考虑低电压穿越能力的风火联运系统暂态稳定分析

Transient stability of power systems with the wind farm and thermal units considering LVRT behaviors

对风火联运系统的暂态稳定性进行机理研究。根据低电压穿越试验的实测波形总结DFIG风机的功率调制行为特征,并采用DFIG的受控功率源模型,在原型系统中研究风场在系统大扰动过程中的作用。风电出力整体水平低时,主导失稳模式为功角失稳,风电出力的瞬时调制能够改变同等功角摇摆程度下的火电电磁功率,进而影响相邻同步机的功角暂态稳定。风电比例足够高时,主导失稳模式转化为功角、电压的混合失稳。若故障期间风场未进入低穿模式,风机的功率源特性使得网络约束呈现非线性,并导致同步机在功角摇摆过程中可能触碰奇异面而发生系统的暂态电压崩溃。当风场进入低穿模式而进行功率调制时,其在故障期间主动降低输出有功,可改变相邻同步机的加、减速特性以及系统距离奇异的程度。风场的无功调制可以支撑系统电压而提高临界功角值。低穿后的有功恢复行为会显著影响系统回到稳定的速度。

This paper studies the transient stability of power systems composed of both the wind farm and thermal unit. According to responses of the DFIG during LVRT testing, this paper adopts a controlled-power-source model to study impacts of DFIGs on transient stability in a rudimentary system. Angle stability plays an important role when wind-power penetration is low. Power modulation of wind farms would affect output of the thermal unit （at the same magnitude of angle swing）, and thus their transient stability of rotor speeds. As wind-power penetration gets higher, the mixed angle and voltage instability mode becomes extraordinarily critical. The reason is that, power systems are possible to approach singularity as power angle swings, because of nonlinear network constraints brought in by the constant-power feature of the DFIG. P-modulation behaviors of wind farms have impacts on both the system＇s distance to singularity and its rate of approaching singularity. Q-modulation behaviors could enhance system voltage level so as to improve the magnitude of singularity angle. The post-fault recovery of wind farms would have an evident effect on the time cost to restore stability.