Resonant DC link soft-switching inverter with low-loss auxiliary circuit

An auxiliary switching device is usually set on the DC bus of the resonant DC link inverter, which restricts the efficiency of the inverter and is also one of the reasons for its not extensive application and promotion in the high-power field. To solve the problem, auxiliary circuits and DC bus of the resonant DC link soft-switching inverter designed in this paper are connected in parallel, and auxiliary switching devices and resonant elements are not connected in series on the DC bus, which help to improve the efficiency and reduce the power losses of the auxiliary resonant circuits. Based on the equivalent circuits in different operating modes, the paper analyzes the working process of the soft-switching inverter, soft-switching realization conditions and design rules. A 10 kW laboratory prototype is built, and through the comparison of the experimental results from it and the hard-switching inverter, it is shown that the efficiency improvement value of the designed inverter at full load is higher than that at light load. Therefore, the soft-switching inverter designed in this paper is conductive to reducing the power losses of the auxiliary resonant circuits and ensuring the efficient use of the electric energy.     

Thermally Stable Hole‐Transporting Materials Based upon a Fluorene Core

We report a new class of diamine hole‐transporting materials (HTMs) based upon a fluorene core. Using a fluorene core, rather than a biphenyl group, leads to enhanced thermal stability, as evidenced by glass‐transition (T_g) temperatures as high as 161 °C for N,N′‐iminostilbenyl‐4,4′‐fluorene (ISF). The fluorene‐based HTMs have lower ionization potentials (I_p) than their biphenyl analogs, which leads to more efficient injection of holes from the indium tin oxide (ITO) anode, and higher quantum efficiencies. Devices prepared with fluorene‐based HTMs were operated under thermal stress. The failure of an organic light‐emitting diode (OLED) under thermal stress has a direct correlation with the thermal stability of the HTM that is in contact with the ITO anode. OLEDs based on ISF are stable to over 140 °C.     

Polymer solar cells with light-trapping structure connected in series by soft contact lamination process

A modified soft contact lamination (SCL) process used to fabricate polymer solar cells (PSCs) with nanostructures was developed. Instead of thermally evaporating the metal electrode directly onto the photoactive or the buffer layer, the metal electrode is firstly deposited onto an elastomeric plate made of polydimethylsiloxane (PDMS), then laminated with a substrate coated with conducting polymer via the SCL process, which provides a non-intrusive way to introduce the metal electrode. Since the PDMS plate is compatible for soft lithography, enabling it to be constructed in a light-trapping structure to enhance the power conversion efficiency. Moreover, the architecture of our SCL-fabricated PSCs is suitable for series connecting individual cells to accumulate output voltages for targeting practical applications.     

Fairness in MIMD Congestion Control Algorithms

The Mulitplicative Increase Multiplicative Decrease (MIMD) congestion control algorithm in the form of Scalable TCP has been proposed for high speed networks. We study fairness among sessions sharing a common bottleneck link, where one or more sessions use the MIMD algorithm. Losses, or congestion signals, occur when the capacity is reached but could also be initiated before that. Both synchronous as well as asynchronous losses are considered. In the asynchronous case, only one session suffers a loss at a loss instant. Two models are then considered to determine which source looses a packet: a rate dependent model in which the packet loss probability of a session is proportional to its rate at the congestion instant, and the independent loss rate model. We first study how two MIMD sessions share the capacity in the presence of general combinations of synchronous and asynchronous losses. We show that, in the presence of rate dependent losses, the capacity is fairly shared whereas rate independent losses provide high unfairness. We then study inter protocol fairness: how the capacity is shared in the presence of synchronous losses among sessions some of which use Additive Increase Multiplicative Decrease (AIMD) protocols whereas the others use MIMD protocols.     

