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Modular multilevel converters (MMCs) have become one of the most promising topologies for high-voltage dc–ac conversion. DC-side fault blocking capability of the MMC has prompted significant research in recent years. In this paper, a new switched capacitor submodule (SCSM) for MMCs is proposed which provides operation with DC fault blocking capability. In addition, successful voltage balancing is achieved with half the number of voltage sensors used with existing MMC cells. Generally, conventional sensor-based balancing techniques require a significant amount of measurements, 2m(N-1) voltage sensors, and 2m current sensors for an N-level m-phase MMC. The proposed cell will thus aid in reducing the complexity of the control system. A detailed illustration of the operational concept of the proposed architecture is presented in this paper. A comparison between the proposed SCSM and other existing MMC cells has been included to highlight the benefits of the proposed SCSM. A simulation model for an MMC-based HVDC system along with the proposed cell has been built to test its performance during normal as well as abnormal operating conditions. The simulation results show the effectiveness of the proposed architecture. [ABSTRACT FROM PUBLISHER]

Offshore wind energy is now seen as a key contributor for the future renewable energy mix. HVDC technology is among the chief technologies enabling widespread use of offshore wind. Thanks to their numerous advantages, voltage-source converter-based-HVDC (VSC-HVDC) systems are expected to be the technology of choice. Unfortunately, most of VSCs are defenseless against dc-side faults, such as two-level VSCs, and half-bridge modular multilevel converters. This paper proposes the buck-boost inverter-based-HVDC system (BBI-HVDC) as a means to overcome the limitations of the classical VSC-HVDC systems. The proposed configuration does not only provide sinusoidal three-phase voltage, but also provides complete blocking capability of ac-side contributions during a dc-side fault. The latter is achieved by simply disabling the gating signals to the switches upon fault detection. The performance of the proposed system is illustrated during normal conditions, ac-side faults, and dc-side faults. A simulation case study comparing the performance of the conventional HVDC converters with the proposed system during dc-side faults is conducted. The simulation results reveal the promising performance under normal operation as well as a significant decrease in the dc fault current due to the ac-side contribution blocking capability of the BBI-HVDC system during dc-side faults. [ABSTRACT FROM AUTHOR]