The voltage-frequency coupled transient stability and risk assessment issues of weak grid-connected large-scale renewable energy plants (REPs) during low voltage ride through (LVRT) have received little attention to date. The shape and mechanism of voltage-frequency coupled transient instability during LVRT are investigated in detail by the voltage-vector-triangle graphic (VTG) method utilized in this article, which avoids complex mathematical calculations. In addition, the margin of the transmission line's voltage angle (MTVA) is defined in this article and is then used to quantitatively assess the transient instability risk of the large-scale REPs during LVRT. Furthermore, the expressions of the MTVA are deduced under different conditions and the major influencing factors, which resulted in instability risk, are determined correspondingly. On this basis, the transient instability risk assessment standard of the large-scale REPs is built and the instability risk minimized scheduling strategy is proposed in this article, which does not change the internal control structure and parameters of the REPs during LVRT. Finally, both the correctness of the VTG method and the risk assessment standard, and the effectiveness of the scheduling strategy proposed in this article are validated by experiments and simulations.

中文翻译：

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大型并网可再生能源电站低电压穿越期间电压-频率耦合暂态失稳特性分析及风险评估


迄今为止，弱并网大型可再生能源电站（REP）低电压穿越（LVRT）期间的电压频率耦合暂态稳定性和风险评估问题很少受到关注。本文采用电压矢量三角图（VTG）方法详细研究了低电压穿越期间电压频率耦合暂态不稳定性的形状和机制，避免了复杂的数学计算。此外，本文定义了输电线路电压角裕度（MTVA），并用于定量评估低电压穿越期间大规模REP的暂态失稳风险。进一步推导了不同条件下MTVA的表达式，并相应地确定了导致不稳定风险的主要影响因素。在此基础上，本文建立了大型REP暂态失稳风险评估标准，提出了低电压穿越期间不改变REP内部控制结构和参数的失稳风险最小化调度策略。最后，通过实验和仿真验证了VTG方法和风险评估标准的正确性以及本文提出的调度策略的有效性。