I'm working on a high power multi-phase DC/DC converter where the load current has some fast transients. We can easily measure the output voltage in the time domain, and also measure the power distribution network impedance in the frequency domain. So, I think I would try converting the time-domain output voltage to frequency-domain, and then do I = V/Z. Now I'm a little confused, because in the frequency domain, does this mean I should convolve V with 1/Z? After getting the frequency-domain current, then I'll convert this back into time-domain with ifft. Or can anyone suggest any other methods to measure the current using another method? This is possibly in the 0-100A range going through tons of BGA balls so I don't think I can measure it directly.