开环同步型单相并网逆变器小干扰建模与弱电网下稳定性分析

Small-disturbance Modeling and Stability Analysis of Single-phase Grid-tied Inverter With Open-loop Synchronization Under Weak Grid

单相并网逆变器中,多采用锁相环(phase-lockedloop,PLL)型闭环同步方法,但PLL引入的低频段负阻特性不利于系统稳定性,在电网阻抗较大时并网逆变器易发生严重失稳。对此,国内外广泛开展了PLL优化或替代技术的研究。其中,开环同步(open-loop synchronization,OLS)方法的无反馈结构使得其自身是完全稳定的,近年来得到了较多关注。然而,OLS结构中非线性特性明显,如何获得准确的小干扰线性化模型仍非常困难,OLS型单相并网逆变器在弱电网下的稳定性仍不清晰。鉴于此,重点研究开环同步型单相并网逆变器小干扰建模与稳定性。借鉴谐波线性化思想,提出OLS的线性化建模方法,建立开环同步型单相并网逆变器的输出阻抗模型。在此基础上,讨论OLS型单相并网逆变器的鲁棒性。较大电网阻抗下,采用OLS的开环同步型单相并网逆变器系统仍有良好的稳定性。通过仿真和对比实验验证上述模型的准确性以及弱电网下OLS的适应性。

In single-phase grid-tied inverters(GTI),the closed-loop synchronization based on phase-locked loop(PLL)is widely used.However,the negative-resistance characteristic introduced by PLL at low-frequency band is not conducive to the GTI stability.When the grid impedance is large,the GTI is prone to serious instability.Hence,extensive studies on the optimization or substitution of PLL are ongiong at home and abroad,in which.open-loop synchronization(OLS)itself is completely stable due to its non-feedback structure,thus receiving much attention in recent years.However,OLS owns obviously nonlinear characteristics,and it is difficult for it to obtain an accurate linearized small-signal model.The stability of GTI with OLS under very weak grid is still unclear.Therefore,this study focuses on the small-signal modeling and stability of GTI with OLS.Inspired by harmonic linearization theory,the linearization modeling method of OLS is proposed,and the output impedance model of GTI with OLS is established.On this basis,the robustness of OLS-GTI is discussed.It is found that the GTI with OLS exhibits excellent stability even under conditions of large grid impedance.The simulation and experimental results verify the accuracy of the above model and the adaptability of OLS under very weak grid.