Superclass of elements which have one port i.e.two electrical
pins of type ComplexPin. The identity of the phasor of the current
flowing into pin p and the phasor of the current flowing
out of pin n is forced by internal current balance.
The only differences to class OnePort are the calculations of the
internal current phasor as well as the values of active and
reactive power. Hence, class OnePortSrc shall only be used to build
source components like voltage sources or current generators.