Single-Phase, Seven-Level Inverter with Triple Voltage Boosting and Self DC-Link Voltage Balancing

In this paper, a two-stage, single-phase, multilevel dc/ac converter for PV system is proposed. The typical two-stage inverter in PV systems requires a high dc-link voltage, and a step-up dc/dc converter is used. However, a two-stage power conversion requires a high number of power electronic components, resulting in higher cost and lower efficiency. Compared to the similar seven-level inverter, the proposed topology provides three times step-up voltage ratio and a smaller number of circuit components. The introduced topology consists of two stages, the front stage is a step-up dc/dc converter-based switched capacitor circuit. This stage provides high voltage boasting ratio and self-balancing dc-link voltage capacitors capability. Furthermore, a soft switching operation for the power switching devices is implemented using the LC-resonant circuit; thus, peak current amplitude can be regulated, electromagnetic noise and switching losses are significantly decreased. The second stage is a seven-level dc/ac inverter and has the advantages of fewer numbers of semiconductor devices. The operating principles and the modulation scheme of both stages are analyzed and discussed. Simulation and experimental results are provided to prove the effectiveness of the presented topology under different operating conditions.