A Nine-Level Transformerless Boost Inverter With Leakage Current Reduction and Fractional Direct Power Transfer Capability for PV Applications

This article describes an integrated voltage-boosting technique, which is essential to achieve compatibility between low-voltage photovoltaic (PV) panels and high-voltage dc links needed for dc-to-ac conversion. To achieve the twin objectives of voltage-boosting and multilevel inversion, this article proposes a transformerless T-type nine-level hybrid boost inverter. To improve the efficiency in the boosting stage of the proposed converter system, a significant portion of the PV energy is directly transferred from the PV source to the load, while the other part is processed through an interleaved converter, which is fused with the inverter. Thus, the proposed converter ensures a higher power density and reduces the power ratings of the semiconductor devices. This article also introduces a modified zone-based pulsewidth modulation (PWM) technique, which achieves a complete elimination of the switching frequency voltage transitions in the total common-mode voltage (TCMV). Thus, this technique mitigates the generation of leakage current while preserving the advantages of conventional multilevel inverters such as low $\text{d}v/\text{d}t$ and inductive power capability. Besides that, a rigorous mathematical analysis for the common-mode equivalent circuit of the proposed configuration is also presented in this article. Detailed simulation and experimental studies are carried out to validate the feasibility of the proposed configuration.