| With the development of power electronic AC technology,all kinds of advanced control technology emerge in an endless stream.Due to voltage capacity constraints of the power electronic devices, the traditional two level inverter commonly used the "high-low-high"manner to obtain high power through the transformer bucking and boosting,or use multiple small capacity inverter units by multi winding transformer to realize, which makes the decrease of the system efficiency and reliability.Therefore,people hope to realize directly high-voltage inverter technology. Because of its broad prospecting high power application,multilevel power conversion technology has become a hot research topic in the field of power electronics. Around the multilevel converters,new topologies and modulation strategies emerge in an endless stream. Due to its advantage of small switching stress, the superior output waveform,easy package and expand, cascaded multilevel inverter are more and more widely used in high voltage variable frequency speed regulation, flexible AC transmission and high voltage DC transmission and other occasions.This paper first systematically introduces the significance and development status of the multilevel inverter, and carries on the detailed elaboration to its several different topological structure, and by the comparative analysis of advantages and disadvantages of these different structures, which leads to superior performance and broad prospects of H bridge cascaded multilevel inverter. Then the paper emphatically introduces in detail the structure and working mechanism of the H bridge cascaded inverter.And on this basis, the paper puts forward the pulse width modulation method of cascaded multilevel inverter, also in a comparative analysis of different methods, this paper draws out the carrier phase shift sinusoidal pulse width modulation strategy, CPS-SPWM strategy, and carries on the thorough analysis research on it.On the other hand, in the modulation process of carrier phase shifted control strategy to cascaded inverter, It is through carrier that modulate the sinusoidal signal, which will generate harmonic component related to carrier. The output harmonic frequency and amplitude has become one of the important indicators to measure PWM multilevel cascade inverter circuit,therefore, we must give accurate analysis and effectively inhibit to the harmonic of CPS-SPWM modulation strategy.The paper finally also focuses on the output characteristics of single-phase cascaded multilevel inverter under CPS-SPWM modulation strategy, including the change regularity of harmonic:with the increasing of H bridge unit number, the output waveform are more and more close to the sine wave, and harmonic content is smaller;at the same time,along with the change of the system parameters such as modulation degree and carrier frequency,the harmonics of the output waveform also has the corresponding change. Finally, this paper carries out the simulation analysis with the application of MATLAB,and finally complete the experiment combining with the actual circuit, achieving the desired effect. |
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