Topology and Control of Novel Hybrid Multilevel Inverter Based on Dual-Flying-Capacitor Structure

This article proposes a novel hybrid multilevel inverter (MLI) that can extend the voltage levels of the dual-flying-capacitor active-neutral-point-clamped (DFCANPC) topology with fewer flying capacitors (FCs). The proposed structure is derived by replacing the conventional FC converters in the DFCANPC circuit with simplified FC converters, which effectively increases the voltage level count from (n+3) to (2n+1−1) with n FCs. Thus, for the same voltage level count, the proposed dual simplified FC (DSFC) inverters require fewer FCs and switches, which reduces the total standing voltage (TSV), cost, and control complexity. In addition, a novel carrier-overlapped phase-disposition PWM scheme is developed, along with an active voltage-balancing control strategy to regulate all capacitor voltages. As a case study, the seven-level (7L) DSFC topology is comparatively analyzed against other MLIs, focusing on total harmonic distortion, power losses, component count, and cost for a transformer-less 6.6 kV/1 MW induction motor drive system. The 7L-DSFC topology reduces the TSV by 14.3% and the cost by 14.4% compared with the 7L-DFCANPC inverter, while maintaining comparable total harmonic distortion and power losses. Finally, the feasibility of the proposed topology is confirmed through experiments conducted on a laboratory-scale induction motor drive prototype.