New self-balancing 7-level inverter with coupled inductors for 1-φ grid-connected renewable energy systems with voltage boosting capability

In this study, a new self-balancing 7-level inverter (SB7LI) topology, suitable for interfacing the low voltage renewables with the power grid, is proposed that uses coupled inductors to generate additional levels in the output voltage. Owing to the presence of a self-balancing circuit, the voltage across the two-input DC capacitors is self-balanced by charging them in series and discharging them in parallel. The self-balancing feature of the proposed SB7LI also obviates the sensing of input DC capacitors' voltages. The SB7LI is controlled using a novel multi-sine wave pulse width modulation strategy. A significant advantage of the proposed SB7LI topology is that it uses fewer power components in comparison with traditional multi-level inverter topologies, which ensures higher power density and compact circuits. This also improves the overall efficiency of the system and reduces the cost. Further, a modified version of the SB7LI is also presented with a reduced number of power components. An additional advantage of coupled inductors is their filtering action on the output voltage/current, which reduces the overall filter requirements. SB7LI can be easily extended to an n-level, 3-φ application. The proposed SB7LI and modified SB7LI are validated through simulations in MATLAB/SIMULINK and hardware experiments on 300 W laboratory prototypes.