Unified Modeling and Practical Assessment of Proportional Grid-Voltage Feedforward in Multiple Reference Frames for LCL-Filtered Power Conversion Systems

Power conversion systems (PCSs) connect dc energy sources to the grid, but background grid-voltage disturbances can degrade grid-current quality. This paper presents a unified derivation and implementation-oriented assessment of proportional grid-voltage feedforward in the abc, αβ, and dq reference frames for an LCL-filtered three-level PCS. The derived disturbance transfer function retains the feedforward term, and attenuation is quantified at the fundamental and selected harmonics. Tests cover gain tuning and voltage harmonics, 10% voltage unbalance, 49–51 Hz operation, SCRs from 10 to 2, ±20% LCL-parameter variation, a 25–50 kW reference ramp, common-mode voltage, and a sixth-harmonic resonant benchmark. With Kff = 0.6, grid-current THD falls from 10.65% to 7.19% in the strong-grid harmonic test; the resonant benchmark reaches 7.05%. At SCR = 3, retuned resonant control gives 20.33% THD versus 11.68% for proportional feedforward, while transferring the strong-grid resonant gain gives 123.02%. The delay-inclusive loop model retains positive stability margins, whereas the switching-model results reveal that the benefit of a fixed feedforward gain is condition-dependent and may diminish or reverse under clean-grid, frequency-deviation, parameter-variation, and weak-grid conditions. Archived 100 kVA waveforms verify stable implementation in all three reference frames. The results clarify the operating conditions under which proportional feedforward is effective, together with its digital implementation requirements and limitations.