Apparatus for controlling an induction motor

• US 6,670,786 B2
• Filed: 12/07/2001
• Issued: 12/30/2003
• Est. Priority Date: 04/23/1999
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Tobari, Kazuaki, Okuyama, Toshiaki
• Primary Examiner(s): Masih, Karen
• Application Number:
  US10/004,814
• Publication Number:
  US 20020060549A1
• Time in Patent Office: 753 Days
• Field of Search: 318/805, 318/807, 318/808, 318/825, 318/798, 318/782, 318/432
• US Class Current: 318/805
• CPC Class Codes: H02P 21/04 specially adapted for very low speeds
• CPC Class Codes: H02P 21/18 Estimation of position or speed
• CPC Class Codes: H02P 21/24 Vector control not involving the use of rotor position or rotor speed sensors
• CPC Class Codes: H02P 21/26 Rotor flux based control
• CPC Class Codes: H02P 2207/01 Asynchronous machines

Abstract

If a speed instruction value is less than a predetermined value, the output current of a power-conversion unit is controlled to be larger than a current value in an ordinary no-load operation, or a frequency instruction value is calculated based on a speed instruction value in place of an estimated speed.

Claims

1. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current-control unit to control current output from the power-conversion unit;

a measuring unit to measure an output frequency instruction value inputted to the power-conversion unit;

a comparator to compare the measured output frequency instruction value with a predetermined value;

wherein the comparator provides an output to the current-control unit to control the current output from the power-conversion unit so as to be larger than a current available during ordinary no-load operation upon a determination by the comparator that the measured output frequency instruction value is less than the predetermined value, the current output from the power-conversion unit being independent of a torque output of the motor.

2. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current-control unit to control current output from the power-conversion unit in accordance with a current instruction value in a d-axis corresponding to a flux axis in a rotating-flux coordinate system;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value inputted to the power-conversion unit;

an estimated rotational speed value measuring unit to measure an estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the current-control unit to control d-axis current so as to be larger than a current available during an ordinary no-load operation upon a determination by the comparator that one of the measured rotational speed instruction value and measured estimated rotational speed value is less than the predetermined value.

3. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current control unit to control current output from the power-conversion unit in accordance with a current instruction value in a q-axis in a rotating-flux coordinate system;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value inputted to the power-conversion unit;

an estimated rotational speed value measuring unit to measure an estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the current-control unit to control q-axis current so as to be larger than a current available during an ordinary no-load operation upon a determination by the comparator that one of the measured rotational speed instruction value and measured estimated rotational speed value is less than the predetermined value.

4. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current-control unit to control current output from the power-conversion unit in accordance with a current instruction value in a d-axis corresponding to a flux axis in a rotating-flux coordinate system and a current instruction value in a q-axis in a rotating-flux coordinate system;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

an estimated rotational speed value measuring unit to measure an estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the current control unit to control d-axis current so as to be a first predetermined value greater than a current available during ordinary no-load operation and controlling q-axis current so as to be less than a second predetermined value upon one of the measured rotational speed instruction value and measured estimated rotational speed value being less than the predetermined value.

5. The apparatus according to claim 4, wherein the second predetermined value is equal to 0.

6. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current-control unit to control current output from the power-conversion unit in accordance with one of a current instruction value in a d-axis corresponding to a flux axis in a rotating-flux coordinate system and a current instruction value in a q-axis in a rotating-flux coordinate system;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

an estimated rotational speed value measuring unit to measure an estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and measured estimated rotational speed value with a predetermined value;

a calculator to calculate a frequency instruction value using the rotational speed instruction value in place of the estimated rotational speed value upon one of the measured rotational speed instruction value and measured estimated rotational speed value being less than the predetermined value.

7. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current-control unit to control current output from the power-conversion unit in accordance with a current instruction value in a d-axis corresponding to a flux axis in a rotating-flux coordinate system;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

an estimated rotational speed value measuring unit to measure an estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the current-control unit to control d-axis current so as to be a predetermined value greater than a current available during ordinary no-load operation and further comprising a calculator to calculate a frequency instruction value using the rotational speed instruction value in place of the estimated rotational speed value upon one of the measured rotational speed instruction value and measured estimated rotational speed value being less than the predetermined value.

8. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a current-control unit to control current output from the power-conversion unit in accordance with a current instruction value in a q-axis in a rotating-flux coordinate system;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

an estimated rotational speed value measuring unit to measure an estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the current-control unit to control q-axis current so as to be greater than a predetermined value and further comprising a calculator to calculate a frequency instruction value using the rotational speed instruction value in place of the estimated rotational speed value upon one of the measured rotational speed instruction value and measured estimated rotational speed value being less than the predetermined value.

9. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a voltage-calculation unit to calculate an output voltage reference value for the power-conversion unit based on an output frequency instruction value to the power-conversion unit and a frequency-calculation unit to control a frequency output from the power-conversion unit in accordance with a rotational speed instruction value;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

a comparator to compare the measured rotational speed instruction value with a predetermined value; and

a current control unit;

wherein the comparator provides a signal to the current-control unit to control d-axis current so as to be at a predetermined value larger than a current available during an ordinary no-load operation upon the measured rotational speed instruction value being less than the predetermined value.

10. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a voltage-compilation unit to calculate an output voltage reference value for the power-conversion unit based on an output frequency instruction value to the power-conversion unit and a frequency-control unit to control a frequency output from the power-conversion unit in accordance with a rotational speed instruction value;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

a comparator to compare the measured rotational speed instruction value with a predetermined value; and

a current control unit;

wherein the comparator provides an output to the current control unit to control q-axis current so as to be larger than a predetermined value upon the measured rotational speed instruction value being less than the predetermined value.

11. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit to control a frequency and voltage output from the power-conversion unit in accordance with a rotational speed instruction value;

an estimated slip frequency value calculator to calculate an estimated slip frequency value in accordance with the voltage output from the power-conversion unit;

a slip frequency value calculator to calculate a slip frequency value in accordance with a current output from the power-conversion unit;

an adder to add the calculated estimated slip frequency value to the calculated slip frequency value to produce a resultant sum;

wherein the adder provides an output to the power-conversion unit to control the frequency output of the power-conversion unit in accordance with the resultant sum.

14. The apparatus according to any one of claims 11-13, wherein the estimated slip frequency value calculator calculates the estimated slip frequency value in accordance with a ratio of a d-axis induced-electromotive force value to a q-axis induced-electromotive force value.

15. The apparatus according to any one of claims 11-13, wherein the estimated slip frequency value calculator calculates the estimated slip frequency value in accordance with one of a d-axis voltage instruction value and a detected d-axis voltage value, and one of a q-axis voltage instruction value and a detected q-axis voltage value.

16. The apparatus according to any one of claims 11-13, wherein the estimated slip frequency value calculator calculates the estimated slip frequency value in accordance with a ratio of a q-axis flux value to a d-axis flux value.

17. The apparatus according to any one of claims 11-13, wherein the estimated slip frequency value calculator calculates the estimated slip frequency value in accordance with a ratio of a q-axis flux value, obtained in accordance with the value of the frequency output from the power-conversion unit and one of a d-axis voltage instruction value and a detected d-axis voltage value, to a d-axis flux value, obtained in accordance with the value of the frequency output of the power-conversion unit and one of a q-axis voltage instruction value and a detected q-axis voltage value.

18. The apparatus according to claim 16, further comprising:

a d-axis flux value calculator to calculate the d-axis flux value in accordance with a ratio of a value obtained by subtracting a sum of a q-axis resistance voltage-decrease and a q-axis leakage-reactance voltage decrease from one of a q-axis voltage instruction value and a detected q-axis voltage value, to the value of the output frequency; and

a q-axis flux value calculator to calculate the q-axis flux value in accordance with a ratio of a value obtained by subtracting a difference between a d-axis resistance voltage-decrease and a d-axis leakage-reactance voltage-decrease from one of a d-axis voltage instruction value and a detected d-axis voltage value, to the value of the output frequency.

