Effect of voltage feedforward loop on the stability of single and multi-parallel inverter system

Nowadays, the single loop current-controlled grid-tied inverters are extensively researched due to the reduced number of sensors, less computation burden, and simple control architecture. In this topology, for grid-side current control, whenever LCL filter resonant frequency (ω
r
) > critical frequency ω
c
= ωs/6 where ω
s
is the control sampling frequency, a fixed non-passive region (NPR) is exhibited by the inverter output admittance in the frequency range of (ω
c
, w
a
), where ωa is the anti-resonant frequency. However, the addition of unit point of common coupling (PC C) voltage feedforward (VFF) loop in the current control can create a shift in the NPR towards the high frequency. Such a variation in the NPR of inverter output admittance can threaten the harmonic stability of single and multi - parallel inverter-grid system connected through the grid impedance especially when power factor correction (PFC) capac-itor is interfaced at the PCC. Therefore, this paper analyzes the impact of NPR on inverter-grid system stability using modeling and bode impedance plots. The effect of VFF loop on single and multiple inverter cases are also discussed along with the simulation results.