Output Voltage Error Compensation for T-type NPC Inverter Applied to Encoder-less Vector Controlled Induction Motor

An accurate output voltage error compensation method for a T-type neutral point clamped (NPC) Inverter which realize encoder-less vector control of induction motor over the wide operation range is proposed. A precise output voltage error measurement for the T-type NPC inverter has been proposed. Moreover, the voltage pulse extinction in the range where the modulation index is around zero, which causes no longer negligible output voltage error in the low-speed operation, has been investigated. Then, dipolar modulation has been proposed to solve this problem. The validity of the proposed voltage error compensation was shown by computer simulation and the experimental results.