Patent ID: 8274767
Filing Date: 2012-09-25
Classification: H02M

Abstract:
1. A protection circuit equipped magnetic energy recovery switch comprising: a magnetic energy recovery switch, interposed between an AC power supply and a load, for storing magnetic energy of a current, and recovering the magnetic energy to the load; and protection means for protecting the magnetic energy recovery switch against an overvoltage or an overcurrent, wherein the magnetic energy recovery switch includes a bridge circuit having two series-connected reverse-conductive type semiconductor switches and two series-connected diodes, two series-connected capacitors respectively connected in parallel to the two series-connected diodes, and control means that controls phases of gate control signals for the reverse-conductive type semiconductor switches in such a way as to alternately perform ON/OFF control on the reverse-conductive type semiconductor switches in synchronization with a frequency of the AC power supply, wherein the protection means includes a voltage detection unit connected between DC terminals of the bridge circuit to detect a voltage across the two series-connected capacitors, a discharge circuit connected between the DC terminals of the bridge circuit and having a discharge resistor and a discharge switch connected in series to each other, and a current detection unit, interposed between the AC power supply and the load, for detecting a current which flows across the load, and wherein the control means controls a gate of the discharge switch so as to short-circuit the discharge switch when an output of the voltage detection unit exceeds a predetermined voltage value, thereby discharging electric charges of the capacitors through the discharge resistor, and performs current limiting control by making a duty ratio of an ON pulse of the gate control signals of the reverse-conductive type semiconductor switches smaller than 0.5 when the output of the current detection unit exceeds a predetermined current value.