Research On Modulation Algorithm And Fault-Tolerant Control Of H-Bridge Cascaded Inverter

Multi-level inverters are widely used in high voltage and high power applications because of its many advantages. H-bridge cascaded inverter is a kind of multi-level inverter, which has become a hot research area. This thesis take H-bridge cascaded inverter as research objects, and its modulation algorithm and fault-tolerant control technology are studied.The topology and working principle of H-bridge cascaded inverter are analyzed in this thesis. The carrier phase-shifted modulation, carrier disposition modulation and carrier switching frequency optimized modulation are studied, and the modulation principle and realization methods are presented. The simulation model of H bridge cascaded inverter is built by simulation software, and the modulation algorithms are analyzed and validated.Traditional multi-level SVPWM has a large amount of computation,and its algorithm is complexity. So, it is difficult to extend to higher level. In order to solve these problems, a SVPWM algorithm based on power cell vector phase shifting superimposition is studied in this thesis. The algorithm is based on two-level SVPWM. It is easy to realize and expand. In addition, a simplified SVPWM algorithm based on mapping principle is studied. This algorithm maps the multi-level vector into two-level vector, which greatly simplifies the workload of the multi-level SVPWM algorithm. This algorithm is applicable to all multi-level inverter topologies. The simulation results verify the correctness of the algorithms.The modulation algorithms of H-bridge cascaded inverter are based on the equal DC voltage of each cell. In view of H-bridge DC voltage range, two modulation algorithms are studied. They are DC voltage unequal one-dimensional vector modulation algorithm and DC voltage unequal feed forward compensation algorithm. The modulation principle and realization methods are presented. The two modulation algorithms are validated by simulation.The fault types of H bridge cascaded inverter are analyzed. A fault diagnosis method based on output phase voltage of inverter is studied. After analyzing the existing problems of traditional fault-tolerant control technology, the neutral point drifting technology is studied. Its principle and realization methods are presented. The correctness of fault diagnosis method and fault-tolerant control technology are verified by simulation.An experimental prototype of H-bridge cascaded inverter is designed. The design of main circuit parameters and control system are presented. The correctness of the modulation algorithms and fault-tolerant control technology studied in this thesis are verified on the experimental prototype.