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Analysis of three phase PWM strategies of three-level inverters

In the area of high voltages and powers, the high quality inverter-fed ac drive is more easily achieved by the use of three-level inverters. For three-level inverters three different PWM control regions can be introduced where different three-phase PWM strategies may be applied. This paper deals with the analysis of that carrier-based three-phase PWM method of three-level inverters which ensures the lowest value of motor harmonic losses. However, the realization of this PWM method is not as simple as the space vector PWM. Except the region III the space vector method cannot provide the equal sharing times of voltage vector on the both sides and in the middle of the sampling cycle. Therefore in the low and middle voltage area this method gives bigger harmonic losses than the optimal PWM method. The results are justified by investigation of motor voltage spectra for optimal version and space vector PWMs and by current and torque simulations