Voltage-Dependent Current Envelope and Power Factor Control for DER Tripping Prevention

Abstract

The increasing penetration of distributed energy resources (DERs) has significantly altered the dynamic behavior of emerging power systems, particularly during severe voltage disturbances. Unlike synchronous generators, inverter-based DERs are inherently current-limited and rely on phase-locked loop (PLL) strategy for grid synchronization, which makes them prone to loss of synchronism during system faults. This paper develops an analytical framework to characterize the synchronism and stability limits of DERs during under-voltage conditions. A DER nonlinear state–space representation is used to mathematically derive conditions that ensure DER synchronism around a feasible equilibrium point. These conditions lead to the formulation of a voltage-dependent DER current envelope that defines the permissible DER current range required for stable fault ride-through (FRT) operation. The analysis shows that, beyond the inverter overcurrent protection constraint, more restrictive current limits may arise from the interactions between DER control dynamics and grid impedance characteristics. The impacts of grid impedance, controller parameters, and DER power factor on the stability boundary are analytically studied. The study examines how and to what extent DER power factor adjustment can enhance stability during faults. Time-domain simulations validate the efficacy of the mathematically derived current envelope and demonstrate the effectiveness of the power factor adjustment in preventing DER tripping events.