# US 5,705,905 A · Source impedance measurement for motor control > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,905 A - Document ID: US5705905A - Status: Granted - Kind: A - Application number: 08/683,673 - Filed: 1996-07-17 - Granted: 1998-01-06 - Earliest claimed: 1996-07-17 - Assignees: Baldor Electric Company - Inventors: Richard D. Wood - Web page: https://patentgrep.com/patent/US5705905A ## CPC - H02P 27/08: with pulse width modulation - G01R 27/02: Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant (by measuring phase angle only G01R25/00) - G01R 31/42: AC power supplies - H02P 23/06: Controlling the motor in four quadrants - H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A power inverter assembly for a three-phase motor includes a resistor of known resistance which is capable of being switched in between the positive and negative DC bus lines that supply power to the power control electronics. When the resistor is switched in, a voltage drop across the bus lines is observed. The magnitude of this voltage drop is then used to determine a percent impedance value which indicates whether the source impedance is sufficient. ## Claims ### Claim 1 A power inverter assembly for an electric motor, comprising: a diode bridge, coupled to power lines from a power source and adapted to convert alternating current carried on said power lines to direct current carried on a positive bus line and a negative bus line; a bus capacitor coupled between said positive and negative bus lines; and a resistor of known resistance value, selectively coupled between said positive and negative bus lines, such that when said resistor is coupled between said positive and negative bus lines, the magnitude .DELTA.V of a resultant voltage drop between said positive and negative bus lines can be observed and correlated with impedance of said power source. ### Claim 2 (depends on 1) A power inverter assembly in accordance with claim 1, further comprising motor control circuitry, coupled to said positive and negative bus lines, for receiving said direct current and supplying power to said electric motor. ### Claim 3 (depends on 2) A power inverter assembly in accordance with claim 2, wherein said motor control circuitry provides pulse-width modulated power to said electric motor. ### Claim 4 (depends on 1) A power inverter assembly in accordance with claim 1, wherein said power source is a three-phase alternating current power supply. ### Claim 5 (depends on 1) A power inverter assembly in accordance with claim 1, wherein said voltage drop magnitude .DELTA.V is correlated with said power source impedance according to the formula: ##EQU13## where: PI represents equivalent series source impedance as a percentage of load impedance, I.sub.FLA is the full load amperage of said power source, R.sub.SIM is the resistance value of said resistor, V.sub.LL is the line-to-line voltage of said power source, and K is a constant coefficient. ### Claim 6 (depends on 5) A power inverter assembly in accordance with claim 5, further comprising a microprocessor for performing said correlation. ### Claim 7 (depends on 5) A power inverter assembly in accordance with claim 5, further comprising circuitry for turning off said motor in response to calculation of a PI value below a predetermined minimum value. ### Claim 8 (depends on 5) A power inverter assembly in accordance with claim 5, wherein said constant coefficient K is determined as a function of known circuit parameters on a case-by-case basis. ### Claim 9 (depends on 1) A power inverter assembly in accordance with claim 1, further comprising a microprocessor for performing said correlation. ### Claim 10 (depends on 1) A power inverter assembly in accordance with claim 1, further comprising circuitry for turning off said motor from said power source in response to a correlation indicating that said power source impedance is below a predetermined minimum level. ### Claim 11 (depends on 1) A power inverter assembly in accordance with claim 1, wherein said voltage drop magnitude .DELTA.V is correlated with said power source impedance according to the formula: PI=K.times.NR.times.NVD where: PI represents the equivalent series impedance as a percentage of load impedance, K is a constant coefficient determined as a function of known circuit parameters on a case-by-case basis, NR is a normalized expression of the resistance of said resistor, and NVD is a normalized expression of .DELTA.V. ### Claim 12 (depends on 11) A power inverter assembly in accordance with claim 11, wherein NR is given by: ##EQU14## where I.sub.FLA is the full load amperage of said power source, R.sub.SIM is the resistance value of said resistor, and V.sub.LL is the line-to-line voltage of said power source. ### Claim 13 (depends on 12) A power inverter assembly in accordance with claim 12, wherein NVD is given by: ##EQU15## ### Claim 14 A method of assessing the impedance of a power source coupled to a power inverter assembly having a diode bridge, coupled to power lines from said power source and adapted to convert alternating current carried on said power lines to direct current carded on a positive bus line and a negative bus line, said method comprising the steps of: (a) coupling a resistor of known resistance value between said positive and negative bus lines; (b) measuring the magnitude