frequency response for an Inverter

Hi,

I'a bit puzzled with obtaining the frequency response of my system including inverter connected to a programmable 3phase voltage source in order to inject disturbance! I am applying a voltage V(t) at a certain frequency f, and I have computed the resulting current as I(t). I want to get the frequency response from these two sine waves not only in one frequency but from fundamental f=50 Hz to 2500 Hz.

I just can't copy that I get for every frequency dividing V/I many values for one frequency and now I'm totally confused to how should I do FFT in order to get the whole response for 50-2500Hz and then plot Bode diagram.

Could you show me a simple procedure to get it!! should I use "system identification toolbox"? or are there any alternative ways!

Thanks in advance