The impact of DFIG control schemes on the negative-sequence based differential protection

Negative-sequence currents at the transmission line terminals are widely adopted in differential protection to achieve excellent sensitivity. The underlying principle is that the traditional power sources (synchronous generators) can be treated as inductive reactance in the negative-sequence network. However, for the transmission lines connected to Doubly-Fed Induction Generator (DFIG) based wind parks (WPs), the negative-sequence currents are controlled by fault-ride-through (FRT) solutions. This paper first analyzes the phasor characteristics between negative-sequence voltage and current of a DFIG-based WP under three typical FRT solutions, and then evaluates their impact on the dynamic performance of negative-sequence differential protection elements (87LQ). The analysis indicates that a certain FRT control strategy would make DFIG-based WP provide capacitive current into the negative-sequence network. This impacts the sensitivity and even results in maloperation as shown for the first time in this work. The analytical results are validated with detailed time domain models and simulations in Simulink.