Method and apparatus for fine resolution brushless motor control

• US 6,744,230 B2
• Filed: 10/29/2002
• Issued: 06/01/2004
• Est. Priority Date: 10/29/2002
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Wilkins, Dean R., Hill, Bryan H.
• Primary Examiner(s): Nappi, Robert
• Assistant Examiner(s): San Martin, Edgardo
• Application Number:
  US10/283,472
• Publication Number:
  US 20040080290A1
• Time in Patent Office: 581 Days
• Field of Search: 318/254, 318/439, 318/438, 318/701, 318/721, 318/738, 318/463, 318/464, 318/244, 318/733, 318/43, 318/609, 318/610, 318/605, 341/111-117
• US Class Current: 318/400.04
• CPC Class Codes: G01P 3/48 by measuring frequency of generated current or voltage in general G01R23/00
• CPC Class Codes: G01P 3/487 delivered by rotating magnets
• CPC Class Codes: H02P 6/17 and for generating speed information

Abstract

A motor controller (30) includes three analog Hall-effect sensors (42, 44, 46) for forming continuous-time signals proportional to the sine and cosine of the position of the rotor (24) of a motor (20). The sine and cosine signals are differentiated to obtain signals proportional to the rotor rate times the sine and cosine values. These integrated values are then multiplied by the cosine and inverse of the sine values, respectively, to obtain values equal to the rotor rate times the square of the cosine and the rotor rate times the square of the sine. These latter two values are summed to obtain an output signal proportional to the rotor rate based on the trigonometric identity sin²(x)+cos²(x)=1. Since the motor controller (30) derives a high-resolution value for the rotor rate, it may be used for fine resolution control of brushless motors and the like.

Claims

1. A method for performing fine resolution motor control comprising the steps of:

forming a first signal proportional to sin(Θ

) and a second signal proportional to cos(Θ

) using a plurality of analog Hall-effect sensors, wherein Θ

is an angular position of a rotor of the motor with respect to a predetermined reference point as a function of time;

differentiating said first and second signals to obtain third and fourth signals, respectively;

multiplying said second and third signals to provide a fifth signal;

forming an inverse of a product of said first signal and said fourth signal to provide a sixth signal; and

summing said fifth and sixth signals to provide an output signal proportional to a rotor rate in response.

2. The method of claim 1 wherein said step of forming said inverse of said product of said first signal and said fourth signal to provide said sixth signal comprises the steps of:

inverting said first signal to form an inverted first signal; and

multiplying said inverted first signal by said fourth signal to obtain said sixth signal.

3. The method of claim 1 wherein said step of forming said first signal proportional to sin(Θ

) and said second signal proportional to cos(Θ

) using said plurality of analog Hall-effect sensors comprises the step of placing first, second, and third analog Hall-effect sensors at substantially uniform intervals around the circumference of said motor.

4. The method of claim 3 wherein said step of forming said first signal proportional to sin(Θ

) further comprises the step of subtracting an output of said second Hall-effect sensor from an output of said first Hall-effect sensor to obtain said first signal.

5. The method of claim 3 wherein said step of forming said second signal proportional to cos(Θ

) further comprises the step of summing an output of said first Hall-effect sensor, an output of said second Hall-effect sensor, and the negative of an output of said third Hall-effect sensor to obtain said second signal.

6. The method of claim 1 further comprising the step of normalizing said first and second signals prior to said step of differentiating.

7. The method of claim 1 further comprising the step of obtaining an instantaneous position of said rotor by taking the arctangent of the ratio of said first signal to said second signal.

8. A method for performing fine resolution motor control comprising the steps of:

placing first, second, and third analog Hall-effect sensors at substantially uniform intervals around the circumference of a motor, said first, second, and third analog Hall-effect sensors producing respective signals X, Y, and Z;

forming a first signal proportional to sin(Θ

) and a second signal proportional to cos(Θ

) in response to said signals X, Y, and Z wherein Θ

is an angular position of a rotor of the motor with respect to a predetermined reference point as a function of time;

differentiating said first signal to obtain a third signal having a value proportional to {dot over (Θ

)} times cos(Θ

) wherein {dot over (Θ

)} is an estimate of a rate of said rotor;

differentiating said second signal to obtain a fourth signal having a value proportional to −

{dot over (Θ

)} times cos(Θ

);

multiplying said second and third signals to obtain a fifth signal proportional to {dot over (Θ

)} times cos²(Θ

);

multiplying an inverse of said first signal and said fourth signal to obtain a sixth signal proportional to {dot over (Θ

)} times sin²(Θ

); and

summing said fifth and sixth signals to obtain an output signal proportional to {dot over (Θ

)}.

9. The method of claim 8 wherein said step of forming said first and second signals comprises the steps of:

subtracting Y from X to form a first difference signal and multiplying said first difference signal by a first predetermined number to form said first signal; and

adding X to Y and subtracting Z to form a second difference signal and multiplying said second difference signal by a second predetermined number to form said second signal.

10. The method of claim 9 wherein said first predetermined number is equal to $\frac{1}{\sqrt{3}}$

and said second predetermined number is equal to $\frac{1}{2}.$

11. The method of claim 8 further comprising performing the steps of placing, deriving, integrating said first signal, and integrating said second signal in hardware circuitry, and performing said steps of multiplying and summing in software.

12. The method of claim 8 further comprising the step of obtaining an instantaneous position of said rotor by taking the aretangent of the ratio of said first signal to said second signal.

13. A motor controller comprising:

first, second, and third Hall-effect sensors positioned at substantially uniform intervals around the circumference of a motor, each of said first, second, and third Hall-effect sensors providing corresponding first, second, and third analog output signals;

a first adder having inputs for receiving said first and second analog output signals, and an output for providing a difference between said first and second analog output signals;

a second adder having inputs for receiving said first, said second, and said third analog output signals and having an output for providing a value equal to the first analog output signal plus the second analog output signal minus said third analog output signal;

a first gain element having an input coupled to said output of said first adder, and an output for providing a first signal proportional to a sine of a position of said rotor;

a second gain element having an input coupled to said output of said second adder, and an output for providing a second signal proportional to a cosine of a position of said rotor;

a first rate block having an input coupled to said output of said first gain element, and an output;

a second rate block having an input coupled to said output of said second gain element, and an output;

a first multiplier having a first input coupled to said output of said first integrator, a second input coupled to said output of said second gain element, and an output;

a second multiplier having a first input coupled to said output of said first gain element through an inverter, a second input coupled to said output of said second integrator, and an output; and

a summing device having a first input coupled to said output of said first multiplier, a second input coupled to said output of said second multiplier, and an output for providing an output signal proportional to a rotor rate signal estimate.

14. The motor controller of claim 13 further comprising a smoothing filter having a first input for receiving said rotor rate estimate, a second input for receiving a rotor position signal, and first and second outputs for providing a smoothed rotor position and a smoothed rotor rate estimate, respectively.

15. The motor controller of claim 14 wherein said smoothing filter comprises:

a first summing device having a first input for receiving said rotor position signal, a second input for coupled to said second output of said smoothing filter, and an output for providing a difference between said first and second inputs thereof;

a multiplication clement having a first input coupled to the output of the first summing device, and an output for providing a product of said first input and a predetermined multiplication factor;

a second summing device having a first input for receiving said rotor rate estimate, a second input coupled to said output of said multiplication element, and an output for providing said first output of said smoothing filter as a sum of said first and second inputs thereof; and

an integrator having an input coupled to said output of second summing device, and an output for providing said second output of said smoothing filter.