Method and apparatus for maximizing utilization of an electric motor under load

• US 4,659,976 A
• Filed: 04/24/1985
• Issued: 04/21/1987
• Est. Priority Date: 04/24/1985
• Status: Expired due to Fees

• Current Assignee: INDRESCO, Inc. (RHI Magnesita NV)
• Original Assignee: Dresser Industries Incorporated (Halliburton Company)
• Inventors: Johanson, Fredrick R.
• Primary Examiner(s): Miller, Charles D.
• Assistant Examiner(s): Ip, Shik Luen Paul
• Application Number:
  US06/726,709
• Time in Patent Office: 727 Days
• Field of Search: 318/314, 318/317, 318/318, 318/326, 318/327, 318/432, 318/433, 318/434, 318/436, 318/437, 318/438, 318/461, 318/462, 318/463, 318/464, 318/465, 318/456, 318/471, 318/472 , 318/473, 318/490, 318/333, 318/334, 318/332, 318/611, 318/628, 318/634, 318/689
• US Class Current: 388/816
• CPC Class Codes: H02P 4/00 Arrangements specially adapted for regulating or controlling the speed or torque of electric motors that can be connected to two or more different electric power supplies vector control H02P21/00
• CPC Class Codes: Y10S 388/904 Stored velocity profile
• CPC Class Codes: Y10S 388/909 Monitoring means
• CPC Class Codes: Y10S 388/93 Load or torque

Abstract

The present invention relates to an electronic device that is used to calculate the actual torque being produced by an electric motor at any instant in time and comparing this value of torque ratiometrically either with the maximum (peak) torque that the motor could produce under the line voltage available at that instant or with rated motor torque, thus giving an indication of whether the motor is approaching stall or is under utilized or over utilized.

Claims

1. A method of adjusting the load on an electric motor having a known speed/torque relationship to maximize its utilization comprising the steps of:

a. generating a first signal representing the actual instantaneous speed of said motor;

b. generating a signal representing the actual instantaneous motor line voltage;

c. comparing said first generated speed signal to data representing a known speed/torque relationship of said motor at said instantaneous voltage to generate a second signal representative of instantaneous actual torque, a third signal representative of rated torque and a fourth signal representative of peak torque at said instantaneous line voltage;

d. comparing said third or fourth signals representing, respectively, the rated or peak torques of said motor at said instantaneous line voltage with said second signal representing actual torque; and

e. varying said load on said motor in accordance with said actual torque comparison to obtain said maximum utilization of said motor.

2. A method of maximizing the utilization of a motor under load as in claim 1 wherein the step of generating a first signal representing the speed of said motor comprises the steps of:

a. storing data signals representing a family of the motor current/speed characteristic curves at, over, and under rated line voltage;

b. generating signals representing actual instantaneous motor operating current; and

c. generating a signal representing the speed of said motor by comparing said signals representing said actual instantaneous voltage and current with said signals representing said family of current/speed/voltage curves.

3. A method as in claim 1 wherein the step of generating a first signal representing the speed of said motor comprises the steps of:

a. generating signals representing actual instananeous motor operating current;

b. utilizing an algorithm to computer generate signals representing a motor current/speed characteristic curve at said actual instantaneous line voltage; and

c. generating a signal representing the speed of said motor by comparing said signals representing said actual instantaneous voltage and current with said signals representing said current/speed/voltage curve.

4. A method as in claim 2 or 3 wherein the step of generating said second signal representing actual torque of said motor comprises the steps of:

a. storing data signals representing the family of speed/torque characteristic curves at, over, and under rated line voltage,

b. comparing said signals representing said actual instantaneous speed and voltage with said signals representing said stored family of speed/torque/voltage curves; and

c. generating said second signal representing actual torque when a comparison is found between said actual instantaneous speed and voltage and said stored speed and voltage.

5. A method as in claim 4 wherein the step of providing a comparison of said actual torque with either of said third or fourth signals representing said peak or said rated torque comprises the steps of:

a. coupling said second signal representing said actual torque to a visual display; and

b. selectively coupling either said third signal representing said rated torque or said fourth signal representing said peak torque to said display whereby a visual comparison of said actual torque with either said rated torque or said peak torque may be displayed thereby enabling an operator to control said motor load according to said comparison.

6. A method as in claim 4 further including the steps of:

a. comparing said second signal representing said actual motor torque with said third signal representing said rated torque;

b. generating a control signal when said second signal representing actual torque exceeds said third signal representing rated torque thereby indicating a possible motor overheat condition; and

c. utilizing said control signal to reduce said motor load until said actual motor torque is equal to said rated torque.

7. A method as in claim 4 further including the steps of:

a. establishing a warning signal representing a value of actual torque with respect to peak torque at any given line voltage signifying approaching motor stall;

b. comparing said second signal representing actual torque with said established motor stall warning signal;

c. generating a control signal when said second signal representing said actual torque exceeds said established motor stall warning signal thereby indicating approaching motor stall; and

d. utilizing said control signal to reduce said motor load until said actual motor torque is less than said established stall warning signal.

