IMPROVED POWER CONVERTER DEVICE FOR DIRECT CURRENT POWER SUPPLY OF AN ELECTRIC ARC FURNACE

摘要

A POWER CONVERTER DEVICE FOR SUPPLYING DIRECT CURRENT TO AN ELECTRIC ARC FURNACE COMPRISES AT LEAST ONE TRANSFORMER WITH ITS PRIMARY FED WITH A THREE-PHASE ALTERNATING CURRENT AND DELIVERING TO AT LEAST ONE SECONDARY A THREE-PHASE CURRENT APPLIED TO A RECTIFIER SYSTEM OUTPUTTING TO THE LOAD RECTIFIED VOLTAGE AND CURRENT. THE RECTIFIER SYSTEM COMPRISES CONTROLLED SEMICONDUCTORS FOR EACH SECONDARY AND A FREEWHEEL CIRCUIT. THE CONTROLLED SEMICONDUCTORS ARE TRIGGERED WITH ESSENTIALLY VARIABLE FIRING ANGLES, MODIFIED TO INCREASE THE DURATION OF CONDUCTION IN THE FREEWHEEL CIRCUIT WHILST REDUCING THE DURATION OF CONDUCTION IN THE TRIGGERED SEMICONDUCTORS, AND VICE VERSA, SO AS TO DELIVER TO THE LOAD A SUBSTANTIALLY CONSTANT ACTIVE POWER OR REACTIVE POWER DESPITE VARIATIONS IN THE IMPEDANCE OF THE LOAD.(FIGURE 8)