THD minimization for railway applications through harmonic spectrum optimization

In this paper an optimized modulation technique is presented for low THD voltage generation onboard rolling stock by means of a voltage source inverter (VSI). The aim of the proposal is to minimize the output voltage THD through the optimization of the harmonic spectrum distribution. The optimal switching pattern has been obtained by means of an optimization method. Regarding conventional modulation techniques such as selective harmonic elimination technique, sinusoidal PWM with third harmonic injection or space vector PWM, the proposed optimized modulation presents lower THD and an extended modulation index because it can operate in the overmodulation region even with lower THD. Theoretical performance has been validated in a scaled-down prototype.