19. The apparatus according to claim 16, further comprising:

a d-axis flux value calculator to calculate the d-axis flux value by integrating a value obtained by subtracting a difference between a d-axis resistance voltage-decrease and a d-axis leakage-reactance voltage-decrease from one of a d-axis voltage instruction value and a detected d-axis voltage value and further subtracting a d-axis induced-electromotive force from a result of the subtraction; and

a q-axis flux value calculator to calculate the q-axis flux value by integrating a value obtained by subtracting a difference between a q-axis resistance voltage-decrease and a q-axis leakage-reactance voltage-decrease from one of a q-axis voltage instruction value and a detected q-axis voltage value and further adding a q-axis induced-electromotive force to a result of the subtraction.

20. The apparatus according to any one of claims 11-13, wherein the slip frequency value calculator calculates the slip frequency value in accordance with a ratio of one of the q-axis current instruction value and the detected q-axis current value to a d-axis flux value.

12. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit;

a voltage-calculation unit to calculate an output voltage reference value for the power-conversion unit in accordance with one of a pair of detected d and q-axis current values and a pair of d and q-axis current instruction values and in accordance with an output frequency instruction value to the power-conversion unit and to control a frequency output from the power-conversion unit in accordance with a rotational speed instruction value;

an estimated slip frequency value calculator to calculate an estimated slip frequency value in accordance with the voltage output from the power-conversion unit;

a slip frequency value calculator to calculate a slip frequency value in accordance with a current output from the power-conversion unit;

an adder to add the calculated estimated slip frequency value to the calculated slip frequency value to produce a resultant sum;

wherein the adder provides an output to the power-conversion unit to control the frequency output of the power-conversion unit in accordance with the resultant sum.

13. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power conversion unit and a current-control unit to control current output from the power-conversion unit and to control a frequency output from the power-conversion unit in accordance with one of a rotational speed instruction value and an estimated rotational speed value;

an estimated slip frequency value calculator to calculate an estimated slip frequency value in accordance with the voltage output from the power-conversion unit;

a slip frequency value calculator to calculate a slip frequency value in accordance with a current output from the power-conversion unit;

an adder to add the calculated estimated slip frequency value to the calculated slip frequency value to produce a resultant sum;

wherein the adder provides an output to the power-conversion unit to control the frequency output of the power-conversion unit in accordance with the resultant sum.

21. A rotational speed-control apparatus to control an induction motor, the apparatus comprising:

a power-conversion unit to control a frequency and voltage output from the power-conversion unit in accordance with a rotational speed instruction value;

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

a comparator to compare the measured rotational speed instruction value with a predetermined value;

wherein the comparator provides an output to the power-conversion unit to control current output from the power-conversion unit so as to be at a predetermined value larger than a current available during an ordinary no-load operation, and to correct the output current in correspondence with a value of a torque output of the motor upon the measured rotational speed instruction value being less than the predetermined value.

24. The apparatus according to any one of claims 21-23, further comprising a d-axis current corrector to correct a value of d-axis current in correspondence with the value of the torque output of the motor.

25. The apparatus according to any one of claims 21-23, further comprising a q-axis current corrector to correct a value of q-axis current in correspondence with the value of the torque output of the motor.

26. The apparatus according to any one of claims 21-23, further comprising a means for obtaining the value of the torque output based on one of a pair of d-axis and q-axis voltage instruction values and a pair of detected d-axis and q-axis voltage values and based on one of a pair of d-axis and q-axis current instruction values and a pair of detected d-axis and q-axis current values, the d-axis and q-axis being axes in a rotating-flux coordinate system.

27. The apparatus according to any one of claims 21-23, further comprising a means for obtaining the value of the torque output based on one of a pair of d-axis and q-axis voltage instruction values and a pair of detected d-axis and q-axis voltage values, the d-axis and q-axis flux values being calculated with the value of the frequency output from the power-conversion unit and based on one of a pair of d-axis and q-axis current instruction values and a pair of detected d-axis and q-axis current values in a rotating coordinate system, the d-axis and q-axis being axes in a rotating-flux coordinate system.

