Harmonic Suppression Method of Grid-Forming Inverter Based on Hybrid Impedance Reshaping Strategy

As a large number of power electronic devices and other nonlinear loads are connected to the power system, the harmonics generated by them cause great harm to the power quality of the power grid. At present, passive filter and active power filter are mainly used to deal with harmonic pollution. Active power filter is widely used, but its main control method for inverter is current mode control. However, the new energy power system shows the characteristics of inertia and insufficient damping. Therefore, the grid-forming inverter with the external characteristics of synchronous generator has attracted more and more attention, but the harmonic suppression strategy for the grid-forming inverter is rarely seen. In this paper, the author proposes a hybrid impedance reshaping strategy, which reduces the impedance of the grid-forming inverter at the harmonic frequency point through voltage feedback, and then series virtual negative impedance for the grid-forming inverter by modifying the voltage loop instruction, which equivalently increase the grid impedance, so that the grid-connected inverter can compensate the harmonics well in the normal working state. The proposed theory is proved by simulation and hardware-in-the-loop experiment.