Research On Control Method Of Neutral Point Flictuation In Neutral-Point-Clamped Three-Level Inverter

With the development of power electronic technology, the three-level inverter has low voltage stress, high voltage conversion rate, and low output harmonic content, become a research hotspot in recent years. Among the three-level inverter topology structure, neutral-point-clamped three-level inverter circuit, which has been widely used, is simple and easy to implement digital modulation method.Neutral-point-clamped three-level inverter topology characteristics leads to neutral voltage fluctuations, which bring the harmonic content of output waveform increases, shorten the service life of switch device. In order to keep the inverter system safe and reliable operation, must to control the neutral voltage. Based on the Neutral-point-clamped three-level inverter as the research object, after studying the existing neutral voltage control method, improved virtual vector control method of neutral voltage, thus provides a new thought of neutral voltage control, the main research content is as follows:1. This thesis introduces the research background and significance of three level inverter, expounds the Neutral-point-clamped three-level inverter sine pulse width modulation and space vector pulse width modulation, analyzed the cause of the problems of neutral voltage fluctuations in Neutral-point-clamped three-level inverter and influence, studied the existing several point control method, compares the advantages and disadvantages of these methods.2. Introduced the idea of virtual vector, and puts forward an improved method on the basis of the virtual vector of neutral voltage control method. This method combines the redundant small vector and the neutral voltage control method of virtual vector, using redundant small vector and virtual vector two methods respectively under the low and high modulation ratio has the strong control ability of neutral voltage, achieved the control purpose of neutral voltage in a relatively wide modulation ratio. The rationality of the method is verified by simulation experiments.3. By constructing the new virtual vector and redraw sector within the small area, extending the ideas of the neutral voltage control of virtual vector to overmodulation area. In the overmodulation region, the use of virtual vector effectively neutr Simulation results show that the effectiveness of the method.control of neutral voltage. Simulation results show the effectiveness of the method.