vesc with sensors efficiency

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
Hummie
Posts: 105
Joined: 10 May 2016, 04:05

vesc with sensors efficiency

Postby Hummie » 02 Sep 2017, 17:14

could someone link me to it if it's already written somewhere but how much more efficient running foc with sensors vs foc without sensors and at what rpms is it relevant? anyone do a comparison?
I ask because sensors are a pain in the ass to put in and seem just another part to break. if they don't help much with efficiency I wont bother as I can get pretty damn good slow speed performance by just adjusting the settings.

rew
Posts: 905
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: vesc with sensors efficiency

Postby rew » 03 Sep 2017, 09:21

Sensorless operation is possible because of the back EMF that happens when a motor turns. That back EMF is proportional to the speed at which the motor turns. In practice, that means it becomes too small to measure when you're going too slow....

All this means that you may need sensors to operate properly at slow speeds (when the back emf is too small).

Without sensors, the trick is to assume a maximum load on the motor and just startup "blindly" hoping that the motor follows the commands you're giving.

So if the controller GUESSES a maximum load of say 1Nm of torque and the load happens to be 1.1Nm, the motor will fail to start.

By default the sensors are only used at slow speed. Above a certain speed, the BEMF is big enough to measure and that is more accurate than using the sensors. Because at slow speeds you're using little energy the actual efficiency at those speeds matter very little on your total trip-energy-use.

So... Don't think your sensors will improve efficiency in real life.


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