Apparatus and method used with AC motors for controlling motor operation

• US 5,495,158 A
• Filed: 09/30/1994
• Issued: 02/27/1996
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Rehm, Thomas, Schmidt, Peter B.
• Primary Examiner(s): Sircus, Brian
• Application Number:
  US08/316,180
• Time in Patent Office: 515 Days
• Field of Search: 318/560-568.25, 318/600-610, 364/148-155, 364/157-166, 364/167.01, 364/172-175, 364/474.12, 364/474.15, 364/474.28, 364/474.29, 364/474.30
• US Class Current: 318/561
• CPC Class Codes: H02P 23/16 Controlling the angular speed of one shaft H02P23/18 takes precedence

Abstract

A method and apparatus for motor control tuning wherein an extremely accurate estimate of inertia is determined by using the second derivative of a desired motor velocity and the torque supplied to a motor is altered as a function of inertia.

Claims

1. A method to be used with a model reference adaptive motor controller where the motor controller receives a command velocity signal and produces the control torque signal that drives a motor at a motor velocity, said method estimates inertia and tunes the controller, the method comprising the steps of:

(a) deriving a motor velocity signal that is indicative of motor velocity;

(b) determining the difference between the motor velocity signal and the command velocity signal to produce an error signal;

(c) determining the second derivative of the command velocity signal to produce a jerk signal;

(d) mathematically combining the jerk signal and the error signal to produce a derivative signal;

(e) integrating the derivative signal to produce an inertia estimate; and

(f) using the inertia estimate to alter the control torque signal.

2. The method as recited in claim 1 wherein the controller includes a feedback loop that provides a feedback torque signal and the step of using the inertia estimate includes the steps of:

(a) determining the first derivative of the command velocity signal to produce an acceleration signal;

(b) mathematically merging the acceleration signal and the inertia estimate to produce a feedforward torque signal; and

(c) adding the feedforward torque signal to a feedback torque signal to produce the motor torque signal.

3. The method as recited in claim 2 wherein the controller receives a torque limit signal and the method further comprises the steps of:

comparing the control torque signal to the torque limit signal; and

if an absolute value of the control torque signal is greater than or equal to the torque limit signal, maintaining the existing inertia estimate.

4. The method as recited in claim 3 further including the steps of:

determining an inertia torque signal;

subtracting the inertia torque signal from the control torque signal to produce a load torque estimate;

comparing the load torque estimate to the limit torque signal; and

if an absolute load torque estimate is greater than or equal to X % of the limit torque signal, maintaining the existing inertia estimate, where X is a predetermined value.

5. The method as recited in claim 4 wherein X is 10.

6. The method as recited in claim 2 wherein the step of mathematically merging includes the step of multiplying the acceleration signal and the inertia estimate.

7. The method as recited in claim 1 wherein the controller includes a feedback loop having a proportional-integral control leg having a proportionality constant and an integrating constant, the method further including the steps of adjusting the proportionality constant and the integrating constant as a function of the inertia estimate.

8. The method as recited in claim 7 wherein the steps of adjusting include the steps of multiplying the inertia estimate by an ideal proportionality constant to produce a corrected proportionality constant and multiplying the inertia estimate by an ideal integrating constant to produce a corrected integrating constant.

9. The method as recited in claim 8 wherein the ideal proportionality constant k_p is 2ζ

ω

_n and the ideal integrating constant is ω

²_n, where ζ

is a damping coefficient and ω

_n is an ideal bandwidth.

10. The method as recited in claim 1 wherein the step of mathematically combining includes the steps of multiplying the jerk signal and the error signal to produce an intermediate signal and multiplying the intermediate signal by a gain signal to produce the derivative signal.

11. A method to be used with a model reference adaptive motor controller for regulating a control torque signal to a motor, the motor controller receives a command velocity signal and produces the control torque signal that drives the motor at a motor velocity, the controller includes a model that produces a model velocity signal indicative of an ideal motor velocity, the controller also includes a feedback loop, the method comprising the steps of:

(a) determining a motor velocity signal indicative of the motor velocity;

(b) determining the first derivative of the command velocity signal to produce an acceleration signal;

(c) determining the second derivative of the command velocity signal to produce a jerk signal;

(d) determining the difference between the motor velocity signal and the model velocity signal to produce an error signal;

(e) mathematically combining the jerk signal and the error signal to produce a derivative signal;

(f) integrating the derivative signal to produce an inertia estimate;

(g) mathematically merging the acceleration signal and the inertia estimate to produce a feedforward torque signal; and

(h) adding the feedforward signal to a feedback signal to produce the control torque signal.

