电压环对光伏虚拟同步机系统稳定性的影响

INFLUENCE OF VOLTAGE LOOP ON STABILITY OF PHOTOVOLTAIC VIRTUAL SYNCHRONOUS GENERATORS

传统的新能源发电设备不具备调频调压能力,为解决这一问题,已有研究提出多种针对光伏逆变电源的稳压与电压穿越策略。在此基础上,为进一步提升光伏电源的调频、孤网运行等方面的能力,有学者提出多种类型的虚拟同步发电机(virtual synchronous generator,VSG)控制策略。VSG控制系统中是否存在电压环是区别不同VSG策略的主要特征之一。目前鲜有研究分析VSG控制系统中的电压环对光伏VSG并网稳定性的影响。为补缺这方面的研究,首先对引入和未引入电压环的2种光伏VSG进行小信号建模,通过计算2种VSG模型的特征根,分析电压环及其参数对系统各种潜在振荡模态的影响,尤其对可能诱发高频谐振和次同步振荡的模态进行分析。在此基础上,研究电压环对光伏VSG并网适应性和频率支撑能力的影响。研究结果表明,在电压等级较低、强度较弱的电网中,光伏VSG控制系统中宜引入电压环。

Traditional renewable power generator does not have the ability of frequency and voltage regulation. Researchers had proposed various voltage regulation and high and low voltage ride though strategies for photovoltaic inverter. On this basis,in order to enhance the frequency modulation and isolated network operation ability for photovoltaic generators,different kinds of virtual synchronous generators(VSG)strategies had been proposed. The significant distinction between various VSG strategies is whether VSG control system includes voltage close loop. No prior literature researches on the oscillation problem of voltage close loop in VSG. To address these issues,small signal models of photovoltaic VSG systems with and without voltage close loop were investigated in this paper. The developed model was used to calculate the eigenvalues for studying the potential oscillation modes,especially the highfrequency or subsynchronous oscillation modes. On the bases of that,the influence of voltage close loop on VSG damping characteristics under various scenarios was researched. Then the effect of voltage close loop on frequency supporting capacity of VSG was also studied in the paper. The results revealed that voltage close loop should be added in VSG when VSG is connected to the low-voltage and weak grid.