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.
A Control Scheme with the Variable-Speed Pitch System for Wind Turbines during a Zero-Voltage Ride Through