12. The method as recited in claim 11 wherein the feedback loop includes a proportional-integral control leg having a proportionality constant and an integrating constant, the method further including the steps of adjusting the proportionality constant and the integrating constant as a function of the inertia estimate.

13. The method as recited in claim 12 wherein the steps of adjusting include the steps of multiplying the inertia estimate by an ideal proportionality constant to produce a corrected proportionality constant and multiplying the inertia estimate by an ideal integrating constant to produce a corrected integrating constant.

14. The method as recited in claim 12 wherein the controller receives a torque limit signal and, the method further comprises the steps of:

comparing the control torque signal to the torque limit signal; and

if the absolute value of the control torque signal is greater than or equal to the torque limit signal, setting the change in inertia estimate equal to zero.

15. The method as recited in claim 14 further including the steps of:

determining the first derivative of the model velocity signal to produce a model acceleration signal;

mathematically combining the model acceleration signal and the inertia estimate to produce a transitional signal;

subtracting the transitional signal from the control torque signal to produce a load torque estimate;

comparing the load torque estimate to the limit torque signal; and

if the load torque estimate is greater than or equal to 10% of the limit torque signal, setting the change inertia estimate equal to zero.

16. A method to be used with a model reference adaptive motor controller for regulating a control torque signal to a motor, the motor controller receives a command velocity signal and produces the control torque signal that drives the motor at a motor velocity, the controller includes a feedback loop, the method comprising the steps of:

(a) deriving a motor signal that is indicative of motor velocity;

(b) determining the difference between the motor signal and the command velocity signal to produce an error signal;

(c) determining the first derivative of the command velocity signal to produce an acceleration signal;

(d) determining the second derivative of the command velocity signal to produce a jerk signal;

(e) mathematically combining the jerk signal and the error signal to produce a derivative signal;

(f) integrating the derivative signal to produce an inertia estimate;

(g) mathematically merging the acceleration signal and the inertia estimate to produce a feedforward torque signal; and

(h) adding the feedforward signal to a feedback signal to produce the control torque signal.

17. An apparatus to be used with a model reference adaptive motor controller for regulating a control torque signal to a motor, the motor controller receives a command velocity signal and produces the control torque signal that drives the motor at a motor velocity, the controller includes a model that produces a model velocity signal indicative of an ideal motor velocity, the apparatus comprising:

(a) a sensor to determine an actual motor velocity signal;

(b) a difference calculator that produces an error signal by determining the deviation between a motor velocity signal and a model velocity signal;

(c) a derivation module that receives the command velocity signal and determines the second derivative of the command velocity signal thus producing a jerk signal;

(d) a multiplier to multiply the jerk signal, the error signal, and a gain to produce a derivative signal;

(e) an integrator that receives and integrates the derivative signal thus producing an inertia estimate; and

(f) a compensator that uses the inertia estimate to derive the motor torque signal.

18. The apparatus as recited in claim 17 wherein the controller includes a feedback loop and the derivation module also determines the first derivative of the command velocity, thus producing an acceleration signal, and the compensator comprises:

(a) a second multiplier that multiplies the acceleration signal and the inertia estimate thus producing a feedforward signal; and

(b) a summing module that adds the feedforward signal to a feedback signal to produce the control torque signal.

19. The apparatus as recited in claim 18 wherein the feedback loop includes a proportional-integral control leg having a proportionality constant and an integrating constant, the apparatus further including an adaptation module that adjusts the proportionality constant and the integrating constant as a function of the inertia estimate.

20. The apparatus as recited in claim 19 wherein the controller receives a torque limit signal and the apparatus further comprises:

a comparator module that compares the control torque signal to the torque limit signal; and

a first blocking module that, if the absolute value control torque signal is greater than the torque limit signal, sets the change in inertia estimate equal to zero.

21. The apparatus as recited in claim 20 further comprising:

a second derivation module that determines the second derivative of the model velocity signal to produce a model jerk signal;

a third multiplier that multiplies the model acceleration signal and the inertia estimate to produce a transitional signal;

a subtractor that subtracts the transitional signal from the control torque signal to produce a load torque estimate;

a second comparator to compare the load torque estimate to the limit torque signal; and

a second blocking module that, if the load torque estimate is greater than or equal to X % of the limit torque signal, sets the inertia estimate equal to zero where X is a predetermined value.

22. The apparatus as recited in claim 20 wherein X is 10.