DRIVER FOR INDUCTION MOTOR AND METHOD OF DRIVING THE SAME

Abstract

An object of the present invention is to provide a driver for an induction motor which performs an operation at an acceleration suitable for the magnitude of a load and is excellent in efficiency, without an acceleration failure.

Description

BRIEF DESCRIPTION OF DRAWINGS

Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:

FIG. 1 is a block diagram showing overall control for a driver for an induction motor according to Embodiment 1 of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a speed and a q-axis magnetic flux in the induction motor according to Embodiment 1 of the present invention.

FIG. 3 is a characteristic diagram showing control for a current against a speed command in Embodiment 1 of the present invention.

FIG. 4 is a block diagram showing an example of a concrete structure of a speed change rate arithmetic operation section 17.

FIG. 5 is a block diagram showing a structure of a speed change rate arithmetic operation section of a driver for an induction motor according to Embodiment 5 of the present invention.

FIG. 6 is a block diagram showing overall control for a driver for an induction motor according to Embodiment 6 of the present invention.

Claims

1. A driver for an induction motor including a power converter for operating the induction motor in a variable speed manner in accordance with a speed command, the driver for an induction motor comprising: a slip frequency arithmetic operation section for arithmetically operating a slip frequency of the induction motor; andchange rate reducing means for reducing a rate of change in the speed command when the arithmetically operated slip frequency approaches a predetermined range corresponding to a maximum torque generation frequency at which a maximum torque is generated.

2. The driver for an induction motor according to claim 1, further comprising a maximum torque generation slip frequency arithmetic operation section for arithmetically operating the maximum torque generation slip frequency at which the induction motor is caused to generate substantially a maximum torque.

3. The driver for an induction motor according to claim 1 or 2, wherein the change rate reducing means that reduces a rate of change in the speed command comprises increase rate reducing means for reducing a rate of increase in the speed command.

4. The driver for an induction motor according to claim 1 or 2, wherein the change rate reducing means for reducing a rate of change in the speed command comprises speed command change rate prevention means for making a rate of change in the speed command substantially zero.

5. The driver for an induction motor according to claim 1 or 2, wherein the change rate reducing means for reducing a rate of change in the speed command comprises speed command reducing means for reducing the speed command.

6. The driver for an induction motor according to claim 1 or 2, wherein the change rate reducing means for reducing a rate of change in the speed command comprises means for setting a rate of change in the speed command in accordance with a maximum torque estimate value.

7. The driver for an induction motor according to claim 1 or 2, further comprising means for correcting a rate of change in the speed command in accordance with a degree that the arithmetically operated slip frequency value approaches the maximum torque generation slip frequency.

8. The driver for an induction motor according to any one of claims 1 to 7, further comprising means for setting an exciting current command Id* as a larger level, in a region in which the speed command or a speed corresponding value is equal to or smaller than a predetermined value, than that in any region other than the region.

9. The driver for an induction motor according to any one of claims 1 to 7, further comprising means for setting a q-axis current command Iq* as a larger level, in a region in which one of the speed command or a speed estimate value is equal to or smaller than a predetermined value, than that in any region other than the region.

10. The driver for an induction motor according to any one of claims 1 to 9, further comprising current control means for controlling a current of the induction motor at a substantially constant level, irrespective of magnitude of a load, in a region in which one of the speed command and the speed estimate value is equal to or smaller than a predetermined value.

11. A driver for an induction motor including a power converter for operating the induction motor in a variable speed manner in accordance with a speed command, the driver for an induction motor comprising: a slip frequency arithmetic operation section for arithmetically operating a slip frequency of the induction motor; andalarm means for generating an alarm adapted to be recognized by a sense of sight and/or a sense of hearing when the arithmetically operated slip frequency approaches a predetermined range corresponding to a maximum torque generation slip frequency at which a maximum torque is generated.

12. The driver for an induction motor according to claim 11, further comprising: the alarm means for generating an alarm when the arithmetically operated slip frequency approaches the predetermined range corresponding to the maximum torque generation slip frequency at which the maximum torque is generated; andchange rate reducing means for reducing a rate of change in the speed command.

13. The driver for an induction motor according to claim 12, wherein the change rate reducing means for reducing a rate of change in the speed command comprises increase rate reducing means for reducing a rate of increase in the speed command.

14. The driver for an induction motor according to any one of claims 11 to 13, further comprising means for setting an exciting current command Id* as a larger level, in a region in which the speed command or a speed corresponding value is equal to or smaller than a predetermined value, than that in any region other than the region.

15. The driver for an induction motor according to any one of claims 11 to 14, further comprising current control means for controlling a current of the induction motor at a substantially constant level irrespective of magnitude of a load.

16. A method of driving an induction motor including a power converter for operating the induction motor in a variable speed manner in accordance with a speed command, the method comprising: the slip frequency arithmetic operation step of arithmetically operating a slip frequency of the induction motor; andthe change rate reducing step of reducing a rate of change in the speed command when the arithmetically operated slip frequency approaches a predetermined range corresponding to a maximum torque generation slip frequency at which a maximum torque is generated.

17. The method of driving an induction motor according to claim 16, wherein the change rate reducing step of reducing a rate of change in the speed command comprises the increase rate reducing step of reducing a rate of increase in the speed command.

18. The method of driving an induction motor according to claim 16 or 17, wherein the change rate reducing step of reducing a rate of change in the speed command comprises the step of setting the rate of change in the speed command in accordance with a maximum torque estimate value.

19. The method of driving an induction motor according to any one of claims 16 to 18, further comprising the step of correcting the rate of change in the speed command in accordance with a degree that the arithmetically operated slip frequency approaches the maximum torque generation slip frequency.

20. The method of driving an induction motor according to any one of claims 16 to 19, further comprising the step of setting an exciting current command Id* as a larger level, in a region in which the speed command or a speed corresponding value is equal to smaller than a predetermined value, than that in any region other than the region.