A Nine-Level Split-Capacitor Active-Neutral-Point-Clamped Inverter and Its Optimal Modulation Technique

This article proposes a novel hybrid nine-level inverter for high-efficiency applications based on the popular five-level active-neutral-point-clamped (5L-ANPC) topology. Compared with conventional ANPC-based topologies, this inverter reduces the required number of active and passive components while avoiding the use of higher voltage switches. Only nine active switches with eight gate drivers and two discrete diodes are used in each phase leg. Moreover, the proposed inverter not only reduces the number of flying capacitors (FCs) but also their rated voltages, which has a positive impact on the reliability, volume, and cost of the converter. Based on switching state redundancies, a voltage control strategy for FCs and neutral points is developed and incorporated into the phase-disposition pulsewidth modulation technique. The developed control method is able to balance the voltages of the FCs with only one sensor under active and reactive power operation. Based on the designed modulation strategy, a mathematical analysis is carried out to determine the capacitance of the FCs. A comprehensive comparison with other nine-level ANPC-based topologies is included to highlight the advantages of the proposed inverter. The performance of the proposed topology with its control strategy is validated through simulation studies and experimental implementation under different conditions.