Analysis of Optical Losses in a Photoelectrochemical Cell: A Tool for Precise Absorptance Estimation

Optical losses in a photoelectrochemical (PEC) cell account for a substantial part of solar‐to‐hydrogen conversion losses, but limited attention is paid to the detailed investigation of optical losses in PEC cells. In this work, an optical model of combined coherent and incoherent light propagation in all layers of the PEC cell based on spectroscopic measurements is presented. Specifically, photoelectrodes using transparent conductive substrates such as F:SnO₂ coated with thin absorber films are focused. The optical model is verified for hematite photoanodes fabricated by atomic layer deposition and successfully used to determine wavelength‐dependent reflection, transmission, layer absorptances, and charge generation rates. Furthermore, the calculated absorptances enable 20–30% more accurate calculations of the absorbed photon‐to‐current efficiency of PEC cells. Our optical model is a powerful tool for the optimization of the optical performance of PEC cells focusing on single absorber or tandem configurations and represents a cornerstone of a complete (optical and electrical) model for PEC water splitting cells.     

An efficient nonfullerene acceptor for all-small-molecule solar cells with versatile processability in environmentally benign solvents

A new structure of dicyanodistyrylbenzene-naphthalimide-based nonfullerene acceptor NIDCSN was synthesized and characterized to have a favorable electron accepting property and versatile processability in various organic solvents. The nonfullerene all-small-molecule solar cells comprising p-DTS(FBTTh₂)₂ as the donor and NIDCSN as the acceptor exhibited a maximum power conversion efficiency of 3.45% with a remarkable open-circuit voltage of 1.04 V, together with similar device performances when fabricated in five different solvents including environmentally benign non-halogenated ones.     

Analysis of the propagation losses of InP/InGaAsP trench waveguides fabricated by focused ion beam

Focused ion beam was used to fabricate 2 mm-long, 4 μm-wide and 4 μm-deep multimode trench waveguides in InP/InGaAsP. An automated stitching method was developed to fabricate mm-long structures using alignment marks. The waveguides were sputtered or etched using I₂ at room temperature and 150 °C stage temperature. The propagation losses induced by the different fabrication techniques were measured and ranged between 50 and 82 dB/cm. A damaged layer with implanted Ga and the sidewall roughness are identified to be the most important causes for the losses. FIB is shown to be a single-step fabrication technique for rapid-prototyping of photonic structures in InP/InGaAsP.     

Effect of light-induced metastable defects on photocarrier lifetime

Creation and annealing of light-induced defects and their effect on photocarrier lifetime have been studied at 120 and 300 K using constant photocurrent method (CPM) and steady-state photoconductivity measurements. A hysteresis-like relation is observed between photoconductivity and light-induced defect density. This relation depends on both degradation temperature and light intensity used for the degradation. A broad, resembling a two-component distribution of defect annealing activation energies together with distribution of recombination coefficients account for the observed changes at 120 K. On the other hand, these distributions are narrower and sharply peaked at about 1 eV for the 300 K measurements. Results indicate that defects which are created at the earlier stages of the illumination have smaller annealing activation energies and higher recombination coefficient (capture cross-section) and these are better recombination centers than the defects with higher annealing activation energies.     

Performance evaluation of the recuperative heat exchanger in a miniature Joule–Thomson cooler

To develop effective heat exchangers for miniature and micro-Joule–Thomson (J–T) cooling system, the performance of the recuperative heat exchanger in a miniature J–T cooler is analyzed and evaluated. The evaluation is based on a theoretical model of the Hampson-type counter-flow heat exchanger. The effect of the pressure and temperature-dependent properties and longitudinal heat conduction are considered. The results of the numerical simulation are validated with the corresponding experimental measurements. The performance of the heat exchanger on effectiveness, flow and various heat conduction losses as well as liquefied yield fraction are analyzed and discussed. The simulation model provides a useful tool for miniature J–T cooler design.     

玉山电网无功补偿的技术经济分析

无功补偿是降低冈损的措施之一。本文就玉山电网无功补偿对降低问损的影响及投资，效益进行了分析探讨。