Protection of Inverter-based Distributed Generation with Series Dynamic Braking Resistor: A Variable Duty Control Approach

Abstract

Fault current level in inverter based distributed generation (IBDG) integrated grid system increases manifold due to high level of IBDG penetration. Nevertheless, for having less detrimental effect of fault in the system fault current must be kept within specified limit as per new grid code. This paper proposes series dynamic braking resistor (SDBR) based protection scheme for IBDG with variable duty control strategy. SDBR is connected with the AC side of the IDBG to insert variable resistance during contingencies depending on the level of fault current. Current at the point of common coupling is employed to detect system disturbances. Feedback control strategy is developed for the control of DC link voltage such that the net power exchange with the DC capacitor is zero. Direct axis inner current control strategy is adopted to transfer IBDG power to grid. Symmetrical three phase to ground and unsymmetrical double line to ground faults are applied in the system to show the efficacy the proposed variable duty based SDBR control technique. The proposed variable duty based SDBR control scheme have been found as an effective solution to limit the fault current for IBDG system as evident from the simulation results.