Voltage Spectra of Three-Level Inverters with Three-Phase Modulation

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 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 so simple as the space vector PWM. At the same time in the low and middle voltage area the space vector PWM method gives bigger harmonic losses than the optimal PWM method. The motor voltage spectrum derivation for both the optimal version and the space vector PWMs are given and the results are checked by straight harmonic computations and by simulations