EMT-Based Sequence Analysis of a Converter-Dominated Microgrid Under Fault and Load Disturbances: Case Study of the NELHA Microgrid

Converter-dominated microgrids exhibit dynamic behaviors during faults and disturbances that differ fundamentally from those of synchronous-machine–dominated systems. This paper develops an electromagnetic transient (EMT) model of a converter-dominated microgrid and applies sequence-domain analysis based on instantaneous symmetrical components to evaluate its dynamic behavior under three scenarios: a single-line-to-ground (SLG) fault, a balanced three-phase short circuit, and a nonlinear load step. Both grid-connected and islanded operating modes are evaluated under matched disturbance types, locations, and timing, using mode-specific source configurations representative of actual microgrid operation. The simulations reveal a pronounced dependence on the operating mode. In grid-connected operation, the grid provides high fault currents, limits neutral shift, and enables rapid voltage recovery. In islanded mode, the effective positive- and zero-sequence impedances are higher, resulting in a reduced fault current, a pronounced zero-sequence voltage, and a larger neutral displacement. The time-domain post-processing clarifies the disturbance structure: SLG faults produce pronounced zero-sequence excursions and stronger phase asymmetry, whereas the 3ϕ faults remain phase-symmetric in theabcdomain and are dominated by the positive-sequence response. The nonlinear load produces measurable asymmetry in the projected sequence quantities together with significant harmonic distortion in the currents. The EMT model captures early-cycle asymmetry, control-imposed current limiting, and sequence interactions that cannot be represented in phasor-domain root-mean-square (RMS) studies. These EMT-derived indicators provide grounding- and protection-relevant insights that can support grounding review, relay-sensitivity checks, and control assessment in converter-dominated microgrids.