Phase Current Reconstruction for the Grid-Side Converter With Four-Switch Three-Phase Topology in a DFIG-WT

To increase the reliability of a doubly fed induction generator-based wind turbine (DFIG-WT), this paper proposes a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) with a phase current reconstruction strategy. The proposed strategy is effective when the semiconductor open-circuit fault and phase current sensor failure occur simultaneously, which is a kind of hybrid fault. Only one current sensor is applied for measuring the currents flowing between the ac and dc sides of the GSC, and the phase current information can be derived by combining this information with the switching states of FSTP GSC. In the proposed current reconstruction strategy, only two scenarios of duty ratio allocation are needed to be considered. In addition, the space vector pulsewidth modulation (SVPWM) technique is simplified by obtaining the unified expressions for the duty ratios for the remaining four switches in GSC, and the sector identification is removed. Besides, the voltage balancing on the dc bus is achieved. Furthermore, the limitation of the proposed current reconstruction strategy is presented, and the dead zones for SVPWM techniques in both six-switch three-phase and FSTP converters are analyzed. Simulations are carried out in MATLAB/Simulink to verify the proposed hybrid fault-tolerant strategy for the GSC in a 1.5-MW DFIG-WT.