基于盖尔圆定理的三相并网逆变器系统稳定判据及稳定性分析

Stability Criterion and Analysis for Three-phase Grid-connected Inverter System Based on Gershgorin Circle Theorem

随着愈来愈多的并网逆变器接入电网,逆变器与电网之间的阻抗交互作用对系统的稳定可靠运行是一个潜在威胁。为此,开展对并网逆变器接入电网的稳定性研究具有重要的意义。建立了在dq坐标系下的三相LCL型并网逆变器小信号阻抗模型。该模型考虑了锁相环和电流环补偿因素对逆变器阻抗特性的影响,提高了模型的精度。在此基础上,对系统的稳定性进行理论分析,系统的稳定性判定具有重要的工程指导意义。为解决传统广义Nyquist稳定判据所需计算量较大、使用困难的问题,提出了一种基于盖尔圆定理的系统稳定性判据,在保证系统稳定的同时大幅降低了计算量,可以作为一种实用的系统稳定区域估算方法。仿真和实验结果与理论分析一致,验证了所提方法的正确性。

As more and more inverters are connected to grid,the impedance interaction between grid-connected inverters and grid will be a potential threat to the stable and reliable operation of the system.Accordingly,it is of significance to study the stability of inverters connected to grid.In this paper,a small-signal impedance model of three-phase LCL-type grid-connected inverter is established,which considers the influence of phase-locked loop(PLL)and current-loop compensation on the impedance characteristics of the inverter.As a result,the model accuracy is improved.On this basis,the theoretical analysis of system stability is performed.Moreover,the stability criterion for the system is of significance in engineering.However,the traditional generalized Nyquist stability criterion is difficult to use because of large computation load.Therefore,a stability criterion based on the Gershgorin circle theorem is proposed,which can greatly reduce the computation load while guaranteeing the system stability.In this way,this criterion can be considered as a practical method for estimating the system’s stable area.Simulation results agree well with the theoretical analysis,which verifies the correctness of the proposed method.