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Evaporation ducts are a particular type of atmospheric stratification that frequently appears on the sea surface. The accurate and timely prediction of the evaporation duct height (EDH) is significant for the practical application of electromagnetic communication equipment. Due to the typical time-series (TS) characteristics of the measured evaporation duct data, we construct an EDH prediction model based on a long short-term memory network (LSTM-EDH model) for the first time. The experimental results show that the LSTM-EDH model’s root-mean-square error (RMSE) is dramatically reduced and can achieve a better fit of the measured EDH compared with the Babin–Young–Carton (BYC), Naval-Postgraduate-School (NPS), and eXtreme Gradient Boosting (XGB) EDH models. Compared with the XGB model, the generalization ability is also greatly improved. [ABSTRACT FROM AUTHOR]

A new hybrid excitation brushless dc generator (HEBLdcG) is comprised of the structure-paralleled permanent magnet machine part and flux modulation machine part (FMMP). The reactive power compensation effect of the HEBLdcG is illustrated and investigated in this paper. It is shown that the operation modes of the FMMP are influenced by both, the field current and armature current. Based on this, the three ranges in terms of the field current are divided. Three typical operation states representatively selected in the three ranges are defined as the power-balance state, compensator state, and short-circuit state, respectively. The short-circuit current can be diminished on account of the reactive power compensation effect. Furthermore, the analysis of the short-circuit characteristics shows that the short-circuit characteristic curve—short-circuit output current versus field current—is not a straight line, due to the saturation of the d-axis flux path of the FMMP. And the HEBLdcG at −8-A field current features the lowest total loss at the short-circuit state. At last, a prototype HEBLdcG is manufactured and the experiments validate the simulations. [ABSTRACT FROM AUTHOR]

With the development of more electric aircraft, higher demand for electrical energy is put forward in generation systems. The constant speed drive is eliminated in variable frequency ac (VFAC) generation systems, which makes integrated starter-generator (SG) can be realized. Considering the inherent defects of wound rotor synchronous SG systems, such as the complex starting excitation methods and rotating rectifiers, this paper proposes a VFAC SG system based on hybrid excitation synchronous machines (HESMs) for aircraft applications. The key technology of HESM-based VFAC SG system is to regulate the field current in such a way that three major modes of VFAC SG system operation for aircraft applications, namely, engine starting operation, transition mode, and generating operation, can be realized effectively. The simulation model of HESM-based VFAC SG system is built and analyzed. A prototype HESM-based VFAC SG system has been designed and developed for experimental verification. The starting operation, transition mode, and generating operation of the prototype HESM-based VFAC SG system are implemented. The feasibility of HESMs to VFAC SG system for safety-critical aircraft applications has been validated. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes the design philosophies of the single-phase main exciter (ME) for an aircraft wound-rotor synchronous machine and investigates its operating characteristics in both generating and starting modes. The fundamental structure and starting–generating system are discussed. The load features of single-phase ME are summarized. The ME has the characteristics of linear current amplifier and approximately constant current source the generating mode, which can be used in the wide range of working temperature. Detailed waveforms and finite-element analysis verify that excitation current $I_{\mathrm {ef}}$ is almost irrelevant to speed but in direct proportion to frequency in the starting mode. Besides, simulated data indicate that the energy transferring efficiency between ME stator and rotor can reach about 55% by the single-phase ac excitation method. Finally, the experimental verification is carried out, and the simulated and experimental data and waveforms of single-phase ME agree well with each other. [ABSTRACT FROM AUTHOR]

An evaporation duct is a particular atmospheric duct that is crucial for marine vessel communication, and one of the most significant indexes to assess it is evaporation duct height (EDH). In this letter, we propose a new method based on a multilayer perceptron (MLP), a classic network in deep learning, to predict the EDH. After so many experiments, the structure of MLP for EDH estimation is chosen as five hidden layer with rectified liner unit activation function. Since this method is essentially some kind of regression, the mean-squared error is chosen as the loss function. To accelerate the training convergence, we choose a self-adaptive optimization scheme called adaptive moment estimation. There are some field observation data sets obtained from some sea areas in northern hemisphere, by which the MLP is trained, to predict the EDH. For single-regional prediction, we use the same input data sets with the Paulus–Jeske (P-J) model, one of the ideal operational models, to predict the EDH. In comparison with the P-J model, the prediction accuracy using our method is significantly escalated in all experimental sea areas, which reveals the efficiency of our method. By cross prediction in distinct sea areas, the consistency between the method and the theory is verified, and this letter yields a new approach of evaporation duct prediction. [ABSTRACT FROM AUTHOR]

In this paper, a new shaded-pole main exciter (ME) with additional short-circuited coils for aircraft three-stage starter–generator (SG) is proposed and investigated. The basic structure, winding configurations, operating principle, and start system structure of the presented shaded-pole ME are illustrated in detail. The comparative study between the original ME and the shaded-pole ME with respect to the starting mode performances is conducted by 2-D finite-element method (FEM). A prototype SG with original ME has been developed, and the experimental results are essentially consistent with the simulation results by the FEM utilized in the predictions in this paper. Simulation data and waveforms verify that the proposed shaded-pole ME is a good candidate for aircraft machines to satisfy the dual function of starter and generator. [ABSTRACT FROM AUTHOR]

In this paper, a novel modeling method for hybrid excitation synchronous machines (HESMs) with radial/axial flux paths via magnetic equivalent circuit (MEC) is proposed. 3-D finite-element analysis (FEA) is essential when analyzing a machine with radial/axial flux paths due to the asymmetry in the axial direction. However, 3-D FEA is computationally expensive and time-consuming, especially during the preliminary design stage. The proposed modeling method is analyzed and validated based on an HESM with magnetic shunting rotor. The fundamental structure and working principle of the HESM with magnetic shunting rotor are introduced. On the basis of 3-D structure, an MEC considering saturation and leakage flux distribution is built and illustrated, as well as field analysis is performed. A 2-D equivalent finite-element model via MEC is built and illustrated. A prototype HESM with magnetic shunting rotor has been designed by the proposed modeling method and developed for experimental verification. With the proposed modeling method, the computational efficiency is significantly improved in the design stage. The proposed modeling method is verified by the good agreement between the predicted and measured results. [ABSTRACT FROM AUTHOR]