跟网型逆变器的非线性模型及稳定性分析方法

Nonlinear Model and Stability Analysis Method for Grid-following Inverter

锁相环为并网逆变器的跟网控制提供了与电网同步的参考信息,但在弱电网下,具有非线性特性的锁相环对系统稳定性会产生一定的影响。由于舍入误差的存在,现有基于线性化锁相环模型而设计的并网逆变器存在稳定性设计不足的风险。为保证模型的准确性以及稳定性分析的可靠性,提出了一种基于非线性状态空间模型的稳定性分析方法。首先,建立了采用二阶广义积分器锁相环的LCL型并网逆变器系统的非线性状态空间模型,确立了锁相环中非线性环节的有界性条件。基于Lyapunov稳定性判据,进一步获得满足全局渐进稳定的矩阵不等式条件。通过逐点分析,明确了锁相环参数以及电网阻抗对系统稳定域的影响。实验结果表明,相比于传统的小信号模型,所提出的非线性分析方法在预测跟网型逆变器系统的稳定性上更加准确和可靠。

The phase-locked loop(PLL) provides reference information synchronized with the grid for the grid-following control of grid-connected inverters. But in the case of weak grids, the PLL with nonlinear characteristics has a certain impact on the stability of the system. Due to the round-off errors, the grid-connected inverters which are designed based on the linearized PLL model may have the risk of instability. In order to ensure the accuracy of the model and the reliability of the stability analysis, a stability analysis method based on the nonlinear state-space model is proposed. First, the nonlinear state-space model of the LCL-type gridconnected inverter system using the second-order generalized integrator based PLL is built, and then the bounded conditions of the nonlinear link in the PLL are established. Based on the Lyapunov stability criterion, the matrix inequality conditions which satisfy the global asymptotic stability are further obtained. By analyzing point by point, the influence of PLL parameters and grid impedance on the stability region of the system is clarified. Experimental results show that, compared with the traditional small signal model, the proposed nonlinear analysis method is more accurate and reliable in predicting the stability of grid-following inverter systems.