BEMF FOC with DRV8302 and SimpleFOC

Hi! Since I achieved to do some open-loop control thanks to the forum, I want now to do some Bemf control. Is it possible now with SimpleFOC ?
I know there’s some topics on that but nothing seems to be very recent.

Yes I did some open loop but except that I really need to do close loop bemf, I don’t need to do sensors closed loop.

Did you read his answer ?
“I don’t think simpleFOC has any BEMF sensing”.
So the answer is no.

There are other sensorless methods being explored in the discord. But you should search more and not open a thread for each question in my opinion.

Yes but since you insist with other closed loop modes I explain to you that what i need is specifically bemf sensing. I asked questions that aren’t clearly answered here and that could also help other persons.If reading questions asked by beginners bother you, you probably should’nt read any forum, and even less answer them.

You got your answer, you can open another thread for the next answer.

@Ara_FOC - from what I’ve read, classical BEMF sensoring is typically used with 6 step trapezoidal. Whilst simplefoc supports trapezoidal, most of us are not using that, instead we are using SinePWM or SpaceVectorPWM.

With trapezoidal you have 6 steps per electrical rotation, and in each step one of the phases is floating / not driven, and the other two are active. So, for the inactive high z phase you’ve got a great opportunity to notice when the BEMF flips from positive to negative (or negative to positive) thus knowing when the next step should be taken. This doesn’t sound that complicated but isn’t FOC.

With FOC, the 3 phases don’t have that gap where you can spot BEMF flipping. Making classical BEMF sensoring impossible (happy to be corrected here!!). There are complicated BEMF estimation techniques (using current measurements or high frequency injection) which work with FOC - I think VESC firmware has that.

With either BEMF or BEMF estimation, it doesn’t work well at low speeds and therefore you need some startup strategy e.g. use closed loop or hall sensors and switch to sensorless when you reach 1000 rpm. The overall solution is therefore quite sophisticated.

I need low speed control so BEMF isn’t that exciting for me.

Thanks for your answer ! I agree with what you’ve said. In my case, what I specifically want to do is to control with a high startup torque, then do a FOC without sensors. I will probably have to implement a startup strategy as you said.
By the way, I didn’t know that I could do some 6 steps commutation sensorless driving, I will try to implement that.

@Ara_FOC, let us know if you manage to switch to 6 step sensorless control at higher speeds, I think that would quite useful for anyone needing a broader speed operation range!

1 Like