Reactive Current Constraints and Coordinated Control of DFIG’s RSC and GSC During Asymmetric Grid Condition

Abstract

Doubly fed induction generator (DFIG) based wind turbines have been found to be very sensitive to asymmetrical grid fault, wherein the harmful oscillations in the electromagnetic torque has being made a big concern. What makes things harder is that latest grid codes require grid-connected wind turbines to possess the ability of positive-and negative-sequence reactive current supporting. Hence, it becomes a guide mechanism to meet the grid codes and to ensure the operation safety of the wind turbines. Even though a tradeoff could be made between them, it is still quite difficult to coordinate the current dispatch of the DFIG's rotor-and grid-side converters (RSC and GSC), since there are totally eight currents needing to be carefully designed, i.e., the positive-and negative-sequence active and reactive currents in each converter. To address this issue, this paper analyzes the reactive current constraints in detail, based on which a coordinated reactive current control strategy is put forward for the DFIG-based wind turbines during asymmetrical grid condition. Simulation studies demonstrate the effectiveness of the proposed strategy. INDEX TERMS Doubly fed induction generator (DFIG), wind turbine, asymmetrical grid, reactive current support, fault ride-through (FRT).

Coordinated Control of DFIG Converters to Comply with Reactive Current Requirements in Emerging Grid Codes

“…In addition to the PNSC-Tem, the negative-sequence current references of GSC have been used in the existing coordinated control strategy to provide I2R. In [28], the negative- sequence current references of GSC are given by:…”

“…The control of the DFIG under unbalanced conditions and the coordination of converters to reduce the mechanical stress have been studied in [23], [24]. However, studies focusing on the controlled I2R injection to the grid are mainly related to the full-size converter (FSC) based WTGs (also referred to as Type-IV WTGs) [25]- [27] except the study presented in [28] focusing on DFIG-based WTGs.…”

“…This control strategy is referred to as the positive-and negative-sequence control focusing on Tem and denoted by PNSC-Tem in this paper. Reference [28] proposes a coordinated control of DFIG converters on the basis of PNSC-Tem, in which the GSC is used to provide I2R to the grid under small voltage unbalances. This coordinated control strategy is denoted as the existing coordinated control in this paper.…”

Methods for protecting network from islanding danger

“…Eltawil et al, 2010;B. Anudeep et al, 2017& H. Xu et al, 2020. The challenge in these passive methods is how to select the convenient threshold (S.I.…”

A new passive islanding detection technique for different zones in utility grid

“…Examples of active islanding detection methods are active frequency drifting (A. , slip mode frequency shift (A. Pouryekta et al, 2018), impedance measurement (H. Abdi et al, 2020), frequency jump (H. Xu et al, 2020), Sandia voltage shift (SVS) (M.F.N. Khan.…”