An Enhanced Modulation Scheme for Multi-Level T-Type Inverter With Loss Balance and Reduction

The multilevel T-type inverter exhibits an inherent challenge of unbalanced power loss distribution among switches. This discrepancy in loss distribution is greatly influenced by the modulation index and the power factor, leading to increased system costs due to the overdesign of power devices and cooling systems based on worst-case scenarios. Furthermore, this loss imbalance will cause uneven device lifetimes, ultimately compromising the overall reliability of the converter system. To address the issue of loss imbalance, this article proposes a comprehensive and generic modulation scheme for the multilevel T-type inverter. The proposed scheme enables the balancing of switching and conduction losses for all switches in the inverter, regardless of the power factor and modulation index, as long as the modulation index is below a specific threshold. Importantly, the proposed scheme ensures that the losses of each individual device and the total converter loss are independent of the power factor and modulation index, which only requires knowledge of the ON-resistance of the power MOSFET. Additionally, the proposed modulation scheme effectively reduces the total loss of the inverter and naturally balances the neutral point potential. The proposed modulation scheme is validated in a 200 kW SiC-based three-level T-type inverter.