Spectrum Analysis of PWM Waveform with DC Bus Voltage Ripple Based on Cascaded H-Bridge Converters

The cascaded H-bridge converter is a promising approach for high voltage and high power applications. A group of series-connected submodules with independent DC power supplies can be used to obtain excellent output voltage performance through low switching frequency. However, the DC bus voltage ripple will cause additional harmonics to the output voltage, which will cause output voltage distortion and reduce the output performance of the converter. This paper theoretically analyzes the harmonic voltage of the pulse width modulation converter with the DC bus voltage ripple, and gives the expression of the output voltage applied by a double Fourier series. This analysis reveals how the modulation signal and DC power supply interact with the carrier signal to produce undesired harmonics in the PWM signal, which provides a theoretical basis for undesired harmonic suppression. The theoretical results from the analysis are validated by simulation results.