22. A rotational speed-control apparatus to control a frequency output from a power-conversion unit for an induction motor in accordance with a rotational speed instruction value using a voltage-calculation unit to calculate an output voltage reference value for the power-conversion unit based on one of a pair of detected d and q-axis current values and a pair of d and q-axis current instruction values and based on a value of the frequency output from the power-conversion unit, the apparatus comprising:

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

a comparator to compare the measured rotational speed instruction value with a predetermined value;

wherein the comparator provides an output to the power-conversion unit to control current output from the power-conversion unit so as to be a predetermined value larger than a current available during an ordinary no-load operation, and to correct the output current in correspondence with a value of a torque output of the motor upon the measured rotational speed instruction value being less than the predetermined value.

23. A rotational speed-control apparatus to control a frequency output from a power-conversion unit for an induction motor in accordance with one of a rotational speed instruction value and an estimated rotational speed value using current-control units for controlling current output from the power-conversion unit, the apparatus comprising:

a rotational speed instruction value measuring unit to measure a rotational speed instruction value;

an estimated rotational speed value measuring unit the estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and the measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the power-conversion unit to control current output from the power-conversion unit so as to be at a predetermined value larger then a current available during an ordinary no-load operation, and to correct the output current in correspondence with a value of a torque output of the motor upon one of the measured rotational speed instruction value and measured estimated rotational speed value being less than the predetermined value.

28. A rotational speed-control apparatus to control a frequency and current output from a power-conversion unit for an induction motor in accordance with a rotational speed instruction value, the apparatus comprising:

a rotational speed instruction value measuring unit to measure the rotational speed instruction value;

a comparator to compare the measured rotational speed instruction value with a predetermined value;

wherein the comparator provides an output to the power-conversion unit to control current output from the power-conversion unit so as to be at a predetermined value larger than a current available during an ordinary no-load operation and to correct the value of the current in accordance with a value obtained by adding a calculated estimated slip frequency value based on a value of a voltage output from the power-conversion unit to a calculated slip frequency value based on a value of current output from the power-conversion unit upon the measured rotational speed instruction value being less than the predetermined value.

31. The apparatus according to any one of claims 28-30, further comprising a means for correcting a value of the d-axis current in correspondence with a sum of the estimated slip frequency value and the calculated slip frequency value.

32. The apparatus according to any one of claims 28-30, further comprising a means for correcting a value of the q-axis current in correspondence with a sum of the estimated slip frequency value and the calculated slip frequency value.

29. A rotational speed-control apparatus to control a frequency output from a power-conversion unit for an induction motor in accordance with a rotational speed instruction value using a voltage-calculation unit to calculate an output voltage reference value based on one of a pair of d-axis and q-axis current instruction values and a pair of detected d-axis and q-axis values in a rotating-flux coordinate system and based on the value of the frequency output of the power-conversion unit, the apparatus comprising:

a rotational speed instruction value measuring unit to measure the rotational speed instruction value;

a comparator to compare the measured rotational speed instruction value with a predetermined value;

wherein the comparator provides an output to the power-conversion unit to control current output from the power-conversion unit so as to be at a predetermined value larger than a current available during an ordinary no-load operation and to correct the value of the current in accordance with a value obtained by adding a calculated estimated slip frequency value based on a value of a voltage output from the power-conversion unit to a calculated slip frequency value based on a value of current output from the power-conversion unit upon the measured rotational speed instruction value being less than the predetermined value.

30. A rotational speed-control apparatus to control a frequency output from a power-conversion unit to drive an induction motor in accordance with one of a rotational speed instruction value and an estimated rotational speed value using a current-control unit to control current output from the power-conversion unit, the apparatus comprising:

a rotational speed instruction value measuring unit to measure the rotational speed instruction value;

an estimated rotational speed value measuring unit to measure the estimated rotational speed value;

a comparator to compare the measured rotational speed instruction value and the measured estimated rotational speed value with a predetermined value;

wherein the comparator provides an output to the power-conversion unit to control current output from the power-conversion unit so as to be a predetermined value larger than a current available during ordinary no-load operation upon one of the measured rotational speed instruction value and the measured estimated rotational speed value being less than the predetermined value.