This paper proposes two novel hybrid rotors permanent magnet (PM) machines for the high torque density in short duration condition operation. In order to enhance the torque performance, the flux concentrated structure of spoke-type PM is employed to increase the air-gap flux density. Meanwhile, the non-magnetic connector of the rotor is employed to eliminate the magnetic flux leakage. The rotors of the conventional machines and the proposed machines are optimized by the finite element analysis (FEA). Furthermore, based on the comparisons of electromagnetic performances for the optimized machines, including the open-circuit flux density, torque, PM eddy current loss, overload capability, the characteristics of the proposed machines are analyzed. The results indicate that the proposed machine can improve the torque at rated and overload operation with growth rate 14.3% and 13.1%, respectively. Finally, a 12-slots/10-pole PM machine is prototyped and FEA is to be validated.
As China's AC transmission system with series capacitor and HVDC transmission technology are widely used in long-distance and large-scale power transmission network, sub-synchronous resonance (SSR) problem becomes more prominent. This paper studied induction generator effect (IGE) and torsional interaction (TI) of synchronous generator by focusing on amplitude and frequency modulation of synchronous generator's flux linkage. IGE involves only electric system dynamics, which will only cause amplitude modulation of flux linkage, resulting in one or two frequency component added in stator current of non-salient pole synchronous generator (NPSG) or salient pole synchronous generator (SPSG) respectively. TI involves both electric and mechanical system dynamics, which will cause both amplitude and frequency modulation of flux linkage, resulting in multiple sub and super-synchronous frequency components added in stator current by means of Bessel function. This result will provide a new reference to understand the SSR phenomena containing multiple frequency components in practical power system. The IEEE first benchmark model is used to demonstrate the accuracy of the analysis results.
This paper provides an empirical study on series arc behavior in low voltage dc microgrids. The response of an R-L-C dc microgrid abstraction towards series arcs is studied experimentally for varying grid inductance, dc voltages, load capacitances and load currents. In order to account for the stochastic nature of arcs, experiments are repeated multiple times under similar conditions to gain statistical significance. Thereby, insight on percentage occurrence and burn time of initiated series arcs is provided. Load side voltage response is studied to gain insight on the expected peak drop and fall time. This empirical evidence was judged to be a necessary requirement in developing a novel series arc extinguishing method from load side power electronic devices.
Abstract The scarcity of narrow bandgap donor polymers matched with perylene diimides (PDI)‐based nonfullerene acceptors (NFAs) hinders improvement of the power conversion efficiency (PCE) value of organic solar cells (OSCs). Here, it is reported that a narrow bandgap donor polymer PDX, the chlorinated derivative of the famous polymer donor PTB7‐Th, blended with PDI‐based NFA boosts the PCE value exceeding 10%. The electroluminescent quantum efficiency of PDX‐based OSCs is two orders of magnitude higher than that of PTB7‐Th‐based OSCs;therefore, the nonradiative energy loss is 0.103 eV lower. This is the highest PCE value for OSCs with the lowest energy loss using the blend of PTB7‐Th derivatives and PDI‐based NFAs as the active layer. Besides, PDX‐based devices showed larger phase separation, faster charge mobilities, higher exciton dissociation probability, suppressed charge recombination, elevated charge transfer state, and decreased energetic disorder compared with the PTB7‐Th‐based OSCs. All these factors contribute to the simultaneously improved short circuit current density, open circuit voltage, and fill factor, thus significantly improving PCE. These results prove that chlorinated conjugated side thienyl groups can efficiently suppress the non‐radiative energy loss and highlight the importance of fine‐modifying or developing novel narrow bandgap polymers to further elevate the PCE value of PDI‐based OSCs.
Abstract In this paper, a miniaturized ultra‐wideband filter with ultra‐wide stopband and high selectivity using a capacitive loading stub in a multimode structure is proposed. The second, third, and fourth harmonics of the proposed filter are all suppressed on account of using a capacitive loading stub, which makes it have the characteristic of an ultra‐wide stopband. In addition, there are two transmission zeros located at the upper stopband close to the passband, which improves the selectivity of the proposed filter. The proposed filter is fabricated and measured, and the result shows the filter with the center frequency f 0 1.185 GHz has 151% 3‐dB fractional bandwidth. Its upper stopband is extended to 9.18 GHz (7.75 f 0 ) and the 20‐dB roll off rate is 212.5 dB/GHz. What's more, the size of the proposed filter is 0.175 λ g × 0.18 λ g , where λ g is the guided wavelength at the center frequency f 0 .
Junctions reflect the important geometrical structure information of the image, and are of primary significance to applications such as image matching and motion analysis. Previous event-based feature extraction methods are mainly focused on corners, which mainly find their locations, however, ignoring the geometrical structure information like orientations and scales of edges. This paper adapts the frame-based a-contrario junction detector(ACJ) to event data, proposing the event-based a-contrario junction detector(e-ACJ), which yields junctions' locations while giving the scales and orientations of their branches. The proposed method relies on an a-contrario model and can operate on asynchronous events directly without generating synthesized event frames. We evaluate the performance on public event datasets. The result shows our method successfully finds the orientations and scales of branches, while maintaining high accuracy in junction's location.
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