Energy storable VSC-HVDC system based on modular multilevel converter

• An energy storable HVDC unidirectional power transmission system is proposed.
• The system includes a diode full bridge rectifier and a MMC with EDLCs.
• DC power and voltage are controllable by controlling on-state SM numbers.
• Stored energy is limited in a certain range by energy management control.

A new High Voltage DC (HVDC) transmission system is proposed in this paper. This new HVDC topology is composed of a diode rectifier, a Modular Multilevel Converter (MMC) with short-term energy storage capability, and dc power cable or transmission line. Compared with conventional MMC HVDC, the proposed topology has the advantages of lower cost due to having only one MMC converter, and short-term energy storage capability. A novel control strategy is proposed by making full use of redundant submodules of MMC and making the dc terminal voltage variable. Energy management control is also proposed to manage input and output power and to limit the stored energy in a certain range. Simulation results verify the viability and effectiveness of this energy storable VSC-HVDC system. The basic principle of the system is further reinforced by experimental results.

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