Analytical Evaluation to Power System Oscillation Damping Capability of DFIG-POD Based on Path Damping Torque Analysis

Abstract

The increasing wind power decreases power system damping and may intensify low-frequency oscillation (LFO). The LFO are usually damped by the power system stabilizer (PSS) at synchronous generator (SG), and now by the power oscillation damper (POD) at doubly-fed induction generator (DFIG). The existing damping torque analysis (DTA) sets the parameters of the PSS and evaluates its damping capability, but can not be applied to the POD due to the difficulty of finding the damping path related to the DFIG and the coupling between the POD and the DFIG, which are studied in this paper. At first, the analytical expression of the coupling between the POD and DFIG is newly derived with linear fractional transformation (LFT) technique. Then the path damping torque analysis (PDTA) is proposed to reconstruct the damping path of the POD. Thirdly, the damping indicator based on the return difference matrix is proposed to evaluate the contribution of damping path to the LFO. Finally, numerical results of test system are given to validate effectiveness and accuracy of the proposed model, and parameter optimization to the multi-input POD (MIPOD) is performed to show the application value of the proposed model.