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Can't reach high speed with HVPM

Andreas Lehner
Prodigy 40 points

Hi to all ,

I’m working  on a system very close to the  HVMotorCtrl+PfcKit_v1.6 , with an F28035  , a different power module and a hw current limit protection at about 25amps .

My target   is to drive a HVPM brushless motor  8 pole  at 10’000 rpm , in sensorless mode , that means about 670 Hz .

 Isr and PWM are 20KHZ , as in the kit .

The system can measure up to 20amps , but I  set the Out max at 0.8 , that means 16amps .

The dc bus is 310Vdc , with higher current that needed .

With this set-up , I can’t go over  7’000 rpm .  What I see is a high current ( more than 20amps ) on the motor phases , while current regulator (pid1_iq.out) Is  less the 0.5 ( 10amps).

I think speed and current regulator are tuned correctly , I think also I’ve something to tune in the SMO .

In  fact I tried to change some parameters in the SMO , obtaining lower current in the phases and higher speed in the motor , but there are higher difference from requested current and measured current , so hw current limiter sometimes  happens .

 

I made some tests with this motor , in the same application , using a commercial FOC frequency converter , and I’m sure less the 10 amps are required , I measured about 5amps  at  rated speed and 8 amps during the ramp-up.

 

Can you suggest something to do ?

Thanks

Andreas

 

  • 0
    TI__Intellectual 930 points

    Andreas

    This typically happens when

    - not enough dc bus voltage is provided

    - PIDs are saturated

    - field weakening is required

    - angle is not sensed/calculated precisely.

     

    I guess your problem is the last one. Before that, make sure that your speed PI output is not saturated and you apply full dc bus voltage for that particular motor.

    Tuning SMO can help to minimize the current level, especially kslide.

     

    Can you create a variable in the software, initialize it as zero and add it to estimated/sensed angle in the code. While spinning the motor gradually increase/decrease this angle offset variable. If the amount of current decrease when you add or subtract  the angle offset, then it means that the estimated angle is not accurate. Thats why you might need to inject more current to create the same torque at a certain operating point. If this is the case you run the motor inefficiently since the field orientation is not achieved as expected. You may need to try this experiment at various speed levels and create a lookup table or a interpolated curve polynomial for angle offset to compensate it. The angle deviation is mostly caused by the low pass filter in the SMO.

     

    Hope this helps. 

     

    Regards

    Bill

  • 0 in reply to Bill13027
    Prodigy 40 points

    Thank you Bill ,

    Unfortunately the first hypothesis was correct :  increasing the Dc Bus voltage from 310V to 400Vdc it works properly .

    The KE of the motor is 0.268 Vs/rad , so it’s clear I need more voltage , in sinus mode , to go up at least to 9'000 rpm ( minimum speed required) .

    The problem is that I’m in comparison with a commercial FOC frequency converter , that works well with 310 Vdc bus and reach 10'000rpm .

    Can you suggest something to do ?

    Thanks

    Andreas