A Hybrid Multicarrier Modulation With Leakage Current Suppression and Power Balancing for Transformerless Cascaded H-Bridge Grid-Connected Inverter

The transformerless cascaded H-bridge grid-connected inverter (TL-CHB-GCI) is an attractive topology in photovoltaic (PV) systems. However, due to lack of electrical isolation, the leakage current will inevitably appear between the grid and the PV panels, which causes electromagnetic interferences (EMI) and potential safety issues. For the operation of TL-CHB-GCI, another requirement is to maintain power balance between PV modules. Existing methods have not been able to address both issues adequately, therefore, a hybrid multicarrier modulation (HMM) method is proposed in this article. First, the TL-CHB-GCI model with parasitic capacitance is established, and the constraints of the leakage current suppression and power balance are derived respectively, where the intersection of vectors under dual constraint is taken as the candidate vectors. Then, based on the set of candidate vectors, a hybrid carrier is constructed, and a cycling strategy is designed. In HMM, the vector optimization ensures low leakage current, while the carrier cycling achieves intermodule power balancing. Furthermore, the proposed method can be generalized to any even-module TL-CHB-GCI. Finally, the effectiveness of the proposed method is verified by simulations and experimental results.