Control Strategy of Equivalent Impedance Angle for Improving Performance of Directional Protection on IIDG Connected Transmission Line

The sensitivity of positive-sequence fault-component-based directional relays has declined when Inverter Interfaced Distributed Generation (IIDG) connects to distribution network. Theoretical analysis shows that the phase angle of IIDG equivalent impedance is not constant at 90°, which leads to a decline in the sensitivity of positive-sequence fault-component-based directional relays. For this reason, the control strategy for constant phase angle of IIDG equivalent impedance is proposed to control the phase angle of IIDG equivalent impedance to be constant at 90°, which further solves the problem that the sensitivity of positive-sequence fault-component-based directional relays declines. PSCAD is used in modelling and simulation, and the simulation results verify that the proposed control strategy achieves the expected control effect and improves the sensitivity of positive-sequence fault-component-based directional relays effectively.