One dimensional cell inversion: A modulation strategy for hybrid cascaded converters

Cascaded converters are being utilised in high-voltage, high-power applications as they can be extended to a large number of levels without introducing significant complexity to the mechanical design. However, StatComs formed from cascaded cells suffer from unequal charging of converter phase-legs during compensation of unbalanced loads. To alleviate this issue energy exchange between cascaded phase-legs is typically achieved using zero sequence voltage or current injection. In this paper the combination of a hybrid cascaded topology and a new modulation scheme facilitate energy exchange. The amount of energy exchange between converter phase-legs in StatCom applications is analysed. The new modulation strategy, termed 1-Dimensional Cell Inversion, improves capacitor voltage balance capability under unbalanced conditions and reduces capacitor voltage ripple in balanced conditions.