Large Signal Synchronizing Instability of PLL-Based VSC Connected to Weak AC Grid
Large Signal Synchronizing Instability of PLL-Based VSC Connected to Weak AC Grid
复制标题
基于 PLL 的 VSC 连接到弱交流电网的大信号同步不稳定性
DOI：
10.1109/tpwrs.2019.2892224
复制
发表时间：
2019-07-01
影响因子：
6.6
通讯作者：
Ji, Feng
中科院分区：
文献类型：
--
作者：
Hu, Qi;Fu, Lijun;Ji, Feng
传统电力系统中常见的大信号同步不稳定性同样存在于电压源换流器（VSC）主导的电力系统中，这一问题的报道和研究也越来越多。本文研究了锁相环同步电压源控制器在弱交流电网中的大信号不稳定性。首先，分析了高栅极阻抗对锁相环动态特性的影响，发现在锁相环中引入了一个附加的反馈环，从而降低了锁相环的性能。建立了与同步发电机转子运动模型相似的分析模型。基于所建立的模型，采用等面积法进行了大干扰稳定性分析。发现大信号不稳定性主要由以下两个因素引起。一是平衡点不存在，这与SG并网系统中机械功率输入曲线与电磁恢复力曲线不相交类似。另一个是由于减速区不足而导致的过渡过程，导致系统不能稳定地从初始点过渡到现有的平衡点。该分析不仅有助于揭示其物理机制，而且为今后的改进措施提供了指导。
Similar large signal synchronizing instability that is common in traditional power system also exists in voltage source converter (VSC) dominated power system, which is increasingly reported and investigated. In this paper, the large signal instability of phase locked loop (PLL) synchronized VSC connected to weak ac grid is investigated. First, the influence of high grid impedance on PLL's dynamics is explored and an additional feedback loop is found to be introduced, which deteriorates the performance of PLL. Then an analysis model that is similar as the rotor motion model of synchronous generator (SG) is developed. Based on the developed model, equal-area method is employed to carry out the large-signal stability analysis. The large signal instability is found to be mainly resulted by the following two factors. One is the nonexistence of equilibrium point, which is similar as that there does not exist intersection between the mechanical power input curve and electromagnetic restoring force curve in SG grid connected system. The other is related with the transition process resulted by insufficient decelerating area, which leads to that the system cannot stably go through the transition from initial point to the existing equilibrium point. The proposed analysis not only contributes to revealing the physical mechanism but also provides guidance for the future improvement measures.