Zero-voltage ride through (ZVRT) is the extreme case of low-voltage ride through (LVRT), which represents the optimal grid-connection capability of wind turbines (WTs). Enforcing ZVRT will improve the dynamic performance of WTs and therefore significantly enhance the resiliency of renewable-rich grids. A control scheme that includes a pitch system is an essential control aspect of WTs riding through voltage dips; however, the existing control scheme with a pitch system for LVRT cannot distinguish between a ZVRT status and a power-loss condition, and, consequently, does not meet the ZVRT requirements. A system-level control scheme with a pitch system for ZVRT that includes pitch system modeling, control logic, control circuits, and overspeed protection control (OPC) is proposed in this paper for the first time in ZVRT research. Additionally, the field data are shared, a fault analysis of an overspeed accident caused by a voltage dip that describes the operating status at the WT-collapse moment is presented, and some existing WT design flaws are revealed and corrected by the fault analysis. Finally, the pitching performance during a ZVRT, which significantly affects the ZVRT performance of the WT, is obtained from laboratory and field tests. The results validate the effectiveness of the proposed holistic control scheme.
Zero-voltage ride through (ZVRT) is the worst-case scenario of low-voltage ride through (LVRT), which indicates the optimal fault-response capability of wind turbines (WTs). The reactive response during ZVRT shows the dynamic performance of WTs during extreme grid faults, which greatly improves the flexibility and robustness of renewable-rich grids. The reactive response of a doubly fed (type-3) WT during ZVRT depends on the control strategy of the converter and the steady-state and transient-state performance of the doubly fed induction generator (DFIG). This paper proposes a reduced-order model for representing the reactive response of a type-3 WT during ZVRT including the control strategy of the converter and the equivalent electric circuit of the DFIG, which simplifies some complicated equations but is practical for modeling a renewable-rich power system in most cases. Some simplified expressions between the reactive energy and a single DFIG parameter are presented, which could satisfy the demands of designing a DFIG. Finally, the method of model consistency verification, the influence analysis of DFIG parameters on the reactive response, the reasonable ranges of DFIG parameters and the fault-response performance of the WT in the theoretically longest ZVRT period are also obtained for reference.
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