Parallel R-L configuration crowbar with series R-L circuit protection for LVRT strategy of DFIG under transient-state

Abstract

This paper proposes an impedance protection circuit configuration to enhance the ride-through of doubly-fed induction generators (DFIGs) based wind turbines (WTs) during faults. The proposed impedance protection circuit configuration comprises of a parallel R-L impedance crowbar and a series R-L impedance circuit. Traditionally, resistive-crowbar (i.e., R-crowbar) circuit is applied as the means of protection for the DFIG WT which efficiently protects the rotor-side converter (RSC) and dc-link capacitor against the effects of severe grid faults. However, the conventional R-crowbar circuit disconnects the RSC leading to the loss of generator excitation control. During that time, the WT generator becomes a conventional squirrel-cage induction generator (SCIG) which obtains its magnetization current from the point of common coupling (PCC) via stator winding terminals. This phenomenon further deepens the voltage-dip at the PCC. Alternatively, integrating the R-crowbar with series R-L branch partially maintains the RSC connection to the rotor winding. Hence the generator excitation control is also partially maintained but oscillations of the rotor currents and dc-link voltage can still affect the ride-through performances of WT driven by the DFIG. With the proposed protection circuit configuration, it compensates the deficiency of the two conventional protection circuits configuration. In order to validate the performance of the proposed scheme, extensive simulation studies are carried out using MATLAB/Simulink software. From the comparative simulation results, improved performances of the DFIG under transient-state are achieved with the proposed protection circuit configuration than the conventional protection circuits.