Control method of compressor motor and inverter equipped with the same method

• US 20020117992A1
• Filed: 12/12/2001
• Published: 08/29/2002
• Est. Priority Date: 12/27/2000
• Status: Active Grant

• Current Assignee: Sanden Corporation (Hisense Home Appliances Group Co., Ltd.)
• Original Assignee: Sanden Corporation (Hisense Home Appliances Group Co., Ltd.)
• Inventors: Kuwabara, Ichirou, Yoshii, Yuuji, Hirono, Daisuke
• Granted Patent: US 6,646,411 B2
• Time in Patent Office: Days
• US Class Current: 318/801
• CPC Class Codes: H02P 23/28 Controlling the motor by varying the switching frequency of switches connected to a DC supply and the motor phases
• CPC Class Codes: H02P 3/18 for stopping or slowing an ac motor

Abstract

A control device for a compressor motor and an inverter according to the present invention monitors the amplitude of a phase current of a three-phase DC motor. As the amplitude of the phase current approaches an overload condition of the inverter or motor, the control device decreases the rotational velocity of the motor by a predetermined rotational deceleration. By reducing the rotational velocity of the motor by a certain deceleration, the control device of the present invention ensures that the motor load, i.e., the amplitude of the phase current, does not reach or exceed an overload condition. By use of this device, it is possible to suppress or reduce effectively the frequency of motor stops caused by an increase in the phase current.

Claims

1. A control device for an inverter, comprising:

switching elements for driving a three-phase DC motor in response to a rotational frequency command signal from an external device;

a calculator for calculating a rotational velocity and a rotational acceleration of said motor in response to a back-emf signal of said motor; and

a detector for detecting an amplitude of a phase current of said motor,

wherein, when said amplitude of said phase current exceeds a first set point I1, motor activation is stopped, and when said amplitude of said phase current is less than said first set point I1 but greater than a second set point α

I2, which is less than said first set point I1, said rotational velocity of said motor is decelerated at a predetermined rate, and when said amplitude of said phase current is less than a third set point α

I3, which is less than said second set point α

I2, said rotational velocity of said motor is accelerated at a predetermined rate, and further wherein α

is a constant.

2. The control device of claim 1, wherein,

an interval between said second set point α

I2 and said first set point I1 is further divided into three subintervals by disposing a fourth set point α

I4 and a fifth set point α

I5 in said interval, and when said amplitude of said phase current falls in one of said subintervals, said rotational velocity of said motor is decelerated by a deceleration predetermined for each of said subintervals.

3. The control device of claim 2, wherein,

said interval between said second set point α

I2 and said first set point I1 is further divided into more than three subintervals by disposing more than two set points in said interval, and when the amplitude of said phase current falls in one of said subintervals, the rotational velocity of said motor is decelerated by a deceleration predetermined for each of said subintervals.

4. The control device of claim 3, wherein,

a magnitude of said predetermined deceleration for each of said subintervals increases as said subintervals approach said first set point I1.

5. The control device of claim 1, wherein,

a value of said first set point I1 is a rated current of said motor.

6. The control device of claim 1, wherein,

a value of said first set point I1 is a rated current of said switching elements.

7. The control device of claim 1, wherein,

a value of said first set point I1 is a rated current of a wire which connects said motor and said switching elements.

8. The control device of claim 1, wherein,

a value of said first set point I1 is a rated current of a connector which connects said switching elements and said motor.

17. The control device of claim 1, wherein,

said constant a has a numerical value of 0.9≦

α

≦

1.0.

9. An inverter, comprising:

a plurality of switching elements for driving a three-phase DC motor in accordance with a rotational frequency command signal from an external device;

a calculator for calculating a rotational velocity and a rotational acceleration of said motor from a back-emf signal of said motor;

a detector for detecting an amplitude of a phase current of said motor; and

a control program comprising an overload suppression routine,

wherein, when said amplitude of said phase current exceeds a first set point I1, said overload suppression routine stops activation of said motor, and when said amplitude of said phase current is less than said first set point I1, but greater than a second set point α

I2, which is smaller than said first set point I1, said overload suppression routine decelerates said rotational velocity of said motor at a predetermined deceleration, and when said amplitude of said phase current is less that a third set point α

I3, which is smaller than the second set point α

I2, said overload suppression routine accelerates the rotational velocity of said motor at a predetermined acceleration, and further wherein α

is a constant.

10. The inverter of claim 9, wherein,

an interval between said second set point α

I2 and said first set point I1 is further divided into three subintervals by disposing a fourth set point α

I4 and a fifth set point α

I5 in said interval and when said amplitude of said phase current falls in one of said subintervals, said overload suppression routine decelerates said rotational velocity of said motor by a deceleration predetermined for each of said subintervals.

11. The inverter of claim 10, wherein,

said interval between said second set point α

I2 and said first set point I1 is further divided into more than three subintervals by disposing more than two set points in said interval, and when the amplitude of said phase current falls in one of said subintervals, said routine decelerates the rotational velocity of said motor by a deceleration predetermined for each of said subintervals.

12. The inverter of claim 11, wherein,

a magnitude of said predetermined deceleration for each of said subintervals increases as said subintervals approach said first set point I1.

13. The inverter of claim 9, wherein,

a value of said first set point I1 is a rated current of said motor

14. The inverter of claim 9, wherein,

a value of said first set point I1 is a rated current of said switching elements.

15. The inverter of claim 9, wherein,

a value of said first set point I1 is a rated current of a wire which connects said motor and said switching elements.

16. The inverter of claim 9, wherein,

a value of said first set point I1 is a rated current of a connector which connects said switching elements and said motor.

18. The inverter of claim 9, wherein,

said constant α

has a numerical value of 0.9≦

α

≦

1.0.

20. The method of claim 19, wherein,

said constant α

has a numerical value of 0.9≦

α

≦

1.0.

19. A method of controlling a compressor motor that is driven by an inverter, comprising:

calculating a rotational velocity and a rotational acceleration of said motor, in response to back-emf signals of said motor;

detecting an amplitude of a phase current of said motor;

when said amplitude of said phase current exceeds a first set point I1, stopping activation of said motor;

when said amplitude of said phase current is less than said first set point I1, but greater than a second set point α

I2, which is less than said first set point I1, decelerating said rotational velocity of said motor at a predetermined rate; and

when said amplitude of said phase current is less than a third set point α

I3, which is less than said second set point α

I2, accelerating said rotational velocity of said motor at a predetermined rate,

wherein, α

is a constant.