Multiple Frequency Harmonic Mitigation Method for Distorted Grid with Grid-Forming Converter and Nonlinear Loads without Additional Sampling

A significant amount of nonlinear loads exacerbate the distorted degree of the grid, and the development of grid-forming (GFM) converters provides new opportunities for power quality improvement. Currently, the difficulty of GFM converters in independently realizing active mitigation of harmonic currents in the whole system is the state perception of other harmonic sources. Therefore, modeling the correlation between the harmonic states of the grid and the GFM converter based on the existing rather than additional sampling is the key factor in guiding harmonic suppression methods. In order to address this issue, this paper first compares the existing GFM harmonic mitigation methods, clarifying the need for differential control of harmonics generated by the GFM converter and loads. Secondly, a coordinated control with a harmonic voltage compensator and virtual impedance is proposed in this paper, and separately suppresses the harmonic components mentioned above. This method only needs the initial harmonic phase of the grid and equates the load to a constant harmonic current source model. Thirdly, this method is improved by considering the change of distorted voltage at PCC on the load, and a more accurate compensator based on the harmonic Notorn model of the load is proposed to achieve better harmonic mitigation performance. Finally, the comparative steady-state and dynamic experiments are provided by a 10kW GFM converter and rectifier load. The results prove the effectiveness and superiority of the proposed methods, and the harmonic currents injected into the grid can be decreased by over 90%.