Locating Sources of Sub-Synchronous Oscillations in Wind Farms Based on Instantaneous Energy Supply on Port and Bicoherence

Abstract

The sub-synchronous oscillation (SSO) which occurred in direct-driven wind generators (DDWG) based wind farms became a research hotspot. The SSO excited the shaft torsional vibration of thermal generators and caused trip failures, leading to economic losses and stabilization problems. However, the existing phasor-based oscillation source locating methods cannot be applied to the SSO since the power system quasi-steady-state assumption was not satisfied in the SSO scenarios. Thus, a novel locating method for SSO sources was urgently required. To fill this gap, this paper proposed an improved method for locating nonlinear sub-synchronous oscillation sources based on Energy Supply on Port (ESP) and bicoherence. The ESP was calculated with the instantaneous values of measured voltages and currents at some predefined network interfaces, i.e., the ports. The tendency of the ESP indicated the transient energy injection from a certain subsystem into the rest of the network during a designated period, which can help figure out the oscillation source of the SSO. After oscillation source localization, the nonlinear index and its threshold were proposed by defining the bicoherence coefficient in consideration of the nonlinear oscillation characteristics. According to the power-quality standard and the comparison of the bicoherence with the threshold, the nonlinearity of the oscillation source was examined. The feasibility and effectiveness of the proposed method were proved in the case study which simulated the oscillation scene of the accident in Hami.