More electric aircraft (MEA) is an important direction for future aircraft development. The printed circuit boards (PCB) of power electronics equipment in MEA operates in a complex environment of low air pressure, square wave voltage, compact layout and strong electromagnetic interference, which makes the PCB more prone to partial discharge (PD). However, the effective detection method and related discharge characteristics for PCB PD under square wave voltage are still unclear. Therefore, this paper proposes a PCB PD detection method based on fluorescent optical fiber, which has good anti-electromagnetic interference ability. The PD characteristics of the PCB with three typical structures under three air pressures are studied, including PD non-breakdown characteristics, changes in optical pulse amplitude and pulse repetition rate during PD aging, PD breakdown path analysis and PCB surface electric field simulation. The analysis shows that air pressure, space charge and PCB surface flatness all have important influences on the PD of PCB under square wave voltage. It provides important theoretical support for the insulation protection design and fault diagnosis of PCB for MEA in the future.@en

More and more printed circuit boards (PCBs) will be used in electric aircraft to achieve higher power density of the on-board electric system, while PCBs in aircraft are more likely to generate partial discharges (PDs) due to external factors such as compact structure and low air pressure. Therefore, this paper proposes a fluorescent fiber-based method for detecting and evaluating PDs on PCBs. The detection method is effectively immune against the presence of the electromagnetic, acoustic and vibration interference. Based on the optical detection, the evolution regularities of PCB surface appearance changes, optical PRPD patterns and optical pulses during the aging process of PCB under different air pressure are analyzed in this paper. Then, 12 assessment features are extracted for the PD aging process, and the contribution of these 12 features to the severity assessment at different air pressures is obtained using the minimal-redundancy-maximal-relevance (mRMR) algorithm. Finally, different numbers of PD features are tested for PD severity assessment by the SVM algorithm. The evaluation results show that the severity assessment method proposed in this paper can achieve an assessment accuracy of at least 91.1% and up to 94.4% under all three air pressures, which has good application and guidance value.

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The integration of phase change materials (PCMs) and metal foam has been widely concerned recently. To decrease non-uniformity of uniform metal foam-PCMs, adaptive metal foam arrangement strategy with increasing porosity from inside to outside has attracted widespread attention. This work conducted a symmetric simulation model of vertical thermal energy storage (TES) tube validated by experiments, for optimization of adaptive metal foam arrangement in basic design (0.94–0.94–0.94). It was followed by assessing the performance of gradient metal foam structures that included 27 cases with radial foam gradients of larger porosity on the outside and smaller porosity on the inside. Results demonstrated that a smaller difference between the inside and outside subregions resulted in better thermal performance when the same porosity of the intermediate subregion was used. More intense natural convection with stronger liquid paraffin vortex could be obtained by an adaptive arrangement. With the same average porosity, the faster phase change evolution, which was influenced by the maximum promotion of stronger natural convection, was achieved by using a larger intermediate porosity and a larger porosity difference between the inside and outside regions. The optimal strategy (0.87–0.94–0.97) could significantly shorten the melting duration as maximal as 17.15% compared with the original uniform (0.94–0.94–0.94), which contributed to efficient vertical metal foam TES systems, also as light and cost-effective as possible while also avoiding sacrificing thermal capacity.

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