Signal conditioning for a current transducer

I am using a current transducer (LPSR 15-NP) to measure the current that is flowing through my AC servo motor powered by my SVPWM PCB. I have currently implemented an open loop control to the motor and it is working perfectly. I need to now design a current control closed loop. For that, I am measuring the current going through the U-V-W phases of my PMSM motor. On the output I am getting a variation of 2.407V to 3.047V. I need a constant voltage so that I can implement my current loop.

How do I do this? Are the connections for my LPSR correct or do I need to add some capacitors for signal conditioning? I do not understand why the LPSR is not simply giving me an output voltage in the range 0-5V as the datasheet suggests.

Do I need to add a True RMS to DC converter on the output of my LPSR 15-NP to get the DC voltage I require? Do I need to add some rectification or some capacitive filtering in my output? Or am I missing something here?

• This sensor output directly follows the high frequency AC current created by the SVPWM driver. Yes, you need filtering and a rectifier.
– Jens
Commented Sep 11, 2023 at 20:25
• You need a high sampling rate if you want to filter this in software, but, yes, I did so myself. Have a look at the minimum load requirement in the datasheet, I am not sure what impact this might have.
– Jens
Commented Sep 12, 2023 at 12:35
• I would solder an R/C low pass and connect this to a scope. Then compare this with the calculated values. Is there always enough CPU power to do the math or is this lagging under some conditions, e.g. other CPU tasks?
– Jens
Commented Sep 12, 2023 at 12:56
• But the sensor delivers a signed value relative to the center voltage of 2.5 V. This includes the current direction.
– Jens
Commented Sep 13, 2023 at 14:28
• No, the LPSR series are true bipolar devices. The signal is a signed value Vout - Vref, where Vref is 2.5 V. The switching transients of PWM current reversal may have such a high amplitute, that you don't see the effective current in this noise. There may be capacitive coupling from the phase line into your ADC. Apply a low frequency sine wave current to verify the bipolar nature of the output.
– Jens
Commented Sep 14, 2023 at 12:48