A Stored Energy Control Based Active DC Filter for the Alternate Arm Converter with an Extended Overlap Period

The Alternate Arm Converter (AAC) is a multilevel Voltage Source Converter (VSC) suitable for HVDC systems with DC-fault blocking capability. In its “Short-Overlap” configuration (SO-AAC) it requires a bulky passive DC filter to suppress the DC current ripple caused by the rectification of the grid currents in the DC link. With an Extended-Overlap period (EO-AAC), an active DC filtering control strategy can be implemented thanks the fact that there is always one phase in overlap mode, providing a continuous control of the DC current. Previous works have been realized considering DC inductors at each pole of the DC link. In this paper, a stored energy control assessment is proposed leading to the deduction of a stored energy model allowing a formal DC current control without DC inductors. The proposed control is supported through a static analysis and dynamic simulation in order to demonstrate its effectiveness.