Help finding transfer function for root locus using Matlab
OK, I got it. To obtain the necessary transfer function in Evan's form, one has to assume \$ \phi_c = 0 \$. Then, the block diagram in question can be converted into:



So \$ P(s) = \Large \frac{p}{\alpha} = \frac{G(s)H(s)}{1 + \frac{k_p}{s} G(s)H(s)}\$.