In distribution systems with T-connected inverter-based resources (IBRs)

differences in control strategies between grid-following and grid-forming IBRs lead to multi-source coupled nonlinear fault current characteristics

potentially causing maloperation or failure of conventional protection schemes. An adaptive pilot impedance protection method

based on equivalent IBR sequence impedance phase angle intervals

is proposed. The phase angle difference intervals between the point of common coupling voltage and positive-sequence output currents of both types of IBRs are quantified according to their fault ride-through control strategies. Impedance characteristics of IBRs in the negative-sequence network are analyzed

and equivalent sequence impedance phase angle intervals for different IBRs are unified in sequence networks to decouple fault characteristics from source-side control dynamics. Consequently

an adaptive positive-sequence impedance protection criterion is constructed based on the phase angle difference between the estimated T-node voltage and differential current. For asymmetric high-resistance faults

this paper proposes an additional protection criterion

which combines the accumulation and polarity product of negative-sequence impedance phase angles

to enhance resistance to transition resistance. Simulation results show that the proposed protection scheme can identify faults within 8 ms

withstand 500 Ω high-resistance faults eliminate the need for sampling data synchronization

and remain unaffected by the type and capacity of IBR.