Sensorless FOC takeover problem

[mikemike9141]

Posted on October 24, 2014 at 14:44

Hi Gigi,

I was playing with sensorless rev-up and found a feature not doing what I expected, or maybe also not knowing how to use it correctly. I use Observer+Cordic scheme, and enabled the ''Rev-up to FOC switch-over'' feature. I extended the duration to 500ms, in order to understand what the library is doing during that time. The result was that the motor started accelerating quickly after end of rev-up, for these 500ms. After that time, FOC took over completely and declerated hard to the desired rpm. If I disable this feature, then everything works fine, I juse hear a click in the motor in the moment FOC takes over. So my question is here: am I doing something wrong, what is this feature for, is it possible that it does not work?

Regards

Frank

[Gigi]

Posted on October 27, 2014 at 09:15

Ciao Frank

This seems the correct behaviour. I try to explain better.

At the end of the rev-up the control is performed using the State Observer electrical angle that respect to the one used during the Rev-up is at 90° with respect of rotor flux. The switch over phase is added for a smoot transition between the two angles.

You can see that the motor accelerate becasue just only after the end of the switch over the speed controller start to work and decelerate the motor to the target speed.

Ciao

Gigi

[mikemike9141]

Posted on October 27, 2014 at 10:15

Hi Gigi,

disabling this feature works well here, but I am not sure if I explained correctly what I am observing... After rev-up, the motor starts accelerating very quickly, reaching maximum speed. This situation lasts as long as the take-over time is running (in my test case, 500ms). When this time is over, then the motor is abruptly decelerating to target speed (as expected in such a situation). Rotor angle calculation during rev-up is correct as far as I can see from the corresponding analog debug signal.

Kind Regards

Frank

[Gigi]

Posted on October 27, 2014 at 10:27

Ciao Frank

As I write,

the speed controller start only after the end of the switch over (take-over), so during the switch over no speed regulation is performed.

Ciao

Gigi

[mikemike9141]

Posted on October 27, 2014 at 11:16

Hi Gigi,

I missed that point, thanks.

Kind Regards

Frank

[hassanbhutta91]

Posted on March 13, 2015 at 11:53

what does mean by OPEN LOOP  FOC?

is it mean generating of space vector PWM without any current sensing feedback?

[murphyding]

Posted on March 15, 2015 at 10:25

''Open loop'' means speed open loop,not current.

[mikemike9141]

Posted on March 16, 2015 at 10:14

Hi Hassan,

during startup, the (sensorless) motor is operated without position feedback, like a stepper motor. However, the current feedback loop is already active, otherwise the controller would not know how much PWM is necessary for a desired current.

This scheme is necessary for the rotor angle/speed observer that cannot ''lock'' onto a stand-still motor because there is no current to observe.

Regards

Frank