An optimal full frequency control strategy for the modular multilevel matrix converter based on predictive control

The modular multilevel matrix converter (M3C) is a promising topology for high-voltage high-power applications. Recent researches have proved its significant advantages for adjustable-speed motor drives compared with the back-to-back modular multilevel converter (MMC). However, the branch energy balancing in the M3C presents great challenge especially at critical-frequency points where the output frequency is close to zero or grid-side frequency. Generally, this balancing control depends on the appropriate injection of inner circulating currents and the common-mode voltage (CMV) whereas their values are hard to determine and optimize. In this paper, an optimization based predictive control method is proposed to calculate the required circulating currents and the CMV. The proposed method features a broad-frequency range balancing of capacitor-voltages and no reactive power in the grid side. For operation at critical-frequency points, there is no increase on branch voltage stresses and limited increase on branch current stresses. A downscaled M3C system with 27 cells is designed and experiment results with the R-L load and induction motor load are presented to verify the proposed control method

A branch current reallocation based energy balancing strategy for the modular multilevel matrix converter operating around equal frequency

The Modular multilevel matrix converter (M3C) is a promising topology for medium-voltage, high-power applications. Due to the modular structure, it is scalable, produces high quality output waveforms and can be fault tolerant. However, the M3C suffers from capacitor-voltage fluctuation if the output frequency is similar to the input frequency. This problem could limit the circuit’s application in the adjustable speed drives (ASD). This paper introduces a theoretical analysis in the phasor-domain to find the branch energy equilibrium point of the M3C when operating with equal input and output frequencies. On the basis of this equilibrium point, a branch current reallocation based energy balancing control method is proposed to equalize the energy stored in the nine converter branches. With this novel control method, the M3C can effectively overcome the capacitor voltage fluctuation without using balancing techniques based on common mode voltage or applying reactive power at the input side

Late Neoarchean subduction-related crustal growth in the Northern Liaoning region of the North China Craton : evidence from ∼2.55-2.50 Ga granitoid gneisses

This study is financially supported by the National Natural Science Foundation of China (Grant Nos. 41272209, 41472165, 41502179, 41530207) and the Central University Basic Scientific Research Business Expenses of China University of Geosciences (Beijing) (Grant No. 2652015038).The North China Craton (NCC), dominated by ∼2.6-2.5 Ga tectonothermal events, provides a natural laboratory to study Neoarchean crustal growth and geodynamic evolution. Late Neoarchean granitoid gneisses are well exposed in the Northern Liaoning Province, located north of the ancient Anshan-Benxi terrane along the northeastern margin of the Eastern Block (EB) of the NCC. LA-ICPMS zircon U-Pb isotopic dating reveal that granitoid gneisses in the Qingyuan area can be grouped into two major episodes, i.e., ∼2559-2534 Ma strongly gneissic quartz dioritic and tonalitic to trondhjemitic gneisses; and ∼2529-2495 Ma weakly gneissic to massive quartz monzodioritic and monzogranitic gneisses, with subordinate tonalitic to trondhjemitic gneisses. The late magmatic episode was accompanied by regionally high-grade metamorphism (∼2510-2495 Ma). Most granitoid gneisses display highly depleted zircon εHf(t2) values (+4.2-+8.1), whereas one monzogranitic gneiss shows negative values of -4.7 to -1.0, indicating late Neoarchean crustal growth with minor involvement of ancient continental materials probably sourced from the Anshan-Benxi terrane. Geochemical and petrogenetic studies reveal that the quartz dioritic magmas were derived from partial melting of plagioclase-poor garnet amphibolites or eclogites metamorphosed from oceanic slab materials, with slab melts contaminated by mantle wedge peridotites during ascent. The tonalitic to trondhjemitic magmas stemmed from partial melting of mainly juvenile metabasaltic rocks with minor metagreywackes of lower arc crust. In comparison, the quartz monzodioritic and monzogranitic magmas were derived respectively from partial melting of depleted mantle sources metasomatized by slab-derived fluids and metagreywackes with different crustal resident ages at middle to lower crustal levels. Combined with previous studies of metavolcanic rocks, the Northern Liaoning Province records late Neoarchean crustal growth, evolving from mid-ocean ridge, through initiation and maturation of an intra-oceanic arc, to arc-continent collision. Arc-continent accretion and possibly slab rollback processes may have triggered reworking of both juvenile arc crust and minor ancient continental margin materials, generating the magmatic precursors for the monzogranitic gneisses. Overall, the intense late Neoarchean crustal growth of the EB was controlled mainly by arc-continent accretion, possibly linked to global assembly of cratonic fragments.PostprintPeer reviewe

