With the continuous increase in distributed energy resources that are being integrated into the utility grid, it becomes necessary for inverters to estimate the grid impedance online to be used for several applications. Despite the fact that online grid impedance estimation techniques using grid-connected inverters gained more attention recently, no comprehensive study has been evaluating the performance of different estimation techniques under several grid conditions. This study proposes an extensive comparison to assess the accuracy of two online frequency-based grid impedance estimation techniques at the fundamental frequency. These two techniques are based on the 75 Hz frequency injection technique and pseudo-random binary sequence injection, respectively. Results from MATLAB/Simulink and PLECS RT Box present the advantages and disadvantages of these estimation techniques and the required trade-offs. This comparison study analyses the effects of disturbance magnitude and its injection time, the variation of grid impedance and non-ideal grid voltage. Furthermore, solutions are proposed to enhance the estimation accuracy of both techniques for non-ideal grid voltage containing inter-harmonics and sub-harmonics. The study concludes with recommendations regarding the best use of these two frequency-based grid impedance estimation techniques to suit a particular low voltage grid scenario.

中文翻译：

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使用并网逆变器的基本电网阻抗估算：两种基于频率的估算技术的比较

随着集成到公用电网中的分布式能源的不断增加，逆变器有必要在线估算用于多种应用的电网阻抗。尽管最近使用并网逆变器的在线电网阻抗估计技术得到了越来越多的关注，但是还没有全面的研究评估在几种电网条件下不同估计技术的性能。这项研究提出了一个广泛的比较，以评估两种在线基于频率的电网阻抗估计技术在基本频率下的准确性。这两种技术分别基于75 Hz频率注入技术和伪随机二进制序列注入。MATLAB / Simulink和PLECS RT Box的结果显示了这些估算技术的优缺点和所需的权衡。这项比较研究分析了干扰量及其注入时间，电网阻抗变化和非理想电网电压的影响。此外，提出了解决方案以提高针对包含间谐波和次谐波的非理想电网电压的两种技术的估计精度。该研究最后提出了关于这两种基于频率的电网阻抗估计技术的最佳使用方法的建议，以适合特定的低压电网情况。此外，提出了解决方案以提高针对包含间谐波和次谐波的非理想电网电压的两种技术的估计精度。该研究最后提出了关于这两种基于频率的电网阻抗估计技术的最佳使用方法的建议，以适合特定的低压电网情况。此外，提出了解决方案以提高针对包含间谐波和次谐波的非理想电网电压的两种技术的估计精度。该研究最后提出了关于这两种基于频率的电网阻抗估计技术的最佳使用方法的建议，以适合特定的低压电网情况。