Three Parts Modulation and Hybrid DC Capacitor Voltage Balancing for a Single-Phase Two-Leg Five-Level NPC Inverter

Abstract

Capacitor voltage unbalance in NPC multilevel inverters is an inherent challenge and has a severe effect on five and higher-level inverters. Current modulation-based voltage balancing schemes for five-level NPC inverters require a high number of switching, especially at high modulation index operations. Moreover, hardware-based voltage balancing techniques come with a high component count. This paper proposes a unique three-part modulation technique combined with a hybrid voltage balancing approach to reduce switching losses and maintain voltage balancing. The modulation is composed of different carrier-based modulations, while the hybrid balancing scheme combines modulation-based and hardware-based balancing techniques. Comparative switching loss analysis demonstrates a reduction in inverter switching associated with the modulation. While the voltage unbalance characteristics of the modulation are determined considering linear loading conditions. Furthermore, balancing capacity analysis and switching loss reevaluation are used to justify the hybrid balancing performance. The concept verification use Matlab-Simulink simulation and hardware experiments on a five-level single-phase NPC inverter setup operated at different modulation index and power factor conditions.