As one of the main types of wind power generation, doubly-fed induction generator (DFIG) has been widely used with the rapid development of new energy. In this paper, the mechanism of insufficient stability of DFIG control system under weak grid is investigated. By constructing small signal model of DFIG in weak grid, the influence loop of phase-locked loop (PLL) on current closed-loop control is analyzed. Based on the small signal model, a compound decoupling control strategy considering the effect of PLL is proposed, which effectively improves the stability margin of DFIG in weak grid. The effectiveness of the proposed strategy is verified by experiments.

随着风力发电机的大规模并网发电,并网点的短路比不断降低.风电机组并网功率增大使得线路阻抗上的压降上升,并网点电压也随之降低,进而导致风力发电机的输出功率受到限制.为改善风机并网在低短路比下电压降低致使输出功率受限的问题,以双馈风力发电机为研究对象,提出了一种基于电压主动支撑的闭环优化控制策略.该方法在实现对并网点电压的支撑的基础上,提高了双馈风电机组在低短路比下的功率传输能力,同时解决了常规电压闭环控制中由功率耦合引发的系统稳定性问题.在优化控制策略下,系统的主导极点阻尼比更大,使得系统更加稳定.最后,在11 kW的双馈电机实验平台上验证了优化控制策略下双馈电机的阶跃响应稳定性更高.

在双馈感应发电机(doubly-fed induction generator,DFIG)基于电压源输出并入弱电网的条件下,针对系统中含有非线性负载的情况,提出一种改善公共连接点(point of common coupling,PCC)谐波电压的方法。首先建立双馈发电机基于电压源下垂并网输出的功率小信号模型。然后根据模型建立谐波源到输出电压的传递函数。以抑制并网点电压的5次和7次谐波为目标,在转子电流内环采用比例积分控制器的基础上,利用准谐振调节器直接提取并网点电压的谐波分量,引入比例前馈补偿,有效降低并网点谐波电压含量和输出功率脉动。最后通过实验验证所提控制策略的有效性。