How does a potentiostatic circuit work?

I still have some doubts about the correct working of a potentiostat circuit, because in some cases it is determined that the amplifier responsible for controlling the potential between the working and the reference electrode and force the current flow between the electrode auxiliary and working electrode, operates in the inverter mode. However, in other explanations, it is said that this amplifier operates in the voltage adder configuration and that the feedback loop would be implemented by the resistance of the solution. What would be the correct explanation about the operation of a potentiostat circuit for an electrochemical cell of 3 electrodes?
 

The summing junction on A (where the two resistors join)has to be at 0V(it is the virtual earth point) For simplicity's sake assume the two resistors on the summing junction are equal. Also assume a 1V drive from the signal source, then the output from B has to be -1V, to give 0V at the summing junction. If the output from B is -1V, then the input to B has to be -1V (it is a high impedance input voltage follower)
Assuming that the whole servo system remains out of saturation, and amplifier A can supply sufficient current, then the very high gain of the feedback loop linearizes the whole system.
So the system is an inverting amplifier, with the summing junction driven by a buffer, and is voltage controlled, the voltage related to the current being driven through the resistance of the cells contents.
If it were current controlled, then the transimpedance amplifier C would be used to drive the summing junction on A.
Thats my take on it,
cheers,
Richard