Novel scheme of the microgrid dynamic stability based on an adaptive protection zone considering low-inertia resources

Multi-directional power exchange, fast dynamics, and fault current reduction of the low-inertia microgrids raise several protection challenges in modern low-inertia power systems. To address these issues, this paper presents an adaptive relay designed to rapidly predict dynamic instability in microgrids by estimating dynamic state variables and employing elliptic adaptive zones. For this, based on phasor signals, dynamic signals are monitored, and based on evaluating operating areas, the relay zone is adapted. Depends on the microgrid signals evaluated through mathematical formulations and the circuit breaker status, the system dynamic state variables and coefficients are estimated. Then, based on the online adjustments of the Microgrid dynamic variables and comparing the results with the relay-adapted zone, proper actions (reclosing/tripping) are decided. During time-moving windows, using online constraints, dynamic variables are monitored and in the case of satisfying the constraint, the reclosing/tripping decisions are determined for nominated circuit breakers. The proposed scheme is an extended concept of traditional double blinders-based impedance relays in which the microgrid frequency Δω and angle δMG deviations are considered the main protective variables. Simulation results indicate the effectiveness of the proposed adaptive scheme for reliable estimation of the relay reclosing and tripping signals through different fault scenarios.