T. Wanjekeche, D.V. Nicolae, and A.A. Jimoh (S. Africa)
Spectral analysis, Cascaded NPC/H-Bridge, Phase Shifted PWM control,
Multilevel inverters have been important devices developed in recently years owing to their capability to increase the voltage and power delivered to the load. The low ratio of switching frequency to output voltage fundamental frequency in high power middle frequency inverter results in high harmonic content and conventional control techniques cannot guarantee good waveform quality. A new and modified phase shifted PWM control technique that reduces output harmonics is presented in this paper. Feedback control schemes are proposed to achieve a fast dynamic response. A theoretical harmonic analysis of the proposed control is carried out using double Fourier transform. Spectral characteristics of the output waveforms of all operating conditions are studies for a five- level and nine- level voltage output. Theoretical results are verified using MATLAB simulation.
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