Small-signal analysis of power system swing modes as affected by wind turbine-generators

The power electronic grid interface of converter-based energy systems such as wind turbine-generators (WTGs) is modifying the dynamics governing power systems. For a fundamental understanding of the impact of power electronic interface on the electromechanical modes, that is, the synchronizing and damping torque on synchronous machines, this paper provides a small-signal analysis about the impact of WTGs on the local mode of a single-machine infinite-bus (SMIB) system. The main contribution is the incorporation of the WTG voltage control into the modal decomposition diagram of Heffron-Phillips and deMello-Concordia. Sensitivity coefficients are developed for the WTG voltage control loop and their impact on the real and imaginary parts of the local mode is illustrated with an example.