Granted Patent B2

US 7,872,441 · App. 11/771,719 · Granted Jan 18, 2011

Abstract

Claims (49)

1. A motor control system, comprising:

an alternating current (AC) motor;

an inverter coupled to the AC motor, the inverter having a DC-link and being configured to provide current and a first amount of reactive power to the AC motor to produce a commanded torque in the AC motor; and

a processor coupled to the AC motor and the inverter, the processor configured to:

monitor a current at the DC-link; and

instruct the inverter to provide a second amount of reactive power to the AC motor to produce the commanded torque in the AC motor if the current at the DC-link of the inverter is one of below and equal to a threshold current amount, the second amount of reactive power being greater than the first amount of reactive power.

2. The system of claim 1 , further comprising a reactive power module coupled to the inverter, the reactive power module configured to alter a first synchronous current command configured to produce the commanded torque to form a second synchronous current command supplied to the inverter to induce the inverter to provide the second amount of reactive power, wherein the second synchronous current command is configured to produce the commanded torque.

3. The system of claim 2 , further comprising a look-up table coupled to the AC motor, the look-up table configured to select the first synchronous current command based on a torque command, a motor speed of the AC motor, and a DC-link voltage.

4. The system of claim 3 , further comprising a first adder coupled to the look-up table and the reactive power module, wherein:

the first synchronous current command includes a d-axis current command obtained from the look-up table;

the first adder is configured to add the d-axis current command to a delta-adjusting d-axis current received from the reactive power module to form an altered d-axis current of the second synchronous current command; and

the delta-adjusting d-axis current command is based on a difference between the current at the DC-link and the threshold current amount.

5. The system of claim 4 , further comprising a second adder coupled to the look-up table and the reactive power module, wherein:

the first synchronous current command includes a q-axis current command obtained from the look-up table;

the second adder is configured to add the q-axis current command to a delta-adjusting q-axis current received from the reactive power module to form an altered q-axis current of the second synchronous current command; and

the delta-adjusting q-axis current command is based on the delta-adjusting d-axis current and the torque value.

6. The system of claim 1 , wherein the inverter is a Z-source inverter.

7. The system of claim 1 , wherein:

the processor is configured to instruct the inverter to provide the current and the first amount of reactive power to the AC motor in response to a commanded torque, the current provided to the AC motor being configured to produce the commanded torque in the AC motor; and

the second amount of reactive power is configured to produce the commanded torque in the AC motor.

8. A method for operating a plurality of inductors in a Z-source inverter providing current to an alternating current (AC) motor in a continuous current mode, the plurality of inductors being coupled to a DC-link, the method comprising the steps of:

operating the Z-source inverter to produce a commanded torque in the AC motor;

determining if a current at the DC-link is one of below and equal to a threshold current amount; and

inducing the AC motor to draw more reactive power to produce the commanded torque if the current at the DC-link is one of below and equal to the threshold current amount.

9. The method of claim 8 , wherein the inducing step comprises the step of adding reactive power to the AC motor.

10. The method of claim 9 , wherein the adding reactive power step comprises the step of controlling the current provided to the AC motor so that the AC motor is induced to draw additional reactive power.

11. The method of claim 8 , wherein the inducing step comprises the step of altering synchronous currents provided to a current regulator providing voltage commands to the inverter.

12. The method of claim 8 , wherein the determining step comprises the step of determining if the plurality of inductors are providing one of the same amount and less current to the inverter than a critical current of the plurality of inductors.

13. The method of claim 8 , further comprising determining synchronous frame current commands configured to produce the commanded torque in the AC motor, wherein:

operating the Z-source inverter comprises operating the Z-source inverter based on the synchronous frame current commands; and

inducing the AC motor to draw more reactive power comprises altering the synchronous frame current commands to provide more reactive power to the AC motor while producing the commanded torque.

14. The method of claim 13 , wherein:

the synchronous frame current commands include a d-axis current command and a q-axis current command; and

altering the synchronous frame current commands comprises:

determining a delta-adjusting d-axis current based on a difference between the current at the DC-link and the threshold current amount;

adding the delta-adjusting d-axis current to the d-axis current command;

determining a delta-adjusting q-axis current based on the commanded torque and the delta-adjusting d-axis current; and

adding the delta-adjusting q-axis current to the q-axis current command.

15. A reactive power module for operating a plurality of inductors in an inverter coupled to an alternating current (AC) motor in a continuous current mode, comprising:

means for determining if a current at a DC-link coupled to the inverter is one of at and below a threshold current amount; and

means for altering a first d-axis current command and a first q-axis current command of a synchronous current command configured to produce a commanded torque in the AC motor to form an altered synchronous current command provided to the inverter to induce the AC motor to draw more reactive power from the inverter, wherein the altered synchronous current command is configured to produce the commanded torque.

16. The reactive power module of claim 15 , wherein the determining means comprises means for subtracting a critical current for the plurality of inductors from the current at the DC-link.

17. The reactive power module of claim 15 , wherein the altering means comprises:

means for determining a delta-adjusting q-axis current based on the commanded torque; and

means for adding the delta-adjusting q-axis current to the first q-axis current command to produce a q-axis current of the altered synchronous current command.

18. The reactive power module of claim 17 , wherein the altering means further comprises:

means for determining a delta-adjusting d-axis current based on a difference between the current at the DC-link and the threshold current amount, wherein the delta-adjusting q-axis current is determined based on the delta-adjusting d-axis current; and

means for adding the delta-adjusting d-axis current to the first d-axis current command to produce a d-axis current of the altered synchronous current.

19. The reactive power module of claim 18 , further comprising means for limiting the delta-adjusting q-axis current and the delta-adjusting d-axis current to respective maximum and minimum values.

Assignments (12)