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Data Availability: The data that support the findings of this study are available from the corresponding author, C. Wen, upon reasonable request. ; Deep-learning-based fault diagnosis of wind turbine has played a significant role in advancing the renewable energy industry. However, the imbalanced data sampled by the supervisory control and data acquisition systems has led to low diagnosis accuracy. Additionally, deep neural networks can encounter issues like gradient vanishing and insufficient feature learning during backpropagation when the model is too deep. This article introduces a novel approach that is based on dynamic weight loss functions to modulate unbalanced data and improve diagnostic accuracy by focusing on misclassification of a small sample number. The proposed approach employs a 1D-CNN model and an ensemble-learning-based convolution neural network (EL-CNN) to enhance diversity of models and complementarity of feature learning. The EL-CNN model addresses the problem of local features being overlooked and provides more accurate results. The effectiveness of this proposed approach is well demonstrated through experimental cases on real wind turbine pitch system fault data. Two different networks using three different loss functions and three state-of-the-art fault diagnosis models are tested, demonstrating the EL-CNN model’s superiority. ; This work was supported in part by the European Union’s Horizon 2020 Research and Innovation Programme under Grant 820776 (INTEGRADDE), the Engineering and Physical Sciences Research Council (EPSRC) of the UK, the Royal Society of the UK, the Alexander von Humboldt Foundation of Germany, the BRIEF Award of Brunel University London, the National Natural Science Foundation of China under Grant 61973209, the Natural Science Foundation of Shanghai of China under Grant 20ZR1421200, and the Capacity Building Project of Shanghai Local Colleges and Universities of China under Grant 22010501100.

Intermediate band materials incorporate a collection of energy levels with special optoelectronic properties within the semiconductor bandgap. This feature broadens the energy range of the solar spectrum useful for photovoltaic conversion and has the potential for enabling both high-current and high-voltage photovoltaic cells. Here we present our preliminary results on a novel intermediate band solar cell based on creating an intermediate band through the incorporation of a large concentration of Ti atoms in a GaAs crystal. The characterization of the material verifies a high concentration of incorporated Ti and the absence of structural defects. The cells show below-bandgap photon absorption with a likely contribution from As antisites and Ga vacancies. The initially degraded open-circuit voltage of the cells exhibits a high voltage recovery from 0.1 V (at room temperature and one-sun irradiance conditions) to 1.4 V (at low temperature and concentrated light).

This paper proposes an optimization framework to deal with the uncertainty in a day-ahead scheduling of smart active distribution networks (ADNs). The optimal scheduling for a power grid is obtained such that the operation costs of distributed generations (DGs) and the main grid are minimized. Unpredictable demand and photovoltaics (PVs) impose some challenges such as uncertainty. So, the uncertainty of demand and PVs forecasting errors are modeled using a hybrid stochastic/robust (HSR) optimization method. The proposed model is used for the optimal day-ahead scheduling of ADNs in a way to benefit from the advantages of both methods. Also, in this paper, the ac load flow constraints are linearized to moderate the complexity of the formulation. Accordingly, a mixed-integer linear programming (MILP) formulation is presented to solve the proposed day-ahead scheduling problem of ADNs. To evaluate the performance of the proposed linearized HSR (LHSR) method, the IEEE 33-bus distribution test system is used as a case study.

Abstract Grid forming control of converter interfaced generation (CIG) requires some form of energy storage to be coupled with the generation. Energy storage systems (ESSs) can be coupled to the CIG either on the DC or the AC side of the power converter. When placed on the DC side, the ESS can provide damping of the variability in the generation but would require significant modification to the wind turbine hardware. The solution with an ESS connected to the AC side is simpler to implement with existing wind turbines but fails to provide damping of the CIG generation. This paper proposes a grid forming control strategy, based on virtual synchronous generator (VSG) control, which allows the ESS installed at the AC-side of the converter to have the same features and dynamic behaviour as those obtained from placement on the DC-side of the converter. In addition, the proposed control can also limit the exchanged power of the ESS within its rating for a safe operation. The proposed control is validated via a detailed Electro-Magnetic Transient (EMT) model and its impact on the grid is quantified via the case study of the All-Island Irish transmission system. Simulation results show that only a small ESS capacity can ensure that the frequency variance satisfies the grid code requirement even in the situation of a very high CIG penetration.

Wind turbine gearbox operates under a wide array of highly fluctuating and dynamic load conditions caused by the stochastic nature of wind and operational wind turbine controls. Micropitting damage is one of failure modes commonly observed in wind turbine gearboxes. This article investigates gear micropitting of high-speed stage gears of a wind turbine gearbox operating under nominal and varying load and speed conditions. Based on the ISO standard of gear micropitting (ISO/TR 15144-1:2010) and considering the operating load and speed conditions, a theoretical study is carried out to assess the risk of gear micropitting by determining the contact stress, sliding parameter, local contact temperature and lubricant film thickness along the line of action of gear tooth contact. The non-uniform distributions of temperature and lubricant film thickness over the tooth flank are observed due to the conditions of torque and rotational speed variations and sliding contact along the gear tooth flanks. The lubricant film thickness varies along the tooth flank and is at the lowest when the tip of the driving gear engages with the root of the driven gear. The lubricant film thickness increases with the increase of rotational speed and decreases as torque and sliding increase. It can be concluded that micropitting is most likely to initiate at the addendum of driving gear and the dedendum of driven gear. The lowest film thickness occurs when the torque is high and the rotational speed is at the lowest which may cause direct tooth surface contact. At the low-torque condition, the varying rotational speed condition may cause a considerable variation of lubricant film thickness thus interrupting the lubrication which may result in micropitting.

Symbiodinium D, a relatively rare clade of algal endosymbiont with a global distribution, has attracted interest as some of its sub-cladal types induce increased thermal tolerance and associated trade-offs, including reduced growth rate in its coral hosts. Members of Symbiodinium D are increasingly reported to comprise low-abundance ‘cryptic’ ( 30 % of corals per site found to harbour the symbiont. When the same samples were analysed using the conventional screening technique, denaturing gradient gel electrophoresis, Symbiodinium D1 was only detected in 12 populations and appeared to be hosted by <12 % of colonies where present (in agreement with other reported low prevalence/absences in O. annularis). Cryptic Symbiodinium D1 showed a mainly uniform distribution across the wider Caribbean region, although significantly more Mesoamerican Barrier Reef corals hosted cryptic Symbiodinium D1 than might be expected by chance, possibly as a consequence of intense warming in the region in 1998. Widespread prevalence of thermally tolerant Symbiodinium in O. annularis may potentially reflect a capacity for the coral to temporarily respond to warming events through symbiont shuffling. However, association with reduced coral calcification means that the ubiquitous nature of Symbiodinium D1 in O.annularis populations is unlikely to prevent long-term declines in reef health, at a time when maintaining reef growth is vital to sustain reef ecosystem function.