Research And Design Of Medium-high Voltage Converter

In recent years, multilevel converters have presented an important development to reach higher power with increasing voltage level. At present, cascaded multicell converter, diode clamped multilevel converter and flying capacitor multilevel converter are 3 mainly converting topologies. Among them, cascaded configuration gains many advantages: reducing harmonics in output voltage and input current, stable stability, and high efficiency. Therefore, cascaded converter has been chosen as the research subject of this paper. Traditional cascaded converter has a noncontrolled diode rectifier in each power cell at the input side that does not permit the regeneration of power from the load to the source. And each power cell uses an input transformer with many secondary windings that cause higher cost and more complex design steps. To solve this problem, a novel cascaded converter with regeneration capability and high power factor is proposed, which has less power parts and dose not use input transformer. Firstly, several topologies and PWM methods for traditional cascaded converter are introduced in the thesis. Secondly, The concept and control strategy of cascaded converter are proposed in detail.And the paper also presents the method to form cascaded converter by connecting cells in series. Next based on switching function and power electronics' principles, mathematical model of five-level converter has been built. With the help of MATLAB, the model is realized in the computer and some simulating results are showed. Afterwards, this paper analyzes the harmonic components of carrier –based PWM strategy with methods of mathematics and simulation. Both of the means receive coincident results which are satisfied. Finally, the hardware design for the new-cascaded converter is introduced. This design has something of significance for the further research of the medium-high voltage converter.