The ability of the voltage controller, C(s), to track the voltage reference, Vref, is analyzed by means of the transfer function between the voltage reference, Vref, and infinite bus voltage, V∞, to the terminal voltage, VWT, which is shown in(1). The transfer function is given by the network equations and the block diagram in Fig. 2. If the q axis of the dq coordinate system is aligned with VWT, the transfer function may be derived as