Stability analysis and duty cycle limitation of grid-connected current control strategy for multiple parallel three-level T-type grid-connected inverters

Multiple parallel three-level T-type inverters (3LT(2)Is) have become the trend in large-power low-voltage applications. In parallel operation of modular 3LT(2)Is, three aspects including current sharing control, circulating current suppression and neutral-point potential (NPP) balance control should be considered. In this study, a grid-connected current control strategy with the ability to independently adjust three control objectives is proposed for the multiple parallel three-level T-type grid-connected inverters. The duty cycle limitation among current sharing, NPP balancing and circulating current and their influence are analysed in detail. The stability analysis of multi-paralleled inverters on the basis of the single-phase equivalent circuit is carried out considering the influence of circulating current. Experimental results prove the validity of the proposed control strategy.