A grid-connected HVDC shunt tap based on series-input parallel-output DC-AC multi-module 2-level voltage source converters

Abstract

Tapping-off a small amount of power from an HVDC transmission line to a three-phase local grid can be achieved by using shunt or series HVDC taps. This paper proposes a new grid-connected HVDC shunt tap. The proposed tap uses series-input, parallel-output multi-module 2-level voltage source converters (VSCs) as an alternative to the conventional single DC-to-AC voltage source converter (VSC) followed by a step down transformer. In the conventional system, semiconductor devices should be connected in series, in order to meet the high-voltage requirements in the HVDC systems. Hence, careful design to ensure dynamic voltage sharing between switches is necessary. The proposed technique is not limited by this constraint, as series connection of semiconductor switches can be avoided by employing a large number of VSC modules. The controller of the proposed system should keep equal DC input voltages, and equal output current sharing. Detailed illustration for the proposed controller is presented in this work. A Simulation study is carried out to show the effectiveness of the proposed architecture and to validate the proposed controller.