Phase-Corrected Proportional Resonant Control for Negative Sequence Current Elimination in High-Power Converters With Low Carrier Ratios

High-power converters operate at low carrier ratios (LCRs) featuring significant digital delay, making it challenging to suppress negative sequence current stably under unbalanced grid voltage. In this article, the worse amplification effect from negative sequence voltage to negative sequence current due to LCR under conventional proportional-integral (PI) control is first revealed and quantitatively explained with the complex transfer function. Furthermore, a phase-corrected proportional resonant (PR) controller is presented to suppress the amplification effect by the newly added pole and enhance the system stability by local phase correction (LPC). Meanwhile, a design scheme for phase correction angles is proposed to improve dynamics. Finally, simulation and experiments are provided to validate the negative sequence current elimination capability under various grid voltage sag depths as high as 100% at different carrier ratios as low as five, enhanced stability, and improved dynamic performance.