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With the development of electric electron technology and controlling technology, controller for driving permanent magnet synchronous motors is used widely. The using of a controller can expand the motor speed range and improve motor runtime performances. However, the output current of a controller contains lots of time harmonics that will have bad infl uences on motor torque and losses. In order to analyze the infl uences of the time harmonics on the motor performances, diff erent time harmonic currents were injected into the motor armature. Taking a 750 W, 250 r/min permanent magnet synchronous motor with hybrid magnet poles (HPPMSM) as an example, the 2-D fi nite model was established. On this basis, the torque ripple and eddy current losses of permanent magnets with diff erent time harmonics were obtained. The infl uences of time harmonics on motor torque ripple and eddy current losses were determined, and the impacting mechanism was revealed. The analyses may be helpful for the optimal design of HPPMSM.
The content of harmonic current increases with an increase in the number of power electronic devices in power grid. When a generator is directly connected to the power grid through a step-up transformer, the influence of the harmonic currents on the generator is inevitable. To study the influences of harmonics on generators, a 24-MW bulb tubular turbine generator is taken as an example in this paper. A 2-D transient electromagnetic field model is established. Through a comparative analysis of the data of experiments and simulations, the correctness of the model is verified. The values of the air gap magnetic density, torque and losses of the generator under various conditions are calculated using the finite element method. Taking the rated condition as a reference, the influence of the harmonic currents on the magnetic flux density is analyzed. It is confirmed that the time harmonic is a key factor affecting the generator performance. At the same time, the effects of harmonic currents on the torque ripple, average torque and eddy current loss of the generator are studied, and the mechanism of the variation of the eddy current loss is also discussed.
The performance of adaptive full order observer for speed sensorless induction motor drives can be improved further though it has been researched for many years. A novel speed estimation algorithm with estimated rotor flux error and the corresponding feedback gain design method are proposed in this paper. Through Lyapunov’s theorem, the stability of proposed speed estimation algorithm is proved. The sensitivity of speed estimation to motor parameter deviation is reduced. Finally the feasibility of proposed two methods is verified by experiments.
Firstly, we applied the X-ray non-destructive testing technology to detect wood defects for getting the images. After graying the images, we calculated their GLCMS(Gray Level Co-occurrence Matrixes), then we normalized GLCMS to obtain the joint probabilities of GLCMS. The feature vectors of images, which included 13 eigenvalues of images were calculated and extracted by the joint probability of GLCMS. The fuzzy BP neural network(abbreviated as FBP) was designed by combining fuzzy mathematics and BP neural network . And the FBP neural network was regarded as the membership function of feature vectors, the outputs of the network was regarded as the degree of membership to the feature vectors in each category. We use the maximum degree of membership method for the pattern recognition of feature vectors, so the automatic identification and classification for feature vectors were achieved , and then the automatic identification of wood defects was realized. By simulated study and training many times, the results shown that the average recognition success rate of the network was more than 90%, and some FBP networks had an extremely high recognition success rate to training samples and test samples.
Since the stator winding of High-Speed Permanent Magnet Generator (HSPMG) has few winding turns and low inductance value, it is more prone to be influenced by harmonic current. Moreover, the operation efficiency and the torque stability of HSPMG will be greatly influenced by harmonic current. Taking a 117 ㎾, 60 000 rpm HSPMG as an example, in order to analyze the effects of harmonic current on HSPMG in this paper, the 2-D finite element electromagnetic field model of the generator was established and the correctness of the model was verified by testing the generator prototype. Based on the model, the losses and torque of the generator under different frequency harmonic current were studied. The change rules of the losses and torque were found out. Based on the analysis of the influence of the harmonic phase angle on torque ripple, it is found that the torque ripple could be weakened through changing the harmonic phase angle. Through the analysis of eddy current density in rotor, the change mechanism of the rotor eddy current loss was revealed. These conclusions can contribute to reduce harmonic loss, prevent demagnetization fault and optimize torque ripple of HSPMG used in distributed power supply system.
