Suppression of Multi-parallel PCS Zero-sequence Circulation without Midpoint Potential Coupling

Parallel three-level PCSs are extensively utilized in high-power applications. A coupling relationship exists between the suppression of zero-sequence circulation and the control of midpoint potential balance in parallel converters, which hampers the inability to complete elimination of zero-sequence circulation. To address this coupling issue, a method for suppressing zero-sequence circulation in three-level converter without midpoint coupling has been proposed. In this approach, it is noted that middle vectors and small vectors can induce shifts in midpoint potential, whereas large vectors and zero vectors do not affect the midpoint potential. Consequently, large vectors along with three redundant zero vectors are selected to participate in PWM. By adjusting the duty of these different redundant zero vectors, the average common-mode voltage within one switching cycle is effectively reduced. Simulation experiments validate that the proposed method significantly enhances the adaptability for suppressing zero-sequence circulation.