Advances in Mechanics Engineering

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Authors: Zhen Yu Nie, Xiao Bin Guo
Abstract: The paper presents the design of three-level variable-frequency power supply device which is used in electric propulsion system of ship The variable-frequency power supply device is controlled by the DSP chip TMS320LF2407, and inverter is neutral point clamped three-level inverter circuit which is consisted by IGBT, and it’s controlled by SVPWM modulator approach to determine switching elements making or breaking. In order to keep the balance of neutral voltage, the paper presents to use the method that two equivalent switch state of short vector work alternatively to cut down the variable quantity of capacitive, and to achieve the voltage balance. Rotor flux orientation vector control of torque closed loop control has taken in the speed control system of propulsion motor. The whole variable-frequency power supply device has some strong points such as working reliably, dynamic response fastly, current ripple small and less harmonic content of output voltage, etc, it has some practical value.
429
Authors: Ying Zhao, Jin Shan Ji, Nai Cheng Du
Abstract: This paper mainly describes the mechanism and elimination method of harmonic in low-voltage power grid. Improve direct current control method in the traditional filter method,filtering the harmonic and timely compensating reactive power in the grid. On this condition, it can make the power grid safe and stability. At the same time simulate the improved direct current control method, and the results verify the correctness and rationality of the control method.
433
Authors: Jin Zhao Zhang
Abstract: According to the three-motor synchronous system, S7-300PLC is as the controller .The three-motors synchronization control platform is constructed based on PC monitoring configuration software of WinCC, so the combination of drive, testing, monitoring, communications and other systems are optimized. The programming software for the lower computer is STEP7V5.3 which supports S7-300PLC.In addition to the hardware configuration, parameter setting, the communications configuration and programming, its function includes starting, maintenance, operation and diagnostics, etc. Then, the system can not only run under the operating system WIN2000/XP matching with the Windows graphical and object-oriented operating principles, but also be provided online debugging capabilities. In the preparation stage of experiment, in order to making the algorithm implementation high accuracy and strong rapid real-time response, the data sample has been optimized to fully reflect the dynamic and static performance of the original system.
438
Authors: Bei Bei Deng
Abstract: This paper designs a kind of IR2110 based on high voltage suspension of driving circuit for electromagnetic valve, using the IR2110high pressure suspension characteristics, the boost circuit to meet the rapid opening stage and maintain the electromagnetic valve stages required for high voltage. The IR2110 based high voltage suspension driving circuit to realize electromagnetic valve is closed quickly, with a control signal frequency range, starting current, maintain the current size, PWM signal frequency and duty cycle can be adjusted advantages.
442
Authors: Cong Mei Zha, Qi Ying Xu, Yong Sheng Zhu
Abstract: Static var generator (SVG) basic principle and control method are introduced in the article, a direct current control method for SVG is put forward based on d-q transformation, this method is also analyzed from theory and made simulation model, the simulation results show that this control method is reasonable and effective.
446
Authors: Ying Wang, Wei He, Zhen Zhu Zhou, Chun Dan Zhu
Abstract: Through the analysis of characteristic of lightning currents, this paper expounded the lightning current wave-form and the primary parameters of it. The previous lightning current models contain only two parameters, wave tail time constant and the peak current value, which is imperfection. In order to solve this problem, a new lightning current model with the additional parameters such as lightning channel radius and velocity of the return stroke was proposed. On the basis of lightning current parameters and wave-form characteristic, we compared the new lightning current model with the double exponential function model, Hodler model and impulse function model. And then the distinctions among the four different models were received and the wave-form of the new model accorded with the characteristic of really lighting current wave-form well. On the other hand, the advantages and disadvantages about the new lightning current model were explained. This new lightning model provides the theoretical basis for further study of lightning electromagnetic field.
450
Authors: Xin Jun Li
Abstract: The three-phase voltage type SPWM inverter output voltage and current harmonic and its generation rule is discussed. And put forward a new easy to implement harmonic suppression strategy, the method through the correct choice of the carrier frequency and the sinusoidal wave superimposed on a three wave makes saddle shaped wave, to produce a corresponding SPWM waveform control inverter switch on-off thus improving the output waveform. Mathematical analysis shows that is helpful to reduce the output voltage THD ( waveform distortion factor ), improved harmonic current loss and torque characteristics, the simulation results prove the validity of these measures and practical.
454
Authors: Zhi Jian Yuan, Yan Li
Abstract: The impact of voltage sags on equipment is usually described by equipment failure probability.It is generally difficult to assess and predict the probability because of the uncertainty of both the nature of voltage sags and the VTL (VTL) of equipment. By defining the equipment failure event caused by voltage sags as a fuzzy-random event, a fuzzy-random assessment model incorporating those uncertainty is developed. The model is able to convert the probability problem of a fuzzy-random variable to that of a common random variable by using λ-cut set. It is thus valuable in theoretical analysis and engineering application. The validity of the developed model is verified by Monte Carlo stochastic simulation using personal computers (PCs)as test equipment.
458
Authors: Guang Wei Liu, Feng Ge Zhang, Jin Xiang Gao
Abstract: In view of the time consuming and sensitive to finite element meshes, the finite element method is not suitable for claw pole machine with outer permanent magnet rotors with complicated and asymmetric 3D structure. A new analytical calculation model based on air-gap magnetic field analysis in polar coordinates is proposed. According to boundary conditions, the radial and tangential flux density is obtained by using the Fourier’s series, and then the cogging torque and no load EMF is calculated. In order to verify the accuracy of the analytical method, the finite element analysis is finished. Moreover, one prototype is manufactured and measured also. The analytical results well agree with those obtained by the FEM and experiments, confirmed the feasibility of this method.
463
Authors: Ting Na Shi, Rui Liu, Hong Feng Li
Abstract: In this paper, a structure of friction feedforward compensation based on electromagnet torque feedback compensation is proposed to improve the speed performance of permanent magnet synchronous motor (PMSM), especially in a low speed range. First, this paper estimates the parameters associated with the friction model via an off-line identification method and compensates friction with the model. Then electromagnet torque feedback compensation is introduced to enhance the robustness of the system. The proposed control scheme is verified by computer simulation.
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