Flexible multi-state switch can make the equipment compact without using the connection transformer. However

there are some problems such as the propagation of zero-sequence components between each power supply area and the expansion of the fault range. Thus

through the classical circuit analysis and sequence component decomposition calculation

the essential characteristics and inherent mechanism of zero-sequence propagation between AC and DC systems are revealed. Moreover

a kind of asymmetrical flexible multi-state switch with a half-bridge modular multilevel converter（MMC） at one end and a hybrid MMC at the other end is proposed. According to the fault situation in different supply areas

two zero-sequence suppression strategies and corresponding sub-module configuration schemes of the hybrid MMC are proposed. In PSCAD/EMTDC software

the characteristics of zero-sequence components suppressed under different supply area faults are compared and analyzed. Finally

the validity of the theoretical analysis and the effectiveness of the asymmetric flexible multi-state switch and its zero sequence control strategy are verified.