Oscillation Suppression Considering Characteristics of Interaction Energy in Grid-Connected DFIG-Based Wind Farms via VSC-HVDC Transmission System

For doubly-fed wind farm connected to flexible DC transmission system, oscillation suppression after fault clearance is very difficult. Addressing this problem, this paper constructs the dynamic energy model of the interconnected system, reveals the mechanism of oscillation instability after fault clearance, and designs an oscillation suppression strategy. First, by considering the dynamic characteristics of the control links in grid-connected doubly-fed wind farm via flexible DC transmission system, the interconnected system is divided into several subsystems, and each subsystem's energy model is constructed. Furthermore, the magnitudes and directions of different interaction energy items are quantitatively analyzed, so that the key control links transmitting and magnifying the system's energy can be screened. On this basis, the corresponding supplementary control links are designed to suppress the system's oscillation. Finally, the accuracy and effectiveness of the proposed oscillation suppression method are verified by hardware-in-loop tests. The results prove that, d-axis subsystem of doubly-fed induction generator (DFIG) rotor side converter (GSC) current inner loop, phase locked loop (PLL) and q-axis subsystem of VSC-HVDC voltage outer loop are the key links inducing the oscillation to occur, and the proposed oscillation suppression strategy shows promising results.