Level-shifted PWM for Cascaded Multilevel Inverters with Even Power Distribution

Cascaded H-bridge multilevel inverters are commonly controlled using multicarrier Phase-Shifted PWM, since it allows an even power distribution among the converter power cells, which can lead to lower harmonic distortion in the input current if an adequate transformer is used. However it is known that other multicarrier methods, like Phase Disposition PWM (PD- PWM) have better output voltage quality with lower distortion. Nevertheless, when used with cascaded inverters, this method produces uneven usage of the converter cells, that disables the harmonic cancelations at the transformer input. This paper presents a modified PD-PWM technique, that combines the benefits of both modulation methods, achieving good output voltage and input current quality.