8. A method as in claim 2 or 3 wherein the step of generating said second signal representing actual torque of said motor comprises the steps of:

a. utilizing an algorithm to computer generate signals representing a motor speed/torque characteristic curve at said actual instantaneous line voltage; and

b. generating said signal representing said actual torque of said motor by comparing said signals representing said actual instantaneous voltage and speed with said computer generated signals representing said torque/speed/voltage curve.

9. A method as in claim 1 further including the step of utilizing an induction motor as said electric motor.

10. Apparatus for adjusting the load on an electric motor having a known speed/torque relationship to maximize its utilization comprising:

a. means for generating a first signal representing the instantaneous speed of said motor;

b. means for generating a signal representing the actual instantaneous motor line voltage;

c. means for comparing said first generated speed signal to data representing a known speed/torque relationship of said motor at said instantaneous voltage to generate a second signal representative of instantaneous actual torque, a third signal representative of rated torque, and a fourth signal representative of peak torque at said instantaneous line voltage;

d. means for comparing said third or fourth signals represnting, respectively, the rated or peak torques of said motor at said instantaneous line voltage with said second signal representing actual torque for generating a signal representing the difference between said rated and peak torque and said actual torque; and

e. means coupled to said torque comparing means for varying said load on said motor in accordance with said actual torque comparison to obtain said maximum utilization of said motor.

11. Apparatus for maximizing the utilization of a motor under load as in claim 10 wherein said means for generating a first signal representing the speed of said motor comprises:

a. means for storing data signals representing a family of the motor current/speed characteristic curves at, over, and under rated line voltage;

b. means for generating signals representing actual instantaneous motor operating current; and

c. means for generating a signal representing the speed of said motor by comparing said signals representing said instantaneous voltage and current with said signals representing said family of current/speed/voltage curves.

12. Apparatus as in claim 11 or 16 wherein the means for generating said second signal representing actual torque of said motor comprises:

a. means for storing data signals representing the family of speed/torque characteristic curves at, over, and under rated line voltage;

b. means for comparing said signals representing said actual instantaneous speed and voltage with said signals representing said stored family of speed/torque/voltage curves; and

c. means for generating said second signal representing actual torque when a comparison is found between said actual instantaneous speed and voltage and said stored speed and voltage.

13. Apparatus as in claim 12 wherein the means for providing a comparison of said actual torque with either of said third and fourth signals representing said peak or said rated torque comprises:

a. means for coupling said second signal representing said actual torque to a visual display; and

b. means for selectively coupling either said third signal representing said rated torque or said fourth signal representing said peak torque to said display whereby a visual comparison of said actual torque with either said rated torque or said peak torque may be displayed thereby enabling an operator to control said motor load according to said comparison.

14. Apparatus as in claim 12 further comprising:

a. means for comparing said second signal representing said actual motor torque with said third signal representing said rated torque;

b. means for generating a control signal when said second signal representing actual torque exceeds said third signal representing rated torque thereby indicating a possible motor overheat condition; and

c. means for utilizing said control signal ot reduce said motor load until said actual motor torque is equal to said rated torque.

15. Apparatus as in claim 12 further comprising:

a. means for establishing a warning signal representing a value of actual torque with respect to peak torque at any given line voltage signifying approaching motor stall;

b. means for comparing said second signal representing actual torque with said established motor stall warning signal;

c. means for generating a control signal when said second signal representing actual torque exceeds said established motor stall warning signal thereby indicating approaching motor stall; and

d. means for utilizing such control signal to reduce said motor load until said actual motor torque is less than said established stall warning signal.

16. Apparatus as in claim 10 wherein the means for generating a first signal representing the speed of said motor comprises:

a. means for generating said signals representing actual instantaneous motor operating current;

b. means for utilizing an algorithm to computer generate signals representing a motor current/speed characteristic curve at instantaneous line voltage; and

c. means for generating a signal representing the speed of said motor by comparing said signals representing said instantaneous voltage and current with said signals representing said current/speed/voltage curve.

17. Apparatus as in claim 11 or 16 wherein the means of generating said second signal representing actual torque of said motor comprises:

a. means for utilizing an algorithm to computer generate signals representing a motor speed/torque characteristic curve at said actual instantaneous line voltage, and

b. means for generating said signal representing said actual torque of said motor by comparing said signals representing said actual instantaneous voltage and speed with said computer generated signals representing said torque/speed/voltage curve.

18. Apparatus as in claim 10 further including an induction motor as said electric motor.

20. Apparatus as in claim 18 wherein said visual display means displays said torque as a bar chart.

19. Apparatus for determining the load on an electric motor having a known speed/torque relationship comprising:

a. means for generating a first signal representing the instantaneous speed of said motor;

b. means for generating a signal representing the actual instantaneous motor line voltage;

c. means for comparing said first generated speed signal to data representing a known speed/torque relationship of said motor at said instantaneous line voltage to generate a second signal representative of instantaneous actual torque of said motor; and

d. means coupled to said comparing means for visually displaying said second signal representing instantaneous actual torque of said motor.

21. Apparatus for determining the load on an electric motor having a known speed/torque relationship comprising:

a. means for generating a first signal representing the instantaneous speed of said motor;

b. means for generating a signal representing the instantaneous motor line voltage; and

c. means for comparing said first generated speed signal to data representing a known speed/torque relationship of said motor at said instantaneous line voltage to generate a second signal representative of instantaneous actual torque of said motor.