An LVRT Control Strategy Based on Flux Linkage Tracking for DFIG-Based WECS

Abstract

For doubly-fed induction generator (DFIG)-based wind energy conversion systems (WECS), large electromotive force (EMF) will be induced in the rotor circuit during grid faults. Without proper protection scheme, the rotor side of DFIG will suffer from over-currents, which may even destroy the rotor side converter (RSC). To mitigate this problem, a new flux linkage tracking-based low voltage ride-through (LVRT) control strategy is proposed to suppress the short-circuit rotor current. Under the proposed control strategy, the rotor flux linkage is controlled to track a reduced fraction of the changing stator flux linkage by switching the control algorithm of RSC during grid faults. To validate the proposed control strategy, a case study of a typical 1.5 MW DFIG-based WECS is carried out by simulation using the full order model in SIMULINK/SimPowerSystems. In the case study, a comparison with a typical LVRT method based on RSC control is given, and the effect of the control parameter on the control performance is also investigated. Finally, the validity of the proposed method is further verified by means of laboratory experiments with a scaled-size DFIG system.Index Terms-Doubly-fed induction generator (DFIG), flux linkage tracking, low voltage ride-through (LVRT), rotor side converter.

Improved FRT control scheme for DFIG wind turbine connected to a weak grid

“…Stator and rotor currents protection maxima are set to 1.5 p.u. Nonetheless, the DFIG system converters, i.e., RSC and GSC can sustain 2 p.u overcurrent for a transitory time [4]. Furthermore, the pitch controller will be triggered in case of severe voltage dips to handle the rotor speed.…”

“…The stator voltage ( Fig. 12.a) drops to 95% during the fault, meanwhile the FRT protection is activated via a fault detection algorithm as that in [4]. Subsequent to the voltage dip, higher stator and rotor transient currents are noticed in Fig.…”

“…Fig.1.b depicts the German and Spanish reactive power support requirement. Basically, reactive current support is substantial for voltage dips with remnant voltage less than 0.9 p.u., while full reactive current support is necessary for severe voltage dips with remnant voltage lower than 0.5 p.u [3], [4]. DFIG WTs, are extensively preferred due to variable speed operation using partial scale converters rated at 25-30% that allows for independent control of active and reactive power [4].…”

“…Basically, reactive current support is substantial for voltage dips with remnant voltage less than 0.9 p.u., while full reactive current support is necessary for severe voltage dips with remnant voltage lower than 0.5 p.u [3], [4]. DFIG WTs, are extensively preferred due to variable speed operation using partial scale converters rated at 25-30% that allows for independent control of active and reactive power [4]. Nevertheless, DFIG is sensitive to the grid faults and thus prone to various serious issues due to the direct connection of its stator to the grid [2]- [4].…”

“…DFIG WTs, are extensively preferred due to variable speed operation using partial scale converters rated at 25-30% that allows for independent control of active and reactive power [4]. Nevertheless, DFIG is sensitive to the grid faults and thus prone to various serious issues due to the direct connection of its stator to the grid [2]- [4].…”