This digest presents a dynamic cancellation control strategy for the inversion stage of the recently proposed high-power-density common-neutral single-dc-bus (CN-SDB) single-phase online uninterruptible power supply (UPS). The inversion stage operates in buck or buck-boost mode depending on the polarity of the output voltage reference and produces a sinusoidal output voltage. Owing to the dual-mode nature of the inversion stage, output voltage regulation with standard feedback control results in a large dc-offset and poor THD. To substantially improve the output voltage THD, a dynamic cancellation control strategy is proposed and an analytical model capturing the dynamics of the inversion stage with the dynamic cancellation control strategy is also presented to facilitate the controller design. A 1-kVA GaN-based prototype of online UPS is designed, built, and tested, and the output voltage THD is experimentally measured across a wide output voltage range. Standard feedback control strategy results in a 10% output voltage THD whereas the dynamic cancellation control strategy results in a 2.6% output voltage THD.
