Voltage sensor output is distorting after a certain voltage.

Thread Starter

Abhinand Ajayan

Joined May 13, 2022
3
I'm running a hardware prototype of a common grounded single stage inverter in open loop and its output voltage is 50 Hz sine wave. But when I sense this output voltage using Besteks VSLV025C sensor, its output is distorted. Upto 50V, sensor output is fine but above that distortion increases as the output voltage increases. I tried with another voltage sensor module and the same issue persists.
My switching frequency is 50kHz. Voltage sensor is calibrated at 3V for 400V.
In the below figure, yellow signal is output voltage taken directly via a differential probe and the pink signal is voltage sensor output for 75V AC rms.
IMG_20220502_194239.jpg
 

LowQCab

Joined Nov 6, 2012
2,037
There doesn't seem to be a readily available Spec-Sheet for a Bestek VSLV025C.
Do You have one You can post ?

Just a couple of guesses .........
The Sensor has poor Frequency-Response at lower-Voltages,
and the distortion You are seeing was there all the time,
or,
your "prototype" gets noisy at higher output-Voltages.
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Thread Starter

Abhinand Ajayan

Joined May 13, 2022
3
There doesn't seem to be a readily available Spec-Sheet for a Bestek VSLV025C.
Do You have one You can post ?

Just a couple of guesses .........
The Sensor has poor Frequency-Response at lower-Voltages,
and the distortion You are seeing was there all the time,
or,
your "prototype" gets noisy at higher output-Voltages.
.
.
.
I'm using the voltage sensor card provided by a local firm. Its specs is attached hereby.

Not noisy at 75V output whose waveform I posted here.

The same voltage sensor is working fine with my colleague's hardware, who is running a conventional single phase inverter with 20kHz switching frequency.
Screenshot_2022-05-13-12-51-22-158_com.google.android.apps.docs_2.jpg
 

LowQCab

Joined Nov 6, 2012
2,037
It seems that You answered your own question .........
You evidently have a problem with your "prototype".

If You will post a Schematic,
( as-built and being tested ),
and supply part-numbers and Spec-Sheets,
maybe someone here can help to spot the problem.
.
.
.
 

Thread Starter

Abhinand Ajayan

Joined May 13, 2022
3
It seems that You answered your own question .........
You evidently have a problem with your "prototype".

If You will post a Schematic,
( as-built and being tested ),
and supply part-numbers and Spec-Sheets,
maybe someone here can help to spot the problem.
.
.
.
Thanks for your time sir.
I found the issue, that sensor output is fine when it is not connected to ADC pin of STM32 microcontroller and it distorts when the sensor output is connected to ADC pin. ADC might be loading the sensor. I hope an op-amp(Voltage follower) between the sensor and ADC will rectify the problem.
Pls share your thoughts and solutions if any.
 

LowQCab

Joined Nov 6, 2012
2,037
The ADC Pin should be relatively high-Impedance, if it's not, something is wrong.

That's not a "Spec-Sheet",
that's promotional advertising blurb.
Looks like some one cobbled it up in their Basement.
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