A three-phase brushless motor it is usually drive by six-state commutation step sequence.
The commutation sequence drive the motor coils in order to make it spin.
The picture above represent a standard commutation scheme, each line is the motor coil status.
Given a 360 degree commution space, each commuation happens takes a 60 degree space.
A coil it is usually driven by mosfet bridge.
The coil can be drive on or off, but we can also drive it in PWM.
The PWM scheme is the way the power gates bridge is controlled in order to drive each motor coil.
In the AVR bldc driver here:
http://davidegironi.blogspot.com/2020/01/an-atmega-brushless-sensored-motor.html
I've implemented 4 PWM scheme.
H PWM L ON: PWM is performed on the ON channel
H ON L PWW: PWM is performed on the OFF channel
H PWM ON: PWM is performed on UWV channels every 60degrees, starting from U ON-ON
H ON PWM: PWM is performed on UWV channels every 60degrees, starting from V OFF-NULL
See above the signal sample recordered using a CD-ROM motor.
H PWM L ON sample
H ON L PWW sample
H PWM ON sample
H ON PWM sample
Notes
- read risk disclaimer
- excuse my bad english
Which one is better.... ?
ReplyDeleteHello. It depends on the motor and how you have to drive it, if you want more speed... to me H PWM L ON works good.
DeleteHi Davide, I tried PWM-ON mode and ON-PWM mode today. My phase voltage results are very similar to yours. But I am still quite surprised that the current results under those two mode are different. While for PWM-ON mode, the current looks wonderful and standard. However for ON-PWM mode, the current waveform become a little bit wired which is not in the common shape anymore. Did you also observe this situation? Do you have any idea/ Because I intuitionlly feed that the PWM chooping mode shouldn't affect the results.
ReplyDeleteHello Bruce, I don't remember that much different between modes with motor that I've checked. There was some different, but not much. It's been a few years I don't look at this project so really I don't have my mind ready to tell you why there is such a behaviour.
DeleteThanks so much for your reply Davide.
Delete