Small-signal model of a decoupled double synchronous reference frame current controller

The converter behavior in harmonic studies or harmonic stability analysis can be evaluated by its output impedance. In order to overcome the nonlinearities introduced by the PLL, linearized models around the operating point are typically used. However, in the case of an imbalance in the system the dq signals are not dc anymore, and therefore, linearization cannot be done. In this paper a Decoupled Double Synchronous Frame PLL is used to eliminate the oscillations in the dq frame signals. The small signal model of this PLL including an unbalanced current controller is presented in this paper.