Research On Neutral-Point-Clamped Three-Level Inverter And Neutral Point Potential Problem

In recent years, with the rapid development of power electronic devices and microprocessors, and researches on energy saving technology are becoming much more attention to us, in the field of the AC speed regulation, high-voltage and high-power multi-level inverter are the focus of the study.With multi-level topology proposed, devices’voltage requirements, high equivalent switch frequency and other problems have been solved. Among many multi-level topologies, diode clamped three-level topology has been most widely used as a practical one. But the solution to the neutral point potential problem due to its own structure needs to put forward urgently. The thesis researches on the high performance AC variable frequency speed control system based on this topology and aimes to work out its inherent problem of the neutral point potential.Firstly, the diode clamped three-level inverter is introduced, then its topology and the working principle are analyzed. Based on these, the space vector pulse width modulation is given as a widely used algorithm applied to the three-level inverter, then the vectors’effect on the neutral point potential is explained. The models of the induction motor on several coordinates are the basic theory of vector control, the rotor field oriented control is analyzed in details in the next part and a system is designed based on the indirect field oriented control. As to neutral point potential problem, many reseaches have been carried out and a solution to the problem called neutral point charge balance method has been demonstrated to solve it in the thesis.On the basis of the theory mentioned above, the control system is simulated in the Matlab/Simulink, the results of simulation prove the control system has a very quick dynamic response and high steady state accuracy. Meanwhile, the simulation results of the system with the neutral point potential control strategy illustrate the problem is solved perfectly, all these verify the effectiveness of the method.Finally, the last part of the thesis draws a summary of the research and gives an analysis and prospect for the future researches.