基于阻抗法的并网逆变器小信号稳定功率极限分析与提高

Analysis and improvement of the small-signal stable power limit of a grid-connected inverter based on an impedance method

随着可再生能源发电在电网中所占比重不断增加,由并网逆变器引发的电力系统小信号稳定性问题日益凸显。为了明确并网逆变器系统运行的功率裕量,增强系统的小信号稳定性,采用阻抗法对并网逆变器的小信号稳定功率极限进行研究。根据广义奈奎斯特稳定判据的边界条件定量计算了并网逆变器的小信号稳定功率极限。结果表明,该功率极限小于静态稳定功率极限,随着电网短路比的减小而减小,随着锁相环带宽的增大而减小。提出了一种改进锁相环结构,从控制的角度等效增大电网短路比,从而提高并网逆变器的小信号稳定功率极限。最后,通过阻抗分析和系统仿真验证了改进锁相环对于提高小信号稳定功率极限的有效性。

As the proportion of renewable energy power generation in the grid continues to increase,the problem of power system small-signal stability caused by grid-connected inverters has become increasingly prominent.To clarify the power margin of the grid-connected inverter system and improve the small-signal stability of the system,the impedance method is used to study the small-signal stable power limit of the inverter.From the boundary conditions of the generalized Nyquist stability criterion,the small-signal stable power limit of the grid-connected inverter is quantitatively calculated.It is pointed out that the power limit is less than the static stability power limit,and decreases with the decrease of the grid short-circuit ratio,and decreases with the increase of the phase-locked loop bandwidth.An improved phase-locked loop structure is proposed to increase the grid short-circuit ratio from the control point of view,thereby improving the small-signal stable power limit of the grid-connected inverter.Finally,the effectiveness of the improved phase-locked loop in improving the small-signal stable power limit is verified by impedance analysis and system simulation.