Method and apparatus for high velocity ripple suppression of brushless DC motors having limited drive/amplifier bandwidth

• US 8,766,578 B2
• Filed: 02/27/2012
• Issued: 07/01/2014
• Est. Priority Date: 02/27/2012
• Status: Active Grant

• Current Assignee: Canadian Space Agency (Government of Canada)
• Original Assignee: Canadian Space Agency (Government of Canada)
• Inventors: Aghili, Farhad
• Primary Examiner(s): Leykin, Rita
• Application Number:
  US13/405,575
• Publication Number:
  US 20130221887A1
• Time in Patent Office: 855 Days
• Field of Search: 318/400.23, 318/432, 318/610, 318/632, 318/799, 700/280
• US Class Current: 318/400.23
• CPC Class Codes: G05B 19/00 Programme-control systems
• CPC Class Codes: H02P 23/14 Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
• CPC Class Codes: H02P 6/10 Arrangements for controlling torque ripple, e.g. providing reduced torque ripple

Abstract

A method and apparatus are provided for ripple suppression of brushless DC motors at any given velocity irrespective of the limited bandwidth of the driver/amplifier supplying the excitation currents to the stator. In a preferred embodiment, Fourier coefficients of the current waveform are calculated as a function of rotor velocity by taking into account the driver/amplifier'"'"'s finite bandwidth dynamics. For a given velocity, Fourier coefficients of the series approximating the waveform (control signal) are calculated as a function of the rotor velocity and the amplifier dynamics, to generate a waveform that results in no torque or velocity pulsations. When changing the motor speed, the coefficients are updated (recalculated) based on the new desired velocity (and amplifier dynamics), resulting in generation of an updated waveform that results in no torque or velocity pulsations at the new motor speed.

Claims

1. A method of driving a load via a brushless DC motor, comprising:

receiving a desired motor velocity ω

_d;

receiving actual velocity ω and

rotor position angle θ

from said load;

generating armature phase drive currents i*_k, for a desired torque τ

_d from the desired motor velocity ω

_d, actual velocity ω and

rotor position angle θ

using a modified commutation law;

amplifying the armature phase drive currents via a driver/amplifier; and

applying the amplified armature phase drive currents i_k to an armature of said brushless DC motor for inducing rotation of said rotor and thereby rotating said load;

wherein the modified commutation law comprises calculating compensated Fourier coefficients c′

of a truncated (finite) Fourier series approximating the armature phase drive currents for said desired motor velocity ω

_d as a function of the actual velocity ω

and transfer function of said driver/amplifier, wherein said modified commutation law further comprises;

a) computing fixed Fourier coefficients c of said Fourier series at zero velocity;

b) computing said compensated Fourier coefficients c′

at said desired motor velocity ω

_d;

c) computing the armature phrase drive currents i*k by modulating the desired torque τ

_dwith said corresponding commutation functions u_k(θ

) according to i*_k(τ

_d,θ

)=τ

_d u_k(θ

), ∀

k=1, . . . , p and

2. The method of claim 1, wherein said fixed Fourier coefficients c are computed according to

3. The method of claim 1, wherein said compensated Fourier coefficients c′

are computed according to c=D<sup>−

1</sup>(ω

)c′

.

4. The method of claim 1, wherein said armature phase drive currents i*_k, are computed by modulating the desired torque τ

_d with said corresponding commutation functions u_k(θ

)according to i*_k(τ

_d,θ

)=τ

_d u_k(θ

), ∀

k=1, . . . , p and

5. A controller for controlling rotation of a load by a brushless DC motor having a stator and a rotor, comprising:

a motion controller for receiving a desired motor velocity ω

_d, actual velocity ω and

rotor position angle θ

from said load;

a commutator for generating armature phase drive currents i*_k, for a desired torque τ

_d from the desired motor velocity ω

_d, actual velocity ω and

rotor position angle θ

;

a driver/amplifier for amplifying the armature phase drive currents and applying the amplified armature phase drive currents i_k to an armature of said stator for inducing rotation of said rotor and thereby rotating said load;

wherein said motion controller and commutator generate said armature phase drive currents i*_k according to a modified commutation law comprising calculating compensated Fourier coefficients c′

of a truncated (finite) Fourier series approximating the armature phase drive currents for said desired motor velocity ω

_d as a function of the actual velocity ω and

transfer function of said driver/amplifier, wherein said modified commutation law further comprises;

a) computing fixed Fourier coefficients c of said Fourier series at zero velocity;

b) computing said compensated Fourier coefficients c′

at said desired motor velocity ω

_d;

c) computing the armature phrase drive currents i*k by modulating the desired torque τ

_d with said corresponding commutation functions u_k(θ

) according to i*hd k(τ

_d,θ

)=τ

_d u_k(θ

), ∀

k=1, . . . , p and

6. The apparatus of claim 5, wherein said fixed Fourier coefficients c are computed according to

7. The apparatus of claim 5, wherein said compensated Fourier coefficients c′

are computed according to c=D<sup>−

1</sup> (ω

)c′

.

8. A brushless DC motor, comprising:

a rotor for rotating a mechanical load;

a stator having armature coils;

controller for receiving a desired motor velocity ω

_d, actual velocity ω and

rotor position angle θ

from said load;

a commutator for generating armature phase drive currents i*_k, for a desired torque τ

_d from the desired motor velocity ω

_d, actual velocity ω and

rotor position angle θ

;

a driver/amplifier for amplifying the armature phase drive currents and applying the amplified armature phase drive currents i_k to the armature coils of said stator for inducing rotation of said rotor and thereby rotating said load;

wherein said controller and commutator generate said armature phase drive currents i*_k according to a modified commutation law comprising calculating compensated Fourier coefficients c′

of a truncated (finite) Fourier series approximating the armature phase drive currents for said desired motor velocity ω

_d as a function of the actual velocity w and transfer function of said driver/amplifier, wherein said modified commutation law further comprises;

a) computing fixed Fourier coefficients c of said Fourier series at zero velocity;

b) computing said compensated Fourier coefficients c′

at said desired motor velocity ω

_d;

c) computing the armature phrase drive currents i*k by modulating the desired torque τ

_d with said corresponding commutation functions u_k(θ

) according to i*<sub>k(τ

d</sub> ,θ

)=τ

_k(θ

), ∀

k=1, . . . , p and

9. The brushless DC motor of claim 8, wherein said fixed Fourier coefficients c are computed according to

10. The brushless DC motor of claim 8, wherein said compensated Fourier coefficients c′

are computed according to c=D<sup>−

1</sup>(ω

)c′

.