ETA-based analysis of small signal stability considering WADC with multiple time delays

Low frequency oscillation occurs frequently in power systems. Wide-area damping controller (WADC) based on Wide-Area Measurement System (WAMS) can effectively suppress inter-area low frequency oscillations. However, with the introduction of global signals, time delays are inevitable. Electromagnetic torque analysis method(ETA) can establish the analytic relation between electromagnetic torque coefficients and control parameters of power component, which is facilitative to analyze small signal stability. Considering that WADC has inherent characteristics of multiple time delays, based on the ETA for equivalent two-machine system, this paper deduces the general mathematics expression among electromagnetic torque coefficients, WADC parameters and time delays. The influence mechanism of time delay on electromagnetic torque coefficients and small signal stability is further analyzed. Based on these analysis, performance of damping control of WADC can be improved, on one hand, time-delay small signal stability region is established under fixed WADC parameters, on the other hand, if small signal stability is not achieved under the given WADC parameters due to set of the time delays, optimization scheme is proposed to carry out parameters coordination according to the measured time delays. Finally, taking two time delays as an example, the paper verifies the effectiveness of the proposed method by comparing the system dynamic performance considering two time delays with the system only considering single time delay and the system without time delay in a two-area four-machine power system.