Tag Archives: commutation-detection

Open-BLDC Sensorless Commutation Detection

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Hi!

As promised I made some videos. First one is showing the maiden run of a motor connected to the breadboard prototype of Open-BLDC.

(There is also a Vimeo version: Maiden Run of Open-BLDC from Piotr Esden-Tempski on Vimeo)

Yes the motor sounds like a truck. The reason is that I am making forced commutation (not detecting the right time to commutate but do it in fixed time) and the PWM duty cycle is higher then it should be. This way the motor is just jumping between the magnets and has a lot of vibrations.

The second video is a demo of sensorless commutation detection.

(There is also a Vimeo version: Open-BLDC Sensorless Commutation Detection Test from Piotr Esden-Tempski on Vimeo)

We are using a novel way without a virtual crosspoint. (you can read it up in this paper) We do it even a little bit differently then described in the paper, there are no comparators and latches. What we do is condition the signal to be in the range of 0V to 3.3V and sample it with the ADC at the right times. This is probably the simplest way to do something like this in the STM32. One can now play around with the data that the ADC delivers. I think there is a lot of stuff that can be done using such an approach.

In the video you may also wonder why it is so loud. Well the PC fan that I just forced onto the rotor is not really the best payload, also it is not balanced well and the bearings in the motor are not the best anymore because of the unbalanced load. ^^ I am also using the simplest and worst PWM scheme that I know of. The so called H PWM L ON scheme.


“H PWM L ON” PWM scheme. Click on the Image to see other PWM schemes.

You can also see in the video that the motor is pretty robust to external disturbances when running in the commutation detection closed loop. Still I am sure that it can be improved. (If you are interested the sourcecode running this can be seen here)

If I am not mistaken then only current measurement is missing in the circuitry. When that is done then I can design the first etched prototype of Open-BLDC. WOOO! 🙂

Cheers Esden

P.S. If you have any comments/ideas feel free to write them in the comment section. ^^

Open-BLDC status report

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Hi!

It has been a pretty long time since my last post. But do not worry there is happening a lot “behind the scenes”. Well not so much behind them because I commit everything I do to the github repository (http://github.com/esden/open-bldc). If you want to follow the progress you can also subscribe to the commit mailinglist and/or the discussion mailinglist. Feel free to write on the mailinglist if you have any questions or just catch me on #uavp channel on the freenode network. (I think that are enough channels of communication 🙂 )

Ok back to the topic. Last week I was able to turn a bldc motor the first time using the bread board prototype of the power stage, the STM32 Olimex H103 evaluation board and firmware that you can find in the repository. The basic PWM scheme that is used by most controllers is implemented and works pretty well. I am also trying out other PWM schemes that may improve efficiency. You may ask why I am doing it now and not after I made a real hardware prototype of the system. The answer is pretty simple. I have to see if and how it is possible, to make sensorless commutation detection, when using different PWM schemes. I had to realize that the schemes have a big influence on the signals that can be captured.

As soon as I have more results I will make a video showing the current state and how the controller behaves when using different approaches. So stay tuned!

Cheers, and I hope hearing from you too in the comments! 🙂