Research On Neutral-Point Potential Balancing Control Of Three-level Neutral Point Clamped Inverter

With the rapid development of national economy,the medium and low voltage equipment has been far from meeting the needs of industrial development.The equipment with high power density,high efficiency,high performance and large capacity has become the focus of research.Three-level neutral-point clamped inverter have been applied in high voltage and large power fields since 1981,because of its simple structure and its modulation method is easy to realize digital.Compared with the two-level inverter,this topology has obvious advantages,but the neutral-point potential deviation of this topology brings great harm to the system,which will affect the normal operation of the system.In order to meet the needs of industrial production,Based on the inherent problem of three-level NPC inverter,the main reserch as follows:1,This thesis introduces the topology and principle of the three-level NPC inverter,The principle and algorithm steps of modulation algorithm of SVPWM and VSVPWM are analyzed in this thesis.2,Analyzes the causes of neutral-point unbalance of the three-level NPC inverter from the aspects of space vector,current,load and device parameters.It is concluded that the neutral point current not equal to zero is the most fundamental reason affects the neutral point potential.Based on the above analysis,several neutral point balance control strategies are introduced in this thesis.3,Due to the deficiency of the modulation strategy of the virtual space vector in the practical application,this thesis makes some improvements to the virtual vector method,and adds a fuzzy controller to control the neutral point potential.The mechanism the mechanism of the control algorithm is analyzed in detail,and a fuzzy controller is designed according to the design process and control algorithm of the fuzzy controller.4.The simulation model of the three-level NPC inverter system is built using Matlab/Simulink,and the simulation analysis is carried out under the conditions of different device parameters and different loads.The simulation results have verified the effectiveness and feasibility of the improved method.According to the simulation results,the advantages and disadvantages of various control methods are compared...