Effects of operational limits of DFIG wind turbines on long-term voltage stability studies

- The effect of DFIG operational limits on long-term voltage stability is analyzed.
- The use of fixed limits during simulations is adequate when wind speed is constant.
- Under ramp up wind speed, DFIG limits should be considered variable in simulations.
- Under ramp down wind speed, the use of fixed limits decreases voltage stability margin.

This paper investigates the effects of doubly fed induction generators (DFIGs) operational limits on long-term voltage stability. DFIG operational limits are defined based on wind generator's capability curve in terms of the actual terminal voltage and wind speed. Also, the limitations of the converter, machine and wind turbine are considered in DFIG control schemes. The evolution of different variables is examined using two models for DFIG operational limits: fixed limits and variable limits. Time domain simulations have been performed in three different cases: constant wind speed, ramp up event, and ramp down event. This study also considers the dynamic models of over excitation limiter (OEL) and on-load tap changers (OLTC) combined with static and dynamic loads. Some important conclusions can be extracted from the simulation results, which can help in choosing the appropriate model to represent the DFIG operational limits in long-term voltage stability studies.