Among the vibration-based fault diagnosis methods for rolling element bearing, the shock pulse method (SPM) combined with the demodulation method is a useful quantitative technique for estimating bearing running state. However, direct demodulation often misestimates the shock value of characteristic defect frequency. To overcome this disadvantage, the vibration signal should be decomposed before demodulation. Empirical mode decomposition (EMD) can be an alternative for preprocess bearing fault signals. However, the trouble with this method’s application is that it is time-consuming. Therefore, a novel method that can improve the sifting process’s efficiency is proposed, in which only one time of cubic spline fitting is required in each sifting process. As a consequence, the time for EMD analysis can be evidently shortened and the decomposition results simultaneously maintained at a high precision. Simulations and experiments verify that the improved EMD method, combined with SPM and demodulation analysis, is efficient and accurate and can be effectively applied in engineering practice.
As a kind of emergency power supply in military fi eld, the high-speed permanent magnet generator (HSPMG) has attracted wide attention to its healthy condition. The loop current (LC) of the inter-turn short-circuit (ITSC) fault seriously endangers the generator unit operation stability and power supply reliability. In order to study the infl uence of pulsating magnetic fi eld produced by LC on the electromagnetic fi eld, the two-dimensional fi nite element model (FEM) of the 117 kW, 60000 rpm HSPMG is established. By comparing calculation result and test data, the accuracy of the model is verifi ed. The fi eld-circuit coupling method is used to reveal the change mechanism of magnetic fi eld symmetry when ITSC fault occurs. By comparing the spatial distribution of the air-gap fl ux density, the relationship among the spatial distribution of the air-gap fl ux density, the elliptical rotating magneto-motive force (MMF) and the current phase angle is determined. The variation of the amplitude of the air-gap fl ux density space harmonic under diff erent fault degree is studied, and the fault characteristics of ITSC fault are obtained, which provides a reference for ITSC fault diagnosis and fault degree identifi cation. In addition, the research also laid a theoretical foundation for the next analysis of the loss and temperature fi eld.
The performance and safety of a geotechnical engineering system are affected by uncertainties. The purpose of Reliability-Based Optimization (RBO) is to find a balanced design that is not only economical but also reliable in the presence of uncertainties. Numerous reliability optimization techniques have been proposed. In this study, the Artificial Bee Colony (ABC) algorithm is employed for reliable optimization of a geotechnical engineering system. The proposed ABC-RBO method combines ABC and First Order Reliability Methods (FORM). Optimization is performed with ABC, while the reliability analysis is performed with FORM, incorporating Excel solver. The proposed method is verified by two geotechnical engineering examples and compared with other methods, and shown to be robust, accurate, and feasible.
1MHz isolated high efficiency high power density DC/DC converter is critical for future industrial applications. The GaN devices have a better performance for such high frequency than silicon device of high breakdown voltage due to their much lower parasitic capacitance. The modeling of the primary switches conduction losses is built in this paper. Based on the model the relation between the NFoM (Rdson⋅Cotr) of primary devices and conduction loss is revealed, thus the lower voltage devices with lower FoM is adopted to implemented the experimental verification. Since the equivalent NFoM is independent of the device count of series connection and is decided by single device, an inputseries output-parallel structure prototype with multiple SRC DCX cells is implemented with low voltage MOSFETs. The 380V-12Vprototype achieves a peak efficiency of 98.3% and a power density of 810W/inch3 with multiple 60V MOSFETs.
Through tensile testing of 15 steel bolt-sphere joints and 15 aluminum alloy bolt-sphere joints, infl uencing rules of material type, high temperature and cooling mode on tensile properties of post-fi re bolt-sphere joints were studied, and then failure modes of the joints were determined. According to experimental data, the calculation formula of residual tension capacity of post-fi re bolt-sphere joints was presented. Experimental data indicated that (1) decreased extension on the mechanical properties of aluminum alloy bolt-sphere joints after high temperature in the fi re was signifi cantly higher than that of the steel bolt-sphere joints; (2) when fi re temperature was lower than 800 °C, the tension capacity of steel bolt-sphere joints could be restored by more than 90% after cooling; (3) when fi re temperature was lower than 500 °C, the tension capacity of aluminum alloy bolt-sphere joints could be restored by more than 50% after cooling; (4) bolt-sphere joints could still satisfy the requirement of “strong node and weak member” after a fi re; and (5) material type and fi re temperature were the main factors that infl uenced post-fi re mechanical properties of bolt-sphere joints.