of a voltage drop between said positive and negative bus lines resulting from said step (a) of coupling; and (c) correlating said voltage drop with said impedance. ### Claim 15 (depends on 14) A method in accordance with claim 14, wherein said power source is a three-phase alternating current power supply. ### Claim 16 (depends on 14) A method in accordance with claim 14, wherein said voltage drop magnitude .DELTA.V is correlated with said power source impedance according to the formula: ##EQU16## where: PI represents the equivalent series source impedance as a percentage of load impedance, I.sub.FLA is the full load amperage of said power source, R.sub.SIM is the resistance value of said resistor, V.sub.LL is the line-to-line voltage of said power source, and K is a constant coefficient. ### Claim 17 (depends on 16) A method in accordance with claim 16, wherein said constant coefficient K is determined as a function of known circuit parameters on a case-by-case basis. ### Claim 18 (depends on 14) A method in accordance with claim 14, wherein said voltage drop magnitude .DELTA.V is correlated with said power source impedance according to the formula: PI=K.times.NR.times.NVD where: PI represents the equivalent series source impedance as a percentage of load impedance, K is a constant coefficient determined as a function of known circuit parameters on a case-by-case basis, NR is a normalized expression of the resistance of said resistor, and NVD is a normalized expression of .DELTA.V. ### Claim 19 (depends on 18) A method in accordance with claim 18, wherein NR is given by: ##EQU17## where I.sub.FLA is the full load amperage of said power source, R.sub.SIM is the resistance value of said resistor, and V.sub.LL is the line-to-line voltage of said power source. ### Claim 20 (depends on 19) A method in accordance with claim 19, wherein NVD is given by: ##EQU18## ### Claim 21 A motor system, comprising: a power source; a power inverter assembly including a diode bridge coupled to power lines from said power source and adapted to convert AC voltage carried on said power lines to DC voltage carried on a positive bus line with respect to a negative bus line; a bus capacitor coupled between said positive and negative bus lines; and a resistor of known resistance value, selectively coupled between said positive and negative bus lines, such that when said resistor is coupled between said positive and negative bus lines, the magnitude .DELTA.V of a resultant voltage drop between said positive and negative bus lines can be observed and correlated with impedance of said power source. ### Claim 22 (depends on 21) A motor system in accordance with claim 21, further comprising motor control circuitry, coupled to said positive and negative bus lines, for receiving said DC voltage and supplying power to an electric motor. ### Claim 23 (depends on 22) A motor system in accordance with claim 22, wherein said motor control circuitry provides pulse-width modulated power to said electric motor. ### Claim 24 (depends on 21) A motor system in accordance with claim 21, wherein said voltage drop magnitude .DELTA.V is correlated with said power source impedance according to the formula: ##EQU19## where: PI represents the percentage difference between actual source impedance and rated source impedance, I.sub.FLA is the full lead amperage of said power source, R.sub.SMI is the resistance value of said resistor, V.sub.LL is the line-to-line voltage of said power source, and K is a constant coefficient. ### Claim 25 (depends on 24) A motor system in accordance with claim 24, further comprising a microprocessor for performing said correlation. ### Claim 26 (depends on 24) A motor system in accordance with claim 24, further comprising circuitry for turning off said motor in response to calculation of a PI value below a predetermined minimum value. ### Claim 27 (depends on 24) A motor system in accordance with claim 24, wherein said constant coefficient K is determined as a function of known circuit parameters on a case-by-case basis. ### Claim 28 (depends on 21) A motor system in accordance with claim 21, further comprising a microprocessor for performing said correlation. ### Claim 29 (depends on 21) A motor system in accordance with claim 21, further comprising circuitry for turning off said motor in response to a correlation indicating that said power source impedance is below a predetermined minimum level. ### Claim 30 (depends on 21) A motor system in accordance with claim 21, wherein said voltage drop magnitude .DELTA.V is correlated with said power source impedance according to the formula: PI=K.times.NR.times.NVD where: PI represents the equivalent series source impedance as a percentage of load impedance, K is a constant coefficient determined as a function of known circuit parameters on a case-by-case basis, NR is a normalized expression of the resistance of said resistor, and NVD is a normalized expression of .DELTA.V. ### Claim 31 (depends on 30) A motor system in accordance with claim 30, wherein NR is given by: ##EQU20## where I.sub.FLA is the full load amperage of said power source, R.sub.SIM is the resistance value of said resistor, and V.sub.LL is the line-to-line voltage of said power source. ### Claim 32 (depends on 31) A motor system in accordance with claim 31, wherein NVD is given by: ##EQU21##