This paper proposes a new control scheme to eliminate the 3rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a 3rd harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup.

中文翻译：

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电网不平衡条件下并网逆变器的控制

本文提出了一种新的控制方案，以消除电网不平衡条件下并网逆变器输出电流中的三次谐波。由于直流母线电压的振荡频率是线路频率的两倍，不平衡电网会对并网逆变器的性能产生不利影响。由于其优于其他现有方法，本文基于瞬时有源无功控制 (IARC) 技术。然而，逆变器输出电流中存在严重的不对称 3 次谐波失真是 IARC 方法的主要挑战，这会损害电能质量要求。本文通过采用使用对称序列分量概念的电流参考生成方法提出 3 次谐波消除方法来增强 IARC 方案。此外，提议的方案通过注入请求的无功电流符合电网规范要求。最后，所提出的方法通过理论和仿真分析进行评估，并使用硬件设置进行实验验证。