Research On Topology And Modulation Method For Hybrid Multilevel Inverter

In recent years, multilevel converters have presented an important development to reachhigher power with increasing voltage levels. The research on the multilevel inverter has beenreceiving wide attention, and becoming hot point in power electronics. Based on traditionalmultilevel topologies, this paper focus on topologies and modulation methods for hybridmultilevel inverters, and a lot of innovation are made. Hybrid multilevel topologies and hybrid modulation methods are firstly defined in thisdissertation. According to the range of the definition, several hybrid topologies and controlmethods are given, analysis of problems for the hybrid topologies are carried out. . Diode-clamp cascaded multilevel inverter based on single-phase 5-level diode-clampinverter is presented. The multilevel waveform is synthesized by adding of each converteroutput voltage. A novel hybrid diode-clamp cascade multilevel converter is firstly put forward. Thenew concept of the converter is based on connection of multiple diode-clamp convertermodules with different dc bus voltages. A new hybrid PWM method is also proposed. Adetailed example is given, and a general discussion of N-cell HDCMC is presented.Experiment validation is also carried out. An asymmetric 5-level inverter is developed in which a half-bridge diode-clampinverter and a conventional half-bridge inverter are connected to a common split-capacitorpower supply. Analysis of a control technique for the inverter, which incorporatessquare-wave synthesis in conjunction with unipolar triangle carried-based PWM method, isincluded. Under the proposed control technique, the new configuration permits faster devicesand high voltage devices operating in synergism. Comparison with five other single-phase5-level inverters is presented in this paper. In order to verify the proposed approach, asingle-phase 5-level asymmetric inverter was constructed and experimental results areprovided. Novel hybrid asymmetric inverters are firstly proposed. Based on asymmetric 5-levelinverter, this paper proposed a new hybrid asymmetric 9-level inverter in which anasymmetric 5-level inverter and an H-bridge inverter with equal dc bus voltage are seriesconnected to form an inverter phase leg. This paper also presents a hybrid asymmetric cascadeinverter based on the connection of multiple asymmetric 5-level inverters. New hybridasymmetric control techniques for the two inverters are proposed. Output spectral analysis iscarried out, experiment validations are provided. III华 中 科 技 大 学 博 士 学 位 论 文 On the base of many hybrid modulation methods proposed in this paper, a generalizedhybrid modulation method and analytical method are firstly given. The derivation of hybridmodulation technique is based on traditional cascaded inverter. The novel concept of themodulation method is to output full PWM waveform by using the least or fewer modules tooutput high frequency PWM waveform, while other modules only need to output lowfrequency stepped-waveforms. Theoretical analysis and derivation based on amplitudecondition and level condition are firstly given. Design procedure of the methods and examplesare presented.