Due to the limitation of working situation, the driving motor for all-electric aircraft (AEA) has a higher requirement on the weight and cooling performance of motor, so the thermal problem of driving motor is more prominent. Therefore, a high-performance cooling system based on heat pipe technology is proposed. The cooling system takes full advantage of the high thermal conductivity of the heat pipe. One end of the heat pipe is inserted into the stator yoke, and the other end is outside the motor, which is connected to an aluminum radiator. First, an experimental test is built to test the cooling performance of the proposed cooling system. Second, based on 3-D transient temperature field simulation, the influences for the axial size of the radiator and thermal conductivity of heat pipe on motor temperature rise are analyzed, which is a great significance to solve the overheating problem for driving motor. Finally, a 22-pole and 24-slot outer rotor surface-mounted permanent magnet synchronous motor (SPMSM) for AEA is designed and manufactured. Temperature rise distribution of prototype under different flight conditions is tested, and the effectiveness of the proposed cooling system is verified. The power density of the driving motor is further improved.

Heat pipe is a heat transfer element with high thermal conductivity, light weight and good temperature equalization, which has broad application prospects in driving motor. Firstly, in order to simplify the complex heat transfer process, according to the heat transfer mechanism of heat pipe, the flow and heat transfer process of working medium is equivalent to a single heat transfer process, which is equivalent to a solid with a high thermal conductivity. A mathematical model of the equivalent thermal conductivity of heat pipe is established to provide a theoretical basis for accurate calculation of thermal conductivity. The effects of shape size, different working temperature, material properties of working medium and contact thermal resistance of heat pipe on their equivalent thermal conductivity and thermal resistance are considered to obtain the equivalent thermal conductivity of heat pipe. On this basis, the experimental test platform of equivalent thermal conductivity of heat pipe is set up, and the accuracy of mathematical model is verified experimentally. Finally, an outer rotor surface-mounted permanent magnet synchronous motor (SPMSM) based on heat pipe cooling technology is designed and manufactured, and the temperature rise distribution under different operating conditions is tested, and the effectiveness of proposed cooling technology is verified.

Most of the current fault diagnosis based on vibration analysis method has fixed feature vectors and is prone to diagnostic errors. To identify the transformer structural faults more effectively, a mechanical structure fault diagnosis method for power transformers based on integrated feature extraction and SABO-PNN is proposed. Firstly, double feature extraction is performed on the original vibration signals based on wavelet packet transform and optimized variational modal decomposition based on the Subtraction-Average-Based Optimizer (SABO). Then, weight coefficients are assigned to the vibration feature vectors based on the fuzzy analytical hierarchy process, and the combined eigenvalues are calculated from the feature vectors and fuzzy weights. The integrated eigenvalues are used as input vectors to improve the probabilistic neural network using the SABO algorithm and train the vibration signals for diagnosis. Based on digital twin technology, a vibration signal monitoring platform is constructed, which can display vibration signals and diagnostic analysis results in real time. Based on the experimental prototype of 400 kVA transformer, the vibration signals from multiple measurement points of the tank under different fault conditions were collected and diagnostic analyses were performed. The test results show that the method can accurately diagnose the mechanical structure faults of the transformer.

In order to overcome the shortcomings of traditional electric excitation claw machine such as large leakage of magnetic field and easy saturation of ferromagnetic materials, a new topology structure with permanent magnet and electrical excited of shunt excitation scheme is proposed for claw-pole machine. Firstly, the output characteristics of voltage and current in power generation and electric state for claw-pole machine are analyzed by 3-D finite element method (FEM). And the influence of different excitation currents on the saturation state of magnetic circuit is calculated. On this basis, the influence of saturation of magnetic circuit is considered for electromagnetic torque and torque ripple. Therefore, under the condition of unsaturated flux density, in order to ensure the fastest and most stable start of the vehicle, it is necessary to obtain the maximum excitation current. Finally, a hybrid-excited claw-pole machine with rated power of 1.5kW is manufactured, and the on-load and no-load characteristics of prototype are tested to verify the feasibility of the hybrid-excited topology proposed.

Line start permanent magnet assisted synchronous reluctance motor (LSPMaSynRM) is an important high-efficiency and high-quality motor. Its parameter matching and operating characteristics are complex, with an increase in salient ratio resulting in a valley in the power factor curve. In this study, the formation principle of power factor curve valley was first deduced by the mathematical model of LSPMaSynRM. Then, the parameter matching principle of power factor curve valley was analyzed in detail. On this basis, the characteristics of load rate corresponding to the critical state of the power factor curve valley were obtained, and its influence on whole load efficiency was analyzed. The design principles for optimal efficiency in wide high-efficiency region and specific load point were obtained. Finally, a 5.5 kW LSPMaSynRM was designed and manufactured to verify the validity of the principle.

Transformer winding subjected to alternating stresses caused by multiple short circuits can fail by fatigue even though the stress is below the yield point. The effect of the mean stress of unidirectional impulse pulsating short-circuit force is not considered in previous studies. Therefore, this paper proposes a general method for assessing the stress fatigue life and damage of transformer winding under short-circuit conditions. Take a 110 kV transformer for an instance, the electromagnetic forces and stresses on the winding under short-circuit conditions were calculated based on electromagnetic-structural coupling. The dynamic measurement of short circuit force is realized by using the piezoelectric thin film polyvinylidene fluoride (PVDF) sensor to verify the accuracy of the simulation calculation. Based on finite element stress results, this paper proposes a five-step method for calculating stress fatigue life, the S - N curve of the copper winding is estimated, and the short-circuit force of the unidirectional impulse is corrected under the consideration of the mean stress effect. Both the fatigue life and damage of transformer winding is analyzed using the Palmgren-Miner model. The proposed methodology can evaluate the number of stress cycles leading to transformer winding failure as well as the weak link of winding fatigue life.