A Novel Modulation Strategy for Split-Inductor Active NPC Inverter With Loss Distribution Balancing and Thermal Stress Reduction

Abstract

Neutral point clamped inverter (NPC) features low harmonics, high efficiency, and low voltage stress, et al. NPC is widely applied in renewable energy power generation systems, such as wind turbine power and photovoltaic. However, due to unbalanced power losses, NPC suffers inherent thermal unbalance among inner and outer power switches. A split-inductor active neutral point clamped inverter (SI-ANPC) was initially proposed to improve the operating reliability, providing the structural basis for balanced loss distributions. With this purpose, a novel modulation strategy with balanced loss distribution for SI-ANPC is proposed in this paper. The modulation strategy is analyzed under the unity and non-unity power factors. In specially, two redundant zero-state paths are fully used. Under the unity power factor, the power switches operate at the switching frequency or maintain the conduction state complementarily. Considering the phase angle in the non-unity power factor situation, the working patterns of power switches are rearranged to reduce the loss difference. The thermal stress is decreased on both occasions. Finally, loss calculation results, experimental waveforms, and thermal images of the inner and outer switches are presented to confirm the effectiveness of the proposed modulation strategy.