考虑光伏发电单元孤岛检测影响的直流电网稳定性分析与阻尼控制

Stability Analysis and Damping Control of DC Grid Considering PV Generators With Island Detection

直流电网适合大规模光伏发电的集成接入。光伏发电单元在接入直流电网运行时,需要依托孤岛检测方法,使得发电单元可以在异常断开状态下得到保护。然而,前馈孤岛检测方法会向直流电网注入扰动,影响光伏发电单元在并网运行时的性能,甚至加剧由于变换器交互作用造成的振荡失稳问题。对此,建立直流电网中光伏发电单元、交直流互联变换器的小信号阻抗模型,并综合考虑最大功率跟踪控制、前馈孤岛检测方法对光伏Buck变换器端口特性的影响,探究影响直流电网稳定性的因素。然后,在不影响孤岛检测的情况下,提出一种有源阻尼稳定控制方法,在并网运行的光伏发电单元的直流电网侧端口串入虚拟电阻,使发电单元在输出不同功率时均有较好的稳定性。最后,仿真研究验证了分析内容的准确性和所提阻尼方法的有效性。

DC grids are becoming more prevalent when integrating large-scale photovoltaic(PV) generators. PV generators should adopt island detection when they are grid-connected, therefore, PV generators can be protected in abnormal disconnection. However, positive feedback island detection would inject disturbance into the DC grid and affect the performance of PV generators during grid-connected operation. It even aggravates the oscillation instability caused by the interaction of converters. To solve this problem, the small-signal impedance models of PV generators and voltage source converter were established. Considering the influence of maximum power tracking control and positive feedback island detection on the port characteristics of PV Buck converter, the factors affecting the stability of DC grid were investigated. Then, a damping control method was proposed without affecting the island detection, in which a virtual resistor was connected to the DC grid side port of the grid-connected PV generators. Therefore, the stability of grid-connected PV generators was improved at different power outputs. Finally, the analysis and proposed control method are verified by simulation results.