Infinite bus model with voltage e. The port voltage is v = e + Zi, where i is the current entering the bus. The default value of the series impedance Z = R + jX is zero.
The magnitude and angle of the voltage e can provided by external input connectors. If useUin = true, the UIn input is used to set the magnitude of voltage e, otherwise the constant value UFixed is used.
Similarly, if useThetaIn = true, the thetaIn input is used to set the phase angle of voltage e, otherwise the constant value thetaFixed is used.