Patterns and Discrimination for the Voltage Instability Induced by Low-Voltage Ride-Through Control Switching in Renewable Energy Stations

Under slow power-flow dynamics, a voltage instability phenomenon induced by low-voltage ride-through (LVRT) control switching rather than by saddle-node bifurcation (SNB) has been observed at a renewable energy station (RES) in China. The phenomenon leads to a large-scale disconnection of RESs. However, the understanding of the patterns and mechanisms of this LVRT-control-switching-induced (LCSI) voltage instability is still insufficient, resulting in potential operating risks for grid-connected RESs. This paper investigates the potential LCSI voltage instability patterns and develops a graphical discrimination method. First, three scenarios involving the triggering of LVRT control switching are identified. Second, a mathematical model of the grid-connected RES system is established. Then, based on the accessibility of equilibrium points, the LCSI voltage instability pattern and the corresponding bifurcation properties in each scenario are revealed. Furthermore, a graphical discrimination method that accounts for both SNB and LCSI voltage instability is proposed. Finally, the existence of three LCSI voltage instability patterns is verified, and the effectiveness and robustness of the proposed graphical discrimination method are validated.