中文摘要：

电网电压不对称骤升时如果仅向电网注入正序感性无功功率,当电网阻抗较大时,会造成没有发生骤升的机端相电压降低,加剧发电机机端电压的不对称度,同时增加定子侧无功功率脉动,因此需要通过定子侧注入相应的负序无功功率进行调节。为了优化电网电压不对称骤升时无功功率的控制策略,首先推导电网电压不对称骤升下双馈风力发电机的数学模型,然后分析转子侧变流器正负序无功电流的分配问题,讨论定子侧正负序无功功率对并网点电网电压支撑、发电机机端电压不对称度和定子侧无功功率脉动的耦合影响变化规律。基于以上分析,为实现电网电压不对称骤升时的复合控制目标,采用一种柔性的的正负序电压闭环的无功功率优化控制策略,最后通过仿真和实验结果验证了该控制策略的有效性和可行性。

英文摘要：

When the grid voltage unsymmetrical swell, if only positive sequence inductive reactive power is injected into the grid and a large grid impedance exists, which will reduce the unchanged terminal phase voltage of the generator, the unbalance factor of the terminal generator voltage will enlarge and the ripple of stator reactive power will become bigger. Therefore, it is necessary to inject a corresponding stator-side negative sequence reactive power to adjust it. In order to optimize the reactive power control strategy when the grid voltage unsymmetrical swells, firstly the mathematical model of doubly fed induction wind generators under the fault mentioned above was deduced. Then this paper analyzed the positive and negative sequence reactive current assignment of the rotor-side converter and discussed the coupling effects of stator-side positive and negative reactive power on the network support at the point of common coupling（PCC）, the generator terminal voltage unbalance factor and the pulsating stator reactive power. Based on the above analysis, a flexible positive and negative sequence closed-loop voltage control strategy of the reactive power optimization was adopted to achieve the composite control objectives when the grid voltages unsymmetrical swell. Finally simulations and experimental results verify the effectiveness and feasibility of the control strategy.