Coherency Identification for Wind-Integrated Power System Using Virtual Synchronous Motion Equation

This paper proposes a new model-based coherency identification method based on the virtual synchronous motion equation (VSME) of the doubly-fed induction generator (DFIG). The latter is derived by taking into account both the dynamic characteristics of the phase-locked loop (PLL) and the active power control model. The proposed VSME reveals the synchronization mechanism of the “virtual angle” and “internal voltage vector” for a wind-turbine-driven generator in mathematics and physics. This significant result allows us to treat the DFIG as a “synchronous machine” with appropriately derived equivalent inertia constant, phase-locked angle and synchronizing torque. Thanks to this formula, the slow-coherency aggregate model for the wind-integrated power system can be easily constructed. It further enables us to resort to the K-Means algorithm to identify coherent generators and investigate the impacts of control parameters on coherency properties. Comparison results with alternative measurement-based methods on the modified IEEE 39-bus and IEEE 118-bus systems demonstrate the effectiveness of the proposed method.