Harmonic Injection Based Distance Protection for Line with Converter-interfaced Sources

Converter-interfaced renewable energy sour-ces are directly integrated into the power system using power electronics, so unique fault characteristics may lead to the maloperation of traditional distance relays. In this article, to deal with this issue, a harmonic injection-based distance protection method is proposed. The controllable harmonic current is injected without revising the controller structure, and the harmonic frequency and magnitude are determined according to the grid feature. Since the proportional integral cannot track the sine component without the static error, the actual frequency response will be deduced using the transfer function. On this basis, the harmonic impedance measured at the relay point can accurately reflect the fault distance due to the disappearance of the remote infeed, so the proposed method has a strong ability to withstand the fault resistance. Meanwhile, it only needs a few modifications to the phasor extraction method in original protection devices, so it is easy for engineering applications. Furthermore, typical fault ride through requirements can be still satisfied. Simulation results in PSCAD and real-time digital simulator verify the proposed method in different fault scenarios.