Study On The High-Voltage Variable Frequency Drive Based On Hybrid Seven-Level Technology

Multilevel technology is the key technology used in high voltage and high power field. Compared with the traditional two-level technology, the multilevel technology has lower requirement to power device on voltage switching frequency and voltage stress. Meanwhile, it has a better performance in the harmonic control and electromagnetic compatibility, so it attracted widespread attention.High voltage inverter is a typical application of multilevel technology in the field of electric drive field. However, most of the high voltage inverter is expensive and bulky, and it is not applicable in the occasions which has the strict requirements to the device volume, weight and cost. The concept of hybrid multilevel provides a useful way for solving this problem.In this thesis, hybrid seven-level converter is the main research object. From the point of view of resolving power flow, the matched modulation method will be analyzed and got, and the results will be applied into the cascaded topology. Finally,the control strategy of hybrid seven-level unit, cascaded, multilevel variable frequency speed regulation system will be got.Firstly, the basic structure and working principle of the cascaded high voltage inverter will be analyzed, and thesis provides vector control method of high voltage inverter, and build the simulation model of variable frequency speed regulation system based on permanent magnet synchronous motor.Secondly, the hybrid seven-level topology has been analyzed, and modulation method for hybrid seven-level topology has been proposed. From the point of view of eliminating the power flow, the method gives full play to the respective advantage of high voltage and high switching frequency of the two kinds of power devices, and realize the complementary advantages.Finally, the hybrid seven-level topology is combined with the cell series multilevel topology to achieve the multilevel voltage output by the improved method ofcarrier phase shift. At the same time, using the neutral shift to achieve the fault processing function of high voltage inverter and improve the reliability of the system.The simulation and experimental results show that the new hybrid cascaded high voltage variable frequency system has good control performance and output effect.