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-cyc les. Certain single-phase converter topologies, when supplied with asymmetr ically distorted voltage wave-forms, respond by injecting significant level s of direct current, even when the mean value of the voltage is zero, In tu rn the de will bias transformers causing a host of undesirable effects. Thi s paper concludes that the existing recommendations for permissible levels of second harmonic must be stricter and proposes a ban on half-controlled t hree-phase converters.