New topology for three-level modified switched capacitor submodule for Modular Multilevel Converter with DC fault blocking capability

Modular Multilevel Converter (MMC) has served as a promising Voltage Source Converter (VSC) for High Voltage Direct Current (HVDC) applications. In this paper, a new MMC Submodule (SM) topology called Modified Switched Capacitor Sub-Module (MSCSM) is proposed. The MSCSM is able to block the DC fault using the power electronics semiconductor diodes due to its intelligent configuration without the need to use circuit breakers and has reduced voltage stress across some switches. In this work, the proposed topology is analyzed along with the modified selection technique used to balance the capacitors voltages using half the number of voltage sensor. Moreover, the submodule behavior due to IGBT open-circuit failure is analyzed and a control scheme is proposed to detect such a fault and provide continuous system operation. Furthermore a comparison between the proposed MSCSM and other available submodule topologies is included to show the benefits of the proposed MSCSM. A simulation model has been developed to validate the proposed architecture and to evaluate its performance. Finally, experimental results using a three-level MMC prototype show the validity of the proposed topology.