PowerStep01 Current drop at medium speed

[Barley]

Hello,

I have a problem to configure the powerstep01. The motor current drops at medium speeds.

• Current mode
• step clock mode
• 1/16 microstep
• 48 Volt

I have set a low acceleration for testing. Everything is fine up to approx. 16 kHz (microstep). That's only 300 rpm. Then the current drops further and further. The maximum speed (in the center of the diagram) is approx. 44.8 kHz (840 rpm).

1,8 [°/step] / 16 [microstep] = 0,1125 [°/microstep]
0,1125 [°/microstep] * 44800 [microsteps/s] = 5040 [°/s]
5040 [°/s] / 360 [°] = 14 [1/s]
14 [1/s] * 60 [s/min] = 840 [rpm]

This is the current configuration:

OCD_TH = 31
FS_SPD = 100
STEP_MODE = 12
GATECFG1 = 226
GATECFG2 = 96
CONFIG = 45952
TVAL_HOLD = 55
T_FAST = 17
TON_MIN = 4
TOFF_MIN = 4

What do I have to set so that the current always remains the same and does not drop?

Many thanks in advance!

[AScha.3]

Hi,

(I never worked with this "motor control" , or similar; but just : in general...)

you go to microstepping (-> small/shorter pulses) and then to hi rpm (-> higher pwm frequ.), but inductivity of motor is ..as it is. So current in coils will decrease , more and more. 

afaik for higher speed you have to go for more current = lower pwm frequency (= no or less microsteps) ;

constant current control is limited to the max. supply voltage / coil inductance -> actual max. possible current.

If come to this limit, you have to change something (motor, drive voltage, pwm frequ. - one, or more of these).

[Barley]

Yes of course, the effect due to inductance exists. I have tried it with a different motor driver (Trinamic TMCM-1160-TMCL). The effect also occurs here, but not as bad!

Blue -> Trinamic
Red/green -> PowerStep01

I expected the PowerStep01 to perform better than the Trinamic. It should be possible for the PowerStep01 to be at least as good. Right?

[AScha.3]

>I expected the PowerStep01

Reality meets expectation. :)

+

Just can you try : set half-step or full step , then see what is max. speed .

+

Maybe there is a setting, to go from microstepping to half- or full step at more than xx rpm ? check.

[Barley]

I have found that the Trinamic runs with 1/8-step and the PowerStep01 with 1/16-step. That's why I set the PowerStep01 to 1/8-step and tested it again.

Now both behave very similarly. There is still one problem. At maximum speed, the PowerStep01 has problems (right side of the measurement). Something must be resonating here. You can see it clearly. The supply voltage also becomes rippled.

Which parameter can I use to improve this behavior?

[AScha.3]

>Which parameter can I use to improve this behavior?

There will be always some "resonance" effects , depending on motor type, pwm frequ. etc.

So you can just try (with this/same motor): other control mode (half-step ?) or avoid this frequencies = limit to lower max. speed .