Harmonic reduction in multiplex convertors by triple-frequency current injection

Conventionally, harmonic filters have hitherto been used to reduce the very undesirable effects of current harmonics in the input current to convertor equipment. The present paper describes an investigation into a new method of eliminating these current harmonics at the source, this being a more fundamental method than merely suppressing their consequences. The cost of the new method is not likely to be more expensive than elaborate filter equipment. The process consists of modifying the primary current waveform by the injection of triple-frequency currents into the convertor. An explanation of the fundamental action is presented, together with an analysis of the effects of triple-frequency current injection upon the harmonics generated by duplex convertor equipment.