Other Parts Discussed in Thread: SFRA
Hi there,
In order to test the SFRA tool to get the plant transfer function (i.e. no controller in the loop), I am feeding a PWM to a RC series circuit and measuring the voltage on the capactior, dfeeding the capacitor voltage back to the adc and getting the SFRA tool to calulate the Plant transfer function, in magnitude and phase.
The PWM switches at 200kHz and the response is calculated around the duty cycle= 0.5. (The interrupt frequency is also 200kHz).
Now, I note that the the theoretical response (capacitor voltage) matches the response calculated by the SFRA tool up to 10kHz only, and afterwards the error in magnitude and phase is increasing (i.e. measured response is very different from theoretical). If the PWM is at 200kHz, the Nyquist limit is 100kHz.
Do you know the reason why the theoretical response starts to be different from the measured one from a frequency of about 10kHz onward?
I attach the measurement results below:
- R=120Ohm, C=47uF
- R=120Ohm, C=9.2uF
Thank you so much.
Leonardo
