Research On Three-level Inverter And Neutral Point Potential Balancing

Nowdays with the increasing shortage of enregy and increasingly serious environmental pollution, research on energy saving technology is becoming more and more attention to us, thereinto, the study on high-voltage and high-power multi-level inverter is becoming a hot spot. Because of the advantages of low voltage requirements, high equivalent switch frequency, no dynamic equalizing and good output waveform, multi-level inverters are widely used in Power System, Transmission Systems, Petrochemical Industry , Ore Mining and so on.However there are many problems need to be sloved in the application process of NPC Multi-level inverters. Neutral point potential unbalancing is one of the more prominent problems. Neutral point potential unbalancing may result in output waveform distortion, switching devices withstand the voltage unbalancing, shorting the life of capacitor, multi-level withering to three or two level. So it must be sloved. In this paper, NPC three-level inverter will be as the research object, and we will study the problem of neutral point potential balancing as well as using a software control strategy to control neutral point potential. This algorithm may also be extended to random mutil-level structure.The mechanism and the influence of NPC three-level inverter neutral point potential imbalancing are analyzed in this paper. Then, by optimizing the control algorithm of SVPWM and using the different effects of the neutral point potential made by active and negative small vectors, a software strategy by adjusting the work time of active and negative small vectors is introduced. After the studying of theory, this paper simulates the balanced algorithm of neutral point potential by MATLAB/SIMULINK simulation software. In the expriments NPC three-level inverter is established with MOSFET and diodes, and DSP of TMS320LF2407A is used to achieve the control algorithm. Simulation and actual experiments verify the effectiveness of the method and obtain a better suppression effect of the neutral point potential shift.