Improved Modulation Strategy With Reduced Switching Loss for Single-Phase Three-Level T-Type Inverter

Single phase three-level T-type inverter (3LT2I)has revealed superior performances in many applications. However, it inevitably faces the challenge of high switching loss and imbalanced neutral point (NP) voltage with the conventional unipolar pulse-width modulation (PWM). To address these issues, an improved modulation strategy with reduced switching loss is proposed to reduce the switching loss and balance the NP voltage simultaneously. Firstly, a novel common mode component injection method is presented to generate P-type and N-type switching sequence based on the carrier based PWM (CB-PWM). With this method, the switch status of one leg is clamped during half of grid voltage fundamental period, so the switching loss is reduced. Then, to further reduce the switching power losses, a new switching function is proposed to realize only one switching status changing in a switching sequence. In addition, the NP voltage balance is maintained by selecting P-type or N-type switching sequence. Simulation and experiment have been conducted to verify the proposed modulation strategy.