what should be the sampling frequency of inductor current ?

Question

I am implementing a digitally controlled cuk converter (average inductor current control technique) with operating frequency of 500 Khz. i have learnt that sampling frequency of inductor current should be same as converter frequency but the controller or processor should be able to update new pwm within 2us (ADC conversion time + computational time < 2us) . which is hard to achieve in real time.so in that case what should be my sampling frequency ? how decreasing the sampling frequency may affect the overall control loop and converter transient response ?

Thank you

Answer 1

how decreasing the sampling frequency may affect the overall control loop and converter transient response ?

Lowering the operating frequency increases the transient response. If the load suddenly changes in value instantaneously the power supply can only respond in the next cycle. If the operating frequency is lower then the time between cycles increases hence transient response to a load change worsens on average.

The control loop will need tweaking also. If the control loop were optimally set for a high operating frequency and the frequency were significantly lowered, I can see that the power supply could become unstable.

It's also worth mentioning that to achieve the same ripple voltage at a lower frequency requires an inductance that is larger and hence more costlier.