Grid interaction of multi‐VSC systems for renewable energy integration

Abstract

Integration of converter-interfaced renewable energy sources (RESs) into the power system and the transfer of power from RESs to remote load centres over high-voltage direct current (HVDC) lines may require connecting multiple voltage-sourced converters (VSCs) to a common alternating current (AC) system. Because of this connection, control loops of various converters will interact through the AC grid, leading to instability and an undesirable transient response. This paper focuses on the system-level integration of multi-VSC systems for the integration of RESs. 𝜇 analysis is used to determine under which control modes the independently stabilized VSCs connected to a common AC system ensure the multi-VSC system stability. Furthermore, a sufficient criterion is proposed for the design of the converters' outer control loops independently to ensure the stability of the interconnected multi-VSC system. For cases of severe interactions, where the interconnected multi-VSC system may become unstable even if individual VSCs are stable, a joint controller design for converters is proposed to stabilize the multi-VSC system. The interaction analysis indicates that employing AC voltage control mode by all the converters causes the highest interaction level, and having more converters in reactive power control mode reduces the impact of interactions on the interconnected system stability.