Disturbance observer for permanent magnet direct current machines

1. A motor control system of a motor, the motor control system comprising:

an observer module configured to:

receive an input voltage signal of the motor;

receive an output current signal from the motor; and

compute a disturbance estimate of the motor control system as a measured state of a plant model of an electrical subsystem of the motor control system, the disturbance estimate expressed as {circumflex over (d)}=−{circumflex over (K)} e {circumflex over (ω)} m −{circumflex over (v)} B , where {circumflex over (d)} is the disturbance estimate, {circumflex over (K)} e is a back-emf constant, {circumflex over (ω)} m is a motor velocity, and {circumflex over (v)} B is brush-drop voltage; and

computing the motor velocity of the motor based on the disturbance estimate as

ω

^

m

=

-

d

^

+

σ

⁡

(

i

a

)

⁢

V

^

0

(

1

-

e

-



i

a

I

^

0



)

K

^

e

,

where V 0 and I 0 are estimated state variables and i a is a motor current.

2. The motor control system of claim 1 , further comprising a velocity module configured to determine an estimated motor velocity of the motor based on the disturbance estimate.

3. The motor control system of claim 1 , wherein the observer module is further configured to add the disturbance estimate with the input voltage signal to compensate for actual disturbance term to facilitate feedforward compensation.

4. The motor control system of claim 1 , wherein the observer module computes the disturbance estimate by tuning a gain matrix using a single scalar value.

5. The motor control system of claim 1 , wherein the motor is a brushed motor.

6. A method for determining a disturbance estimate for a motor control system, the method implemented by a control module of the motor control system, the method comprising:

receiving an input voltage signal of a motor controlled by the motor control system;

receiving an output current signal from the motor; and

computing the disturbance estimate of the motor control system as a measured state of a plant model of an electrical subsystem of the motor, the disturbance estimate including a first component based on a back-emf of the motor, and a second component based on a brush-drop voltage across the motor, the disturbance estimate expressed as {circumflex over (d)}=−{circumflex over (K)} e {circumflex over (ω)} m −{circumflex over (v)} B , where {circumflex over (d)} is the disturbance estimate, {circumflex over (K)} e is a back-emf constant, {circumflex over (ω)} m is a motor velocity, and {circumflex over (v)} B is the brush-drop voltage; and

computing the motor velocity estimate of the motor based on the disturbance estimate by extracting the motor velocity estimate from the disturbance estimate based on the back-emf constant.

7. The method of claim 6 , further comprising blending the disturbance estimate with the input voltage signal to provide feedforward compensation.

8. The method of claim 7 , wherein adding the disturbance estimate to the input voltage signal comprises compensating the actual disturbance signal.

9. The method of claim 6 wherein computing the disturbance estimate comprises tuning a gain matrix of an observer module using a single scalar value to converge an estimated output current from a disturbance observer module with the output current signal from the motor.

10. The method of claim 6 , wherein the motor is a permanent magnet brushed motor.

11. An electric power steering (EPS) system comprising:

a motor; and

a motor control system comprising a controller module configured to:

receive an input voltage signal of the motor;

receive a measured output current signal of the motor; and

compute a disturbance estimate of the motor control system, which is modeled as a state variable of a plant model of an electrical subsystem of the motor, the disturbance estimate expressed as {circumflex over (d)}=−{circumflex over (K)} e {circumflex over (ω)} m −{circumflex over (v)} B , where {circumflex over (d)} is the disturbance estimate, {circumflex over (K)} e is a back-emf constant, {circumflex over (ω)} m is a motor velocity, and {circumflex over (v)} B is a brush-drop voltage; and

determine an estimated motor velocity of the motor based on the disturbance estimate by extracting the estimated motor velocity using the back-emf constant of the motor.

12. The electric power steering system of claim 11 , wherein the control module is further configured to blend the disturbance estimate with the input voltage signal to provide feedforward compensation to the motor control system.

13. The electric power steering system of claim 12 , wherein blending the disturbance estimate with the input voltage signal comprises increasing the input voltage signal by the value of the disturbance estimate to compensate for a disturbance signal.