In this paper, an equivalent model of zero-sequence circulations is established for three-level inverters in direct parallel parallel systems of coac-dc bus, and it is classified according to the generation mechanism and characteristics of zero-sequence circulations.Aiming at the low-frequency component of zero-sequence circulation, a method of adjusting the zero-sequence voltage component based on proportional complex integral (PCI) of first-order all-pass filter is proposed, and the controller parameters are designed according to the stability requirements of the control system.Finally, the simulation and experimental platform verify the effectiveness of the proposed control method in suppressing zero-sequence circulation.