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Abstract:In this paper, a load adaptive control method to improve the efficiency and dynamic performance of the Phase-Shifted Full-Bridge (PSFB) converter which works under a wide range of load conditions is presented. The proposed control method can be used as a battery charger since this application demands a wide range of load conditions. The composition of the PSFB converter's losses and the loss analysis model are both discussed. According to this model, the optimum switching frequency which results in minimum power loss is adopted to improve the efficiency. The relationship between switching frequency and power loss is formulated over a wide load range. Indicated by this kind of relationship, the proposed controller adjusts the switching frequency at different load currents. Moreover, an adaptive gain adjustment controller is applied to replace the traditional controller, with the aim to improve the dynamic performance which is influenced by the changes of the switching frequency and load current. In addition, the experimental results show that the maximum improvement of efficiency is up to 20%. These results confirm the effectiveness of the proposed load adaptive control method.

The development of carbon nanocomposite with high-performance electromagnetic interference (EMI) shielding has become vitally important for next-generation intelligent electronic devices. However, efficient EMI shielding for highly flexible and miniaturized devices is still a challenge. Here, a highly flexible and thin composite film composed of vertical graphene nanosheets (VGSs) and polyimide (PI) for EMI shielding is proposed. VGSs are prepared by activation-induced thermal chemical vapor deposition (CVD) for the first time, and the composite film is prepared by composing VGSs with PI via in situ polymerization. With the isotropic urchin-like nanostructure and agglomeration-free dispersion of VGSs, rich electrons conduction paths, enclosure nanostructure, and countless interfaces are constructed in PI matrix. The optimal composite film shows superior EMI shielding performance (an average EMI shielding effectiveness of 31.37 dB in the frequency range of 8.2–12.4 GHz can be detected with a thickness of 151 μm). Furthermore, the composite film also shows excellent thermal management performance. Suitable flexibility and robustness allow the composite film to bear even 2000 continuous bending cycles, and without appreciably decreasing its EMI shielding and thermal management performance, which establishes potentials for applications in EMI shielding and thermal management.

Abstract:As a basic building block in power systems, the three-phase voltage-source inverter (VSI) connects the distributed energy to the grid. For the inductor-capacitor-inductor (LCL)-filter three-phase VSI, according to different current sampling position and different reference frame, there mainly exist four control schemes. Different control schemes present different impedance characteristics in their corresponding determined frequency range. To analyze the existing resonance phenomena due to the variation of grid impedances, the sequence impedance models of LCL-type grid-connected three-phase inverters under different control schemes are presented using the harmonic linearization method. The impedance-based stability analysis approach is then applied to compare the relative stability issues due to the impedance differences at some frequencies and to choose the best control scheme and the better controller parameters regulating method for the LCL-type three-phase VSI. The simulation and experiments both validate the resonance analysis results.

improving the fast-charging performances of LIBs, in which the enhancements of anode materials are undisputedly important. [4] Graphite, the most commonly used anode material in LIBs, mainly faces the following problems: 1) The small interlayer distance of graphite (0.33 nm) is far from sufficient to perform rapid Li + transport; 2) During the fast charging, high current densities result in Li dendrite growth on graphite anode and thereby raising serious safety concerns; [5,6] 3) With the specific capacity of graphite anode approaching its ceiling (372 mAh g −1 ), further increase in capacity is expected to encounter huge challenges and thus limited energy density. Various anode materials, such as metal oxides (SnO 2 ), [7] metal sulfides (WS 2 , SnS 2 , Sb 2 S 3 ), [8] SiO x (0 < x < 2), [9] metals (Sn, Sb, Ge, Li), etc., [10,11] have been extensively explored as anode materials for fastcharging LIBs.Among them, tungsten disulfide (WS 2 ) with tunable interlayer distance, high theoretical capacity (432 mAh g −1 ), and large density (7.6 g cm −3 , about three-times larger than graphite) has drawn significant attention as fast-charging anode material for LIBs. [12][13][14] However, several critical challenges, such as sluggish ion diffusion kinetics, poor intrinsic electrical conductivity, and large volume fluctuations upon cycling, should be addressed for the successful utilization of WS 2 in fast-charging LIBs. Defect engineering in terms of heteroatom doping with the strong capabilities of regulating the electronic structure and increasing ion storage sites shows huge advantages to offer the fast-charging capability. [15,16] Besides, the fabrication of nano structured WS 2 and conducted coatings is also a feasible strategy, [17] which shortens ion and electron diffusion path and increases electrical conductivity. However, the unimproved electron and ion transport inside WS 2 brings limited improvement of fast-charging capability. Constructing the few-layer WS 2 /carbon layer-by-layer stacked structure has been confirmed as an available strategy towards the above issues, [18] which increases the contact area between WS 2 and carbon, thus accelerating ionic and electronic transport. Nevertheless, maximizing the molecular layer contact area of WS 2 and C by constructing a stacked structure of single-layer WS 2 and C to further improve ionic and electronic transport is still a huge challenge and has not been realized so far.

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