弱电网条件下并网逆变器的锁相环静态稳定分析

Static stability analysis of phase-locked loop in grid-connected inverters under weak grid condition

在新能源发电经由逆变器接入电网的系统中,并网逆变器的稳定性将随着接入点短路比的减小而降低。目前,学术界针对这一问题已有较多研究,但大多是基于状态空间模型线性化后利用相关控制理论进行分析,缺乏直观的机理分析。采用忽略了电流内环响应时间的准稳态模型,重点对并网逆变器中锁相环的静态稳定性进行分析,得出了与传统单机无穷大系统中类似的静态稳定判据。由此稳定判据能直观得出并网逆变器维持同步前提下的输出功率极限,并指出当并网逆变器超出此功率极限时将以过电压的形式失去稳定。采用并网逆变器的详细模型进行仿真分析,验证了所提静态稳定判据的正确性。

In the system of renewable energy generation connecting to the power grid through an inverter,the stability of the grid-connected inverter will decrease as the short-circuit ratio of interconnection point decreases.At present,academics have done a lot of researches about this issue.However,most of them are based on the linearized state-space model and analyzed with related control theories which have a lack of mechanism analysis.This paper uses a quasi-steady state model that ignores the response time of the current loop,and studies the static stability of phase-locked loop in the grid-connected inverter.A static stability criterion similar to the traditional one-machine infinite bus system is obtained,which can intuitively draw the power limit of grid-connected inverter under the constraint of synchronization.It is pointed out that when the grid inverter exceeds this power limit,it will lose stability in the form of overvoltage.The simulation analysis is carried out with the detailed model of the grid-connected inverter to verify the correctness of the proposed static stability criterion.