| Hybrid cascaded multilevel inverter is the improvement of traditional cascade multilevel inverter topology, its topology has many forms, and this paper focuses on the form of dc voltage sources of different magnitude. The biggest advantage of this hybrid cascaded multilevel inverter is that in the condition of the same number of output voltage level, it greatly reduces the number of independent dc supply. But, in some specific applications, dc supply has to be only one. Focused on this problem, this paper gets a novel hybrid cascaded multilevel inverter which has two-stage topology and bi-directional power flow by adding a high frequency link in the dc side, and it can realize one dc supply. This method has the advantages of low total harmonic distortion, high quality of output voltage waveform and small volume.At first, this paper introduces the research status and development trend of the multilevel technology in topology and modulation strategy. By using a high frequency link in the conventional hybrid cascaded multilevel inverter, it realized a novel inverter. The thesis analyzes the two-stage topology of the novel inverter in detail, gives circuit structure and working principle of preceding stage and backward stage, establishes mathematical model of backward stage, gets relationship between the input and output, studies the power distribution in the novel inverter, provides evidence for the rationality of using high frequency link. Then this paper introduces the control strategy, control of preceding stage is the duty ratio0.5modulation because the purpose of high frequency inverter is producing square waveform, and control of backward stage is based on nearest level modulation. The paper gives the principle and mathematical model of nearest level modulation. Fourier analysis is used in study of output voltage waveform and the effect of modulation ratio on output voltage is discussed in detail. Focused on different dc supply, this paper gives two kinds of control strategy. Based on theory analysis, the feasibility of circuit structure and control strategy is shown by Simulink simulated results.Finally, the design of hardware and software is completed. The hardware design mainly includes power circuit, driving circuit, sampling circuit, etc. And the software design is based on DSP chip of TMS32OF28335. Combined with its CCS4.2simulation platform and XDS100V2simulator, the paper completes design of control program. The debug to the prototype and the analysis of the final experimental waveforms confirm the correctness of the theoretical analysis and simulation analysis. |
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