Late Neoarchean crust-mantle geodynamics : evidence from Pingquan Complex of the Northern Hebei Province, North China Craton

This study is financially supported by the National Natural Science Foundation of China (Grant Nos. 41530207, 41502179, 41472165, 41602198) and Central University Basic Scientific Research Business Expenses (Grant No. 2652015038). PAC acknowledges support from Australian Research Council grant FL160100168.A late Neoarchean intra-oceanic arc along the northwestern margin of Eastern Block (EB), North China Craton, provides important insights into the nature of Archean mantle sources and crust-mantle geodynamics. The Pingquan Complex and the entire Northern Hebei Province (NHB) are located in the middle part of the arc, and overlap the northern extent of the Trans-North China Orogen. Zircon U-Pb isotopic age data reveal that the Pingquan Complex consists of ∼2537-2515 Ma dioritic gneisses, ∼2506-2503 Ma amphibolites, and ∼2491 Ma quartz monzodioritic to monzogranitic gneisses, and they show dominantly positive zircon εHf(t) (-0.6-+5.4) that are lower than coeval model depleted mantle values. Geochemical data for the Pingquan rocks and synchronous metabasalts and granitoid gneisses of Huai’an-Xuanhua and Dantazi complexes in the NHB are integrated. Except for the monzogranitic gneisses that were derived from partial melting of juvenile metagreywackes, the other rocks of the Pingquan Complex were derived from a metasomatized lithospheric mantle, and subjected to variable fractionation of clinopyroxene, hornblende and plagioclase, without significant crustal contamination. Moderately depleted zircon εHf(t), and high Sm/Hf and Nb/Ta (mostly of 1.34-3.96 and 15.50-32.58) suggest that the lithospheric mantle was enriched by subducted pelagic sediments metamorphosed to rutile-bearing eclogites before melting. Late Neoarchean crust-mantle geodynamic processes in the NHB are reconstructed. Intra-oceanic subduction initiated offshore of the northwestern margin of the EB at ∼2.55 Ga or earlier. Partial melting of slab basalts occurred at ∼2542-2499 Ma, with the melts contaminated by mantle wedge materials forming TTGs. Meanwhile, the sub-arc lithospheric mantle was enriched by fluids and melts released from slab basalts and pelagic sediments, and partial melting of this moderately depleted mantle generated ∼2537-2503 Ma diorites and basalts. Following final accretion of the arc onto the continental margin of the EB, the slab rollback/breakoff and asthenospheric mantle upwelling triggered partial melting of the metasomatized lithospheric mantle and crustal anatexis, generating ∼2491 Ma quartz monzodioritic and monzogranitic rocks. Accordingly, the NHB records Neoarchean crustal growth linked to oceanic subduction and arc-continent accretion, and highlights the importance of resolving the nature of mantle sources and crust-mantle interactions in understanding Archean crustal growth and evolution.PostprintPeer reviewe

PreDiff: Precipitation Nowcasting with Latent Diffusion Models

Earth system forecasting has traditionally relied on complex physical models that are computationally expensive and require significant domain expertise. In the past decade, the unprecedented increase in spatiotemporal Earth observation data has enabled data-driven forecasting models using deep learning techniques. These models have shown promise for diverse Earth system forecasting tasks but either struggle with handling uncertainty or neglect domain-specific prior knowledge, resulting in averaging possible futures to blurred forecasts or generating physically implausible predictions. To address these limitations, we propose a two-stage pipeline for probabilistic spatiotemporal forecasting: 1) We develop PreDiff, a conditional latent diffusion model capable of probabilistic forecasts. 2) We incorporate an explicit knowledge control mechanism to align forecasts with domain-specific physical constraints. This is achieved by estimating the deviation from imposed constraints at each denoising step and adjusting the transition distribution accordingly. We conduct empirical studies on two datasets: N-body MNIST, a synthetic dataset with chaotic behavior, and SEVIR, a real-world precipitation nowcasting dataset. Specifically, we impose the law of conservation of energy in N-body MNIST and anticipated precipitation intensity in SEVIR. Experiments demonstrate the effectiveness of PreDiff in handling uncertainty, incorporating domain-specific prior knowledge, and generating forecasts that exhibit high operational utility.Comment: Technical repor

