# US 8,274,767 B2 · Magnetic energy regeneration switch provided with protection circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,274,767 B2 - Document ID: US8274767B2 - Status: Granted - Kind: B2 - Application number: 13/062,514 - Filed: 2008-11-13 - Published: 2011-09-15 - Granted: 2012-09-25 - Earliest claimed: 2008-11-13 - Assignees: MERSTech, Inc. - Inventors: Shiro Fukuda - Web page: https://patentgrep.com/patent/US8274767B2 ## CPC - H02M 5/293: using semiconductor devices only - H02M 1/32: Means for protecting converters other than automatic disconnection - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) ## Abstract A protection circuit equipped magnetic energy recovery switch including a magnetic energy recovery switch having at least two reverse-conductive type semiconductor switches and two capacitors employs a protection circuit and control method for protecting the capacitors against an overvoltage or short-circuited discharge, and protecting the reverse-conductive type semiconductor switches and a load against an overvoltage or overcurrent, and can be used as a controller or a current limiter. ## Claims ### Claim 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. ### Claim 2 (depends on 1) The protection circuit equipped magnetic energy recovery switch according to claim 1, wherein when the output of the current detection unit returns to the predetermined value, the control means sets back the duty ratio of the ON/OFF pulse of the gate control signal of the reverse-conductive type semiconductor switch to 0.5 and terminates current limiting control. ### Claim 3 (depends on 1) The protection circuit equipped magnetic energy recovery switch according to claim 1, wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off all the reverse-conductive type semiconductor switches to cut off the current. ### Claim 4 (depends on 1) The protection circuit equipped magnetic energy recovery switch according to claim 1, wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls the gate of the discharge switch so as to discharge electric charges of the two capacitors to set the voltage to substantially zero, and then controls gates of the reverse-conductive type semiconductor switches so as to turn on all the reverse-conductive type semiconductor switches so that the current becomes conductive in both directions. ### Claim 5 (depends on 1) The protection circuit equipped magnetic energy recovery switch according to claim 1, wherein the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off all the reverse-conductive type semiconductor switches to cut off the current, when an output of the current detection unit exceeds a predetermined current value. ### Claim 6 (depends on 1) The protection circuit equipped magnetic energy recovery switch according to claim 1, wherein the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off only that of the reverse-conductive type semiconductor switches which is on, thereby cutting off the current, when an output of the current detection unit exceeds a predetermined current value. ### Claim 7 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, first and second capacitors connected in series to each other and 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, between DC terminals of the bridge circuit, a first voltage detection unit connected in parallel to the first capacitor to detect a voltage of the first capacitor, a second voltage detection unit connected in parallel to the second capacitor to detect a voltage of the second capacitor, a first discharge circuit connected in parallel to the first capacitor and having a first discharge resistor and a first discharge switch connected in series to each other, a second discharge circuit connected in parallel to the second capacitor and having a second discharge resistor and a second 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 gates of the discharge switches so as to short-circuit the first discharge switch when an output of the first voltage detection unit exceeds a first predetermined value, thereby discharging electric charge of the first capacitor through the first discharge resistor, and short-circuit the second discharge switch when an output of the second voltage detection unit exceeds a second predetermined value, thereby discharging electric charge of the second capacitor through the second 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. ### Claim 8 (depends on 7) The protection circuit equipped magnetic energy recovery switch according to claim 7, wherein when the output of the current detection unit returns to the predetermined value, the control means sets back the duty ratio of the ON/OFF pulse of the gate control signal of the reverse-conductive type semiconductor switch to 0.5 and terminates current limiting control. ### Claim 9 (depends on 7) The protection circuit equipped magnetic energy recovery switch according to claim 7, wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off all the reverse-conductive type semiconductor switches to cut off the current. ### Claim 10 (depends on 7) The protection circuit equipped magnetic energy recovery switch according to claim 7, wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls the gate of the discharge switch so as to discharge electric charges of the two capacitors to set the voltage to substantially zero, and then controls gates of the reverse-conductive type semiconductor switches so as to turn on all the reverse-conductive type semiconductor switches so that the current becomes conductive in both directions. ### Claim 11 (depends on 7) The protection circuit equipped magnetic energy recovery switch according to claim 7, wherein the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off all the reverse-conductive type semiconductor switches to cut off the current, when an output of the current detection unit exceeds a predetermined current value. ### Claim 12 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 two inversely series-connected reverse-conductive type semiconductor switches, series-connected first and second capacitors connected in parallel thereto, a wiring connecting an intermediate node between the two inversely series-connected reverse-conductive type semiconductor switches and an intermediate node between the two series-connected first and second capacitors, 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 first voltage detection unit connected in parallel to the first capacitor to detect a voltage of the first capacitor, a second voltage detection unit connected in parallel to the second capacitor to detect a voltage of the second capacitor, a first discharge circuit connected in parallel to the first capacitor and having a first discharge resistor and a first discharge switch connected in series to each other, a second discharge circuit connected in parallel to the second capacitor and having a second discharge resistor and a second 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 gates of the discharge switches so as to short-circuit