Research On Midpoint Voltage Balance And Common Mode Voltage Suppression Method Of Three-level Inverter

The NPC three-level inverter is one of the most widely used inverter types.The problems of unbalanced midpoint voltage and high common-mode voltage amplitude are related to the performance and practical application of the inverter.The midpoint voltage imbalance is an inherent problem of this type of inverter,which directly affects the quality of the output voltage waveform of the inverter and the life of the device;although the common mode voltage does not have a significant impact on the performance of the inverter,but the high common-mode voltage will cause harm to the surrounding operators and equipment,and also reduce the stability of the inverter.If these two problems are not controlled,it will have a great impact on the operation of the inverter,and even hinder the development and wide application of the inverter.In view of the development status of NPC three-level inverters,combined with the control requirements of midpoint voltage balance and common-mode voltage suppression,this paper proposes an IVSVPWM method by improving the traditional virtual space vector modulation method,and introduces a method based on genetic particles.The closed-loop control of the group algorithm effectively realizes the midpoint voltage balance and the effect of suppressing the common mode voltage amplitude.First of all,this paper takes the NPC type three-level inverter as the research goal,analyzes its topology,working principle and dynamic commutation principle in detail,and establishes a mathematical model based on space vector,and analyzes this type of inverter in detail.The causes and hazards of the problem of unbalanced midpoint voltage and high common-mode voltage amplitude.Secondly,the implementation process of the traditional space vector modulation method and the virtual vector modulation method is studied in detail.In view of the large number of trigonometric function operations in the90°coordinate system of the traditional method,the60°coordinate system is introduced,and the coordinate transformation and the per-unitization of the vector are used to calculate the The computational complexity of the algorithm is greatly simplified;Aiming at the problem of high common-mode voltage amplitude in the traditional virtual vector modulation method,a new virtual vector is defined,which realizes the balance of the midpoint voltage of the NPC three-level inverter and reduces the common-mode voltage amplitude.Then,in view of the midpoint voltage fluctuation problem that may occur in the actual operation of the NPC inverter due to some reasons,dynamic adjustment parameters are introduced,and a closed-loop control strategy based on GA-PSO is introduced to realize the real-time monitoring of the midpoint voltage.Finally,a simulation model is built in Matlab/Simulink to simulate the traditional VSVPWM method,the IVSVPWM method proposed in this paper,and the method after introducing the closed-loop control strategy based on GA-PSO.The results show that the method proposed in this paper has better midpoint voltage Balance and common-mode voltage suppression effects prove the effectiveness of the method proposed in this paper.