Resonance Suppression Strategy for Grid-FormingInverters Based on Grid-Voltage Feedforward

Abstract

 With the growing reach and adoption of renewable energy, the
grid impedance rises significantly, resulting in weak and extremely weak grid
conditions that seriously threaten grid stability. Consequently, grid-forming
inverters, capable of providing voltage and frequency support, have garnered
widespread attention. However, under weak grid conditions, Delays from
digital control alters the output impedance performance grid-forming inverters to
exhibit negative damping characteristics. Resonance problems at mid and high
frequencies arise from the coupling between this output impedance and grid
impedance. To address this problem, this paper introduces the passivity theory
from the perspective of inverter output impedance and proposes an impedance
reshaping strategy based on grid voltage feedforward, transforming the inverter
output impedance from active to passive. First, an impedance model of the grid
forming inverter is established to analyze the mechanism of resonance
generation, and the non-passive characteristics of the output impedance are
verified based on passivity theory. Second, through an analysis of the inverter
impedance, a novel voltage feedforward function is derived and designed.By
appropriately configuring the feedforward parameters, Satisfying passivity
conditions at all frequencies, the inverter output impedance achieves resonance
suppression. Ultimately, a 10 kW inverter prototype verifies the accuracy of
theoretical derivations and the feasibility of the presented control schem.