Simultaneous Switching Loss Reduction and Neutral-Point Voltage Balance Scheme for Single-Phase Three-Level T-Type Inverter

Single-phase three-level T-type inverter (3LT
²
I) has revealed superior performances in many applications. However, it inevitably faces the challenge of high switching loss and imbalanced neutral-point voltage with conventional carrier based pulsewidth modulation (CBPWM). To address these issues, an improved CBPWM strategy with maximum offset voltage injection is proposed to reduce the switching loss and balance the neutral voltage simultaneously. Neutral-point voltage balance is maintained by selecting P-type or N-type switching sequence, which depends on the sign of offset voltage. Also, switching loss is mitigated by reducing the number of total switching commutation. First, the restriction of injected offset voltage is investigated and when the offset voltage is maximum, the switching commutation is reduced. Then, to further reduce the number of switching commutation, a new set of carrier signals are proposed to realize zero switching commutation between P-type and N-type switching sequences. After the analysis, the proposed modulation method also has better common-mode voltage restriction and faster response of neutral-point voltage balance. Simulation and experiment have been conducted to verify the theoretical analysis.