High current DC choppers in the metals industry

The recent market introduction of larger power switching devices has made the use of DC-to-DC converters, previously used in lower power applications, commercially viable. The DC-to-DC converter, otherwise known as a DC chopper, has made inroads to applications where conventional thyristor and saturable reactor diode rectifiers were in use, in applications such as electro-winning, DC arc furnaces, graphite resistive heating, plasma torches and smelting. The DC chopper system has many operational benefits over conventional diode or thyristor rectifiers, such as: low output ripple; fast dynamic response; reduced flicker generation; high line power factor over its whole power operating range; minimal harmonic distortion of the AC feeder, without the use of harmonic traps; elimination of power factor correction equipment usually associated with thyristor rectifiers; higher system efficiencies over total output power range; and reduction in over all system size and cost. These benefits and the application of chopper supplies as they apply to the metals industry are described in this paper.