If using the nodal analysis for a certain circuit one usually chooses a node as reference node such that one can reach as many other nodes as possible. Unfortunately 99% of the literature I found on this subject seems to assume that one can alway find such a node that reaches every other node within a single branch.
Consider the following example:
One can see that obviously it's not possible to reach every node within a single branch, even if we change the reference node.
My text book states that one would need to use a super node in such a situation, as also shown in the example with node #4.
I assume this is due to our equations not being linear independent if we would consider #4 a "normal" node.
Please provide me some insight in why we have to use a super node here and if my assumption is correct. I'd highly appreciate to see some kind of mathematical proof.
Best Answer
I've never heard of this as a criterion for choosing the reference node. Usually one of the nodes connected to the power supply is the reference node. This might chance to also be connected to a large number of circuit branches.
In any case, it does not matter which node is chosen as the reference node. It won't affect the solution at all (except to offset the numerical values of the node voltages to all be relative to the chosen reference).
A super node is needed when there is an independent voltage source in the circuit.