电网不平衡故障下，两级式光伏逆变器的直流母线电压及并网电流会不稳定，从而导致光伏逆变器由于过压或者过流而脱网，而光伏逆变器的脱网又会恶化电网系统的安全运行，从而造成更为严重的事故。针对这一问题，首先在分析三相光伏并网逆变系统结构及控制的基础上，提出电网故障下保持系统直流母线电压及并网电流稳定的控制策略，并且采用所提控制策略下的光伏并网逆变器能够在电网故障期间对其提供一定的无功支持。最后，搭建了三相光伏并网逆变系统的数字仿真及物理实验平台，结果验证了所提控制策略在电网不平衡故障下的有效性与优越性。%DC bus voltage and grid-connected current of the traditional two-stage PV inverter will be unstable under power grid′s unbalanced fault,which causes the PV inverter′s outage due to overvoltage or overcurrent. Outage of the PV inverter can worsen the secure operation of power grid and cause more serious accidents. To solve this problem,a control strategy was presented based on analysis of the three-phase PV grid-connected inverter system′s topology and control method. During the fault of power grid,the proposed strategy could not only ensure the stability of DC bus voltage and grid-connected current,but also make the PV inverter to provide a certain reactive power support to the grid. An experimental system and digital simulation platform of the three-phase PV grid-connected inverter system were built,and the validity and superiority of the proposed control strategy under the power grid′s unbalanced fault are verified by simulation results.
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