Hi.
I build prototype of BLDC motor high power driver, drive 18Amp RMS and peak 30Amp. I work with Hall Effects sensor to implement trapezoidal wave commutation to the motor.
in high velocity (Acceleration >2000rpm) I get pure trapezoidal wave, look like I have problem in the zero point, the wave look like distortion and I am acctually don't know why.
I try to tuning the PI parameter with no success.
please see the attach waveform in high & low speed and advice.
Regards
Arie Gez.
Hi. I think it could be a problem with the modulator. What modulation method do you use? The second reason could be the velocity calculation. Maybe in low speed range your calculations aren't precise enought . How do you calculate the velocity?
La "back-emf" ne dépend pas du convertisseur mais uniquement du bobinage statorique et de la configuration des aimants dans le rotor.
La vitesse du rotor ne peut pas déformer la "back-emf" seulement si le circuit magnétique est saturé. Par contre,cela n'est pas possible lors d'un fonctionnement en générateur à vide.
Voici un papier qui peut vous aider.
Cordialement,
Romain Mignot.
The "back-emf" does not depend on the converter but only of the stator winding and configuration of the magnets in the rotor.
The rotor speed can not distort the "back-emf" only if the magnetic circuit is saturated. For against, this is not possible when a vacuum generator in operation.
Here is a paper which can help.
Regards,
Romain Mignot.
The paper above correctly descrbes the issue without the real life complication of saturation in the steel changing the inductance value and as the speed increases the MMF and the current change their phase relationship reducing phase margin in the control loop. Different pole parameters will alter the shape of the back EMF. I have built and stabilised a motor system such as this with a ST71141 microprocessor. To stabilise the operastion I used a set of 5 PID variables that changed according to speed. Another problem I found was integral wind up. I addressed this by discarding the integral componet. Look at the BEMF by swithcing the motor off and looking with a CRO. The MMF can be llooked at if you build a sensor into the winding. Hope this helps
The armature reaction at low speed and high speed differs. Mr Gez would have given voltage as well as current waveforms for different speed. If air gap is more, the cogging torque has little role on the induced EMF in the winding, but if air gap is less the cogging torque is likely to distort the EMF as well current waveforms.
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