SUPPRESSION OF LOCAL RESONANCE CURRENT

PURPOSE:To suppress a local resonance current by rapidly supplying 2-phase short-circuit current by a voltage inverter. CONSTITUTION:A power is supplied through an input transformer 5 to a rectifier 6. A power factor improving capacitor (SC) 3 is provided before the transformer 5. A controller 72 discriminates the polarity of a phase current detected by a current detector 74 to control ON, OFF the corresponding switching element of an inverter 71 on the basis of the result to supply a necessary short-circuit current. An AC reactor 73 suppresses the change rate of the supplied current. Since the necessary short-circuit current is supplied from the inverter 71, it is not necessary to supply it from the SC3, and can suppress a local resonance current.