Research On Control Method Of Neutral Point Voltage Balancing In Three-level Inverter

With the rapid development of modern power electronic technology and digital control technology,multi-level inverter has attracted more and more attention and become a hot topic in domestic and overseas research.The multi-level inverter has been widely used in the field of ac/dc energy conversion,high voltage high capacity ac motor frequency control,power quality control and so on.Compared with the traditional multilevel inverter two level inverter,output voltage harmonic content is low,the voltage stress of switching device is subjected to small,low switching frequency,small switch loss,high efficiency inverter.In the application and research of multi-level inverter,three-level inverter is the most widely used.In this paper,the inherent problem of tri-level inverter is analyzed qualitatively and quantitatively.In qualitative analysis,from the perspective of space vector to judge the only vector and vector affects the balance of neutral voltage,and the positive and negative small vector of neutral voltage balance effect is different,it is becoming the key factor of controlling neutral voltage.In the quantitative analysis,the reference vector is used as an example in the large sector I,and the formula is used to calculate the midpoint current of the reference vector in different small sectors.We have a basic understanding of the imbalance of the middle point potential,and then the control idea of the neutral potential balance is analyzed,and the method to control the neutral potential balance is further found.Based on the high frequency of this project,the control algorithm of midpoint potential in SVPWM modulation method is given,and the simulation model is established,and the simulation waveform proves the effectiveness of the control method.According to the design requirements,a complete set of experimental apparatus for diode clamping type tri-level inverter is set up under laboratory conditions.The main circuit includes parameter calculation and selection,drive circuit and control circuit design.The control circuit includes the sampling circuit,the DSP hardware circuit and the CPLD hardware circuit.DSP is responsible for controlling data collection and instruction output,etc.CPLD is responsible for fault logic judgment and alarm feedback of global circuit.The temperature field simulation of power devices and radiators is carried out for the heating problem caused by switching tube loss.Finally,the experimental results show that the reliability of the hardware design and the correctness of the control method are proved by the experiment of the platform device of diode clamping type tri-level inverter.