Control Strategy for Multi-infeed MMC-based HVDC System Connected to Weak Grid

In this paper, the control strategy for multi-infeed MMC-based HVDC system (MI-MMC) connected to weak grid is presented. In order to imitate the behavior of a synchronous generator (SG), the synchronous generator emulation control (SGEC) method for the MMC station is proposed. The SGEC includes three loops, namely active power and frequency loop (Pf loop), reactive power and voltage loop (QU loop) as well as inner current loop. The Pf loop is used to emulate the swing equation of the SG. The exciter of the SG is mimicked by the QU loop. The inner current loop is developed to fast current and voltage regulations as well as current limiting. Besides, a novel control called dynamic power allocation for the MI-MMC system is proposed. This control scheme not only can precisely allocate the power among MMC stations, but also can play the role of secondary frequency regulation and maintaining the output voltage stability. Finally, the proposed control strategy is verified through the PSCAD/EMTDC simulation.