A branch current reallocation based energy balancing strategy for the modular multilevel matrix converter operating around equal frequency

Modular multilevel matrix converter (M3C) is a promising topology for medium-voltage high-power applications. Due to the modular structure, it features easy scalability, high quality output waveforms and superior fault tolerance. However, M3C suffers serious capacitor-voltage fluctuation if the output frequency gets closer to the input frequency. This limits its use in the adjustable-speed-drive (ASD) applications. This paper introduces a theoretical analysis in phasor-domain to find the branch energy equilibrium point of M3C when operating around equal frequency. On the basis of this equilibrium point, a branch current reallocation based energy balancing control method is proposed to equalize the energy stored in the nine converter branches. With this novel control method, M3C can effectively overcome the capacitor voltage fluctuation with neither using common voltage nor applying reactive power at the input side

Analysis of fishing vessel accidents with Bayesian network and Chi-square methods

Commercial fishing is an important industry that generates income directly or indirectly to many people in the world. It is impossible to carry out a fishing activity on this scale without a vessel. Therefore, fishing vessels are the most important element of modern fishing industry. Fishing vessels play a key role in fishing, transporting and storing fish. Thousands of people die every year as a result of fishing vessel accidents. In order to carry out sustainable fishing operations, fishing vessel accidents should be investigated and measures should be taken to prevent them. Therefore, in this study for analysing of accidents occurred between 2008 and 2018 in fishing vessels, with full lengths of 7 m and above, Bayesian network, chi-square methods were used. As a result, recommendations were made to prevent accidents. Also, Accident (Bayes) Network, which summarizes the occurrence of accidents on fishing vessels, is presented. These networks allow to understand the occurrence of accidents in fishing vessels and to estimate the occurrence of accidents in variable conditions. It was also found that there was a significant relationship between accident category and vessel length, vessel age, loss of life and loss of vessel

Prevalent presence of periodic actin-spectrin-based membrane skeleton in a broad range of neuronal cell types and animal species

Actin, spectrin, and associated molecules form a periodic, submembrane cytoskeleton in the axons of neurons. For a better understanding of this membrane-associated periodic skeleton (MPS), it is important to address how prevalent this structure is in different neuronal types, different subcellular compartments, and across different animal species. Here, we investigated the organization of spectrin in a variety of neuronal- and glial-cell types. We observed the presence of MPS in all of the tested neuronal types cultured from mouse central and peripheral nervous systems, including excitatory and inhibitory neurons from several brain regions, as well as sensory and motor neurons. Quantitative analyses show that MPS is preferentially formed in axons in all neuronal types tested here: Spectrin shows a long-range, periodic distribution throughout all axons but appears periodic only in a small fraction of dendrites, typically in the form of isolated patches in subregions of these dendrites. As in dendrites, we also observed patches of periodic spectrin structures in a small fraction of glial-cell processes in four types of glial cells cultured from rodent tissues. Interestingly, despite its strong presence in the axonal shaft, MPS is disrupted in most presynaptic boutons but is present in an appreciable fraction of dendritic spine necks, including some projecting from dendrites where such a periodic structure is not observed in the shaft. Finally, we found that spectrin is capable of adopting a similar periodic organization in neurons of a variety of animal species, including Caenorhabditis elegans, Drosophila, Gallus gallus, Mus musculus, and Homo sapiens

A New Era in the Quest for Dark Matter

There is a growing sense of `crisis' in the dark matter community, due to the absence of evidence for the most popular candidates such as weakly interacting massive particles, axions, and sterile neutrinos, despite the enormous effort that has gone into searching for these particles. Here, we discuss what we have learned about the nature of dark matter from past experiments, and the implications for planned dark matter searches in the next decade. We argue that diversifying the experimental effort, incorporating astronomical surveys and gravitational wave observations, is our best hope to make progress on the dark matter problem.Comment: Published in Nature, online on 04 Oct 2018. 13 pages, 1 figur