotaxis of M. amblycephala macrophages on neutrophils was not affected by them. These findings suggested that fucoidan and laminarin enhanced the phagocytic capacity of M. amblycephala macrophages via activation of MaINTL and up-regulation of the expression of downstream cytoskeletal remodeling related genes Rac1 and WASP. Therefore, fucoidan and laminarin could be used as immune enhancers to improve host immunity and disease resistance in M. amblycephala, which provided novel insights into the prevention and protection of fish bacterial diseases.

Sexual maturation provides economically important traits in poultry production. Research on the initiation mechanism of sexual maturity is of great significance for breeding high-yield laying hens. However, the underlying mechanisms are not fully clear. Here, one hundred and fifty Chahua No. 2 laying hens (the CH2 group, which has precocious puberty) and one hundred and fifty Wu Liang Shan black-bone laying hens (the WLS group, a late-maturing chicken breed) with similar weights and ages were randomly selected. ELISA was used to determine the secretion levels of luteinizing hormone (LH), estradiol (E2), and progesterone (P4) in 150-day-old serum and small yellow follicle (SYF) tissues. A histology examination, immunohistochemistry, and quantitative real-time PCR (qPCR) were used to explore the molecular mechanism of how some genes related to oxidative stress affect sexual maturation. The results showed that the secretion levels of LH, E2, and P4 in the CH2 group serum and SYF were higher than those in the WLS group. The results of the real-time PCR of all genes showed that the expression levels of cytochrome P450 family 11 subfamily A member 1, steroidogenic acute regulatory protein, follicle-stimulating hormone receptor, and cytochrome P450 family 19 subfamily A member 1 in the CH2 group were significantly higher than those in the WLS groups (p < 0.001). Untargeted metabolomics combined with multivariate statistical analysis was used to identify biomarkers of SYF tissues in the CH2 and WLS groups. A trajectory analysis of the principal component analysis (PCA) results showed that the samples within the group were clustered and that the samples were dispersed between the CH2 and the WLS groups, indicating that the results of the measured data were reliable and could be used for further research. Further analysis showed that a total of 319 metabolites in small yellow follicles of the CH2 and WLS groups were identified, among which 54 downregulated differential metabolites were identified. These 54 metabolites were found as potential CH2 biomarkers compared with WLS at 150 days, and the different expressions of L-arginine, L-prolinamide, (R)-4-hydroxymandelate, glutathione, and homovanillic acid were more significant. Twenty metabolic pathways were found when significantly differential metabolites were queried in the KEGG database. According to the impact values of the metabolic pathways, eighteen differential metabolites belonged to the mTOR signaling pathway, glutathione metabolism, ABC transporters, the cell ferroptosis pathway, and D-arginine and D-ornithine metabolism. Interestingly, we identified that the cell ferroptosis pathway played an important role in chicken follicle selection for the first time. The histology and immunohistochemistry of SYF showed that the number of granulosa cells increased in the CH2 groups and the expression levels of glutathione peroxidase 4, tumor protein p53, ribosomal protein S6 kinase, and sterol regulatory element binding protein 1 in the granulosa cell layer were upregulated in the CH2 group at the time of sexual maturation. Furthermore, we also speculated that the antioxidant system may play an indispensable role in regulating sexual maturity in chickens. Overall, our findings suggest differentially expressed metabolites and metabolic pathways between CH2 and WLS chickens, providing new insights into the initiation mechanism of sexual maturation.