Application of a SHE-PWM modulation for a low switching frequency motor drive with harmonic investigation using the DTFT

This paper presents a study related to an electric drive composed by an induction machine fed by a NPC (neutral point clamped) frequency inverter, extending also to ANPC (active neutral point clamped) topologies, and IGBTs commanded by a SHE-PWM (selective harmonic elimination pulse width modulation) logic pattern. This work also addresses a concern related to the number of dv/dts reproduced in a fundamental period of a waveform, which is related to the semiconductors switching frequency. These dv/dts cause degradations to electric motors and its mitigation contributes minimizing problems on windings, insulations and bearings erosion. A SHE-PWM pattern with very low switching frequency is presented with simulations and experimental results mitigating the 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> and 7 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonics for the entire drive voltage index modulation range. These harmonics have high amplitude and low frequency, causing high drive losses, and can be reduced by a modulation with semiconductors switching in a frequency equivalent to 360Hz, with high quality and symmetrical voltage and currents waveforms. SHE-PWM was compared with POD-PWM at the same switching rate, through simulation and harmonic content investigated by the DTFT (Discrete Time Fourier Transform).