Commutation with 6280 DAQ Card

[serkanb]

Hello,

I want to perform parameter identification of a three phase brushless DC servo motor. Basically I want to obtain mass moment of inertia, viscous damping coefficient and coulomb friction at the bearing. To do so, I plan to apply a step voltage input to the motor terminals and collect the position information with a DAQ card. I know the inductance and resistance values of the motor windings as well as the I want to perform parameter identification of a three phase brushless DC servo motor.
Basically I want to obtain mass moment of inertia, viscous damping coefficient and coulomb friction at the bearing.
To do so, I plan to apply a step voltage input to the motor terminals and collect the position information with a DAQ card.
I know the inductance and resistance values of the motor windings as well as the torque constant of the motor.
So when I apply a step voltage input to the terminals of the motor, I would know the torque that is applied.
And since I know the torque that is applied and also collect the position data I would be able to plot torque vs. position curve and would be able to obtain the necessary parameters from this graph.

My problem is; I don't know how i can apply a step voltage input to a three phase brushless DC motor.
Is it possible to use a DAQ card (I have a PCI 6280 DAQ card) for commutation? If it's possible is there an example about commutation of brushless dc motor?
I don't want to use a motion control card to perform the commutation since I want to observe the motor dynamics only.

Regards.

[Jochen]

Hello,

for commutation you need to synchronize the output signals to the absolute rotational position of your motor. Typically this is done by implementing a lookup table to output values according to the motor's angle of rotation. This operation requires deterministic real-time behavior, so you could use a DAQ board with LabVIEW Real-Time, but for your application an FPGA-based R-Series device is probably a much better choice.

Instead of generating analog output signals, with an R-Series device you could directly generate PWM signals with sinusoidal duty cycles to control an external FET amplifier.

Here you can find example code for such a setup.

I hope this helps.

Kind regards,

Jochen Klier

National Instruments