Derivation of the Generalized Phase-Shifted Angles by Using Phasor Diagrams for the CHB Converter With Unbalanced DC Voltage Sources

The cascaded H-bridge (CHB) converter is widely used in a lot of applications. When the dc port voltages of the inverter cells are the same, the conventional modulation strategy can ensure that there is no double switching frequency harmonic component. However, when the dc voltages are unbalanced, which is very common in practical applications, voltage distortion occurs. Focused on the harmonic reduction at twice switching frequency, this article proposes an insightful calculation method from the geometrical point of view. The proposed method uses the phasor diagrams to obtain the phase-shifted angles for the CHB converter with any number of inverter cells. The calculation process is very clear and no complex mathematical optimization algorithm is required. Finally, the effectiveness of the proposed method is verified by the experimental CHB platform with five inverter cells.