the first discharge switch when an output of the first voltage detection unit exceeds a predetermined value, thereby discharging electric charge of the first capacitor through the first discharge resistor, and short-circuit the second discharge switch when an output of the second voltage detection unit exceeds a predetermined value, thereby discharging electric charge of the second capacitor through the second 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. ### Claim 13 (depends on 12) The protection circuit equipped magnetic energy recovery switch according to claim 12, wherein when the output of the current detection unit returns to the predetermined value, the control means sets back the duty ratio of the ON/OFF pulse of the gate control signal of the reverse-conductive type semiconductor switch to 0.5 and terminates current limiting control. ### Claim 14 (depends on 12) The protection circuit equipped magnetic energy recovery switch according to claim 12, wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off all the reverse-conductive type semiconductor switches to cut off the current. ### Claim 15 (depends on 12) The protection circuit equipped magnetic energy recovery switch according to claim 12, wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls the gate of the discharge switch so as to discharge electric charges of the two capacitors to set the voltage to substantially zero, and then controls gates of the reverse-conductive type semiconductor switches so as to turn on all the reverse-conductive type semiconductor switches so that the current becomes conductive in both directions. ### Claim 16 (depends on 12) The protection circuit equipped magnetic energy recovery switch according to claim 12, wherein the control means controls gates of the reverse-conductive type semiconductor switches so as to turn off all the reverse-conductive type semiconductor switches to cut off the current, when an output of the current detection unit exceeds a predetermined current value. ### Claim 17 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 wherein when a period of time during which the output of the voltage detection unit is greater than the predetermined voltage value exceeds a predetermined time, the control means controls the gate of the discharge switch so as to discharge electric charges of the two capacitors to set the voltage to substantially zero, and then controls gates of the reverse-conductive type semiconductor switches so as to turn on all the reverse-conductive type semiconductor switches so that the current becomes conductive in both directions. ### Claim 18 (depends on 17) The protection circuit equipped magnetic energy recovery switch according to claim 17, wherein the protection means further includes a current detection unit, interposed between the AC power supply and the load, for detecting a current which flows across the load, 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 value. ### Claim 19 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, first and second capacitors connected in series to each other and 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, between DC terminals of the bridge circuit, a first voltage detection unit connected in parallel to the first capacitor to detect a voltage of the first capacitor, a second voltage detection unit connected in parallel to the second capacitor to detect a voltage of the second capacitor, a first discharge circuit connected in parallel to the first capacitor and having a first discharge resistor and a first discharge switch connected in series to each other, a second discharge circuit connected in parallel to the second capacitor and having a second discharge resistor and a second discharge switch connected in series to each other, and wherein the control means controls gates of the discharge switches so as to short-circuit the first discharge switch when an output of the first voltage detection unit exceeds a first predetermined value, thereby discharging electric charge of the first capacitor through the first discharge resistor, and short-circuit the second discharge switch when an output of the second voltage detection unit exceeds a second predetermined value, thereby discharging electric charge of the second capacitor through the second discharge resistor, and then controls gates of the reverse-conductive type semiconductor switches so as to turn on all the reverse-conductive type semiconductor switches so that the current becomes conductive in both directions. ### Claim 20 (depends on 19) The protection circuit equipped magnetic energy recovery switch according to claim 19, wherein the protection means further includes a current detection unit, interposed between the AC power supply and the load, for detecting a current which flows across the load, 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 value. ### Claim 21 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 two inversely series-connected reverse-conductive type semiconductor switches, series-connected first and second capacitors connected in parallel thereto, a wiring connecting an intermediate node between the two inversely series-connected reverse-conductive type semiconductor switches and an intermediate node between the two series-connected first and second capacitors, 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 first voltage detection unit connected in parallel to the first capacitor to detect a voltage of the first capacitor, a second voltage detection unit connected in parallel to the second capacitor to detect a voltage of the second capacitor, a first discharge circuit connected in parallel to the first capacitor and having a first discharge resistor and a first discharge switch connected in series to each other, a second discharge circuit connected in parallel to the second capacitor and having a second discharge resistor and a second discharge switch connected in series to each other, and wherein the control means controls gates of the discharge switches so as to short-circuit the first discharge switch when an output of the first voltage detection unit exceeds a predetermined value, thereby discharging electric charge of the first capacitor through the first discharge resistor, and short-circuit the second discharge switch when an output of the second voltage detection unit exceeds a predetermined value, thereby discharging electric charge of the second capacitor through the second discharge resistor, and then controls gates of the reverse-conductive type semiconductor switches so as to turn on all the reverse-conductive type semiconductor switches so that the current becomes conductive in both directions. ### Claim 22 (depends on 21) The protection circuit equipped magnetic energy recovery switch according to claim 21, wherein the protection means further includes a current detection unit, interposed between the AC power supply and the load, for detecting a current which flows across the load, 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 value.