基于超级电容的永磁同步风力发电机不对称故障穿越方法

风电系统与电网之间的相互影响越来越大，需要并网风电机组具有故障穿越能力来保证电网安全运行。为了提高永磁同步风力发电机组(PMSG)在不对称电网故障下的穿越能力，提出了一种基于超级电容储能的PMSG风电机组的故障穿越方法。该方法采用双向直流变换器将超级电容器组连接在交直交变流器的直流母线上，通过对超级电容的吞吐功率进行控制，限制了故障情况下交直交变流器直流侧电压上升，并降低了不对称故障引起的直流母线电压2倍工频纹波。同时在网侧换流器的控制中采用电网负序电压前馈的方法，消除并网电流负序分量。结合低电压穿越标准，对超级电容的容量选取进行了讨论，并建立了超级电容器及其功率变换电路的数学模型，设计了超级电容储能系统的控制器。采用Matlab软件，对1 MW机组的仿真结果表明，所提出的不对称故障穿越方法，可同时减小并网电流负序分量和直流母线电压的2倍工频纹波，提高了机组不对称故障穿越能力，验证了文中提出的故障穿越策略的有效性。

An asymmetric fault ride-through control method forPMSG wind turbine based onsuper-capacitors

With the rapid increasing interaction between wind turbines and power systems, wind turbines have to have the fault ride-through (FRT) capability to ensure the safe operation of power grid. In order to improve the asymmetric FRT capability of permanent magnet synchronous generator (PMSG) wind turbine, a novel control FRT method based on super-capacitors is proposed. In this method, super-capacitors are connected to the DC bus of AC-DC-AC converter via a bi-directional DC-DC converter, and the power processed by the super-capacitors is controlled to limit the increasing of the DC bus voltage of the AC-DC-AC converter in grid failure condition, and to reduce the 2nd order voltage ripple in the DC bus. Meanwhile, the proposed control method employs the grid voltage feed-forward approach to reduce the negative sequence current component in the grid side converter. According to the low voltage ride through (LVRT) standard, the selection of the super-capacitor capacity is also discussed, and then a mathematical model of the super-capacitor with the bi-directional DC-DC converter is established for designing the controller. Simulation results for a 1MW PMSG wind turbine by MATLAB show that the proposed control method reduces both the negative sequence current component in grid side converter and the 2nd order voltage ripple in DC link at the same time. The results also demonstrate that the asymmetric FRT capability of PMSG wind turbine is improved, which verifies the effectiveness of the proposed control method in this paper.