I made a DC-DC converter its ideal transfer function is: $$ V_0(D) = DV_i $$
I took measurements of its response and then made a linear regression, I got this result:
$$ V_0(D) = 0.98DV_i -0.42 $$
Quite similar to the expected value. Now, can I say that the system has a linear response?
strictly speaking, the system response should be zero when the input is zero, but in this case, if D = 0:
$$ V_0 = -0.42 $$
What would be the correct way to refer at the response of this system?
Here is a plot of the theoric response, red, vs experimental values green. The 0.42 basically represents an offset because the losses of the system.