Shanghai University

About: Shanghai University is a education organization based out in Shanghai, Shanghai, China. It is known for research contribution in the topics: Microstructure & Graphene. The organization has 59583 authors who have published 56840 publications receiving 753549 citations. The organization is also known as: Shànghǎi Dàxué.

Topology Deduction and Analysis of Voltage Balancers for DC Microgrid

Abstract: A voltage balancer that transfers unipolar dc bus configuration to bipolar dc bus configuration has been widely employed in dc microgrid. Fortunately, unbalanced power flow between positive and negative dc buses can be eliminated through a well-designed voltage balancer. Based on the analysis of a Buck/Boost-type voltage balancer, a deduction method for a series of voltage balancers is proposed in this paper, and is further investigated by applying to other existing voltage balancers. Consequently, several new topologies are proposed for various purpose of improvement with respect to the characters of existing topologies. Furthermore, four new topologies, i.e., Cuk-type, Super-Sepic/Zeta-type, and interleaved Buck/Boost-type voltage balancers have been proposed, which are compared with existing ones in terms of key characters. Finally, the interleaved Buck/Boost topology has been selected as an example for verification and a laboratory prototype is therefore built. The experimental results show a promising effect of current sharing and a good dynamic characteristic of the proposed interleaved average current control strategy based on interleaved sampling while maintaining a balanced power flow between the two dc buses.

Multilayer NiO@Co3O4@graphene quantum dots hollow spheres for high-performance lithium-ion batteries and supercapacitors

Abstract: In the present study, we designed and prepared multilayer NiO@Co3O4 hollow spheres decorated with graphene quantum dots (NiO@Co3O4@GQDs) through a rational solvothermal treatment. The decoration of the GQDs endowed the hybrid structure with excellent electrochemical behaviors in lithium-ion batteries (LIBs) and supercapacitors (SCs). The core–shell NiO@Co3O4 hollow structure was designed based on the stepwise lithium storage mechanism (first in the Co3O4 shell and then in the NiO core). The carboxyl-functionalized GQDs led to reduced interfacial resistance and increased surface area for electrochemical reactions. The high polarity of the carboxyl functionalized GQDs also showed a strong affinity to the Li+ in LIBs and K+/OH− in SCs. As an anode for LIBs, it demonstrated a large reversible capacity of 1158 mA h g−1 (NiO@Co3O4 contribution: ∼1327 mA h g−1) after 250 cycles at 0.1 A g−1. As a SC cathode, it held an impressive high specific capacitance of 1361 F g−1 (748.5 C g−1) at 1 A g−1, and retained 76.4% capacitance after 3000 cycles. Moreover, the assembled all-solid-state asymmetric supercapacitors (ASCs) (NiO@Co3O4@GQDs//AC) could deliver an energy density of 38.44 W h kg−1 and a superior cyclability (84.3% retention after 10 000 cycles).

Electrically pumped photonic integrated soliton microcomb

Abstract: Microcombs provide a path to broad-bandwidth integrated frequency combs with low power consumption, which are compatible with wafer-scale fabrication. Yet, electrically-driven, photonic chip-based microcombs are inhibited by the required high threshold power and the frequency agility of the laser for soliton initiation. Here we demonstrate an electrically-driven soliton microcomb by coupling a III–V-material-based (indium phosphide) multiple-longitudinal-mode laser diode chip to a high-Q silicon nitride microresonator fabricated using the photonic Damascene process. The laser diode is self-injection locked to the microresonator, which is accompanied by the narrowing of the laser linewidth, and the simultaneous formation of dissipative Kerr solitons. By tuning the laser diode current, we observe transitions from modulation instability, breather solitons, to single-soliton states. The system operating at an electronically-detectable sub-100-GHz mode spacing requires less than 1 Watt of electrical power, can fit in a volume of ca. 1 cm3, and does not require on-chip filters and heaters, thus simplifying the integrated microcomb. Chip-based frequency combs promise many applications, but full integration requires the electrical pump source and the microresonator to be on the same chip. Here, the authors show such integration of a microcomb with < 100 GHz mode spacing without additional filtering cavities or on-chip heaters.

An Adaptive Control Strategy for Virtual Synchronous Generator

Abstract: The adoption of the virtual synchronous generator (VSG) has attracted wide attention because of the equivalent operating mechanism as a synchronous generator, providing a feasible scheme for the distributed generation connected to utility grid. However, the delivered power and frequency of the VSG may easily oscillate when the dramatic power fluctuation occurred in the distribution generation system. Fortunately, the oscillation can be damped though adjusting the rotating inertia and damping coefficient. Thus, to investigate the influences of parameters perturbation on the active power and frequency for a VSG, the small-signal model is derived and the dynamic performances are analyzed in detail. Then, based on the results of parameters analysis, an adaptive control strategy is proposed in this paper. And an optimal damping ratio can be maintained throughout the whole process of operation to suppress the oscillation of power and frequency. Therefore, the dynamic performances of the VSG are enhanced since the dynamic indexes such as the response time and overshoots are optimized. In the end, a prototype of single-phase VSG has been built and the proposed adaptive control strategy has been verified through experimental results.