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Spikes in motor current?

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seyyah

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I'm measuring an ac motor current via hall based sensor, at the same time via resistor to make a comparison. I filter the output of the sensor via low pass rc filter. I get good enough signal when rotor is locked and the waveform of the current is sinusoidal. But when motor rotates, sinusoidal form is get deformed and there are a lot of noise(spikes) on the waveform. What causes this noise and how can i eliminate it? Both resistor and hall effect based sensor gives the same respond about this noise.

Added after 34 minutes:

I investigate the signal via scope and saw that main spikes are at switching frequency. How can i prevent these switching effects not to affect measurements?
 

Whats the value of your low pass filter?
To eleminate the effect of noise you should have low pass filter such that its cutoff frequency iswell below the switching frequency and well above the control loop frequency (control response time)
 

Hi;
What switching frequency?! 50Hz!
AC (induction) motor is similar to transformer. ( from point of view equivalent circuit) and not to be genarate noise, glich and spike.

Regards
Davood Amerion
 

switching frequency is 10khz, cut off frequency is 1khz.
 

Hi;
It seem you use 3 phase motor driver! ok.
I think this phenomena related to motor driver not to motor.
as i say before, motor equivalent circuit is very similar to transformer.
if you use (direct) 50Hz or other type of driver, motor current patern (wave form) will be diferent.

Regards
Davood Amerion

try to bring low filter cutoff frequency. for ex. 100Hz.
 

I realized that the deformation on the current signal is due to dead time. I have a problem with the scope and pc connection and i couldn't be able to get an image of the wave form. Anyway think like this; The fundamental frequency of the current is between 0-100Hz sinusoidal. Sinusoidal signal has spikes on it at 10KHz(switching frequency).
 

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