Motor current shaping
View Patent ↗A method and apparatus is disclosed for generating a drive signal that is applied to a coil in a motor. The drive signal is applied during a period (commutation period) between a commutation event and the immediately following commutation event when the coil is energized. The drive signal comprises pulses which vary over the duration of the commutation period.
1. A method for driving a motor comprising generating a drive signal to energize a coil comprising said motor for operating said motor at a desired rotational speed, and energizing said coil with said drive signal during a first commutation period, wherein said generating a drive signal includes a step of generating a first plurality of pulses having a first duty cycle followed by step of generating a second plurality of pulses fewer in number than said first plurality of pulses and having a second duty cycle less than said first duty cycle, the second plurality of pulses occurring at the end of said first commutation period.
2. The method of claim 1 wherein said generating a drive signal further comprises a step of generating a third plurality of pulses subsequent to said step of generating a first plurality of pulses and prior to said step of generating a second plurality of pulses.
3. The method of claim 2 wherein said third plurality of pulses have a third duty cycle less than the first duty cycle and greater than the second duty cycle.
4. The method of claim 1 wherein said motor is a brushless DC motor.
5. The method of claim 1 wherein said motor is a incorporated in a fan.
6. A fan comprising a motor and a controller to generate drive signals to operate said motor, said controller operable to generate drive signals according to the method of claim 1 .
7. A method for managing noise generated during operation of a fan, said fan comprising a brushless DC motor, the method comprising generating drive signals to energize stator coils that comprise said brushless DC motor, said drive signals operating said motor at a given rotational speed, wherein said generating drive signals includes, for a first commutation period, generating a first plurality of pulses having a first duty cycle followed by step of generating a second plurality of pulses fewer in number than said first plurality of pulses and having a second duty cycle less than said first duty cycle, the second plurality of pulses occurring at the end of said first commutation period.
8. The method of claim 7 wherein said generating drive signals for said first commutation period further comprises a step of generating a third plurality of pulses subsequent to said step of generating a first plurality of pulses.
9. A method for operating a fan motor comprising energizing a coil of said fan motor during a first commutation period to operate said fan motor at a given rotational speed, including generating a plurality of pulses during said first commutation period, including generating a first plurality of pulses having a first duty cycle followed by step of generating a second plurality of pulses fewer in number than said first plurality of pulses and having a second duty cycle less than said first duty cycle, the second plurality of pulses occurring at the end of said first commutation period.
10. The method of claim 9 wherein said motor is a brushless DC motor.
11. A fan comprising a fan motor and a controller to generate drive signals to operate said fan motor, said controller operable to generate drive signals according to the method of claim 9 .
12. A brushless DC motor comprising:
a plurality of stator coils;
means for generating a pulse-width-modulated (PWM) signal to energize a first coil among said plurality of stator coils during a first commutation period for operation of said DC motor at a desired rotational speed, the duration of said PWM signal being substantially equal to said first commutation period, said PWM signal comprising a plurality of first pulses and a plurality of second pulses fewer in number than said first pulses and having a duty cycle shorter than a duty cycle of said first pulses, said second pulses occurring at the end of said commutation period; and
means for energizing said first coil during said first commutation period by applying said PWM signal thereto.
13. The motor of claim 12 as incorporated in a fan.