In this article, the transient synchronization process of the grid-connected voltage source converters (VSC) is studied detailly. Firstly, the phase-locked loop (PLL)-synchronized VSC is modeled according to the rotor motion equation of synchronous generator (SG). Furthermore, the VSC's damping ratio is derived, and the effects of the VSC's control parameters and the operation status on the equivalent power angle (EPA) is investigated. Moreover, the influence of the PLL's parameters and the voltage dips degree on the VSC's transient frequency behavior are analyzed. Analysis result reveals that the VSC's damping ratio decreases once the grid voltage drops, so that the EPA and frequency of the VSC may appear large overshoot and oscillation, which may trigger the frequency protection and deteriorate the VSC's transient stability. In order to ensure that the VSC can smoothly operate to new equilibrium points, an improved PLL is proposed, which can adaptively adjust the VSC's damping ratio for different voltage sags. The proposed method can not only reduce the overshoot of the EPA but also restrain the VSC's frequency dips degree. Finally, the simulations and experimental tests validate the effectiveness of the theoretical analysis.

中文翻译：

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电网严重故障时基于改进PLL的并网VSC暂态稳定控制策略

在本文中，详细研究了并网电压源转换器（VSC）的瞬态同步过程。首先，根据同步发电机（SG）的转子运动方程，对锁相环（PLL）同步的VSC进行建模。此外，推导了VSC的阻尼比，并研究了VSC的控制参数和运行状态对等效功率角（EPA）的影响。此外，分析了PLL参数和电压骤降程度对VSC瞬态频率行为的影响。分析结果表明，一旦电网电压下降，VSC的阻尼比就会降低，因此EPA和VSC的频率可能会出现较大的过冲和振荡，从而可能触发频率保护并恶化VSC'。瞬态稳定性。为了确保VSC可以平稳地工作到新的平衡点，提出了一种改进的PLL，该PLL可以针对不同的电压骤降自适应地调整VSC的阻尼比。所提出的方法不仅可以减少EPA的过冲，而且可以限制VSC的频率骤降度。最后，仿真和实验测试验证了理论分析的有效性。