Asymmetric Full Bridge Sub-module Topology of MMC with DC Fault Blocking Capability

For MMC-HVDC system with half-bridge sub-module(HBSM), the DC fault ride-through capability is a key problem to be solved. Thus, we propose an asymmetric full bridge sub-module(AS-FBSM) topology of multilevel modular converter(MMC) with DC fault blocking capability. With the half number of capacitors reversed by the diode continuous flow path, the DC fault current is suppressed. Meanwhile, the fault point arc reignition is prevented by using the unidirectional conductivity of diode. Then, the dynamics of AS-FBSM for DC fault ride-through under DC pole-to-pole short circuit fault condition is analyzed in detail. The PSCAD/EMTDC simulation results show that DC fault current formula is correct, and AS-FBSM can clear the DC fault current in milliseconds. Finally, compared with other sub module topologies with DC fault blocking capability, the DC fault blocking capability of AS-FBSM is the same as Hybrid SM, DCDSM, and so on, but weaker than FBSM and SBSM. Apart from FBSM and SBSM, the amount of the components of other topologies including AS-FBSM is generally the same. In terms of the number of devices inserted in the loop under normal working state, AS-FBSM and EHSM are the closest to HBSM. © 2019, High Voltage Engineering Editorial Department of CEPRI. All right reserved.