A Decentralized Nonlinear Harmonic Power Sharing Scheme Considering Harmonic Residual Capacity and Working Conditions of Fundamental Load

The proper harmonic power sharing in an islanded microgrid plays a significant role in reliable system operation. Virtual-impedance-or-admittance-based strategies are intuitive and effective solutions. However, there is an inherent tradeoff between harmonic sharing accuracy and power quality. Besides, optimal capacity utilization has not been considered in most existing methods. Facing these issues, a nonlinear droop scheme, between harmonic residual capacity (HRC) and virtual impedance, is proposed in this article. Under the proposed scheme, harmonic residual capacity is defined and utilized to share harmonic power. Different working conditions of the fundamental load and corresponding control target are analyzed to determine the variable droop coefficient. Therefore, the proposed scheme can render an optimal utilization of the converter capacity and adjust the inherent tradeoff dynamically and adaptively. It contributes to a more flexible harmonic sharing in the islanded microgrid and enhances the ability to avoid overload risk. Furthermore, the communication line is unnecessary, leading to high reliability and expandability. Finally, the feasibility and effectiveness of the scheme are verified by simulation and experimental results.