双馈风场串补系统次同步振荡紧急控制策略

在新能源侧振荡抑制措施失效的情况下,双馈风电场与串补相互作用诱发的次同步振荡会造成大量风机脱网,对系统稳定性产生不利影响。现有振荡抑制措施无法保证在任何情况下都能可靠抑制振荡,因此需要网侧主动对风场进行紧急控制。文中基于频域阻抗判据,针对辐射型网络网侧选切过程中实时计算量过大的问题制定紧急控制策略,以达到降低计算量,减少决策时间的目的。在极坐标系下推导新能源侧频域阻抗实部与支路阻抗模值相角的关系,根据实部变化量分三步进行判断:首先排除"切除无效机组";其次在余下的机组中筛选紧急控制作用有效的机组;最后根据复阻抗量的投影大小确定切除顺序以防过切。基于国内某风电场经串补送出电网实际参数,通过PSCAD仿真试验对所提策略的有效性进行仿真验证,仿真结果表明按照文中所述切除策略进行紧急控制可有效提升系统在次同步振荡过程中的系统阻尼,避免振荡快速发散。

Emergency control strategy for subsynchronous oscillation of DFIG-based wind farms with a series-compensated line

When the oscillation suppression measures on the new energy side fail,the sub-synchronous oscillation induced by the interaction between the double-fed wind farm and the series compensation will result in grid disconnection of a large number of wind-driven generators,causing adverse effect on system stability. Since the existing measures cannot guarantee reliable oscillation suppression under any circumstances,it is necessary to take the initiative to conduct emergency control of the wind field at the network side. On the basis of frequency domain impedance,an emergency control strategy is formulated to address the problem of excessive real-time calculation during slicing of radial network,so as to reduce the amount of calculation and decision-making time. The relationship between the real part of the frequency domain impedance and the mode value,phase angle of branch impedance at the new energy side under the polar coordinate system is deduced,followed by a three-step judgement depending on the change of the real part. Firstly,the ''suspension of invalid units'' is excluded. Secondly,the valid units with effective emergency control are selected from the rest units. Thirdly,the order of suspension is determined based on the size of projection of the complex impedance,so as to prevent excessive suspension. On the basis of the actual parameters of transmitted grid after series compensation at a domestic wind field,the effectiveness of the proposed strategy is subject to PSCAD simulation. The simulation result shows that emergency control with adoption of the proposed strategy herein can effectively improve the system damping during the sub-synchronous oscillation and prevent rapid divergence of oscillation.