Sensor calibration and parameter identification in a multi-phase motor drive

• US 20080265819A1
• Filed: 04/26/2007
• Published: 10/30/2008
• Est. Priority Date: 04/26/2007
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Wang, Jin, Chen, Chingchi, Degner, Michael W.
• Granted Patent: US 7,646,160 B2
• Time in Patent Office: Days
• US Class Current: 318/490
• CPC Class Codes: G01R 31/42 AC power supplies

Abstract

In a multi-phase motor drive that includes a bus capacitor, a multi-phase motor, a multi-phase inverter, multiple switches each having an on-state and an off-state, and multiple current sensors each being in series with respective phase winding, a method for checking the accuracy of circuit parameters of the motor drive, including using the switches to produce a first loop that includes the capacitor bank, a first phase winding, a first current sensor, a second phase winding, and a second current sensor, using the current sensors to determine a magnitude of current in the first and second phase windings, comparing a magnitude of current indicated by the first current sensor and the second current sensor, and determining a magnitude of a difference between the current in the first and second phase windings.

Claims

1. In a multi-phase motor drive that includes a bus capacitor, a multi-phase motor, a multi-phase inverter connecting the bus capacitor with each phase winding of the motor, multiple switches, each switch having an on-state and an off-state and being in series with a phase winding, and multiple current sensors, each current sensor being in series with respective phase winding, a method for checking the accuracy of circuit parameters of the motor drive, comprising the steps of:

(a) using the switches to produce a first loop that includes the capacitor bank, a first phase winding, a first current sensor that indicates current in a first phase winding, a second phase winding, and a second current sensor that indicates current in the second phase winding;

(b) using the first and second current sensors to determine a magnitude of current in the first and second phase windings;

(c) comparing a magnitude of current indicated by the first current sensor and the second current sensor; and

(d) determining from step (c) a magnitude of a difference between the current in the first and second phase windings.

2. The method of claim 1, further comprising:

using a third current sensor to determine a magnitude of current in the third phase winding; and

determining a current offset of the third phase winding.

3. The method of claim 1, further comprising:

determining the voltage across the capacitor bank;

using the first current sensor and the second current sensor to determine the loop current; and

using the loop current and the voltage across the capacitor bank to estimate the inductance of the first and second phase windings.

4. The method of claim 3, further comprising:

changing the state of the switches to produce a second loop that includes the first and second phase windings, the first current sensor, and the second current sensor; and

using the estimated inductance of the first and second phase windings to estimate the forward-voltage drop across the first and second phase switches.

5. In a motor drive that includes a bus capacitor, a first multi-phase motor, a first multi-phase inverter connecting the bus capacitor with the first motor, a second multi-phase motor, a second multi-phase inverter in parallel with the first inverter and connecting the bus capacitor with each phase winding of the second motor, multiple switches, each switch having an on-state and an off-state and being in series with a phase winding, and multiple current sensors, each current sensor being in series with respective phase winding, a method for checking the current indicated by sensors for the first inverter with the current indicated by the sensors for the second inverter, comprising the steps of:

exhausting energy in the bus capacitor;

allowing current to circulate through phase windings of the first motor and phase windings of the second motor;

increasing a magnitude of voltage across the bus capacitor;

monitoring the rate of change of voltage across the bus capacitor;

comparing the magnitude of current in the current sensors when the rate of change of voltage across the bus capacitor becomes zero;

determining from the comparing step a magnitude of a difference between the current in the phase windings of the first motor and the phase windings of the second motor.

6. The method of claim 5 wherein the motor drive includes a DC power source, and the step of exhausting energy in the bus capacitor further includes the steps of:

disconnecting the power source;

using the switches to deliver current to the phase windings of the first motor and the second motor until energy in the bus capacitor is exhausted.

7. The method of claim 5 wherein the step of increasing the magnitude of voltage across the bus capacitor further includes the step of:

adjusting the state of the switches in the second inverter such that current in the phase windings of the first motor become equal to the current in the phase windings of the second motor.

8. The method of claim 5 wherein the step of increasing the magnitude of voltage across the bus capacitor further includes the step of:

turning off the switches of the second inverter;

allowing current in the phase windings of the second motor to flow through the second inverter to the bus capacitor; and

allowing current in the phase windings of the first motor to flow from the bus capacitor through the first inverter and first motor to the bus capacitor, thereby increasing a voltage across the bus capacitor, due to having a net positive current to the capacitor.

