一种改进型级联多电平拓扑及其频谱分析

Topology and Spectral Analysis of an Improved Hybrid Cascade Multilevel Converter

近些年,多电平拓扑结构特别是级联和二极管钳位这两种拓扑在中高压大功率领域中得到广泛的关注和应用。本文对这两种多电平拓扑结构的优缺点进行分析,根据目前电力电子器件的发展特点,将具有相同母线电压的一个二极管钳位H桥拓扑与若干个H桥级联,形成一种具有实用价值的改进型逆变器拓扑结构,并对其进行研究。针对这种拓扑结构,分析了一种方波合成与单极性三角波载波PWM相结合的混合调制方法。该方法能使开关速度较快的器件和耐压值较高的器件一起协同工作。而后通过分析得出该拓扑并不存在混合多电平拓扑通常存在的直流侧电流倒灌的问题,并通过对混合调制过程本质的剖析,建立起调制过程的三维模型,并通过双Fourier级数展开和繁琐的数学推导,求得了输出电压的严格解析表达式,为输出PWM波形的频谱分析提供了一种启发性的思路。最后实验针对整个方案进行了验证,给出了实验结果。

Cascade and neutral-point-clamped（NPC） converter have become increasingly popular in recent years due to their practicability.This paper presents an improved hybrid cascade multilevel converter that is derived from these two topologies.The proposed converter is the series-connection of a diode-clamp converter and several H-bridge converters with the equal dc bus voltage.According to this topology,a hybrid modulation method which incorporates square-wave synthesis in conjunction with unipolar triangle carried-based PWM method is illustrated.By this method,higher voltage devices and faster devices can operate in synergism.Based on the anatomy of hybrid modulation process in nature,3-D mathematic model is built.Further,by the double Fourier series expansion and intricate derivation,a rigorous output analytic solution is acquired,which facilitates the evaluation of spectra accurately.The feasibility and the advantages of the topology are validated by the experiment.