Research on Resonance Suppression Methods for GFL Inverters in Microgrids under Weak Power Grid

With a high proportion of renewable energy generation connected to the power grid, power grid is gradually becoming electrified and presenting a weak power grid state. In weak power grid, GFL converters are prone to occur resonance. Therefore, a GFL converter resonance suppression method based on grid voltage feedforward(GVF)+symmetric phase-locked loop structure(SPLL) is proposed. Firstly, an impedance model is established and stability analysis is done for GFL inverter. To suppress negative resistance effect caused by PLL, GVF method considering PLL is introduced, and small signal impedance modeling and stability analysis are performed on it. Secondly, to eliminate the impact of asymmetric PLL, SPLL is introduced on the basis of GVF to further enhance the system’s resonance suppression ability. Finally, an experimental platform for GVF+SPLL grid following inverter resonance suppression system is established for experimental testing. The experimental results show that GVF+SPLL method has stronger resonance suppression ability, compared to GVF/unimproved method, and system harmonic content has decreased from 21.27% to 2.14%. Meanwhile, under the background of power grid harmonics, the GVF+SPLL method also has stronger harmonic suppression ability compared to the GVF/unimproved method.