基于改进等面积法则的并网逆变器同步稳定性分析

Synchronization Stability Analysis of Grid-connected Inverter Based on Improved Equal Area Criterion

随着新能源渗透率的不断提高,电力电子化电力系统的稳定运行面临新的挑战。近年来,并网逆变器在大扰动下的同步不稳定现象频发。传统等面积法则由于直接忽略了阻尼项对暂态稳定性的影响,使得稳定边界的计算误差较大,容易导致稳定结果的误判。为此,提出了一种改进等面积法则,用于分析弱电网条件下并网逆变器的大干扰同步稳定性。针对基于锁相环的逆变器并网系统,建立其二阶非线性暂态模型。通过将其与同步发电机的转子摇摆方程进行类比,得到并网逆变器系统等效的机械功率、电磁功率和依赖于功角的非线性阻尼项。为了定量分析负阻尼的影响,提出了一种基于阻尼项缩放和线性逼近的改进等面积法则,有效提高了暂态稳定域的估计精度。与经典的Lyapunov方法相比,所提出改进等面积法则的保守性更小。最后,基于MATLAB仿真和硬件在环实验,验证了所提方法的有效性和优越性。

With the continuous increase of the penetration rate of renewable energy,the stable operation of power systems dominated by power electronics faces new challenges.In recent years,the synchronization instability of grid-connected inverters under large disturbances has taken place frequently.Since the traditional equal area criterion directly ignores the influence of the damping terms on transient stability,the large calculation error of the stability boundary leads to the misjudgment of the stability results.Therefore,an improved equal area criterion is proposed to analyze the large-disturbance synchronization stability of gridconnected inverters under weak grid conditions.A second-order nonlinear transient model is established for the grid-connected inverter system based on phase-locked loop (PLL).By comparing it with the rotor swing equations of the synchronous generator,the equivalent mechanical power,the electromagnetic power and the nonlinear damping term which depends on the operation states of the grid-connected inverter system are obtained.In order to quantitatively analyze the influence of negative damping,an improved equal area criterion based on the scaling of damping term and the linear approximation is proposed,which effectively improves the estimation accuracy of the transient stability margin.Compared with the Lyapunov-based methods,the proposed improved equal area criterion is less conservative.Finally,the extensive simulations based on MATLAB/simulink and the hardware-in-the-loop experiment are presented to verify the effectiveness and superiority of the proposed method.