直流电压时间尺度下光伏并网控制系统稳定性分析

随着光伏发电并网规模的扩大，由其换流器控制系统动态特性所引起的小干扰稳定性问题愈加突出。由于单台光伏发电单元容量较小，并网光伏发电系统中往往包含大量光伏发电单元，系统模型阶数较高，极大地增加了稳定性分析的复杂程度。因此，为提出一种较为简单有效的稳定性判别方法，本文首先通过时间尺度分解的方法建立了并网光伏发电系统在直流电压时间尺度下的小干扰稳定分析降阶模型，随后在该模型的基础上由劳斯-赫尔维茨判据推导得出了系统的小干扰稳定判据，并结合判据分析了直流电压控制时间尺度下影响系统小干扰稳定性的关键因素，辨识出三个影响稳定性的不利因素：重负荷、弱连接、不恰当的控制参数设置。通过仿真算例验证了所提出稳定性判据的正确性和有效性。结果表明：所得出的稳定性判据能有效地对并网光伏发电系统在直流电压时间控制尺度下的小干扰稳定性进行评估，并且该评估方法不需要对系统建立复杂高阶的模型，极大地简化了计算和分析过程。

Stability analysis of grid-connected photovoltaic generation control system under DC voltage timescale

With the expansion of grid-connected photovoltaic power generation, the problem of small-disturbance stability caused by the dynamic characteristics of its converter control system has become increasingly prominent. Due to the small capacity of a single photovoltaic power generation unit, the grid-connected photovoltaic power generation system often contains a large number of photovoltaic power generation units, as a result, the model of the system is high, which greatly increases the complexity of stability analysis. Therefore, in order to propose a relatively simple and effective stability discrimination method, this paper first establishes a reduced-order model of small-disturbance stability analysis of grid-connected photovoltaic power generation system under DC voltage control timescale through the timescale decomposition method, and then deduces the small-disturbance stability criterion of the system by applying the Routh-Hurwitz criterion on the basis of this model. From the criterion, the key factors affecting the small-disturbance stability of the system under DC voltage control timescale are analyzed, and identified three main unfavorable affecting factors: the heavy loading condition, the condition of weak grid connection, improper setting of parameters of converter control systems. The correctness and effectiveness of the proposed stability criterion are verified by simulation examples. The results show that the stability criterion can effectively evaluate the small-disturbance stability of the grid-connected photovoltaic power generation system under DC voltage control timescale, and the evaluation method does not need to establish a complex high-order model of the system, which greatly simplifies the calculation and analysis process.