Three-level Inverter Technology Practical

In recent years, the development of the three-level inverter has been widely used in the electrical drives area. The emergence of three-level inverter topology provides an effective way for the realization of high voltage and high power inverter. The research and development of three-level inverter are very significant to the aspects of technology and practical application. This paper conducts deep analyses and research based on the three-level inverter.Firstly, this paper introduces the topology of three-level inverter main circuit and control requirements, the basic principle, character and PWM control strategy, as well as the problems in debugging and the related solutions.The neutral potential imbalance is an inherent problem of three-level topological structure.This paper analyses the intrinsic causes in neutral voltage imbalance and presents the voltage balance method based on a hysteresis loop control. The method dynamically controls two capacitor voltage, according to the load current direction of different combinations, adjusts the small redundant vectors , fully considers the medium vectors of impact on the neutral point potential balance, and analyses the reference voltage vectors falling into one or two small vector redundant small triangle when switching states choice, the order of switch and sequence of time allocation.Carrier modulation is one kind modulation mode of multi-level inverters. In this paper, the modulation strategy based on the carrier used in three-level inverter is studied and analyzed, the harmonic characteristics of different modulation strategies are compared, and the relationship of modulation degree and total harmonic distortion is obtained. The conclusion is validated by the results of simulation and experimentation.The hardware design of main circuit and control circuit will be a direct impact on the operation of inverter performance. This paper introduces the hardware design of the inverter main circuit and control circuit at locale industry, and the relevant parameters are drawn from the combination of theoretical arithmetic and practical tests. This paper analyses voltage imbalance of inverter inside and outside RCD buffer loop when it works, and gives a detailed snubber loop buffer algorithm.Finally, based on the research mentioned above, the paper develops the experimental apparatus of the 690V/600kW high power middle voltage frequency inverter, and the operation result at field industry is given out in this paper. The result indicates that the inverter can achieve a good waveform and performance.