弱电网下LCL滤波并网逆变器自适应电流控制

An Adaptive Current Control for Grid-connected LCL-filtered Inverters in Weak Grid Case

由电网电压谐波以及电网阻抗变化等引起的电网不确定性严重影响LCL型并网逆变器的电流控制。电网电压比例前馈因实现方便且可有效地抑制电网谐波的作用而获得了广泛的关注,但少有文献探讨其在电网阻抗大幅变化即弱电网下的性能。该文分析表明,弱电网下该前馈补偿会大幅降低电流控制的稳定裕度。随着电网阻抗中感性成分的增大稳定裕度变差,最终导致不稳定。此外,低次谐波电流抑制也会失效。针对上述问题,提出一种基于电网阻抗估测的自适应控制方法,即时修正用于前馈补偿的电压以及调整调节器参数以保证较好的相位裕度或高带宽。对比分析以及实验研究表明提出的方案可有效地提高LCL滤波并网逆变器的电网适应性。

Grid uncertainties including the grid distortions and the varied grid impedance challenge the current control of grid-connected LCL-filtered inverters. The simple proportional grid voltage feed-forward provides high rejections of low-order distortions. However, the study concerning the grid impedance has not been presented. In this paper, the current control with the grid feed-forward considering the varied grid impedance was studied. The stability margins are decreased and even the instability is yielded if the grid feed-forward is adopted and the grid inductive impedance increases. Besides, low-order current harmonics rejections are aggravated. Thus, an adaptive control based on estimating the grid impedance is proposed to solve this problem. With the use of the estimated grid impedance, the voltage signal used for the grid feed-forward compensation is modified, and the controller parameter is adjusted to maintain a good phase margin. Comparative analysis and experiments have indicated that the proposed method successfully improved the ability of LCL-filtered inverters against the uncertainty of grid conditions.