A 4000V input auxiliary power supply with series connected SiC MOSFETs for MMC-based HVDC system

Modular multi-level converter (MMC) is composed of many sub-modules (SMs). Each SM needs an independent auxiliary power supply to drive IGBT and control the system. In HVDC system, the input of the MMC is connected directly to DC bus. So, the input voltage of the auxiliary power supply (APS) is very high. Traditional solution for the APS is the input-series output-parallel structure topology. However, this solution brings severe challenges, such as: input voltage and output current unbalance between the converters, out of synchronization when start-up, and difficulty in input voltage protection. Series connected MOSFETs is another straightforward solution for the APS. In this paper, a novel auxiliary power supply solution for MMC based HVDC system is proposed. It is able to handle extremely high input voltage from 300V to 4000V by using five MOSFETs connected in series. The design procedure of the proposed APS as well as the voltage balance scheme, driving method is discussed in detail. The proposed auxiliary power supply is verified and demonstrated through a 60W prototype. Experimental results demonstrate that the purposed APS can work stably and reliably. It simplifies the structure and reduces the cost effectively even for thousands of voltages.