Connectors PositivePlug and NegativePlug are nearly identical.
The only difference is that the icons are different in order to
identify more easily the plugs of a component. Usually, connector
PositivePlug is used for the positive and connector NegativePlug
for the negative plug of an electrical component.
Connector Plug is a composite connector containing m Pins
(Modelica.Electrical.Analog.Interfaces.Pin).