On the need for strict second harmonic limits

Even harmonics, especially the second harmonic, cause waveform distortions characterized by asymmetries between the positive and the negative half-cycles. Certain single-phase power converter topologies, when supplied with asymmetrically distorted voltage waveforms, respond by injecting significant levels of direct current, even when the mean value of the voltage is zero. In turn the DC will bias transformers causing a host of undesirable effects. This paper concludes that the existing recommendations for permissible levels of second harmonic must be stricter and proposes a ban on half-controlled three-phase power converters.