Analysis and Mitigation of Subsynchronous Oscillation Based on Nonlinearity Dominant Mode Index

In this paper, modal series was used to investigate the second-order nonlinear dynamic characteristic of subsynchronous oscillation. First the derivatives of the second- and first-order solutions were compared under large disturbance conditions to explain the advantage of the former. Then the nonlinearity dominant index of modal series was defined which reveals the network subsynchronous mode is the dominant mode. This mode would participate in the second-order nonlinear interaction with the other modes under large disturbance. So the parameters of subsynchronous damping controller were tuned first to damp SSO and minimize the second-order interaction. The validness of the controller was proved by comparing the error index. The controller not only ensures the small signal stability of power system, but also reduces SSO risks under large disturbance.