9. In a multi-phase motor drive that includes a capacitor bank, a multi-phase motor, a multi-phase inverter connecting the bus capacitor with each phase winding of the motor, including multiple inverter switches, each inverter switch having an on-state and an off-state and being in series with a phase winding, and multiple inverter current sensors, each inverter current sensor being in series with a respective phase winding, and a boost DC/DC converter connected across the bus capacitor and including a converter inductor, a converter capacitor, multiple converter switches, and a converter current sensor located in a current path between the converter inductor and the converter capacitor, a method for cross checking the current indicated by the converter current sensor with the current indicated by the inverter current sensors, comprising the steps of:

exhausting energy in the bus capacitor and the converter capacitor;

recharging the bus capacitor;

producing free resonance between the converter inductor and the converter capacitor;

comparing a magnitude of current in the converter current sensor to a magnitude of current in the phase windings when a rate of change of voltage across the bus capacitor becomes zero; and

determining from the comparing step a magnitude of a difference between the current in the phase winding and the magnitude of current in the converter.

11. The method of claim 9 wherein the motor drive includes a DC power source, and the step of exhausting energy in the bus capacitor and the inverter capacitor further includes the step of:

disconnecting the power source;

using the inverter switches to drain current from the bus capacitor and converter capacitor through the phase windings of the motor.

12. The method of claim 9 wherein the step of recharging the bus capacitor further comprises the steps of:

turning off the inverter switches and the converter switches;

conducting that motor inductive energy to the bus capacitor;

increasing a voltage across the bus capacitor; and

reducing current through the phase windings.

13. The method of claim 9 wherein the step of producing free resonance further comprises the steps of:

turning on at least one of the converter switches; and

electrically connecting the converter inductor and the converter capacitor.

14. In a multi-phase motor drive that includes a bus capacitor, a multi-phase motor, a multi-phase inverter connecting the bus capacitor with each phase winding of the motor, multiple switches, each switch having an on-state and an off-state and being in series with a phase winding, and multiple current sensors, each current sensor being in series with respective phase winding, a method for checking the capacitance of the bus capacitor, comprising the steps of:

charging the bus capacitor to a first voltage;

discharging the bus capacitor through a bleed resistor until the voltage across the bus capacitor reaches a second voltage;

determining the expected length of the discharge period of the bus capacitor;

measuring the discharge period of the bus capacitor;

comparing the calculated and expected lengths of the discharge period;

if the measured discharge period is shorter than the expected discharge period, operating switches in a boost DC/DC converter and the multi-phase inverters to charge the bus capacitor to a third voltage;

operating switches in the boost DC/C converter and multi-phase inverter with controlled time intervals to create controlled current oscillation between the bus capacitor and motor winding;

discharging the bus capacitor through the first and second phase windings during a predetermined interval until the voltage across the bus capacitor approaches zero voltage;

using the change in voltage across the bus capacitor and the current in the phase windings during the interval to calculated the expected capacitance of the bus capacitor;

comparing the nominal magnitude of the bus capacitor with the calculated magnitude of the bus capacitor; and

replacing the bus capacitor if the nominal magnitude of the bus capacitor is substantially different than the calculated magnitude of the bus capacitor.

15. The method of claim 14 further comprising step of replacing the bleed resistor or a connection between the bleed resistor and the motor drive if the measured discharge period is shorter than the expected discharge period and the nominal magnitude of the bus capacitor is substantially equal to the calculated magnitude of the bus capacitor.

16. The method of claim 14 wherein step of discharging the bus capacitor through the first and second phase windings during a predetermined interval until the voltage across the bus capacitor approaches zero voltage further comprises the step of:

using the switches to produce a first loop that includes the capacitor bank, a first phase winding, a first current sensor that indicates current in a first phase winding, a second phase winding, and a second current sensor that indicates current in the second phase winding.

17. The method of claim 16 wherein step of charging the bus capacitor through the first and second phase windings further comprises the step of:

switching the state of the switches used to produce the first loop.

18. The method of claim 14 further comprising the step of using the motor drive with the current bus capacitance and the bleed resistor if the measured discharge period is substantially equal to the calculated discharge period.

19. The method of claim 14 further comprising the step of replacing either the bleed resistor or a connection between the bleed resistor and the motor drive if the measured discharge period is longer than the calculated discharge period.

20. The method of claim 14 further comprising the step of replacing the inductor in boost DC/DC converter if the inductance is smaller than a predetermined value.

21. The method of claim 14, further comprising the steps of:

for inductance monitoring, operating switches in the boost DC/DC converter and the multi-phase inverters to charge the bus capacitor to a third voltage with continuous current flowing through the inductor of the boost converter; and

using the current change in the inductor, on time of the lower switch in the boost DC/DC converter, and the input voltage to the boost DC/DC converter to calculate the inductance of the inductor in the boost DC/DC converter.