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Modular multilevel matrix converter (M3C) is a new topology of AC-AC power converter, which has very broad application in low frequency transmission system, high-power asynchronous motor speed regulation and low offshore wind power transmission. Due to the power coupling effect of the two frequencies, the capacitive voltage of M3C bridge arms is prone to instability when the grid voltage is asymmetric. Firstly, the arm power of M3C under unbalanced input conditions is calculated, and the power distribution law among the arms of two different power balance method is summarized. On this basis, the influence of low-frequency circulating currents on the arm power is analyzed. Under the premise of ensuring the balance of input and output power of the system, a capacitor voltage balance control strategy based on the construction of circulating currents is proposed, which avoids the introduction of negative sequence current on the grid side. Under unbalanced conditions, the capacitor voltage can be quickly balanced by the capacitor voltage closed-loop control and direct power compensation strategy. The constructed low-frequency circulating currents only flow inside the converter, and will not affect the decoupling operation of M3C input and output sides. The effectiveness of the proposed control strategy is verified by a 220 kV, 400 MW M3C system implemented in MATLAB.

With the rapid development of radioactive-ion-beam facilities worldwide, many exotic nuclear phenomena have been observed or predicted in nuclei far from the β-stability line or close to the neutron (proton) drip lines, such as halos in atomic nuclei and shape decoupling in deformed halo nuclei. The study of exotic nuclear phenomena, including halos, is at the frontier of current nuclear physics research. The covariant density functional theory (CDFT) is one of the most successful models in nuclear physics. The CDFT has been widely used to study structures and properties of exotic nuclei. The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) has been developed and achieved a self-consistent description of deformed halo nuclei by including deformation and continuum effects, with the deformed relativistic Hartree-Bogoliubov equations solved in the Dirac Woods-Saxon basis. The DRHBc theory has been used to predict the deformed halo structure in 44Mg and the shape decoupling between the core and halo. The theory has also been used to address unresolved problems concerning the radius and configuration of valence neutrons in 22C, deformed halos in carbon and boron isotopes, particles in the classically forbidden regions in magnesium isotopes, and other similar phenomena. The rotational excitation of deformed halos has been investigated by implementing an angular momentum projection based on the DRHBc theory. This investigation has shown that the effects of deformed halos and shape decoupling are also present in the low-lying rotational excitation states of deformed halo nuclei.

In this paper, a new multifunctional compound, 1,1′-(oxalylbis(4,1-phenylene))bis(1H-pyrrole-2,5-dione) (BVM), is grafted onto crosslinked polyethylene (XLPE) by radical-initiated grafting to play triple roles as a voltage stabilizer, space-charge inhibitor and crosslinking auxiliary and to achieve the purpose of comprehensively enhancing the DC dielectric properties of polymers while decreasing the type and number of additives. By analyzing the DC breakdown field strength, current density and space-charge distribution of the materials at different temperatures, it is demonstrated that BVM grafting can comprehensively and effectively enhance the electrical properties of the materials, with little dependence on temperature. The BVM molecule has two polar groups and an effective molecular structure that acts as a voltage stabilizer, thus enabling the introduction of dense, uniform, deeply trapped energy levels within the material to inhibit the space charge and to capture high-energy electrons to prevent damage to the material structure; however, the two functions do not affect each other. This is also consistent with first-principles calculations and quantum-chemical calculations. Gel content testing shows no effect on polymer crosslinking, even with a 27.8% reduction in the amount of the crosslinking agent di-isopropyl peroxide (DCP), which reduces the damage to the polymer's electrical resistance caused by the byproducts of DCP decomposition. Therefore, grafting multifunctional BVM compounds to improve the dielectric characteristics of polymers is a viable area of study in the development of high-voltage direct current (HVDC) cable materials. [ABSTRACT FROM AUTHOR]