# US 8,274,803 B2 · Low stress soft charge circuit for diode front end variable frequency drive > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,274,803 B2 - Document ID: US8274803B2 - Status: Granted - Kind: B2 - Application number: 12/655,327 - Filed: 2009-12-29 - Published: 2011-02-17 - Granted: 2012-09-25 - Earliest claimed: 2009-01-09 - Assignees: Yaskawa America, Inc. - Inventors: Mahesh M. Swamy; Tsuneo Joe Kume - Web page: https://patentgrep.com/patent/US8274803B2 ## CPC - H02M 1/36: Means for starting or stopping converters - H02J 7/04: Regulation of charging current or voltage - H02J 7/96: in response to battery voltage - H02M 5/458: using semiconductor devices only - H02J 7/345: {using capacitors as storage or buffering devices} - 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) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY ## Abstract A variable frequency drive comprises a diode rectifier receiving multiphase AC power from a source and converting the AC power to DC power. An inverter receives DC power and converts the DC power to AC power to drive a load. A link circuit is connected between the diode rectifier and the inverter and comprises a DC bus to provide a relatively fixed DC voltage for the inverter. A bus capacitor is across the bus. A soft charge circuit limits inrush current to the bus capacitor. The soft charge circuit comprises an inductor connected between the source and the link circuit and a switch circuit in the link circuit for selectively providing a semiconverter configuration or a full bridge converter configuration to provide two stage charging of the bus capacitor. ## Claims ### Claim 1 A voltage source inverter comprising: a rectifier having an input for receiving multi phase AC power and converting the AC power to DC power at an output; an inverter for receiving DC power and converting the DC power to AC power; a link circuit connected between the rectifier circuit and the inverter circuit and comprising a DC bus having first and second rails to provide a relatively fixed DC voltage for the inverter, and a bus capacitor across the first and second rails; and a soft charge circuit to limit inrush current to the bus capacitor, the soft charge circuit comprising an inductor connected between the rectifier input and the second rail and a switch circuit in the second rail between the rectifier output and the bus capacitor to provide two stage charging of the bus capacitor. ### Claim 2 (depends on 1) The voltage source inverter of claim 1 wherein the inductor comprises a wye connected inductor having a neutral point connected to the second rail. ### Claim 3 (depends on 1) The voltage source inverter of claim 1 wherein the soft charge circuit further comprises a blocking diode connected between the second rail and the inductor. ### Claim 4 (depends on 1) The voltage source inverter of claim 1 wherein the soft charge circuit further comprises a sensing circuit for sensing bus voltage and a control circuit for controlling the switch circuit responsive to sensed voltage. ### Claim 5 (depends on 4) The voltage source inverter of claim 4 wherein the sensing circuit comprises a voltage divider connected across the link circuit. ### Claim 6 (depends on 1) The voltage source inverter of claim 1 wherein the soft charge circuit further comprises a control circuit for controlling the switch circuit responsive to a select time period. ### Claim 7 (depends on 4) The voltage source inverter of claim 4 wherein the control circuit turns the switch off if sensed voltage is below a select brown out level voltage. ### Claim 8 A variable frequency drive comprising: a diode rectifier receiving multi phase AC power from a source and converting the AC power to DC power; an inverter for receiving DC power and converting the DC power to AC power to drive a load; a link circuit connected between the diode rectifier and the inverter and comprising a DC bus to provide a relatively fixed DC voltage for the inverter, a bus capacitor across the bus; and a soft charge circuit to limit inrush current to the bus capacitor, the soft charge circuit comprising an inductor connected between the source and the link circuit and a switch circuit in the link circuit for selectively providing a semiconverter configuration or a full bridge converter configuration to provide two stage charging of the bus capacitor. ### Claim 9 (depends on 8) The variable frequency drive of claim 8 wherein the inductor comprises a wye connected inductor having a neutral point connected to the link circuit. ### Claim 10 (depends on 8) The variable frequency drive of claim 8 wherein the soft charge circuit further comprises a blocking diode connected between the link circuit and the inductor. ### Claim 11 (depends on 8) The variable frequency drive of claim 8 wherein the soft charge circuit further comprises a sensing circuit for sensing DC bus voltage and a control circuit for controlling the switch circuit responsive to sensed voltage. ### Claim 12 (depends on 11) The variable frequency drive of claim 11 wherein the sensing circuit comprises a voltage divider connected across the link circuit. ### Claim 13 (depends on 8) The variable frequency drive of claim 8 wherein the soft charge circuit further comprises a control circuit for controlling the switch circuit responsive to a select time period. ### Claim 14 A soft charge circuit for a diode rectifier front end variable frequency drive comprising: a DC bus having a positive rail and a negative rail to provide a relatively fixed DC voltage, a bus capacitor across the bus, an inductor connected between a diode rectifier input and the negative rail and a switch circuit in the negative rail to provide two stage charging of the bus capacitor. ### Claim 15 (depends on 14) The soft charge circuit of claim 14 wherein the inductor comprises a wye connected inductor having a neutral point connected to the second rail. ### Claim 16 (depends on 14) The soft charge circuit of claim 14 wherein the soft charge circuit further comprises a blocking diode connected between the second rail and the inductor. ### Claim 17 (depends on 14) The soft charge circuit of claim 14 wherein the soft charge circuit further comprises a sensing circuit for sensing DC bus voltage and a control circuit for controlling the switch circuit responsive to sensed voltage. ### Claim 18 (depends on 17) The soft charge circuit of claim 17 wherein the sensing circuit comprises a voltage divider connected across the link circuit. ### Claim 19 (depends on 14) The soft charge circuit of claim 14 wherein the soft charge circuit further comprises a control circuit for controlling the switch circuit responsive to a select time period. ### Claim 20 (depends on 17) The soft charge circuit of claim 17 wherein the control circuit turns the switch off if sensed voltage is below a select brown out level voltage.