PWM strategies of three-level inverter-fed AC drives

In the region of high voltage and power, a high quality inverter-fed AC drive is more easily obtained by the use of multi-level inverters. In the first case three-level inverters should be taken into consideration. One of the important quality indexes of the PWM technique is the inverter-fed motor harmonic losses. They can be characterized by the generalized loss-factor. It is shown that for three-level inverters three different PWM regions can be introduced where different PWM strategies should be applied. The paper deals with computations of the generalized loss-factor of three-level inverters in the case of space vector modulation and the comparison of the different PWM methods on the basis of this factor. It is shown that the generalized loss-factors of three-level inverters are 4-35 times lower than those are for two-level inverters.